SlideShare a Scribd company logo
1
Light and Optics
This chapter discusses the general aspects of light and the response of the human eye towards light
with different wavelengths and frequencies. Sources of light and the comparison between eye and
camera are given. Reflection, refraction, the measurement of lens speed and losses as per the F
and T numbers and depth of field are explained. Lens formats, angle of view of lenses, C and CS
mounts and back focusing of lenses are also discussed.
Learning objectives:
After studying this chapter you will have a basic understanding of:
• The response of human eye towards light
• The different sources of light
• Eye persistence in motion pictures
• The difference between eye and camera
• Optical elements
• The basics of lenses and lens types
• Back-focus adjustment and ND Filters
1.1 Introduction
In general, objects are classified into two types. They are:
• Luminous bodies
• Non- Luminous bodies
Luminous bodies are those that can generate light. For example, the sun, stars, comets and other
such bodies are luminous bodies. On the other hand, objects that cannot produce light by
themselves, but reflect the light that falls on them, are called non-luminous bodies. For example,
the Moon, planets, humans, bricks, plastic, metals etc are non-luminous bodies.
The Sun, Stars and glow-worms are natural sources of light. Apart from these natural sources of
light, there are some man-made, artificial sources of light such as a wax-candle, oil-lamp, torch,
electric light bulb and Light Emitting Diode (LED) etc.
The intensity of light at any place is measured in terms of lumens present on unit area. This unit is
called foot candle (Lux is the modern unit). One foot candle is equal to 10.76 lux.
2 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems2
1.2 Human eye and light
Light is an electromagnetic radiation which is measured in wavelength or frequency, the same as
radio signals. Wavelength is usually measured in nanometres (nm) while frequency is measured in
hertz (Hz). Higher the frequency, the shorter is the wavelength. Out of the different frequencies,
visible light falls in the range of 400nm to 700nm as shown in the Figure 1.1. Here, 400nm
corresponds to violet and 700nm corresponds to red.
There are various colours between the violet and red wavelengths, blue, blue-green, green, yellow-
green, yellow, orange. All these colours produce different effects on the human eye retina.
Figure 1.1
Spectrum distribution of light, with associated wavelengths
Ref: http://www.sciencesway.com/vb/t6526
The eye shows its greatest reaction to green light. Green light produces the highest output on the
retina where as red and violet light produces the least output. The eye’s spectral sensitivity is
higher at green light, not at red or violet, because the largest amount of the sun’s energy that
penetrates the earth’s atmosphere is in the range of 555nm. This is represented graphically in
Figure 1.2.
Figure 1.2
Response of eye at different wavelengths
Ref: http://www.bunkerofdoom.com/laser/response/index.html
Light and Optics 3
1.2.1 Additive and subtractive mixing
Red, green and blue are referred to as primary colours. To produce any secondary colour we have
to mix two or three primary colours in different proportions, resulting in magenta, yellow, etc. The
mixing of primary colours to produce new colours is called additive mixing and the reproducing of
primary colours from the secondary colours is called subtractive mixing. This is illustrated in
Figure 1.3.
Figure 1.3
Principle of additive mixing and subtractive mixing
Television screens use additive mixing to produce the colour images we see on the screen. Printing,
on the other hand, uses the secondary colours to produce a colour image on the page or photo
quality paper. Hence the use of yellow, magenta and cyan toners in colour printers.
1.2.2 The human eye
The Retina is a photosensitive area of the eye which is composed of millions of cells called cones
and rods. Cones are sensitive to medium and bright intensity light and can also sense colour. Rod
cells are sensitive to lower light levels and cannot distinguish between colours. We use the rod cells
to see at night which makes it harder to distinguish colours. Cones cease to react once the level of
light falling on them drops below 1 lux. The rods are 10,000 times more sensitive than the cones.
There are approximately 10 million cones and over 100 million rod cells in each eye.
The cross section of a human eye is shown in Figure 1.4.
Figure 1.4
Cross section of the human eye
Ref: http://academia.hixie.ch/bath/eye/home.html
4 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems4
Focusing of the eye is necessary to see objects at different distances. If focusing of the eye is
affected then the eye may be considered defective. Major defects found in the eye due to lack of
correct focusing are:
• Hyperopia (farsightedness)
• Myopia (nearsightedness)
There are many other defects in the eye, although the above defects are the most common. These
defects can be corrected by using different lenses. A convex lens is used to correct hyperopia (see
Figure 1.5) and a concave lens is used to correct myopia (see Figure 1.6).
Figure: 1.5
Correcting hyperopia through glass
Figure: 1.6
Correcting myopia through glass
Ref: http://www.d.umn.edu/~jfitzake/Lectures/DMED/Vision/Optics/RefractiveErrors.html
In the same way that different types of lenses are used to assist focussing in the human eye,
different types of lenses are used in CCTV to focus objects at different distances.
1.3 Sources of light
For video surveillance in outdoor areas, artificial lighting by different light sources, such as
tungsten, tungsten- halogen, metallic arc, mercury, sodium, xenon, IR lamp, LED IR arrays etc are
required. These are selected according to the requirement, safety consideration and the quality of
the video picture. The colour temperature of different light sources is shown in Figure 1.7.
Light and Optics 5
Figure 1.7
Colour Temperature of different light sources
Artificial lighting is the process of illuminating a scene with a high level of evenly distributed light
so that each and every object, place or person available at that point is clearly visible.
Figure 1.8
Spectral output range for common sources of artificial light
Ref: http://www.olympusmicro.com/primer/lightandcolor/lightsourcesintro.html
The temperature at which an imaginary perfect black body is heated and consequently produces
light is called colour temperature. Max Plank, a German physicist and the founder of quantum
theory, explains the relation between the peak wavelengths radiated and the temperature to which
the body is heated as: λm=2896/T
Where:
• λ is wavelength in microns
• T is temperature in degrees Kelvin.
There are five different standard sources of “standard white light”. They are referred to as
Illuminants A, B, C, D6500, and E.
6 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems6
Illuminant A: is a warm light with a color temperature of 2845°K. A tungsten lamp at 2800°K
produces this shade of white light.
Illuminant B: is close to sunlight at noon. Filtering the light from Illuminant ‘A’ gives radiation of
Illuminant B i.e. white light. The correlation colour temperature of B is 4880o
K.
Illuminant C: is the same as diffused light from an overcast sky. When Illuminant A is filtered
Illuminant C is obtained. The correlation colour temperature of C is 6770o
K.
Illuminant D6500: is the standard used for color TV. An average daylight colour temperature is
represented by source D6500. It is a mix of direct and diffused skylight and is not obtained by
filtering any other source. The correlation colour temperature is 6500o
K
Illuminant E: is referred to as “equal energy white”. It is a hypothetical white and is equivalent to a
light source comprising all wavelengths of visible equal light. Source E has uniformly distributed
radiation which looks like a flat horizontal line. It is used for calculation only.
1.3.1 Light units
The science that deals with light is called photometry and the units used are called photometric
units. Important terms associated with light and their units are discussed below.
Luminous intensity (I)
Luminous intensity is the illuminating power of a primary light source, radiated in all directions.
The associated unit of measurement is the candela (cd). 1 candela is equal to approximately the
amount of light energy generated by a standard candle. 1 cd is 1/60 the light emitted from 1cm2
of a
black body heated to a temperature of molten platinum 2042°K.
Luminous flux (F)
Luminous Flux is the measure of the flow of light in one second and is measured in lumens (lm).
One lumen is the quantity of luminous flux that falls on a unit area surface at a unit distance from a
light source of 1 candela in one second.
Luminous flux = luminous intensity (lumens)/ 4П
Illumination (E)
Illumination of a surface is the amount of luminous flux falling on a surface and is measured in
lumens per unit area.
One lux = 1 lumen per square meter (lm/m2
)
Figure 1.9
Light units and their meanings
Ref: http://www.handprint.com/HP/WCL/color3.html
Light and Optics 7
When luminous flux of one lumen falls on an area of 1m2
then it is called meter candela or lux (lx).
Different light units and their meanings are shown in figure 1.9.
The Inverse Square Law of Illumination:
The illumination of a surface decreases as the square of the distance of the illuminated surface from
the light source. At 1 meter from a 1 candela source the illumination of the surface is 1 lux (1
lumen per m2
). At 2 meter the illumination is 1/22
= 0.25 lux.
In basic terms this can be shown as:
E = I / d2
lux
Where E = Illumination (lux)
I = Luminous intensity of source (cd)
d = the distance from the light source (m)
Different levels of indoor and outdoor illuminations are shown in Figure 1.10 and Figure 1.11
respectively.
Figure 1.10
Typical levels of indoor illumination
Ref: http://a-kingnet.com/index.php?route=product/category&path=39_40
Figure 1.11
Typical levels of illumination at outdoor
Ref: http://a-kingnet.com/index.php?route=product/category&path=39_40
The vergence is inversely proportional to the distance. This can be explained by considering the
following example.
Consider a source which emits light or radiation onto a surface at different points. If the points are
at differing distances from the source as shown in Figure 1.12 the following results:
• Distance A from the source: At this point or on the surface the rays are highly
divergent and wavefronts are strongly curved
8 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems8
• Distance B from the source: Here the rays are less divergent and wavefronts are less
curved
• Infinity distance form the source: Rays are parallel in nature and the wavefronts are a
plane.
Figure 1.12
The amount of divergence of the light is inversely proportional to the distance from the source of light at distance ‘A’ has
more vergence than that at B
Ref: http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v1/v1c030.html
Luminance (L)
Luminance is the measure of light emitted from a surface. This light may be in the form of radiated
light or reflected light. Luminance can be measured in two ways, using either candela or lumens
per square area.
1 nit = 1 candela per sq m (cd/m2
)
1 stilb (sb) = 1 candela per sq cm (cd/cm2
)
1 apostilb = 1 lumen per sq m (lm/m2
)
1 lambert = 1 lumen per sq cm (lm/cm2
)
Table 1.1 shows the light levels under day time and night time conditions.
Table 1.1
Light levels under daytime and night time conditions
Illumination
Conditions Foot-Candles
(FtCd)
(lux) Comments
Direct sunlight 10,000 107,500
Full daylight 1000 10,750
Overcast day 100 1,075
Very dark day 10 107.5
Twilight 1 10.75
Deep twilight 0.1 1.075
Daylight range
Full moon 0.01 0.1075
Quarter moon 0.001 0.01075
Starlight 0.0001 0.001075
Overcast light 0.00001 0.0001075
Low light level range
Light and Optics 9
International Standards for Units (SI units)
SI units are the standardized units used for the measurement of quantity or quality of components
which are accepted world wide. Table 1.2 shows the international standards used in the
measurement of light and related factors.
Table 1.2
SI units
Unit Symbol Measure
Kelvin [K] temperature
Candela [cd] luminous intensity
The derived SI unit
The table below shows the derived SI units.
Table 1.3
Derived SI unit
Quantity Unit Symbol /
Definition
Velocity Meter/second m/s
Acceleration Meters per second per
second
2
s
m
Frequency Hertz Hz =1/s
Density Kilograms per cubic meter
3
m
kg
Energy Work Joule J=N·m
Illumination Lux lx = lm/m2
Luminous flux Lumen lm =
cd·steradian
Luminance Nit nt = cd/m2
1.4 Eye persistence – motion pictures
Eye persistence is the most important “eye defect” used in cinematography and television.
Persistence depends on the intensity of light and brightness to see the picture in motion. Pictures
have to change quickly so as to avoid flicker and to give a feeling of motion when logically
consecutive pictures are played. When these pictures move faster than the persistency of the eye,
the motion of pictures looks like a moving picture. The eye responds differently to different
wavelengths as shown in Figure 1.13.
10 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems10
Figure 1.13
Response of eye towards different wavelength
Ref: http://videocodecs.blogspot.com/
A video camera records images with a speed of 25/30 pictures per second. For a low intensity
projector, 24 frames per second, is required.
Television uses the same principle as that of the human eye. It projects pictures by a method called
‘interlaced scanning’ as shown in Figure 1.14. The pictures are created by scanning and the
pictures are projected by lines. As the number of lines increase, the clarity increases. These lines
are projected from left to right and top to bottom.
Three major television systems exist. They are:
• PAL (Phase Alternating Line)
• NTSC (National Television System Committee)
• SECAM (Sequential Couleur Avec Memoire or Sequential Colour with Memory).
Although the picture projection and scanning is the same, the lines and the frames, or images, per
second changes and the method of colour coding is different.
• PAL : 625 Scanning Lines / 50 Interlaced Pictures Per Second
• NTSC : 525 Scanning Lines / 60 Interlaced Pictures Per Second
• SECAM: 625 Scanning Pictures (Used To Be 819) / 50 Interlaced Pictures Per
Second.
Figure 1.14
Two interlaced fields build up a complete TV picture frame
Ref: http://www.hardwarezone.com/features/view/123917/page:2
Light and Optics 11
1.5 Comparison between eye and camera
The similarities between eye and camera are illustrated in Figure 1.15.
Figure 1.15
Eye and camera similarities
Both eye and camera are similar in nature. In the same way that the retina captures pictures, the
camera sensor captures the picture, scans it and produces images. The camera lens can focus on an
object that is close or far away, according to the settings made. Where as a human eye can focus on
the near or far away object automatically according to the requirement.
In the human eye there is a spot referred to as the blind spot where nothing can be seen. When we
consider both the eyes at the same time we cannot have the same view from both the left and right
eye because of the presence of the blind spot. Thus, what we see is the combinational image of both
the left and right eye. This differs from a camera where there is no blind spot.
To transmit the information from the camera to a monitor we have to connect cables, where as in
the case of the eye, nerves transfer the information to the brain.
The information stored in a camera will not be deleted unless and until it is deleted manually, but
this is not the case with the human eye.
The pupil that is present in the eye can change its size rapidly according to the requirement, where
as in case of a camera it does not change rapidly.
1.6 Optical elements
1.6.1 Lenses as optical elements
The basic lenses used in optics are concave and convex lens.
Concave lenses are used when the objects are to be shown smaller when compared to the actual
size of the object. They have a negative focal length with a virtual focus. On the other hand, convex
lenses are used when the objects are to be shown bigger compared to the actual size of the object.
They have a positive focal length with a real focus.
12 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems12
The important properties of lenses are:
• Optical plane: The plane passing through the centre of the lens
• Optical axis: The axis perpendicular to the centre of the optical plane
• Focus: The point where the rays falling parallel to the optical axis converge
• Focal length: The distance between the optical plane and the focus (in meters)
• Diopter: An inverse value of the focal length, where the focal length is stated in
meters.
Figure 1.16 shows the properties of a lens.
Figure 1.16
Properties of a lens
There are different types of lenses with varying lens sizes and materials. Some of the different
types are as follows:
• Plano–Convex (A lens which is plane on one side and convex on the other side)
• Plano-Concave (A lens which is plane on one side and concave on the other side)
• Bi-convex, also referred to as a Converging lens (A lens which is convex on both
sides)
• Bi-concave, also referred to as a Diverging lens (A lens which is concave on both
sides)
• Convex-Concave (A lens which is convex on one side and concave on the other side).
Figure 1.17 shows the different types of lenses.
Figure 1.17
Types of lenses
Different focal lengths can be achieved by the combined use of different types of lenses with
different focal lengths. Lenses can be joined by applying transparent glue. To obtain a particular
focal length, design engineers use mathematical calculations. The assembly of a lens is shown in
Figure 1.18.
Light and Optics 13
Figure 1.18
Lens assembly
1- Lens Clip; 2- Lens 1; 3- Lens spacer; 4- Lens 2; 5- Lens 3; 6- Lens holder
The factors that determine lens quality are lens design, element manufacture, mechanical
composition and electronics (refers to auto iris and motorized lenses). Following are the parameters
considered under each factor.
Lens design:
• Number of elements
• Relative position
• Aberration correction in the design stage.
Lens element manufacture:
• Glass type
• Technology and type of glass manufacturing (heating, cooling, cleanness)
• Precision of grinding and polishing (very important)
• Anti reflection coatings of the glass (micrometer layers for minimizing losses).
Lens mechanical composition:
• The lens’ positional fixing and stability (shock, temperature)
• The lens’ moving mechanics (especially zooming, focusing, iris leaves)
• Internal light reflections (matte black absorption)
• Gears used for motorized lenses (plastic, metal, precision).
Electronics (refers to auto iris and motorized lenses):
• Auto iris electronics quality
• Electric consumption
• Zoom and focus control circuitry.
1.6.2 Reflection and Refraction
Light travels from one medium to another. When light travelling in a straight line strikes a plane
mirror it bounces back at an angle, this is referred to as reflected light. This phenomenon is called
reflection and Figure 1.19 shows this in detail.
14 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems14
Figure 1.19
Light Reflection from a plane mirror
Ref:http://www.cssforum.com.pk/css-compulsory-subjects/everyday-science/everyday-science-notes/17029-glossory-
physics-2.html
When light travels from one medium to another (for example, consider a glass slab or water as one
medium and air as another medium), it bends slightly at the boundaries of the medium, rather than
reflecting back. This process is referred to as refraction and Figure 1.20 shows this in detail.
Figure 1.20
Light refraction through glass and water
Ref: http://micro.magnet.fsu.edu/optics/lightandcolor/refraction.html
Due to refraction, light loses its speed. The wavelength of the light changes as it penetrates from
one medium to another. When a white light passes through a prism, its wavelength changes and
appears as a spectrum of seven colours referred to as rainbow colours. Figure 1.21 shows the
details of light spectrum.
Figure 1.21
White light refraction through a prism
Ref: http://www.123rf.com/photo_7114848_light-dispersion-illustration-hi-res-3d-rendering.html
Light and Optics 15
Images captured by the eye or the camera are possible because light penetrates through the eye or
the camera lens and leaves an image on them.
1.7 Basis of lenses
1.7.1 Contrast Transfer Function (CTF) and Modulation Transfer Function
(MTF)
Contrast Transfer Function (CTF) is used to evaluate and compare the performances of different
microscopes.
Definition: CTF is the function which modulates the amplitudes and phases of the electron
diffraction pattern formed in the back focal plane of the objective lens. A chart consisting of white
and black strips is used to measure the resolution of the lens. The white and black stripes are
usually referred to as lines per millimetre. CTF is a characteristic which shows the response of the
lens to various densities of the lines per millimetre.
In TV lenses, the characteristic of a lens is similar to a continuous variation because the optical
signal is converted in to an electrical signal. This characteristic is known as Modulation Transfer
Function (MTF).
In practice, it is easy to produce black and white strips than producing continuous variation
between the black and white strips. CTF is much easier to measure than MTF.
CTF is analogous to Modulation Transfer Function (MTF). In electrical engineering, MTF is used
for modulation in the output signal to the signal frequency. CTF graphs the percentage contrast as a
function of spatial frequency and thereby characterizes the information transmission capability of
optical systems. The intensity recorded at zero spatial frequency in the CTF is a quantification of
the average brightness of the image.
CTF is a performance measure of an imaging system and can be determined for the functional
components of the imaging system. Performance of a system can be determined as a product of the
CTF curves for each component. Modifications performed in magnification and concomitant
adjustments of pixel geometry will result in improvement of CTF.
Figure 1.22
CTF and MTF
Ref: http://www.microscopyu.com/articles/optics/mtfintro.html
16 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems16
CTF is given by the following equation:
( ) ⎥⎦
⎤
⎢⎣
⎡
ΠΔ+
Π
−= 243
5
2
sin kfkCkT λλ
Where:
Cs = The quality of the objective lens defined by spherical aberration coefficient
l = Wave-length defined by accelerating voltage
Δf = The defocus value
k = Spatial frequency
Figure 1.23
CTF plot for an imaginary 200 keV plot microscope
(a) When envelope functions are not applied
(b) When envelope functions are applied
MTF is similar to CTF except that MTF uses sine wave spatial frequencies and CTF uses square
wave. MTF is an important aid to objective evaluation of the image forming capability of an optical
system.
Due to the errors in the optics, such as manufacturing, assembly and alignment errors, the overall
performance of the system decreases. As a result the dark and light shades, or the image in the
image plane, will not be the same as that of the original patterns. At zero spatial frequency, MTF is
normalized to unity. If spatial frequency is low the value of MTF is close to 1 and decreases as the
spatial frequency increases and reaches zero. This is the limit of resolution and the cut-off
frequency for a given optical system.
Spatial frequency
Spatial frequency is the characteristic of any structure that is periodic in space. It refers to the
number of pairs of bars imaged within a given distance of a retina.
Spatial frequency is never constant and it varies up and down and from point to point. Modulation
‘M’ for a given spatial frequency ‘ν’ is given as:
II
)I-(I
M(v)
minmax
minmax
+
=
Where:
I max = maximum intensities
I min = minimum intensities
Light and Optics 17
MTF is given as:
(v)M
(v)M
(v)MTF
object
image
=
Figure 1.24
MTF curves for two different lenses
1.7.2 Camera Lens
Lens selection is based on a number of lens characteristics and specifications. The science of
optical lenses is a very large subject and will not be covered in any great depth in this manual.
However a few lens terms need to be defined. Note a very simplistic approach has been used in the
following cases.
Focal Length (f): the distance between the optical centre of the lens and the principle focus. See
Figure 1.25.
Effective Aperture (N'): the diameter of the opening within the lens system which controls the
amount of light passed by the lens to the camera pickup device. See Figure 1.25.
Relative Aperture (N): also referred to as the f/stop number. It is obtained by dividing the FOCAL
LENGTH of the lens by the EFFECTIVE APERTURE. The effective aperture is shown, for
example, as f/5.6. The following list shows the standard f/stops - f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8,
f/11, f/16 and f/22.
Iris: usually an almost circular, variable diameter opening within the lens system, which when
reduced in diameter, reduces the amount of light transmitted by the lens to the pickup device. As
the diameter of the iris is reduced the Effective Aperture is reduced, the brightness of the image
reduces and the Depth of Field is increased. See Figure 1.25.
Field of View (FOV or w): also referred to as Angle of View. This is the vertical and horizontal
angles which the lens covers and is related to the Focal Length of the lens. A short focal length
results in a large angle of view. As the focal length increases the angle reduces. See Figure 1.26.
Depth of Field (T): the distance over which a subject may extend when the lens is focussed as
sharply as possible on one part of it, without the image becoming noticeably un-sharp. See Figure
1.27.
All these characteristics interact with one another and figure 1.25 shows the basic lens parameters.
In reality the lens of the camera would be a number of lens elements, but this diagram will aid in
explaining the characteristics of the lenses that must be considered.
18 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems18
Figure 1.25
Basic lens parameters
Figure 1.26
Field of view
Figure 1.27
Depth of Field
Figure 1.26 shows how the field of view is reduced as the focal length is increased. This results in a
close up or telephoto type of lens and the short focal length results in a wide angle lens.
Light and Optics 19
A normal basic camera lens has a focal length of about 50mm which gives a field of view equal to
47ø, while 200mm gives 12ø (telephoto) and 20mm gives 94ø (wide angle). The image size is set
by the size of the pickup device being used in the camera and is usually slightly smaller than the
maximum scanned area. The focal plane is the point at which the pickup device is placed in the
optical system. Thus the image is focused at this point to give an image of height 'h'.
Depth of Field is an important consideration, as already stated, this is the area over which an image
will remain in focus. Figure 1.27 shows four lenses. In all of these diagrams the image size is the
same and the bottom two (b, d) are exactly the same, while the top two (a, c) have one of the lens
parameters changed, resulting in a reduction of the Depth of Field. In order to aid in the
comparisons, the object distance has remained the same. The object height has also remained the
same, except in Figure 1.27 (a), which is smaller, as discussed below.
The two lenses in Figure 1.27(a) and 1.27(b) are shown with the same aperture setting, only the
focal length has been adjusted. The lens in Figure 1.27(a) shows the focal length increasing,
resulting in a smaller angle of view and a reduced Depth of Field. Another point to note is that a
smaller object will result in an image of the same size, as the one below. This is due to the focal
length of the lens also setting the angle of view. Short focal lengths give a wider angle of view,
while a long focal length results in a narrow angle of view. Thus, for a wide angle lens (short focal
length) focusing becomes easier and more of the image will be in focus.
The aperture of a fixed focal length lens also controls the Depth of Field, as shown in Figures 1.27
(c) and 1.27(d). The larger the aperture, which is the same as using a larger lens, the smaller the
Depth of Field. The smallest aperture gives a very large Depth of Field, in fact a pin-hole size
aperture results in an infinite Depth of Field.
Although not shown in Figure 1.27, the distance from the lens that the object is focussed will also
result in changing Depth of Field. The dotted lines passing through the centre of the lens shows the
field of view. If these lines were extrapolated beyond the points shown and the object moved
(keeping the height of the object equal to the distance between the dotted lines), the solid ray lines
would move, changing the area known as the Depth of Field.
Moving the object closer to the lens means the ray lines would point up and down at a very steep
angle, not unlike Figure 1.27(c). While moving the object toward infinity, the ray lines begin to
spread, to give an infinite Depth of Field. The height of the object must also increase to give the
same size image on the pickup device. Inversely if the object has remained the same, the image is
going to be significantly smaller. Note, also, that objects very close to the lens will not be in focus.
This can be shown by looking at any of the lenses in Figure 1.27. The distance where the object
remains in focus, from the object to the lens, is smaller than that behind the object.
The use of an automatic focus system will thus affect the Depth of Field. However, this could be an
advantage, particularly when reversing. In this case, the image will remain in constant focus and as
the object gets so close that a collision between the object and the vehicle may occur (when the
object is very close to the lens, the Depth of Field reduces), the detail will be of more use to the
driver than that of an out of focus image.
Adjusting the aperture has already been shown to affect the Depth of Field, but a changing aperture
also reduces the amount of light being transmitted by the lens to the pickup device. The iris is used
to perform this function. Another means of adjusting the amount of light transmitted is to use a
Neutral Density (ND) Filter. Thus the iris can be opened further and the same amount of light can
be transmitted to the pickup device, while at the same time the Depth of Field remains unchanged.
Putting all this information together gives some guidelines which need to be followed when
selecting a lens. The first consideration is how wide an angle (Field of View) is required to give the
best coverage. Once this is decided, the speed of the lens (maximum Effective Aperture in relation
to the Focal Length i.e. Relative Aperture) should be considered. Thus a lens of f/1 is faster than a
lens of f/2.8.
20 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems20
The term speed of a lens relates to the exposure time in the photography field. The faster lens
allows more light to be transmitted and would be a requirement for night driving. However during
the day the iris would have to close right down. The iris and ND filters would work together to
provide the best Depth of Field and image illumination of the pickup device to provide noise free
pictures.
Depth of Field is the biggest problem, since for the system to work correctly, as much of the
displayed image must be in focus as possible. Object focus would then be set to provide the best
Depth of Field. Therefore, Depth of Field is the total area under the field in focus. A smaller depth
of field has a small area in focus and vice versa.
A larger depth of field occurs in the following cases:
• The type of lens used changes the depth of field (if a wide angle lens is used, depth of
field is larger when compared to that of a telephoto lens)
• When the F-stop setting is high
• When high resolution cameras are used.
Figure 1.28
Depth of field with different F- stops
Ref: http://audster.wordpress.com/2010/05/05/back-to-basics-part-1-the-aperture/
Figure 1.29
Near and Far focus Limits of Depth of field
Ref: http://www.learnslr.com/slr-beginner-guide/depth-of-field-explained
The selection of the lens will thus be dependent on the selection of the camera and its related
sensitivity.
Light and Optics 21
1.7.3 Focal (F) and Transmission (T) numbers
F-number
F-number is the ratio of the focal length of a lens to the effective aperture diameter. It is a measure
of lens speed and is a dimensionless quantity.
Lens light gathering ability is an important factor to be considered in an indoor environment. On a
camera the F number is adjusted in discrete steps called f-stops. F numbers are usually written as
F/x where F is the focal length and x is the aperture.
The F-number of a lens can be measured by setting up a light source behind the F-number of a lens,
thereby setting the lens to full aperture. A parallel beam of light is seen to emerge through the lens,
whose diameter can be measured. These, when divided into focal length, are called f/aperture.
More light will pass through the lens when the F-number is less. Decreasing the F-number by a
factor of 1.414 (i.e. √2) doubles the exposure and increasing it with the same factor will decrease
the exposure to half of its value. When the F-number is doubled, it increases light passing power of
a lens by a factor of 4 (i.e. 22
) and vice versa. For camera lens usage F-numbers are invariably
rounded off to whole numbers or one decimal point (e.g. f/4 or f/5.6). Hyper focal distances and
depth of field calculations always use the f/aperture of a lens, not the T stop.
T-stop
T-stop is the amount of light that passes through a lens after all the losses, such as absorption,
internal reflections and scattering. T-stops are the means used to measure the efficiency and
consistency of a lens; therefore the exposure settings for any situation are related to the T-stop. T-
stops are used for the comparison of lenses, by illuminating a piece of translucent material in the
focal plane of each lens.
The intensity of light projected through the lens is measured along the optical axis with an incident
light meter. If one lens is required to be set, at say f/5.6 for a given reading on the photometer, then
any other lens which is set similarly should give the same reading.
T-stops are always smaller (higher in number) than f/apertures, i.e. a lens set at f/5.6 may equal T6.
The differential may also be expressed as a percentage and will remain consistent throughout the
aperture range of the lens.
Example: T= f/no of aperture/root of normalized transmission, i.e. if f=1.8 and the transmission
=81% then T=1.8/ROOT 0.81 =T=2
1.8 Types of lenses
1.8.1 Manual, automatic and motorized iris lenses
The Iris is a mechanism used to vary the light falling on the imaging device. It determines the light
falling on the sensor.
Manual iris lenses
Definition: A lens with a manual adjustment to set the iris opening is known as manual iris lens.
These lenses are used for fixed lighting applications where cameras are readily accessible and the
light levels are constant. Manual iris lens cameras are not suitable for external applications as
lighting levels are constantly changing in a scene and the wrong level of light will enter the camera
as the lens cannot prevent it. Automatic electronic shutters in the camera will prevent the wrong
level of light to some extent but they are sensitive to very small changes in light levels.
22 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems22
Automatic iris lenses
The drawback of the manual iris lens can be overcome be using an automatic iris lens. An
automatic iris lens is best suited for cameras used for outdoor scenes as they can cope with the
variation of light. Two types of automatic iris lenses exist; these are discussed below.
Types of automatic iris lenses
Automatic iris lenses are categorized into two types as follows:
• Video driven automatic iris lenses
• DC driven automatic iris lenses.
In DC Automatic Iris lenses, input is taken from the camera that resembles a DC Signal, there by
representing a particular F-stop. Video Driven Automatic Iris lenses depend upon the video signal
that is originated from the camera which is determined by comparing the amplitude of a reference
voltage to the video signal that is coming from the camera, in order to check whether the iris is
opened or closed. The camera determines the amplitude of the video signal by calculating the mean
of the most recent captured image. When the video signal amplitude is more than the reference
voltage, the iris will close until the signal amplitude is reduced. The lens will open when the video
signal amplitude of the iris is below the reference signal.
Motorized iris lenses
These lenses offer remote control of the iris. Here, control action is set by the operator according to
the light conditions. The iris is adjusted by a small electric motor controlled by signals generated
from the remote operators control system. With the development of Charged Coupled Device
(CCD) cameras this type of zoom lens is becoming increasingly popular.
1.8.2 Spherical and Aspherical lenses
Spherical Lenses
Spherical lenses are those which have a sphere shaped surface i.e. they have a spherical curvature.
These lenses do not bring parallel light rays to a single focus. The focus depends on the distance of
the light ray from the centre of the lens. If the distance of the ray from the centre of the lens is far,
then the point of convergence is nearer to the lens and vice-versa. This phenomenon is called
‘focus shift’ and is illustrated in Figure 1.30.
Figure 1.30
Focus shift of a spherical lens
Ref: http://www.physicsinsights.org/simple_optics_spherical_lenses-1.html
Some of the limitations of spherical lenses are:
• High definition of the large aperture lenses, compensating spherical aberrations
• Correction of distorted images with wide angle lenses
• Compact and high quality zoom lenses.
These problems can be minimized by using aspherical lenses.
Light and Optics 23
Aspherical lenses
These lenses have a non-spherical surface to converge all light rays to a single focal point and
incorporate some optical characteristics. Aspherical lenses are smaller and lighter in weight than
the lenses which employ properties of spherical elements. They are cheaper to manufacturer and
improve optical performance.
The surface of an aspherical lens does not conform to the shape of a sphere, as shown in Figure
1.31. The moulding techniques and hybrid elements of the glass/polymer structure of the aspherical
lens allows economical production. Aspherical lenses are commonly used for the aberration
correction level needed for illumination systems. Aspherical lenses have an advantage of shorter
focal length and larger aperture than compared to spherical lenses of equal diameter and spherical
aberration correction.
Aspherical lenses are attached to video camera lenses to reduce focal length and act as a wide angle
converter. An aspherical auto iris lens is shown in Figure 1.32.
Figure 1.31
Aspherical lens
http://www.arri-rental.com/camera/lenses/35mm-prime-lenses/zeiss-master-prime-lenses/zoom-in.html
Figure 1.32
Aspherical auto iris lens
Ref: http://www.directindustry.com/prod/geutebruck/camera-objective-lenses-28815-210256.html
Spherical aberration
High-angle rays are brought to a premature focus by lens aberrations so that the point object
appears blurred in the image plane. This is illustrated in Figure 1.33.
Figure 1.33
Spherical aberration
1.8.3 Zoom lenses
Zoom lenses have the advantage of varying focal lengths. The focal length can be adjusted by
turning a ring on the lens, also referred to as twist zoom. In some older versions of this type of lens,
24 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems24
the zooming action was performed by pushing and pulling the lens. The latest zoom lenses give a
lot of flexibility as they can be adjusted by turning the zoom ring.
Figure 1.34
Image of a lily pod taken from the middle of the pond with a zoom lens
Figure 1.35
Zoom Lens
1.8.4 Fixed focal length lenses
Lenses with constant focal length are referred to as fixed focal length lenses or prime lenses.
Zooming is not possible with this type of lens and the camera would need to be moved closer to the
object if zooming is required. The advantage of using this type of lens is that they are lighter in
weight and smaller when compared to zoom lenses. Their construction does not need multiple
pieces of glass (known as elements).
Figure 1.36
Fixed focal length lens
1.9 Lenses as applied in CCTV
1.9.1 Image and lens formats in CCTV
A camera images the angular extent of a given scene and this is referred to as the ‘angle of vision’.
This vision is equal in all directions when an object is viewed through a lens and is conical in
shape. The image projected by the lens is spherical in shape and the camera sensor is rectangular in
shape, irrespective of the imaging circle.
For example: Consider a 1.27 cm portion on a 1.693cm chip. A lens of a bigger format will project
an image circle much larger than the actual chip size. If a bigger lens is used on a smaller chip,
there will be no corners cut off or any other deformation.
Light and Optics 25
When there is a reduction in the imaging pickup, a reduction of relative resolution is observed as
the area used is very small. Apart from this, the CCD blocks the excessive light which is around the
chip that in turn may be reflected inside the lens.
The images will be affected if there are surfaces that are not neutralized sufficiently with a black
metal finish.
1.9.2 Angle of view
The angle of view of a camera is the angular extent of a given screen. It can be measured
horizontally, vertically or diagonally, but the horizontal view is used as a reference. The angle of
view differs with the focal length of the lens. The following rules should be observed when
analysing the angle of view:
• As the focal length decreases, the angle of view becomes wider and vice versa
• With the same lens, as the size of the CCD chip decreases, the angle of view becomes
narrower
• The vertical angle of view can be determined if the horizontal angle of view is
known.
A viewfinder calculator (see Figure 1.37) and an optical viewfinder (see Figure 1.38) are the two
instruments used for finding the angle of view. Most camera and lens manufacturers provide useful
on-line tools to calculate the angle of view. Software CCTV Installation tools can also be used.
A viewfinder calculator is round or ruler shaped. Different parameters such as the CCD chip size,
camera and object distance and object width are used to determine the focal length. Optical
viewfinders are used by photographers to gain focus on an image.
Figure 1.37
Various lens calculators
Ref:http://sliderulemuseum.com/HSRC/38621.jpg
26 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems26
Figure 1.38
Optical view finder
1.9.3 C-mount, CS-mount and back focus
There are two standards for distance between the back-flange of the lens and the CCD image plane.
They are:
• C-mount
• CS-mount.
C-mount
C-mount is denoted as 17.5mm. This standard has been used since the early days of the tube
cameras. It consists of a metal ring with 1.00/32mm thread and the front surface area is 17.5mm
away from the image plane.
CS-mount
A mount used for smaller cameras and lens design is CS-mount and it is denoted as 12.5mm. In
this, the same thread is used as in the case of the C-mount, but is approximately 5mm closer to the
image plane. This preserves compatibility with the old C-mount format. It allows cheaper and
smaller lenses to be manufactured to suit smaller CCD chip sizes.
C and CS mount lens are shown in Figure 1.39.
Figure 1.39
C and CS mount lens
Ref: http://www.icpdas.com/products/Vision/mavis/vision_glossary_a~m.htm
1.10 Back-focus Adjustment
When a lens’ back-flange is adjusted in relation to the CCD image plane, it is referred to as back-
focusing. This concept is very useful when zoom lenses are used in CCTV. The output for the
zoom lens, when focused at different distance objects, is shown in Figure 1.40. The optic-CCD
distance in zoom lenses has to be precise in order to achieve good focus throughout the zoom
range. Back-focusing adjustment is performed with a low F-Stop.
Back focus is the distance from the last glass surface of a lens to the focused image on the sensor.
Light and Optics 27
When the camera is zoomed in and focused clearly, but the zoom out makes the images go out of
focus, then it is termed as a back focus problem. This is a problem associated only with zoom
lenses.
The back focus adjustment is performed at the back of the lens barrel, near the camera body.
Because the back focus lens is designed to stay in one place, a little lever has to be loosened in
order to move this ring. Once the adjustments are final, the level should be carefully twisted back
in tightly so the back focus isn’t accidentally disturbed.
Figure 1.40
Zoom lens focusing at different distance objects
Ref:http://thecareyadventures.com/blog/2011/aperture-31-days-to-better-photography/
Methods that assist with opening the iris to the maximum extent are as follows:
• Adjust the back-focus at low light levels in the workshop
• Adjust the back-focus in the late afternoon
• Adjust the back-focus at daytime by using external ND filters
• If a camera with CCD iris is used then the optical iris can be opened fully, even
during daylight, as the CCD iris will compensate for excessive light.
1.11 Neutral Density filter (ND filter)
A neutral density filter is a light filter which is used to reduce the intensity of light passing through
the lens. It filters the light spectrum evenly without affecting the colour and contrast. They are
generally gray in colour. The effect of the filter depends on the depth of the gray colour. This filter
is also referred to as gray filter or ND filter.
Figure 1.41
ND4 and ND8 filters
If the shutter speed is kept constant and an ND filter is added, aperture must be increased to
maintain the same exposure.
28 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems28
Figure 1.42
Relation between aperture and the shutter speed
An ND filter can be used with all types of film and video cameras, but is especially valuable when
working with high-speed films or long-exposure motion applications.
Different ND filter manufacturers may use different ways to indicate the amount of light an ND
filter can reduce or attenuate. There are two typical systems as shown in Table 1.4.
Table 1.4
Indication of the amount of light an ND filter can reduce
Density Reduction
of F-stops
0.1
3
1
0.2
3
2
0.3 1
0.4
3
1
1
0.5
3
2
1
0.6 2
0.7
3
1
2
0.8
3
2
2
0.9 3
1.0
3
1
3
2.0
3
2
6
3.0 10
4.0
3
1
13
For example, ND filters marked as 0.3, 0.6 and 0.9 reduce the light by one, two and three stops.
ND’s marked as 2×, 4× and 8× indicate reducing 1 (i.e. 2=21
), 2 (i.e., 4=22
), and 3 (i.e., 8=23
) stops.
ND2, ND4 and ND8 mean they reduce the light by one, two and three stops, respectively.
Light and Optics 29
When a slower shutter speed is used, moving objects may appear blurred creating a sense of
motion, see Figure 1.43.
Figure 1.43
Image when slower shutter speed is used with both ND4 and ND8 filters
(Ref: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-ND.html)
ND filters are used to open up the aperture while maintaining constant shutter speed. See Figure
1.44.
Figure 1.44
Image with larger aperture
(a) With no ND filter
(b) With ND4 Filter
(c) With ND8 filter
(Ref: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-ND.html)
Note: Remember that a larger aperture results in a smaller Depth of Field. The images in Figure
1.44 were all taken with a shutter speed of 1/30 second. The left image used F10.7 and no filter, the
statue and background are all in focus. Using a ND4 filter reduces the aperture to F5.4, the
background is now blurred and the statue is isolated from the background. Using the ND8 filter
reduces the aperture to F3.9, now the statue is well isolated from the background and shows a sense
of distance.
ND filters can be stacked together and the effect is to multiply the attenuation, although doing so
may produce underexposed images.
ND filters can be fitted to the lens externally by screwing them to the front of the lens. See Figure
1.41. ND filters can also be found built into the lens body and can be variable density discs or
rotating wheel with different ND filters fitted to the disc.
1.12 Summary
This chapter summarizes the following:
• Objects are classified as luminous and non-luminous bodies. Luminous bodies are
those which generate light, for example, the sun, stars, etc. Non-luminous bodies are
those which do not produce light, but reflect the light which falls on them. Light is
electromagnetic radiation.
30 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems30
• Visible light falls between the range of 400nm and 700nm in the electro magnetic
spectrum, where 400nm is violet light and 700nm is red. The eye shows the greatest
reaction towards green colour, as and when green colour falls on it. The largest
amount of the sun’s energy that penetrates through the earth’s atmosphere is in the
range of 555nm.
• Red, green and blue are primary colours and secondary colours can be formed by
using the additive process.
• A human eye is made up of millions of cells called cones and rods. Cones are
sensitive towards medium and high intensity light where as the rods are sensitive
towards low light levels.
• Luminous intensity is the illuminating power of a primary light source, radiated in all
directions. The associated unit of measurement is candela (cd).
• Luminous Flux is the luminous intensity, but in a certain solid angle. The unit of
measurement for luminous intensity is 4П (pi) radians and is measured in lumens
(lm).
• Illumination of a surface is the amount of luminous flux on a unit area.
• Luminous is defined as the brightness of a surface either of a primary or secondary
light source. The unit of measurement for surface intensity is Ft-Cd (Foot-Candle).
• There are three colours in a Cathode Ray Tube (CRT), red, blue and green.
• The relationship between the peak wavelengths radiated, and the temperature to
which a body is heated, is given as λm=2896/T. Where, λ is wavelength, T is
temperature.
• Persistence depends on the intensity of light and brightness to be able to see a picture
in motion. Pictures have to change quickly as to avoid flicker, when logical
consecutive pictures are played.
• There are three basic television systems. These are PAL (Phase Alternating Line),
NTSC (National Television System Committee), and SECAM (Sequential Couleur
Avec Memoire or Sequential Colour with Memory).
• PAL : 625 Scanning Lines / 50 Interlaced Pictures Per Second
• NTSC : 525 Scanning Lines /60 Interlaced Pictures Per Second
• SECAM: 625 Scanning Pictures (Used To Be 819) /50 Interlaced Pictures Per
Second
• Both the eye and camera are similar in process but different in function.
• When light travelling in a straight line strikes a plane mirror it bounces back at an
angle, this is referred to as reflected light. This phenomenon is referred to as
reflection.
• Penetration of light through different mediums is called refraction
• The speed and wavelength of light changes due to refraction
• The basic type of lenses used in optics are concave and convex lenses
Light and Optics 31
• The factors that determine lens quality are lens design, element manufacture,
mechanical composition and electronics (refers to automatic iris and motorized
lenses).
• CTF is used to evaluate and compare the performances of different microscopes.
• CTF is the function which modulates the amplitudes and phases of the electron
diffraction pattern formed in the back focal plane of the objective lens.
• MTF is similar to CTF, except that MTF uses sine wave spatial frequencies and CTF
uses square wave.
• Spatial frequency: The characteristic of any structure that is periodic in space. It
refers to the number of pairs of bars imaged within a given distance of a retina.
• F-number is the ratio of the focal length of a lens to the effective aperture diameter.
• T-stop is the amount of light that passes through a lens after all the losses like
absorption, internal reflections and scattering.
• Depth of field is the total area under the field in focus. Smaller depth of field has a
small area in focus and vice versa.
• An iris is a mechanism used to vary the light falling on the imaging device. It
determines the light falling on the sensor.
• A lens with a manual adjustment to set the iris opening is known as Manual Iris lens.
• An automatic iris lens is best suited for cameras used for outdoor scenes.
• Automatic iris lenses are categorized into two types as follows:
• Video driven automatic iris lenses
• DC driven automatic iris lenses
• Motorized lenses offer remote control of the iris.
• Spherical lenses are those which have a sphere shaped surface. Focus shift occurs in
spherical lenses.
• Aspherical lenses have a non-spherical surface to converge all the light rays to a
single focal point.
• Spherical aberration: High-angle rays are brought to a premature focus by lens
aberrations so that the point object appears blurred in the image plane.
• Zoom lenses have the advantage of variable focal lengths.
• Lenses with constant focal length are referred to as fixed focal length lenses or prime
lenses.
• A camera images the angular extent of a given screen and this is referred to as the
angle of vision.
• The angle of view of a camera is the angular extent of a given screen.
32 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems32
• A viewfinder calculator and optical viewfinder are the two instruments used for
finding the angle of view.
• There are two standards for distance between the back-flange of the lens and the CCD
image plane. They are:
• C-mount
• CS-mount
• Back focus is the distance from the last glass surface of a lens to the focused image
on the sensor.
• When the camera is zoomed in and focused clearly, but the zoom out makes the
images fall out of focus, then this is referred to as a back focus problem.
• ND Filters can be used to reduce the amount of light entering the lens.
• Some modern lenses have internal ND filter discs.

More Related Content

What's hot

micro:bit亮度感測應用
micro:bit亮度感測應用micro:bit亮度感測應用
micro:bit亮度感測應用
吳錫修 (ShyiShiou Wu)
 
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
The Air Force Office of Scientific Research
 
Image formation & rad quality
Image formation & rad quality Image formation & rad quality
Image formation & rad quality
MeritaKOXHAJ
 
Makalah visible light[1]
Makalah visible light[1]Makalah visible light[1]
Makalah visible light[1]
hikmahyani567
 
Wave
WaveWave
Capturing images
Capturing imagesCapturing images
Capturing images
Richie Merkz
 
Principle of lumination design
Principle of lumination designPrinciple of lumination design
Principle of lumination design
wasim shaikh
 
LED optics in Flashlight
LED optics in FlashlightLED optics in Flashlight
LED optics in Flashlight
canfang
 
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
Shimadzu Scientific Instruments
 
Dukane 8421 DLP projector
Dukane 8421 DLP  projectorDukane 8421 DLP  projector
Dukane 8421 DLP projector
SchoolVision Inc.
 
Physics pp presntation ch 14
Physics pp presntation ch 14Physics pp presntation ch 14
Physics pp presntation ch 14
josoborned
 
Dukane 8420 dlp projector
Dukane 8420 dlp projectorDukane 8420 dlp projector
Dukane 8420 dlp projector
SchoolVision Inc.
 
Display performance and their physics
Display performance and their physicsDisplay performance and their physics
Display performance and their physics
Brian Kim, PhD
 
The light
The lightThe light
The light
Ciera_Johl
 

What's hot (14)

micro:bit亮度感測應用
micro:bit亮度感測應用micro:bit亮度感測應用
micro:bit亮度感測應用
 
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
Inside the Wavelength: Seeing Really Small Objects with Light - Professor Sir...
 
Image formation & rad quality
Image formation & rad quality Image formation & rad quality
Image formation & rad quality
 
Makalah visible light[1]
Makalah visible light[1]Makalah visible light[1]
Makalah visible light[1]
 
Wave
WaveWave
Wave
 
Capturing images
Capturing imagesCapturing images
Capturing images
 
Principle of lumination design
Principle of lumination designPrinciple of lumination design
Principle of lumination design
 
LED optics in Flashlight
LED optics in FlashlightLED optics in Flashlight
LED optics in Flashlight
 
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
Characterization of Light Emitting Diodes and Compact Fluorescent Lamps by UV...
 
Dukane 8421 DLP projector
Dukane 8421 DLP  projectorDukane 8421 DLP  projector
Dukane 8421 DLP projector
 
Physics pp presntation ch 14
Physics pp presntation ch 14Physics pp presntation ch 14
Physics pp presntation ch 14
 
Dukane 8420 dlp projector
Dukane 8420 dlp projectorDukane 8420 dlp projector
Dukane 8420 dlp projector
 
Display performance and their physics
Display performance and their physicsDisplay performance and their physics
Display performance and their physics
 
The light
The lightThe light
The light
 

Viewers also liked

Beyond Touchscreens: Designing Great TV Apps
Beyond Touchscreens: Designing Great TV AppsBeyond Touchscreens: Designing Great TV Apps
Beyond Touchscreens: Designing Great TV Apps
Eric Elia
 
Oracle ADF Architecture TV - Design - Designing for Internationalization
Oracle ADF Architecture TV - Design - Designing for InternationalizationOracle ADF Architecture TV - Design - Designing for Internationalization
Oracle ADF Architecture TV - Design - Designing for Internationalization
Chris Muir
 
Investigating personalisation when designing remote controls for smart TV - R...
Investigating personalisation when designing remote controls for smart TV - R...Investigating personalisation when designing remote controls for smart TV - R...
Investigating personalisation when designing remote controls for smart TV - R...
Sarah Mizzi
 
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
Living Online
 
Hybrid digital broadcasting methods
Hybrid digital broadcasting methodsHybrid digital broadcasting methods
Hybrid digital broadcasting methods
fungfung Chen
 
Lumi legend profile
Lumi legend profileLumi legend profile
Lumi legend profile
LumiLegend NingBo
 
Practical DNP3 and Modern SCADA Systems
Practical DNP3 and Modern SCADA SystemsPractical DNP3 and Modern SCADA Systems
Practical DNP3 and Modern SCADA Systems
Living Online
 
Lcd & led tv technologies
Lcd & led tv technologiesLcd & led tv technologies
Lcd & led tv technologies
Mohammad Ali Khan
 
You’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
You’ve Only Got Two Eyeballs: Designing Products for the Responsive WebYou’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
You’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
David Sherwin
 
Flat Panel Display
Flat Panel DisplayFlat Panel Display
Flat Panel Display
Prateek Malik
 
Researcher KnowHow: Getting Published with IEEE
Researcher KnowHow: Getting Published with IEEEResearcher KnowHow: Getting Published with IEEE
Researcher KnowHow: Getting Published with IEEE
LivUniLibrary
 
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECTMOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
Sindhu Ashok
 
SONY Bravia : Strategic Sales Management
SONY Bravia : Strategic Sales ManagementSONY Bravia : Strategic Sales Management
SONY Bravia : Strategic Sales Management
Ayush Parekh
 
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
Inhacking
 
Python 101: Python for Absolute Beginners (PyTexas 2014)
Python 101: Python for Absolute Beginners (PyTexas 2014)Python 101: Python for Absolute Beginners (PyTexas 2014)
Python 101: Python for Absolute Beginners (PyTexas 2014)
Paige Bailey
 
TV Nights: Designing Your MVE/MVP
TV Nights: Designing Your MVE/MVPTV Nights: Designing Your MVE/MVP
TV Nights: Designing Your MVE/MVP
Guita Gopalan
 
Sales & Operations Planning Process
Sales & Operations Planning ProcessSales & Operations Planning Process
Sales & Operations Planning Process
Harshal Badgujar
 
Learn 90% of Python in 90 Minutes
Learn 90% of Python in 90 MinutesLearn 90% of Python in 90 Minutes
Learn 90% of Python in 90 Minutes
Matt Harrison
 
Simple Steps to UX/UI Web Design
Simple Steps to UX/UI Web DesignSimple Steps to UX/UI Web Design
Simple Steps to UX/UI Web Design
Koombea
 
The Outcome Economy
The Outcome EconomyThe Outcome Economy
The Outcome Economy
Helge Tennø
 

Viewers also liked (20)

Beyond Touchscreens: Designing Great TV Apps
Beyond Touchscreens: Designing Great TV AppsBeyond Touchscreens: Designing Great TV Apps
Beyond Touchscreens: Designing Great TV Apps
 
Oracle ADF Architecture TV - Design - Designing for Internationalization
Oracle ADF Architecture TV - Design - Designing for InternationalizationOracle ADF Architecture TV - Design - Designing for Internationalization
Oracle ADF Architecture TV - Design - Designing for Internationalization
 
Investigating personalisation when designing remote controls for smart TV - R...
Investigating personalisation when designing remote controls for smart TV - R...Investigating personalisation when designing remote controls for smart TV - R...
Investigating personalisation when designing remote controls for smart TV - R...
 
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
Troubleshooting, Designing & Installing Digital & Analog Closed Circuit TV Sy...
 
Hybrid digital broadcasting methods
Hybrid digital broadcasting methodsHybrid digital broadcasting methods
Hybrid digital broadcasting methods
 
Lumi legend profile
Lumi legend profileLumi legend profile
Lumi legend profile
 
Practical DNP3 and Modern SCADA Systems
Practical DNP3 and Modern SCADA SystemsPractical DNP3 and Modern SCADA Systems
Practical DNP3 and Modern SCADA Systems
 
Lcd & led tv technologies
Lcd & led tv technologiesLcd & led tv technologies
Lcd & led tv technologies
 
You’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
You’ve Only Got Two Eyeballs: Designing Products for the Responsive WebYou’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
You’ve Only Got Two Eyeballs: Designing Products for the Responsive Web
 
Flat Panel Display
Flat Panel DisplayFlat Panel Display
Flat Panel Display
 
Researcher KnowHow: Getting Published with IEEE
Researcher KnowHow: Getting Published with IEEEResearcher KnowHow: Getting Published with IEEE
Researcher KnowHow: Getting Published with IEEE
 
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECTMOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
MOVIE TICKET BOOKING-COMPUTER SCIENCE C++ PROJECT
 
SONY Bravia : Strategic Sales Management
SONY Bravia : Strategic Sales ManagementSONY Bravia : Strategic Sales Management
SONY Bravia : Strategic Sales Management
 
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
SE2016 UI/UX Alina Kononenko "Designing for Apple Watch and Apple TV"
 
Python 101: Python for Absolute Beginners (PyTexas 2014)
Python 101: Python for Absolute Beginners (PyTexas 2014)Python 101: Python for Absolute Beginners (PyTexas 2014)
Python 101: Python for Absolute Beginners (PyTexas 2014)
 
TV Nights: Designing Your MVE/MVP
TV Nights: Designing Your MVE/MVPTV Nights: Designing Your MVE/MVP
TV Nights: Designing Your MVE/MVP
 
Sales & Operations Planning Process
Sales & Operations Planning ProcessSales & Operations Planning Process
Sales & Operations Planning Process
 
Learn 90% of Python in 90 Minutes
Learn 90% of Python in 90 MinutesLearn 90% of Python in 90 Minutes
Learn 90% of Python in 90 Minutes
 
Simple Steps to UX/UI Web Design
Simple Steps to UX/UI Web DesignSimple Steps to UX/UI Web Design
Simple Steps to UX/UI Web Design
 
The Outcome Economy
The Outcome EconomyThe Outcome Economy
The Outcome Economy
 

Similar to Troubleshooting, Designing, & Installing Digital & Analog Closed Circuit TV Systems

Uee unit 4
Uee unit 4Uee unit 4
Uee unit 4
Sanjay Gohil
 
Illumination.
Illumination.Illumination.
Illumination.
Shabina Yasmin
 
1585680250EEE_552_Slides.ppt
1585680250EEE_552_Slides.ppt1585680250EEE_552_Slides.ppt
1585680250EEE_552_Slides.ppt
SolankiParthS
 
Illumination.ppt
Illumination.pptIllumination.ppt
Illumination.ppt
Sivakumar Chellamuthu
 
Photometry
Photometry Photometry
Photometry
Mero Eye
 
chapter02.pdf
chapter02.pdfchapter02.pdf
chapter02.pdf
ssuser80eb8f
 
Computer vision - light
Computer vision - lightComputer vision - light
Computer vision - light
Wael Badawy
 
Lightning for network videos
Lightning for network videosLightning for network videos
Lightning for network videos
Axis Communications
 
Chapter 2
Chapter 2Chapter 2
Chapter 2
Mary Haas
 
Elements of Visual Perceptions Structure
Elements of Visual Perceptions StructureElements of Visual Perceptions Structure
Elements of Visual Perceptions Structure
Harmanjot5678
 
ELECTRICAL UTILISATION AND TRACTION
ELECTRICAL UTILISATION AND TRACTIONELECTRICAL UTILISATION AND TRACTION
ELECTRICAL UTILISATION AND TRACTION
SekharVadde1
 
Reflection-refraction.ppt
Reflection-refraction.pptReflection-refraction.ppt
Reflection-refraction.ppt
HaifaChaoshinAli
 
Reflection-refraction.ppt
Reflection-refraction.pptReflection-refraction.ppt
Reflection-refraction.ppt
simonckt1
 
Lect 02 first portion
Lect 02   first portionLect 02   first portion
Lect 02 first portion
Moe Moe Myint
 
Lect 02 first portion
Lect 02   first portionLect 02   first portion
Lect 02 first portion
Moe Moe Myint
 
03-Digital Image Fundamentals (5)as.pptx
03-Digital Image Fundamentals (5)as.pptx03-Digital Image Fundamentals (5)as.pptx
03-Digital Image Fundamentals (5)as.pptx
meharwanwadhwanibscs
 
03-Digital Image Fundamentals (1) Computer .pptx
03-Digital Image Fundamentals (1) Computer .pptx03-Digital Image Fundamentals (1) Computer .pptx
03-Digital Image Fundamentals (1) Computer .pptx
meharwanw
 
Lecture 2
Lecture 2Lecture 2
Lecture 2
QC Labs
 
Raffles Institute_Perception of light and Photometric Character
Raffles Institute_Perception of light and Photometric CharacterRaffles Institute_Perception of light and Photometric Character
Raffles Institute_Perception of light and Photometric Character
Sandra Draskovic
 
02 lecture 16 april
02 lecture 16 april02 lecture 16 april
02 lecture 16 april
Anisur Rahman
 

Similar to Troubleshooting, Designing, & Installing Digital & Analog Closed Circuit TV Systems (20)

Uee unit 4
Uee unit 4Uee unit 4
Uee unit 4
 
Illumination.
Illumination.Illumination.
Illumination.
 
1585680250EEE_552_Slides.ppt
1585680250EEE_552_Slides.ppt1585680250EEE_552_Slides.ppt
1585680250EEE_552_Slides.ppt
 
Illumination.ppt
Illumination.pptIllumination.ppt
Illumination.ppt
 
Photometry
Photometry Photometry
Photometry
 
chapter02.pdf
chapter02.pdfchapter02.pdf
chapter02.pdf
 
Computer vision - light
Computer vision - lightComputer vision - light
Computer vision - light
 
Lightning for network videos
Lightning for network videosLightning for network videos
Lightning for network videos
 
Chapter 2
Chapter 2Chapter 2
Chapter 2
 
Elements of Visual Perceptions Structure
Elements of Visual Perceptions StructureElements of Visual Perceptions Structure
Elements of Visual Perceptions Structure
 
ELECTRICAL UTILISATION AND TRACTION
ELECTRICAL UTILISATION AND TRACTIONELECTRICAL UTILISATION AND TRACTION
ELECTRICAL UTILISATION AND TRACTION
 
Reflection-refraction.ppt
Reflection-refraction.pptReflection-refraction.ppt
Reflection-refraction.ppt
 
Reflection-refraction.ppt
Reflection-refraction.pptReflection-refraction.ppt
Reflection-refraction.ppt
 
Lect 02 first portion
Lect 02   first portionLect 02   first portion
Lect 02 first portion
 
Lect 02 first portion
Lect 02   first portionLect 02   first portion
Lect 02 first portion
 
03-Digital Image Fundamentals (5)as.pptx
03-Digital Image Fundamentals (5)as.pptx03-Digital Image Fundamentals (5)as.pptx
03-Digital Image Fundamentals (5)as.pptx
 
03-Digital Image Fundamentals (1) Computer .pptx
03-Digital Image Fundamentals (1) Computer .pptx03-Digital Image Fundamentals (1) Computer .pptx
03-Digital Image Fundamentals (1) Computer .pptx
 
Lecture 2
Lecture 2Lecture 2
Lecture 2
 
Raffles Institute_Perception of light and Photometric Character
Raffles Institute_Perception of light and Photometric CharacterRaffles Institute_Perception of light and Photometric Character
Raffles Institute_Perception of light and Photometric Character
 
02 lecture 16 april
02 lecture 16 april02 lecture 16 april
02 lecture 16 april
 

More from Living Online

Practical Troubleshooting and Problem Solving of Modbus Protocols
Practical Troubleshooting and Problem Solving of Modbus ProtocolsPractical Troubleshooting and Problem Solving of Modbus Protocols
Practical Troubleshooting and Problem Solving of Modbus Protocols
Living Online
 
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
Living Online
 
Practical Project Management for Engineers and Technicians
Practical Project Management for Engineers and TechniciansPractical Project Management for Engineers and Technicians
Practical Project Management for Engineers and Technicians
Living Online
 
Mechanical, Electrical and Instrumentation Engineering for Non-Engineers
Mechanical, Electrical and Instrumentation Engineering for Non-EngineersMechanical, Electrical and Instrumentation Engineering for Non-Engineers
Mechanical, Electrical and Instrumentation Engineering for Non-Engineers
Living Online
 
Hands on Data-Communication, Networking and TCP/IP Troubleshooting
Hands on Data-Communication, Networking and TCP/IP TroubleshootingHands on Data-Communication, Networking and TCP/IP Troubleshooting
Hands on Data-Communication, Networking and TCP/IP Troubleshooting
Living Online
 
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Living Online
 
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
Living Online
 
Practical Energy Efficiency, Design, Engineering & Auditing
Practical Energy Efficiency, Design, Engineering & AuditingPractical Energy Efficiency, Design, Engineering & Auditing
Practical Energy Efficiency, Design, Engineering & Auditing
Living Online
 
High Voltage Electrical Compliance and Safety Operating Procedures
High Voltage Electrical Compliance and Safety Operating ProceduresHigh Voltage Electrical Compliance and Safety Operating Procedures
High Voltage Electrical Compliance and Safety Operating Procedures
Living Online
 
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
Living Online
 
Cybersecurity for Automation Control and SCADA Systems
Cybersecurity for Automation Control and SCADA SystemsCybersecurity for Automation Control and SCADA Systems
Cybersecurity for Automation Control and SCADA Systems
Living Online
 
Practical Process Control
Practical Process ControlPractical Process Control
Practical Process Control
Living Online
 
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
Living Online
 
Hands on Data Communications, Networking & TCP/IP Troubleshooting
Hands on Data Communications, Networking & TCP/IP TroubleshootingHands on Data Communications, Networking & TCP/IP Troubleshooting
Hands on Data Communications, Networking & TCP/IP Troubleshooting
Living Online
 
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Living Online
 
Practical Industrial Flow Measurement for Engineers and Technicians
Practical Industrial Flow Measurement for Engineers and TechniciansPractical Industrial Flow Measurement for Engineers and Technicians
Practical Industrial Flow Measurement for Engineers and Technicians
Living Online
 
Practical Distribution & Substation Automation (Incl. Communications) for Ele...
Practical Distribution & Substation Automation (Incl. Communications) for Ele...Practical Distribution & Substation Automation (Incl. Communications) for Ele...
Practical Distribution & Substation Automation (Incl. Communications) for Ele...
Living Online
 
Practical Boiler Control & Instrumentation for Engineers & Technicians
Practical Boiler Control & Instrumentation for Engineers & TechniciansPractical Boiler Control & Instrumentation for Engineers & Technicians
Practical Boiler Control & Instrumentation for Engineers & Technicians
Living Online
 
Practical Arc Flash Protection for Electrical Safety Engineers and Technicians
Practical Arc Flash Protection for Electrical Safety Engineers and TechniciansPractical Arc Flash Protection for Electrical Safety Engineers and Technicians
Practical Arc Flash Protection for Electrical Safety Engineers and Technicians
Living Online
 
Practical Analytical Instrumentation in On-line Applications
Practical Analytical Instrumentation in On-line ApplicationsPractical Analytical Instrumentation in On-line Applications
Practical Analytical Instrumentation in On-line Applications
Living Online
 

More from Living Online (20)

Practical Troubleshooting and Problem Solving of Modbus Protocols
Practical Troubleshooting and Problem Solving of Modbus ProtocolsPractical Troubleshooting and Problem Solving of Modbus Protocols
Practical Troubleshooting and Problem Solving of Modbus Protocols
 
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
Practical Routers and Switches including TCI/IP and Ethernet for Engineers an...
 
Practical Project Management for Engineers and Technicians
Practical Project Management for Engineers and TechniciansPractical Project Management for Engineers and Technicians
Practical Project Management for Engineers and Technicians
 
Mechanical, Electrical and Instrumentation Engineering for Non-Engineers
Mechanical, Electrical and Instrumentation Engineering for Non-EngineersMechanical, Electrical and Instrumentation Engineering for Non-Engineers
Mechanical, Electrical and Instrumentation Engineering for Non-Engineers
 
Hands on Data-Communication, Networking and TCP/IP Troubleshooting
Hands on Data-Communication, Networking and TCP/IP TroubleshootingHands on Data-Communication, Networking and TCP/IP Troubleshooting
Hands on Data-Communication, Networking and TCP/IP Troubleshooting
 
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
 
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
Practical Fundamentals of Heating, Ventilation & Air-Conditioning (HVAC) for ...
 
Practical Energy Efficiency, Design, Engineering & Auditing
Practical Energy Efficiency, Design, Engineering & AuditingPractical Energy Efficiency, Design, Engineering & Auditing
Practical Energy Efficiency, Design, Engineering & Auditing
 
High Voltage Electrical Compliance and Safety Operating Procedures
High Voltage Electrical Compliance and Safety Operating ProceduresHigh Voltage Electrical Compliance and Safety Operating Procedures
High Voltage Electrical Compliance and Safety Operating Procedures
 
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
Practical Routers & Switches (Including TCPIP and Ethernet) for Engineers and...
 
Cybersecurity for Automation Control and SCADA Systems
Cybersecurity for Automation Control and SCADA SystemsCybersecurity for Automation Control and SCADA Systems
Cybersecurity for Automation Control and SCADA Systems
 
Practical Process Control
Practical Process ControlPractical Process Control
Practical Process Control
 
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
Inspection, Testing and Commissioning of Electrical Switchboards, Circuit Bre...
 
Hands on Data Communications, Networking & TCP/IP Troubleshooting
Hands on Data Communications, Networking & TCP/IP TroubleshootingHands on Data Communications, Networking & TCP/IP Troubleshooting
Hands on Data Communications, Networking & TCP/IP Troubleshooting
 
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
Fundamentals of Instrumentation, Process Control, PLCs and SCADA for Plant Op...
 
Practical Industrial Flow Measurement for Engineers and Technicians
Practical Industrial Flow Measurement for Engineers and TechniciansPractical Industrial Flow Measurement for Engineers and Technicians
Practical Industrial Flow Measurement for Engineers and Technicians
 
Practical Distribution & Substation Automation (Incl. Communications) for Ele...
Practical Distribution & Substation Automation (Incl. Communications) for Ele...Practical Distribution & Substation Automation (Incl. Communications) for Ele...
Practical Distribution & Substation Automation (Incl. Communications) for Ele...
 
Practical Boiler Control & Instrumentation for Engineers & Technicians
Practical Boiler Control & Instrumentation for Engineers & TechniciansPractical Boiler Control & Instrumentation for Engineers & Technicians
Practical Boiler Control & Instrumentation for Engineers & Technicians
 
Practical Arc Flash Protection for Electrical Safety Engineers and Technicians
Practical Arc Flash Protection for Electrical Safety Engineers and TechniciansPractical Arc Flash Protection for Electrical Safety Engineers and Technicians
Practical Arc Flash Protection for Electrical Safety Engineers and Technicians
 
Practical Analytical Instrumentation in On-line Applications
Practical Analytical Instrumentation in On-line ApplicationsPractical Analytical Instrumentation in On-line Applications
Practical Analytical Instrumentation in On-line Applications
 

Recently uploaded

一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
nedcocy
 
AN INTRODUCTION OF AI & SEARCHING TECHIQUES
AN INTRODUCTION OF AI & SEARCHING TECHIQUESAN INTRODUCTION OF AI & SEARCHING TECHIQUES
AN INTRODUCTION OF AI & SEARCHING TECHIQUES
drshikhapandey2022
 
paper relate Chozhavendhan et al. 2020.pdf
paper relate Chozhavendhan et al. 2020.pdfpaper relate Chozhavendhan et al. 2020.pdf
paper relate Chozhavendhan et al. 2020.pdf
ShurooqTaib
 
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
PriyankaKilaniya
 
FULL STACK PROGRAMMING - Both Front End and Back End
FULL STACK PROGRAMMING - Both Front End and Back EndFULL STACK PROGRAMMING - Both Front End and Back End
FULL STACK PROGRAMMING - Both Front End and Back End
PreethaV16
 
openshift technical overview - Flow of openshift containerisatoin
openshift technical overview - Flow of openshift containerisatoinopenshift technical overview - Flow of openshift containerisatoin
openshift technical overview - Flow of openshift containerisatoin
snaprevwdev
 
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEERDELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
EMERSON EDUARDO RODRIGUES
 
Supermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdfSupermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdf
Kamal Acharya
 
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdfAsymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
felixwold
 
Digital Twins Computer Networking Paper Presentation.pptx
Digital Twins Computer Networking Paper Presentation.pptxDigital Twins Computer Networking Paper Presentation.pptx
Digital Twins Computer Networking Paper Presentation.pptx
aryanpankaj78
 
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
sydezfe
 
Open Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surfaceOpen Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surface
Indrajeet sahu
 
Ericsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.pptEricsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.ppt
wafawafa52
 
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
DharmaBanothu
 
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTERUNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
vmspraneeth
 
SELENIUM CONF -PALLAVI SHARMA - 2024.pdf
SELENIUM CONF -PALLAVI SHARMA - 2024.pdfSELENIUM CONF -PALLAVI SHARMA - 2024.pdf
SELENIUM CONF -PALLAVI SHARMA - 2024.pdf
Pallavi Sharma
 
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
ydzowc
 
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
Sou Tibon
 
Accident detection system project report.pdf
Accident detection system project report.pdfAccident detection system project report.pdf
Accident detection system project report.pdf
Kamal Acharya
 
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
OKORIE1
 

Recently uploaded (20)

一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
一比一原版(爱大毕业证书)爱荷华大学毕业证如何办理
 
AN INTRODUCTION OF AI & SEARCHING TECHIQUES
AN INTRODUCTION OF AI & SEARCHING TECHIQUESAN INTRODUCTION OF AI & SEARCHING TECHIQUES
AN INTRODUCTION OF AI & SEARCHING TECHIQUES
 
paper relate Chozhavendhan et al. 2020.pdf
paper relate Chozhavendhan et al. 2020.pdfpaper relate Chozhavendhan et al. 2020.pdf
paper relate Chozhavendhan et al. 2020.pdf
 
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
 
FULL STACK PROGRAMMING - Both Front End and Back End
FULL STACK PROGRAMMING - Both Front End and Back EndFULL STACK PROGRAMMING - Both Front End and Back End
FULL STACK PROGRAMMING - Both Front End and Back End
 
openshift technical overview - Flow of openshift containerisatoin
openshift technical overview - Flow of openshift containerisatoinopenshift technical overview - Flow of openshift containerisatoin
openshift technical overview - Flow of openshift containerisatoin
 
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEERDELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
DELTA V MES EMERSON EDUARDO RODRIGUES ENGINEER
 
Supermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdfSupermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdf
 
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdfAsymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
Asymmetrical Repulsion Magnet Motor Ratio 6-7.pdf
 
Digital Twins Computer Networking Paper Presentation.pptx
Digital Twins Computer Networking Paper Presentation.pptxDigital Twins Computer Networking Paper Presentation.pptx
Digital Twins Computer Networking Paper Presentation.pptx
 
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
一比一原版(uoft毕业证书)加拿大多伦多大学毕业证如何办理
 
Open Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surfaceOpen Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surface
 
Ericsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.pptEricsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.ppt
 
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
A high-Speed Communication System is based on the Design of a Bi-NoC Router, ...
 
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTERUNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
UNIT-III- DATA CONVERTERS ANALOG TO DIGITAL CONVERTER
 
SELENIUM CONF -PALLAVI SHARMA - 2024.pdf
SELENIUM CONF -PALLAVI SHARMA - 2024.pdfSELENIUM CONF -PALLAVI SHARMA - 2024.pdf
SELENIUM CONF -PALLAVI SHARMA - 2024.pdf
 
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
原版制作(Humboldt毕业证书)柏林大学毕业证学位证一模一样
 
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
309475979-Creativity-Innovation-notes-IV-Sem-2016-pdf.pdf
 
Accident detection system project report.pdf
Accident detection system project report.pdfAccident detection system project report.pdf
Accident detection system project report.pdf
 
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
DESIGN AND MANUFACTURE OF CEILING BOARD USING SAWDUST AND WASTE CARTON MATERI...
 

Troubleshooting, Designing, & Installing Digital & Analog Closed Circuit TV Systems

  • 1. 1 Light and Optics This chapter discusses the general aspects of light and the response of the human eye towards light with different wavelengths and frequencies. Sources of light and the comparison between eye and camera are given. Reflection, refraction, the measurement of lens speed and losses as per the F and T numbers and depth of field are explained. Lens formats, angle of view of lenses, C and CS mounts and back focusing of lenses are also discussed. Learning objectives: After studying this chapter you will have a basic understanding of: • The response of human eye towards light • The different sources of light • Eye persistence in motion pictures • The difference between eye and camera • Optical elements • The basics of lenses and lens types • Back-focus adjustment and ND Filters 1.1 Introduction In general, objects are classified into two types. They are: • Luminous bodies • Non- Luminous bodies Luminous bodies are those that can generate light. For example, the sun, stars, comets and other such bodies are luminous bodies. On the other hand, objects that cannot produce light by themselves, but reflect the light that falls on them, are called non-luminous bodies. For example, the Moon, planets, humans, bricks, plastic, metals etc are non-luminous bodies. The Sun, Stars and glow-worms are natural sources of light. Apart from these natural sources of light, there are some man-made, artificial sources of light such as a wax-candle, oil-lamp, torch, electric light bulb and Light Emitting Diode (LED) etc. The intensity of light at any place is measured in terms of lumens present on unit area. This unit is called foot candle (Lux is the modern unit). One foot candle is equal to 10.76 lux.
  • 2. 2 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems2 1.2 Human eye and light Light is an electromagnetic radiation which is measured in wavelength or frequency, the same as radio signals. Wavelength is usually measured in nanometres (nm) while frequency is measured in hertz (Hz). Higher the frequency, the shorter is the wavelength. Out of the different frequencies, visible light falls in the range of 400nm to 700nm as shown in the Figure 1.1. Here, 400nm corresponds to violet and 700nm corresponds to red. There are various colours between the violet and red wavelengths, blue, blue-green, green, yellow- green, yellow, orange. All these colours produce different effects on the human eye retina. Figure 1.1 Spectrum distribution of light, with associated wavelengths Ref: http://www.sciencesway.com/vb/t6526 The eye shows its greatest reaction to green light. Green light produces the highest output on the retina where as red and violet light produces the least output. The eye’s spectral sensitivity is higher at green light, not at red or violet, because the largest amount of the sun’s energy that penetrates the earth’s atmosphere is in the range of 555nm. This is represented graphically in Figure 1.2. Figure 1.2 Response of eye at different wavelengths Ref: http://www.bunkerofdoom.com/laser/response/index.html
  • 3. Light and Optics 3 1.2.1 Additive and subtractive mixing Red, green and blue are referred to as primary colours. To produce any secondary colour we have to mix two or three primary colours in different proportions, resulting in magenta, yellow, etc. The mixing of primary colours to produce new colours is called additive mixing and the reproducing of primary colours from the secondary colours is called subtractive mixing. This is illustrated in Figure 1.3. Figure 1.3 Principle of additive mixing and subtractive mixing Television screens use additive mixing to produce the colour images we see on the screen. Printing, on the other hand, uses the secondary colours to produce a colour image on the page or photo quality paper. Hence the use of yellow, magenta and cyan toners in colour printers. 1.2.2 The human eye The Retina is a photosensitive area of the eye which is composed of millions of cells called cones and rods. Cones are sensitive to medium and bright intensity light and can also sense colour. Rod cells are sensitive to lower light levels and cannot distinguish between colours. We use the rod cells to see at night which makes it harder to distinguish colours. Cones cease to react once the level of light falling on them drops below 1 lux. The rods are 10,000 times more sensitive than the cones. There are approximately 10 million cones and over 100 million rod cells in each eye. The cross section of a human eye is shown in Figure 1.4. Figure 1.4 Cross section of the human eye Ref: http://academia.hixie.ch/bath/eye/home.html
  • 4. 4 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems4 Focusing of the eye is necessary to see objects at different distances. If focusing of the eye is affected then the eye may be considered defective. Major defects found in the eye due to lack of correct focusing are: • Hyperopia (farsightedness) • Myopia (nearsightedness) There are many other defects in the eye, although the above defects are the most common. These defects can be corrected by using different lenses. A convex lens is used to correct hyperopia (see Figure 1.5) and a concave lens is used to correct myopia (see Figure 1.6). Figure: 1.5 Correcting hyperopia through glass Figure: 1.6 Correcting myopia through glass Ref: http://www.d.umn.edu/~jfitzake/Lectures/DMED/Vision/Optics/RefractiveErrors.html In the same way that different types of lenses are used to assist focussing in the human eye, different types of lenses are used in CCTV to focus objects at different distances. 1.3 Sources of light For video surveillance in outdoor areas, artificial lighting by different light sources, such as tungsten, tungsten- halogen, metallic arc, mercury, sodium, xenon, IR lamp, LED IR arrays etc are required. These are selected according to the requirement, safety consideration and the quality of the video picture. The colour temperature of different light sources is shown in Figure 1.7.
  • 5. Light and Optics 5 Figure 1.7 Colour Temperature of different light sources Artificial lighting is the process of illuminating a scene with a high level of evenly distributed light so that each and every object, place or person available at that point is clearly visible. Figure 1.8 Spectral output range for common sources of artificial light Ref: http://www.olympusmicro.com/primer/lightandcolor/lightsourcesintro.html The temperature at which an imaginary perfect black body is heated and consequently produces light is called colour temperature. Max Plank, a German physicist and the founder of quantum theory, explains the relation between the peak wavelengths radiated and the temperature to which the body is heated as: λm=2896/T Where: • λ is wavelength in microns • T is temperature in degrees Kelvin. There are five different standard sources of “standard white light”. They are referred to as Illuminants A, B, C, D6500, and E.
  • 6. 6 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems6 Illuminant A: is a warm light with a color temperature of 2845°K. A tungsten lamp at 2800°K produces this shade of white light. Illuminant B: is close to sunlight at noon. Filtering the light from Illuminant ‘A’ gives radiation of Illuminant B i.e. white light. The correlation colour temperature of B is 4880o K. Illuminant C: is the same as diffused light from an overcast sky. When Illuminant A is filtered Illuminant C is obtained. The correlation colour temperature of C is 6770o K. Illuminant D6500: is the standard used for color TV. An average daylight colour temperature is represented by source D6500. It is a mix of direct and diffused skylight and is not obtained by filtering any other source. The correlation colour temperature is 6500o K Illuminant E: is referred to as “equal energy white”. It is a hypothetical white and is equivalent to a light source comprising all wavelengths of visible equal light. Source E has uniformly distributed radiation which looks like a flat horizontal line. It is used for calculation only. 1.3.1 Light units The science that deals with light is called photometry and the units used are called photometric units. Important terms associated with light and their units are discussed below. Luminous intensity (I) Luminous intensity is the illuminating power of a primary light source, radiated in all directions. The associated unit of measurement is the candela (cd). 1 candela is equal to approximately the amount of light energy generated by a standard candle. 1 cd is 1/60 the light emitted from 1cm2 of a black body heated to a temperature of molten platinum 2042°K. Luminous flux (F) Luminous Flux is the measure of the flow of light in one second and is measured in lumens (lm). One lumen is the quantity of luminous flux that falls on a unit area surface at a unit distance from a light source of 1 candela in one second. Luminous flux = luminous intensity (lumens)/ 4П Illumination (E) Illumination of a surface is the amount of luminous flux falling on a surface and is measured in lumens per unit area. One lux = 1 lumen per square meter (lm/m2 ) Figure 1.9 Light units and their meanings Ref: http://www.handprint.com/HP/WCL/color3.html
  • 7. Light and Optics 7 When luminous flux of one lumen falls on an area of 1m2 then it is called meter candela or lux (lx). Different light units and their meanings are shown in figure 1.9. The Inverse Square Law of Illumination: The illumination of a surface decreases as the square of the distance of the illuminated surface from the light source. At 1 meter from a 1 candela source the illumination of the surface is 1 lux (1 lumen per m2 ). At 2 meter the illumination is 1/22 = 0.25 lux. In basic terms this can be shown as: E = I / d2 lux Where E = Illumination (lux) I = Luminous intensity of source (cd) d = the distance from the light source (m) Different levels of indoor and outdoor illuminations are shown in Figure 1.10 and Figure 1.11 respectively. Figure 1.10 Typical levels of indoor illumination Ref: http://a-kingnet.com/index.php?route=product/category&path=39_40 Figure 1.11 Typical levels of illumination at outdoor Ref: http://a-kingnet.com/index.php?route=product/category&path=39_40 The vergence is inversely proportional to the distance. This can be explained by considering the following example. Consider a source which emits light or radiation onto a surface at different points. If the points are at differing distances from the source as shown in Figure 1.12 the following results: • Distance A from the source: At this point or on the surface the rays are highly divergent and wavefronts are strongly curved
  • 8. 8 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems8 • Distance B from the source: Here the rays are less divergent and wavefronts are less curved • Infinity distance form the source: Rays are parallel in nature and the wavefronts are a plane. Figure 1.12 The amount of divergence of the light is inversely proportional to the distance from the source of light at distance ‘A’ has more vergence than that at B Ref: http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v1/v1c030.html Luminance (L) Luminance is the measure of light emitted from a surface. This light may be in the form of radiated light or reflected light. Luminance can be measured in two ways, using either candela or lumens per square area. 1 nit = 1 candela per sq m (cd/m2 ) 1 stilb (sb) = 1 candela per sq cm (cd/cm2 ) 1 apostilb = 1 lumen per sq m (lm/m2 ) 1 lambert = 1 lumen per sq cm (lm/cm2 ) Table 1.1 shows the light levels under day time and night time conditions. Table 1.1 Light levels under daytime and night time conditions Illumination Conditions Foot-Candles (FtCd) (lux) Comments Direct sunlight 10,000 107,500 Full daylight 1000 10,750 Overcast day 100 1,075 Very dark day 10 107.5 Twilight 1 10.75 Deep twilight 0.1 1.075 Daylight range Full moon 0.01 0.1075 Quarter moon 0.001 0.01075 Starlight 0.0001 0.001075 Overcast light 0.00001 0.0001075 Low light level range
  • 9. Light and Optics 9 International Standards for Units (SI units) SI units are the standardized units used for the measurement of quantity or quality of components which are accepted world wide. Table 1.2 shows the international standards used in the measurement of light and related factors. Table 1.2 SI units Unit Symbol Measure Kelvin [K] temperature Candela [cd] luminous intensity The derived SI unit The table below shows the derived SI units. Table 1.3 Derived SI unit Quantity Unit Symbol / Definition Velocity Meter/second m/s Acceleration Meters per second per second 2 s m Frequency Hertz Hz =1/s Density Kilograms per cubic meter 3 m kg Energy Work Joule J=N·m Illumination Lux lx = lm/m2 Luminous flux Lumen lm = cd·steradian Luminance Nit nt = cd/m2 1.4 Eye persistence – motion pictures Eye persistence is the most important “eye defect” used in cinematography and television. Persistence depends on the intensity of light and brightness to see the picture in motion. Pictures have to change quickly so as to avoid flicker and to give a feeling of motion when logically consecutive pictures are played. When these pictures move faster than the persistency of the eye, the motion of pictures looks like a moving picture. The eye responds differently to different wavelengths as shown in Figure 1.13.
  • 10. 10 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems10 Figure 1.13 Response of eye towards different wavelength Ref: http://videocodecs.blogspot.com/ A video camera records images with a speed of 25/30 pictures per second. For a low intensity projector, 24 frames per second, is required. Television uses the same principle as that of the human eye. It projects pictures by a method called ‘interlaced scanning’ as shown in Figure 1.14. The pictures are created by scanning and the pictures are projected by lines. As the number of lines increase, the clarity increases. These lines are projected from left to right and top to bottom. Three major television systems exist. They are: • PAL (Phase Alternating Line) • NTSC (National Television System Committee) • SECAM (Sequential Couleur Avec Memoire or Sequential Colour with Memory). Although the picture projection and scanning is the same, the lines and the frames, or images, per second changes and the method of colour coding is different. • PAL : 625 Scanning Lines / 50 Interlaced Pictures Per Second • NTSC : 525 Scanning Lines / 60 Interlaced Pictures Per Second • SECAM: 625 Scanning Pictures (Used To Be 819) / 50 Interlaced Pictures Per Second. Figure 1.14 Two interlaced fields build up a complete TV picture frame Ref: http://www.hardwarezone.com/features/view/123917/page:2
  • 11. Light and Optics 11 1.5 Comparison between eye and camera The similarities between eye and camera are illustrated in Figure 1.15. Figure 1.15 Eye and camera similarities Both eye and camera are similar in nature. In the same way that the retina captures pictures, the camera sensor captures the picture, scans it and produces images. The camera lens can focus on an object that is close or far away, according to the settings made. Where as a human eye can focus on the near or far away object automatically according to the requirement. In the human eye there is a spot referred to as the blind spot where nothing can be seen. When we consider both the eyes at the same time we cannot have the same view from both the left and right eye because of the presence of the blind spot. Thus, what we see is the combinational image of both the left and right eye. This differs from a camera where there is no blind spot. To transmit the information from the camera to a monitor we have to connect cables, where as in the case of the eye, nerves transfer the information to the brain. The information stored in a camera will not be deleted unless and until it is deleted manually, but this is not the case with the human eye. The pupil that is present in the eye can change its size rapidly according to the requirement, where as in case of a camera it does not change rapidly. 1.6 Optical elements 1.6.1 Lenses as optical elements The basic lenses used in optics are concave and convex lens. Concave lenses are used when the objects are to be shown smaller when compared to the actual size of the object. They have a negative focal length with a virtual focus. On the other hand, convex lenses are used when the objects are to be shown bigger compared to the actual size of the object. They have a positive focal length with a real focus.
  • 12. 12 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems12 The important properties of lenses are: • Optical plane: The plane passing through the centre of the lens • Optical axis: The axis perpendicular to the centre of the optical plane • Focus: The point where the rays falling parallel to the optical axis converge • Focal length: The distance between the optical plane and the focus (in meters) • Diopter: An inverse value of the focal length, where the focal length is stated in meters. Figure 1.16 shows the properties of a lens. Figure 1.16 Properties of a lens There are different types of lenses with varying lens sizes and materials. Some of the different types are as follows: • Plano–Convex (A lens which is plane on one side and convex on the other side) • Plano-Concave (A lens which is plane on one side and concave on the other side) • Bi-convex, also referred to as a Converging lens (A lens which is convex on both sides) • Bi-concave, also referred to as a Diverging lens (A lens which is concave on both sides) • Convex-Concave (A lens which is convex on one side and concave on the other side). Figure 1.17 shows the different types of lenses. Figure 1.17 Types of lenses Different focal lengths can be achieved by the combined use of different types of lenses with different focal lengths. Lenses can be joined by applying transparent glue. To obtain a particular focal length, design engineers use mathematical calculations. The assembly of a lens is shown in Figure 1.18.
  • 13. Light and Optics 13 Figure 1.18 Lens assembly 1- Lens Clip; 2- Lens 1; 3- Lens spacer; 4- Lens 2; 5- Lens 3; 6- Lens holder The factors that determine lens quality are lens design, element manufacture, mechanical composition and electronics (refers to auto iris and motorized lenses). Following are the parameters considered under each factor. Lens design: • Number of elements • Relative position • Aberration correction in the design stage. Lens element manufacture: • Glass type • Technology and type of glass manufacturing (heating, cooling, cleanness) • Precision of grinding and polishing (very important) • Anti reflection coatings of the glass (micrometer layers for minimizing losses). Lens mechanical composition: • The lens’ positional fixing and stability (shock, temperature) • The lens’ moving mechanics (especially zooming, focusing, iris leaves) • Internal light reflections (matte black absorption) • Gears used for motorized lenses (plastic, metal, precision). Electronics (refers to auto iris and motorized lenses): • Auto iris electronics quality • Electric consumption • Zoom and focus control circuitry. 1.6.2 Reflection and Refraction Light travels from one medium to another. When light travelling in a straight line strikes a plane mirror it bounces back at an angle, this is referred to as reflected light. This phenomenon is called reflection and Figure 1.19 shows this in detail.
  • 14. 14 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems14 Figure 1.19 Light Reflection from a plane mirror Ref:http://www.cssforum.com.pk/css-compulsory-subjects/everyday-science/everyday-science-notes/17029-glossory- physics-2.html When light travels from one medium to another (for example, consider a glass slab or water as one medium and air as another medium), it bends slightly at the boundaries of the medium, rather than reflecting back. This process is referred to as refraction and Figure 1.20 shows this in detail. Figure 1.20 Light refraction through glass and water Ref: http://micro.magnet.fsu.edu/optics/lightandcolor/refraction.html Due to refraction, light loses its speed. The wavelength of the light changes as it penetrates from one medium to another. When a white light passes through a prism, its wavelength changes and appears as a spectrum of seven colours referred to as rainbow colours. Figure 1.21 shows the details of light spectrum. Figure 1.21 White light refraction through a prism Ref: http://www.123rf.com/photo_7114848_light-dispersion-illustration-hi-res-3d-rendering.html
  • 15. Light and Optics 15 Images captured by the eye or the camera are possible because light penetrates through the eye or the camera lens and leaves an image on them. 1.7 Basis of lenses 1.7.1 Contrast Transfer Function (CTF) and Modulation Transfer Function (MTF) Contrast Transfer Function (CTF) is used to evaluate and compare the performances of different microscopes. Definition: CTF is the function which modulates the amplitudes and phases of the electron diffraction pattern formed in the back focal plane of the objective lens. A chart consisting of white and black strips is used to measure the resolution of the lens. The white and black stripes are usually referred to as lines per millimetre. CTF is a characteristic which shows the response of the lens to various densities of the lines per millimetre. In TV lenses, the characteristic of a lens is similar to a continuous variation because the optical signal is converted in to an electrical signal. This characteristic is known as Modulation Transfer Function (MTF). In practice, it is easy to produce black and white strips than producing continuous variation between the black and white strips. CTF is much easier to measure than MTF. CTF is analogous to Modulation Transfer Function (MTF). In electrical engineering, MTF is used for modulation in the output signal to the signal frequency. CTF graphs the percentage contrast as a function of spatial frequency and thereby characterizes the information transmission capability of optical systems. The intensity recorded at zero spatial frequency in the CTF is a quantification of the average brightness of the image. CTF is a performance measure of an imaging system and can be determined for the functional components of the imaging system. Performance of a system can be determined as a product of the CTF curves for each component. Modifications performed in magnification and concomitant adjustments of pixel geometry will result in improvement of CTF. Figure 1.22 CTF and MTF Ref: http://www.microscopyu.com/articles/optics/mtfintro.html
  • 16. 16 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems16 CTF is given by the following equation: ( ) ⎥⎦ ⎤ ⎢⎣ ⎡ ΠΔ+ Π −= 243 5 2 sin kfkCkT λλ Where: Cs = The quality of the objective lens defined by spherical aberration coefficient l = Wave-length defined by accelerating voltage Δf = The defocus value k = Spatial frequency Figure 1.23 CTF plot for an imaginary 200 keV plot microscope (a) When envelope functions are not applied (b) When envelope functions are applied MTF is similar to CTF except that MTF uses sine wave spatial frequencies and CTF uses square wave. MTF is an important aid to objective evaluation of the image forming capability of an optical system. Due to the errors in the optics, such as manufacturing, assembly and alignment errors, the overall performance of the system decreases. As a result the dark and light shades, or the image in the image plane, will not be the same as that of the original patterns. At zero spatial frequency, MTF is normalized to unity. If spatial frequency is low the value of MTF is close to 1 and decreases as the spatial frequency increases and reaches zero. This is the limit of resolution and the cut-off frequency for a given optical system. Spatial frequency Spatial frequency is the characteristic of any structure that is periodic in space. It refers to the number of pairs of bars imaged within a given distance of a retina. Spatial frequency is never constant and it varies up and down and from point to point. Modulation ‘M’ for a given spatial frequency ‘ν’ is given as: II )I-(I M(v) minmax minmax + = Where: I max = maximum intensities I min = minimum intensities
  • 17. Light and Optics 17 MTF is given as: (v)M (v)M (v)MTF object image = Figure 1.24 MTF curves for two different lenses 1.7.2 Camera Lens Lens selection is based on a number of lens characteristics and specifications. The science of optical lenses is a very large subject and will not be covered in any great depth in this manual. However a few lens terms need to be defined. Note a very simplistic approach has been used in the following cases. Focal Length (f): the distance between the optical centre of the lens and the principle focus. See Figure 1.25. Effective Aperture (N'): the diameter of the opening within the lens system which controls the amount of light passed by the lens to the camera pickup device. See Figure 1.25. Relative Aperture (N): also referred to as the f/stop number. It is obtained by dividing the FOCAL LENGTH of the lens by the EFFECTIVE APERTURE. The effective aperture is shown, for example, as f/5.6. The following list shows the standard f/stops - f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22. Iris: usually an almost circular, variable diameter opening within the lens system, which when reduced in diameter, reduces the amount of light transmitted by the lens to the pickup device. As the diameter of the iris is reduced the Effective Aperture is reduced, the brightness of the image reduces and the Depth of Field is increased. See Figure 1.25. Field of View (FOV or w): also referred to as Angle of View. This is the vertical and horizontal angles which the lens covers and is related to the Focal Length of the lens. A short focal length results in a large angle of view. As the focal length increases the angle reduces. See Figure 1.26. Depth of Field (T): the distance over which a subject may extend when the lens is focussed as sharply as possible on one part of it, without the image becoming noticeably un-sharp. See Figure 1.27. All these characteristics interact with one another and figure 1.25 shows the basic lens parameters. In reality the lens of the camera would be a number of lens elements, but this diagram will aid in explaining the characteristics of the lenses that must be considered.
  • 18. 18 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems18 Figure 1.25 Basic lens parameters Figure 1.26 Field of view Figure 1.27 Depth of Field Figure 1.26 shows how the field of view is reduced as the focal length is increased. This results in a close up or telephoto type of lens and the short focal length results in a wide angle lens.
  • 19. Light and Optics 19 A normal basic camera lens has a focal length of about 50mm which gives a field of view equal to 47ø, while 200mm gives 12ø (telephoto) and 20mm gives 94ø (wide angle). The image size is set by the size of the pickup device being used in the camera and is usually slightly smaller than the maximum scanned area. The focal plane is the point at which the pickup device is placed in the optical system. Thus the image is focused at this point to give an image of height 'h'. Depth of Field is an important consideration, as already stated, this is the area over which an image will remain in focus. Figure 1.27 shows four lenses. In all of these diagrams the image size is the same and the bottom two (b, d) are exactly the same, while the top two (a, c) have one of the lens parameters changed, resulting in a reduction of the Depth of Field. In order to aid in the comparisons, the object distance has remained the same. The object height has also remained the same, except in Figure 1.27 (a), which is smaller, as discussed below. The two lenses in Figure 1.27(a) and 1.27(b) are shown with the same aperture setting, only the focal length has been adjusted. The lens in Figure 1.27(a) shows the focal length increasing, resulting in a smaller angle of view and a reduced Depth of Field. Another point to note is that a smaller object will result in an image of the same size, as the one below. This is due to the focal length of the lens also setting the angle of view. Short focal lengths give a wider angle of view, while a long focal length results in a narrow angle of view. Thus, for a wide angle lens (short focal length) focusing becomes easier and more of the image will be in focus. The aperture of a fixed focal length lens also controls the Depth of Field, as shown in Figures 1.27 (c) and 1.27(d). The larger the aperture, which is the same as using a larger lens, the smaller the Depth of Field. The smallest aperture gives a very large Depth of Field, in fact a pin-hole size aperture results in an infinite Depth of Field. Although not shown in Figure 1.27, the distance from the lens that the object is focussed will also result in changing Depth of Field. The dotted lines passing through the centre of the lens shows the field of view. If these lines were extrapolated beyond the points shown and the object moved (keeping the height of the object equal to the distance between the dotted lines), the solid ray lines would move, changing the area known as the Depth of Field. Moving the object closer to the lens means the ray lines would point up and down at a very steep angle, not unlike Figure 1.27(c). While moving the object toward infinity, the ray lines begin to spread, to give an infinite Depth of Field. The height of the object must also increase to give the same size image on the pickup device. Inversely if the object has remained the same, the image is going to be significantly smaller. Note, also, that objects very close to the lens will not be in focus. This can be shown by looking at any of the lenses in Figure 1.27. The distance where the object remains in focus, from the object to the lens, is smaller than that behind the object. The use of an automatic focus system will thus affect the Depth of Field. However, this could be an advantage, particularly when reversing. In this case, the image will remain in constant focus and as the object gets so close that a collision between the object and the vehicle may occur (when the object is very close to the lens, the Depth of Field reduces), the detail will be of more use to the driver than that of an out of focus image. Adjusting the aperture has already been shown to affect the Depth of Field, but a changing aperture also reduces the amount of light being transmitted by the lens to the pickup device. The iris is used to perform this function. Another means of adjusting the amount of light transmitted is to use a Neutral Density (ND) Filter. Thus the iris can be opened further and the same amount of light can be transmitted to the pickup device, while at the same time the Depth of Field remains unchanged. Putting all this information together gives some guidelines which need to be followed when selecting a lens. The first consideration is how wide an angle (Field of View) is required to give the best coverage. Once this is decided, the speed of the lens (maximum Effective Aperture in relation to the Focal Length i.e. Relative Aperture) should be considered. Thus a lens of f/1 is faster than a lens of f/2.8.
  • 20. 20 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems20 The term speed of a lens relates to the exposure time in the photography field. The faster lens allows more light to be transmitted and would be a requirement for night driving. However during the day the iris would have to close right down. The iris and ND filters would work together to provide the best Depth of Field and image illumination of the pickup device to provide noise free pictures. Depth of Field is the biggest problem, since for the system to work correctly, as much of the displayed image must be in focus as possible. Object focus would then be set to provide the best Depth of Field. Therefore, Depth of Field is the total area under the field in focus. A smaller depth of field has a small area in focus and vice versa. A larger depth of field occurs in the following cases: • The type of lens used changes the depth of field (if a wide angle lens is used, depth of field is larger when compared to that of a telephoto lens) • When the F-stop setting is high • When high resolution cameras are used. Figure 1.28 Depth of field with different F- stops Ref: http://audster.wordpress.com/2010/05/05/back-to-basics-part-1-the-aperture/ Figure 1.29 Near and Far focus Limits of Depth of field Ref: http://www.learnslr.com/slr-beginner-guide/depth-of-field-explained The selection of the lens will thus be dependent on the selection of the camera and its related sensitivity.
  • 21. Light and Optics 21 1.7.3 Focal (F) and Transmission (T) numbers F-number F-number is the ratio of the focal length of a lens to the effective aperture diameter. It is a measure of lens speed and is a dimensionless quantity. Lens light gathering ability is an important factor to be considered in an indoor environment. On a camera the F number is adjusted in discrete steps called f-stops. F numbers are usually written as F/x where F is the focal length and x is the aperture. The F-number of a lens can be measured by setting up a light source behind the F-number of a lens, thereby setting the lens to full aperture. A parallel beam of light is seen to emerge through the lens, whose diameter can be measured. These, when divided into focal length, are called f/aperture. More light will pass through the lens when the F-number is less. Decreasing the F-number by a factor of 1.414 (i.e. √2) doubles the exposure and increasing it with the same factor will decrease the exposure to half of its value. When the F-number is doubled, it increases light passing power of a lens by a factor of 4 (i.e. 22 ) and vice versa. For camera lens usage F-numbers are invariably rounded off to whole numbers or one decimal point (e.g. f/4 or f/5.6). Hyper focal distances and depth of field calculations always use the f/aperture of a lens, not the T stop. T-stop T-stop is the amount of light that passes through a lens after all the losses, such as absorption, internal reflections and scattering. T-stops are the means used to measure the efficiency and consistency of a lens; therefore the exposure settings for any situation are related to the T-stop. T- stops are used for the comparison of lenses, by illuminating a piece of translucent material in the focal plane of each lens. The intensity of light projected through the lens is measured along the optical axis with an incident light meter. If one lens is required to be set, at say f/5.6 for a given reading on the photometer, then any other lens which is set similarly should give the same reading. T-stops are always smaller (higher in number) than f/apertures, i.e. a lens set at f/5.6 may equal T6. The differential may also be expressed as a percentage and will remain consistent throughout the aperture range of the lens. Example: T= f/no of aperture/root of normalized transmission, i.e. if f=1.8 and the transmission =81% then T=1.8/ROOT 0.81 =T=2 1.8 Types of lenses 1.8.1 Manual, automatic and motorized iris lenses The Iris is a mechanism used to vary the light falling on the imaging device. It determines the light falling on the sensor. Manual iris lenses Definition: A lens with a manual adjustment to set the iris opening is known as manual iris lens. These lenses are used for fixed lighting applications where cameras are readily accessible and the light levels are constant. Manual iris lens cameras are not suitable for external applications as lighting levels are constantly changing in a scene and the wrong level of light will enter the camera as the lens cannot prevent it. Automatic electronic shutters in the camera will prevent the wrong level of light to some extent but they are sensitive to very small changes in light levels.
  • 22. 22 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems22 Automatic iris lenses The drawback of the manual iris lens can be overcome be using an automatic iris lens. An automatic iris lens is best suited for cameras used for outdoor scenes as they can cope with the variation of light. Two types of automatic iris lenses exist; these are discussed below. Types of automatic iris lenses Automatic iris lenses are categorized into two types as follows: • Video driven automatic iris lenses • DC driven automatic iris lenses. In DC Automatic Iris lenses, input is taken from the camera that resembles a DC Signal, there by representing a particular F-stop. Video Driven Automatic Iris lenses depend upon the video signal that is originated from the camera which is determined by comparing the amplitude of a reference voltage to the video signal that is coming from the camera, in order to check whether the iris is opened or closed. The camera determines the amplitude of the video signal by calculating the mean of the most recent captured image. When the video signal amplitude is more than the reference voltage, the iris will close until the signal amplitude is reduced. The lens will open when the video signal amplitude of the iris is below the reference signal. Motorized iris lenses These lenses offer remote control of the iris. Here, control action is set by the operator according to the light conditions. The iris is adjusted by a small electric motor controlled by signals generated from the remote operators control system. With the development of Charged Coupled Device (CCD) cameras this type of zoom lens is becoming increasingly popular. 1.8.2 Spherical and Aspherical lenses Spherical Lenses Spherical lenses are those which have a sphere shaped surface i.e. they have a spherical curvature. These lenses do not bring parallel light rays to a single focus. The focus depends on the distance of the light ray from the centre of the lens. If the distance of the ray from the centre of the lens is far, then the point of convergence is nearer to the lens and vice-versa. This phenomenon is called ‘focus shift’ and is illustrated in Figure 1.30. Figure 1.30 Focus shift of a spherical lens Ref: http://www.physicsinsights.org/simple_optics_spherical_lenses-1.html Some of the limitations of spherical lenses are: • High definition of the large aperture lenses, compensating spherical aberrations • Correction of distorted images with wide angle lenses • Compact and high quality zoom lenses. These problems can be minimized by using aspherical lenses.
  • 23. Light and Optics 23 Aspherical lenses These lenses have a non-spherical surface to converge all light rays to a single focal point and incorporate some optical characteristics. Aspherical lenses are smaller and lighter in weight than the lenses which employ properties of spherical elements. They are cheaper to manufacturer and improve optical performance. The surface of an aspherical lens does not conform to the shape of a sphere, as shown in Figure 1.31. The moulding techniques and hybrid elements of the glass/polymer structure of the aspherical lens allows economical production. Aspherical lenses are commonly used for the aberration correction level needed for illumination systems. Aspherical lenses have an advantage of shorter focal length and larger aperture than compared to spherical lenses of equal diameter and spherical aberration correction. Aspherical lenses are attached to video camera lenses to reduce focal length and act as a wide angle converter. An aspherical auto iris lens is shown in Figure 1.32. Figure 1.31 Aspherical lens http://www.arri-rental.com/camera/lenses/35mm-prime-lenses/zeiss-master-prime-lenses/zoom-in.html Figure 1.32 Aspherical auto iris lens Ref: http://www.directindustry.com/prod/geutebruck/camera-objective-lenses-28815-210256.html Spherical aberration High-angle rays are brought to a premature focus by lens aberrations so that the point object appears blurred in the image plane. This is illustrated in Figure 1.33. Figure 1.33 Spherical aberration 1.8.3 Zoom lenses Zoom lenses have the advantage of varying focal lengths. The focal length can be adjusted by turning a ring on the lens, also referred to as twist zoom. In some older versions of this type of lens,
  • 24. 24 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems24 the zooming action was performed by pushing and pulling the lens. The latest zoom lenses give a lot of flexibility as they can be adjusted by turning the zoom ring. Figure 1.34 Image of a lily pod taken from the middle of the pond with a zoom lens Figure 1.35 Zoom Lens 1.8.4 Fixed focal length lenses Lenses with constant focal length are referred to as fixed focal length lenses or prime lenses. Zooming is not possible with this type of lens and the camera would need to be moved closer to the object if zooming is required. The advantage of using this type of lens is that they are lighter in weight and smaller when compared to zoom lenses. Their construction does not need multiple pieces of glass (known as elements). Figure 1.36 Fixed focal length lens 1.9 Lenses as applied in CCTV 1.9.1 Image and lens formats in CCTV A camera images the angular extent of a given scene and this is referred to as the ‘angle of vision’. This vision is equal in all directions when an object is viewed through a lens and is conical in shape. The image projected by the lens is spherical in shape and the camera sensor is rectangular in shape, irrespective of the imaging circle. For example: Consider a 1.27 cm portion on a 1.693cm chip. A lens of a bigger format will project an image circle much larger than the actual chip size. If a bigger lens is used on a smaller chip, there will be no corners cut off or any other deformation.
  • 25. Light and Optics 25 When there is a reduction in the imaging pickup, a reduction of relative resolution is observed as the area used is very small. Apart from this, the CCD blocks the excessive light which is around the chip that in turn may be reflected inside the lens. The images will be affected if there are surfaces that are not neutralized sufficiently with a black metal finish. 1.9.2 Angle of view The angle of view of a camera is the angular extent of a given screen. It can be measured horizontally, vertically or diagonally, but the horizontal view is used as a reference. The angle of view differs with the focal length of the lens. The following rules should be observed when analysing the angle of view: • As the focal length decreases, the angle of view becomes wider and vice versa • With the same lens, as the size of the CCD chip decreases, the angle of view becomes narrower • The vertical angle of view can be determined if the horizontal angle of view is known. A viewfinder calculator (see Figure 1.37) and an optical viewfinder (see Figure 1.38) are the two instruments used for finding the angle of view. Most camera and lens manufacturers provide useful on-line tools to calculate the angle of view. Software CCTV Installation tools can also be used. A viewfinder calculator is round or ruler shaped. Different parameters such as the CCD chip size, camera and object distance and object width are used to determine the focal length. Optical viewfinders are used by photographers to gain focus on an image. Figure 1.37 Various lens calculators Ref:http://sliderulemuseum.com/HSRC/38621.jpg
  • 26. 26 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems26 Figure 1.38 Optical view finder 1.9.3 C-mount, CS-mount and back focus There are two standards for distance between the back-flange of the lens and the CCD image plane. They are: • C-mount • CS-mount. C-mount C-mount is denoted as 17.5mm. This standard has been used since the early days of the tube cameras. It consists of a metal ring with 1.00/32mm thread and the front surface area is 17.5mm away from the image plane. CS-mount A mount used for smaller cameras and lens design is CS-mount and it is denoted as 12.5mm. In this, the same thread is used as in the case of the C-mount, but is approximately 5mm closer to the image plane. This preserves compatibility with the old C-mount format. It allows cheaper and smaller lenses to be manufactured to suit smaller CCD chip sizes. C and CS mount lens are shown in Figure 1.39. Figure 1.39 C and CS mount lens Ref: http://www.icpdas.com/products/Vision/mavis/vision_glossary_a~m.htm 1.10 Back-focus Adjustment When a lens’ back-flange is adjusted in relation to the CCD image plane, it is referred to as back- focusing. This concept is very useful when zoom lenses are used in CCTV. The output for the zoom lens, when focused at different distance objects, is shown in Figure 1.40. The optic-CCD distance in zoom lenses has to be precise in order to achieve good focus throughout the zoom range. Back-focusing adjustment is performed with a low F-Stop. Back focus is the distance from the last glass surface of a lens to the focused image on the sensor.
  • 27. Light and Optics 27 When the camera is zoomed in and focused clearly, but the zoom out makes the images go out of focus, then it is termed as a back focus problem. This is a problem associated only with zoom lenses. The back focus adjustment is performed at the back of the lens barrel, near the camera body. Because the back focus lens is designed to stay in one place, a little lever has to be loosened in order to move this ring. Once the adjustments are final, the level should be carefully twisted back in tightly so the back focus isn’t accidentally disturbed. Figure 1.40 Zoom lens focusing at different distance objects Ref:http://thecareyadventures.com/blog/2011/aperture-31-days-to-better-photography/ Methods that assist with opening the iris to the maximum extent are as follows: • Adjust the back-focus at low light levels in the workshop • Adjust the back-focus in the late afternoon • Adjust the back-focus at daytime by using external ND filters • If a camera with CCD iris is used then the optical iris can be opened fully, even during daylight, as the CCD iris will compensate for excessive light. 1.11 Neutral Density filter (ND filter) A neutral density filter is a light filter which is used to reduce the intensity of light passing through the lens. It filters the light spectrum evenly without affecting the colour and contrast. They are generally gray in colour. The effect of the filter depends on the depth of the gray colour. This filter is also referred to as gray filter or ND filter. Figure 1.41 ND4 and ND8 filters If the shutter speed is kept constant and an ND filter is added, aperture must be increased to maintain the same exposure.
  • 28. 28 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems28 Figure 1.42 Relation between aperture and the shutter speed An ND filter can be used with all types of film and video cameras, but is especially valuable when working with high-speed films or long-exposure motion applications. Different ND filter manufacturers may use different ways to indicate the amount of light an ND filter can reduce or attenuate. There are two typical systems as shown in Table 1.4. Table 1.4 Indication of the amount of light an ND filter can reduce Density Reduction of F-stops 0.1 3 1 0.2 3 2 0.3 1 0.4 3 1 1 0.5 3 2 1 0.6 2 0.7 3 1 2 0.8 3 2 2 0.9 3 1.0 3 1 3 2.0 3 2 6 3.0 10 4.0 3 1 13 For example, ND filters marked as 0.3, 0.6 and 0.9 reduce the light by one, two and three stops. ND’s marked as 2×, 4× and 8× indicate reducing 1 (i.e. 2=21 ), 2 (i.e., 4=22 ), and 3 (i.e., 8=23 ) stops. ND2, ND4 and ND8 mean they reduce the light by one, two and three stops, respectively.
  • 29. Light and Optics 29 When a slower shutter speed is used, moving objects may appear blurred creating a sense of motion, see Figure 1.43. Figure 1.43 Image when slower shutter speed is used with both ND4 and ND8 filters (Ref: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-ND.html) ND filters are used to open up the aperture while maintaining constant shutter speed. See Figure 1.44. Figure 1.44 Image with larger aperture (a) With no ND filter (b) With ND4 Filter (c) With ND8 filter (Ref: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-ND.html) Note: Remember that a larger aperture results in a smaller Depth of Field. The images in Figure 1.44 were all taken with a shutter speed of 1/30 second. The left image used F10.7 and no filter, the statue and background are all in focus. Using a ND4 filter reduces the aperture to F5.4, the background is now blurred and the statue is isolated from the background. Using the ND8 filter reduces the aperture to F3.9, now the statue is well isolated from the background and shows a sense of distance. ND filters can be stacked together and the effect is to multiply the attenuation, although doing so may produce underexposed images. ND filters can be fitted to the lens externally by screwing them to the front of the lens. See Figure 1.41. ND filters can also be found built into the lens body and can be variable density discs or rotating wheel with different ND filters fitted to the disc. 1.12 Summary This chapter summarizes the following: • Objects are classified as luminous and non-luminous bodies. Luminous bodies are those which generate light, for example, the sun, stars, etc. Non-luminous bodies are those which do not produce light, but reflect the light which falls on them. Light is electromagnetic radiation.
  • 30. 30 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems30 • Visible light falls between the range of 400nm and 700nm in the electro magnetic spectrum, where 400nm is violet light and 700nm is red. The eye shows the greatest reaction towards green colour, as and when green colour falls on it. The largest amount of the sun’s energy that penetrates through the earth’s atmosphere is in the range of 555nm. • Red, green and blue are primary colours and secondary colours can be formed by using the additive process. • A human eye is made up of millions of cells called cones and rods. Cones are sensitive towards medium and high intensity light where as the rods are sensitive towards low light levels. • Luminous intensity is the illuminating power of a primary light source, radiated in all directions. The associated unit of measurement is candela (cd). • Luminous Flux is the luminous intensity, but in a certain solid angle. The unit of measurement for luminous intensity is 4П (pi) radians and is measured in lumens (lm). • Illumination of a surface is the amount of luminous flux on a unit area. • Luminous is defined as the brightness of a surface either of a primary or secondary light source. The unit of measurement for surface intensity is Ft-Cd (Foot-Candle). • There are three colours in a Cathode Ray Tube (CRT), red, blue and green. • The relationship between the peak wavelengths radiated, and the temperature to which a body is heated, is given as λm=2896/T. Where, λ is wavelength, T is temperature. • Persistence depends on the intensity of light and brightness to be able to see a picture in motion. Pictures have to change quickly as to avoid flicker, when logical consecutive pictures are played. • There are three basic television systems. These are PAL (Phase Alternating Line), NTSC (National Television System Committee), and SECAM (Sequential Couleur Avec Memoire or Sequential Colour with Memory). • PAL : 625 Scanning Lines / 50 Interlaced Pictures Per Second • NTSC : 525 Scanning Lines /60 Interlaced Pictures Per Second • SECAM: 625 Scanning Pictures (Used To Be 819) /50 Interlaced Pictures Per Second • Both the eye and camera are similar in process but different in function. • When light travelling in a straight line strikes a plane mirror it bounces back at an angle, this is referred to as reflected light. This phenomenon is referred to as reflection. • Penetration of light through different mediums is called refraction • The speed and wavelength of light changes due to refraction • The basic type of lenses used in optics are concave and convex lenses
  • 31. Light and Optics 31 • The factors that determine lens quality are lens design, element manufacture, mechanical composition and electronics (refers to automatic iris and motorized lenses). • CTF is used to evaluate and compare the performances of different microscopes. • CTF is the function which modulates the amplitudes and phases of the electron diffraction pattern formed in the back focal plane of the objective lens. • MTF is similar to CTF, except that MTF uses sine wave spatial frequencies and CTF uses square wave. • Spatial frequency: The characteristic of any structure that is periodic in space. It refers to the number of pairs of bars imaged within a given distance of a retina. • F-number is the ratio of the focal length of a lens to the effective aperture diameter. • T-stop is the amount of light that passes through a lens after all the losses like absorption, internal reflections and scattering. • Depth of field is the total area under the field in focus. Smaller depth of field has a small area in focus and vice versa. • An iris is a mechanism used to vary the light falling on the imaging device. It determines the light falling on the sensor. • A lens with a manual adjustment to set the iris opening is known as Manual Iris lens. • An automatic iris lens is best suited for cameras used for outdoor scenes. • Automatic iris lenses are categorized into two types as follows: • Video driven automatic iris lenses • DC driven automatic iris lenses • Motorized lenses offer remote control of the iris. • Spherical lenses are those which have a sphere shaped surface. Focus shift occurs in spherical lenses. • Aspherical lenses have a non-spherical surface to converge all the light rays to a single focal point. • Spherical aberration: High-angle rays are brought to a premature focus by lens aberrations so that the point object appears blurred in the image plane. • Zoom lenses have the advantage of variable focal lengths. • Lenses with constant focal length are referred to as fixed focal length lenses or prime lenses. • A camera images the angular extent of a given screen and this is referred to as the angle of vision. • The angle of view of a camera is the angular extent of a given screen.
  • 32. 32 Troubleshooting, Designing and Installing Digital and Analog Closed Circuit TV Systems32 • A viewfinder calculator and optical viewfinder are the two instruments used for finding the angle of view. • There are two standards for distance between the back-flange of the lens and the CCD image plane. They are: • C-mount • CS-mount • Back focus is the distance from the last glass surface of a lens to the focused image on the sensor. • When the camera is zoomed in and focused clearly, but the zoom out makes the images fall out of focus, then this is referred to as a back focus problem. • ND Filters can be used to reduce the amount of light entering the lens. • Some modern lenses have internal ND filter discs.