A lens works by refracting light as it passes from one medium to another. The most common types of lenses are biconvex and biconcave lenses. Biconvex lenses are converging lenses that form real images, while biconcave lenses are diverging lenses that form virtual images. Different types of lenses include wide-angle lenses, normal lenses, telephoto lenses, macro lenses, and specialty lenses like fisheye lenses. Proper lens selection and care is important to avoid damage from dirt, scratches, shocks, and water.

1. Sajjad KayaniSajjad Kayani
PTV Training Academy

2. WHAT IS A LENS ?
Lens works on the principle of refraction, which means bending of light
as it passes from one medium to the other.
A lens is an optical device which transmits and refracts light, converging
or diverging the beam. A simple lens consists of a single optical element.
A compound lens is an array of simple lenses (elements) with a common
axis; the use of multiple elements allows more optical aberrations to be
corrected than is possible with a single element.
Lenses are typically made of glass or transparent plastic.

3. TYPES OF LENS IN RAY OPTICS
The most commonly used lenses are:
1.Biconvex
2.Biconcave

4. BICONVEX LENSES
1. These lenses are converging in nature. The light rays refracts inwards
after passing through the lens.
2. Such lenses creates Real Images. The image formed is said to
be real because the rays of light from the object pass through the film
and are inverted (upside down).

5. USES OF CONVEX LENS:
1. CAMERAS:
A camera consists of three main parts.
a) The body which is light tight and contains all the mechanical parts.
b) The lens which is a convex (converging) lens).
c) The film or a charged couple device in the case of a digital camera.
2. Magnifying glass, Microscopes, Telescopes
3. Human eyes
4. Spectacles
5. Rear View Mirrors

6. BICONCAVE LENSES
1. Concave lenses are thinner at the middle. Rays of light that pass through
the lens are spread out (they diverge). A concave lens is a diverging lens.
2. The image formed is virtual and diminished (smaller)

7. USES OF CONCAVE LENS:
1. FLASHLIGHTS
2. LASERS
3. PEEPHOLES
4. REFLECTORS
5. STREET LIGHTS

8. TYPES OF LENS IN PHOTOGRAPHY
Lens Focal Lengths Lens Type Photography Type
Less than 20mm Extreme Wide
Angle
Architecture
21mm - 35mm Wide Angle Landscape
35mm-70mm Normal Normal Street and
Documentary
80mm-135mm Medium Telephoto Portraiture
135mm-300mm Telephoto Telephoto Sports
and Wildlife
Greater than
300mm
Super Telephoto Wildlife

9. EXTREME WIDE ANGLE LENSES
Super-wide lenses provide a dynamic perspective of the world around us, well
beyond the scale of eyesight.
Normal vision comfortably takes in a 45-50° angle of
view, corresponding to the standard 50mm lens in 35mm film photography.
The extreme-wide perspective begins with a 90° field of view, which emerges
through
lenses of 21mm and shorter focal length in 35mm film photography, and 15mm or
shorter focal length in most digital cameras.
Yet extreme wide-angle photography is available for
everyday picture-taking, expands visual horizons and can even warp space.

10. IMAGE RESULTS OF
EXTREME WIDE ANGLE LENSES

12. WIDE ANGLE LENSES
A wide-angle lens is a lens with a short focal length that takes in a wide view.
This type of lenses can be called wide-angle, short focal length, short lens and
zoom out but refer to the same thing - lenses that capture a wide expanse of a
scene.
Wide-angle lenses are typically used when the subject is in the extreme
foreground and the photographer wants the background in focus as well.
This property can be used to create a dramatic effect and change the perspective
in your images as objects very close to the camera loom much larger than those
farther in the background.

13. DISADVANTAGES OF WIDE ANGLE
LENSESLens Flare
Lens flare is a "sun spot" or light from some other source that hits the lens and scatters, forming
bright streaks, random polygonal shapes, or a glowing halo effect. Wide-angle lenses are more
prone to picking up these stray beams of light than are regular lenses, and the flares can be
distracting within the image.
Image Distortion
A wide-angle lens has a tendency to distort cylindrical objects at the edges of the lens, curving
straight lines. The wider the angle, the more distortion. A fish-eye lens is an extreme example of
this distortion. Straight lines or objects--such as buildings--appear to curve upward. These objects
are actually bent by the optics of the lens.
Vignetting
Some wide-angle lenses may produce a vignetted effect, where the image tends to become
gradually darker towards the outer edges. This is due to more light reaching the center of the
image than the outer edge of the frame.

14. IMAGE RESULTS
WIDE ANGLE LENSES

15. NORMAL LENSES
In photography, a normal lens is a lens that reproduces a field of view that generally
looks "natural" to a human observer under normal viewing conditions, as compared with
lenses with longer or shorter focal lengths which produce an expanded or contracted
field of view that distorts the perspective when viewed from a normal viewing distance.
For still photography, a lens with a focal length about equal to the diagonal size of
the film or sensor format is considered to be a normal lens.
Its angle of view is similar to the angle subtended by a large-enough print viewed at a
typical viewing distance equal to the print diagonal, this angle of view is about 53°
diagonally.

16. ADVANTAGES OF NORMAL LENSES
A lens of normal focal length has several advantages over a lens that is substantially
longer or shorter.
1. A normal lens suits the requirements of most photographic situations. It is ideal for the subjects
that interest the majority of photographers.
2. It is usually faster than lenses of other focal lengths, allowing for easier framing and focusing,
higher shutter speeds to stop more action, and full exposures under dimmer lighting conditions.
3. It is generally sharper and better corrected than telephoto, wide angle and zoom lenses although
the difference is usually quite small.
4. Even with its extra speed and clarity a normal lens is smaller and lighter than any telephoto or
zoom lens and most wide angle lenses.
5. For complex optical reason, normal lenses are able to focus much closer than those of longer
focal length. Although wide angle lenses often have this ability too, their enormous depth of field
makes precise focusing more difficult than with normal lenses.

17. IMAGE RESULTS NORMAL LENSES

18. TELLEPHOTO LENSES
(MEDIUM AND SUPER)
A telephoto lens is a camera lens designed to enable people to take long focal length
pictures using a lens with an actual length which is shorter than the focal length.
In photography , a telephoto lens is a specific type of a long-focus lens in which the
physical length of the lens is shorter than the focal length. This is achieved by
incorporating a special lens group known as a telephoto group.
Telephoto lenses are sometimes broken into the further sub-types of
MEDIUM TELEPHOTO: lenses covering between a 30° and 10° field of view (85mm to
135mm in 35mm film format).
SUPER TELEPHOTO: lenses covering between 8° through less than 1° field of view
(over 300mm in 35mm film format)

19. DISADVANTAGES OF TELEPHOTO
LENSES
Depth of Field
Because telephoto lenses have such long focal lengths, often 200 mm or longer, the depth of field you
can achieve with them is drastically lower than with a standard or wide-angle lens.
Perspective
A telephoto lens has a much narrower perspective than both the human eye and other lenses. This
narrow perspective drastically limits the amount of a scene or subject you can include in your picture.
Portability
Telephoto lenses are more cumbersome than standard or wide-angle lenses, and carrying them can be
difficult while traveling or attending crowded events. Super telephoto lenses can weigh 10 to 12 lbs.
(5 to 6 kg).
Expense
Telephoto lenses are often much more expensive than standard lenses (up to several hundred dollars
more for an entry-level model), giving you one final reason not to buy one unless you want to do
sports or nature photography.

20. IMAGE RESULTS OF TELEPHOTO LENSES

21. SPECIALIST LENSES
1. The Fisheye Lens
The widest optic is the fisheye lens, designed to capture half of the total
field of view surrounding the photographer; that is, a 180° diagonal view.
In the case of at least one major lens manufacturer, fisheye optics were initially
produced to aid in police work, to enable the recording of an entire crime scene
in a single photograph.
Only after some years were the lenses made available to the public.

22. IMAGE RESULTS OF FISHEYE LENSES

23. SPECIALIST LENSES
2. Macro Lens
Marco lenses or lenses with a macro mode are used for close up photography of insects or
flowers. They have similar properties to a normal lens, but they are able to focus a lot closer to
the subject.
The camera lenses with the longer focal lengths come in very handy for taking close ups of
subjects that might otherwise be scared away. The optical quality of a macro lens is normally
very high.

24. IMAGE RESULTS OF MACRO LENSES

25. Lens Accessories
If your camera has a fixed lens, you may be able to use lens converters to
decrease or increase its focal length. There are two popular accessories for
cameras with interchangeable lenses. Both fit between the lens and the camera
body.
1. Extenders extend the range of the lens. For example, a 2x lens converter will
make a 100mm lens into a 200mm lens.
2. Extension tubes are used to increase magnification in macro close-up
photography.

26. Considerations When Buying a Lens
The optical quality of the lens: The better the lens, the better it can capture - resolve - fine
details. In most cases, the optical quality of digital camera lenses go hand in hand with the price of
the camera and the resolution of the sensor.
The speed of the lens: A lens' speed is determined by the maximum amount of light the lens is
capable of transmitting- the largest f-stop value. Some camera lenses can capture larger amounts of
light than others, generally because they have a greater diameter that can transmit more light.
The focusing range of the lens: The minimum focus distance of a lens determines how close you
can get to a subject. If too close, the image will be blurry. Some camera lenses can focus closer than
others. The ability to get up-close and personal with your subject can be very important in some
types of photography.
The magnification range of the lens: The zoom range determines how much or how little of a
particular subject you can include in an image from a particular shooting distance. At the widest
settings (wide-angle settings), you can take in broad sweeps of landscape, whereas in the narrowest
view (telephoto), you can reach out and bring a distant object much closer.

27. LENS CARE:
There are four main types of external damage sources to be concerned about.
A.Dirt C. Shock
B.Scratches D. Water
Dirt:
Dirt is a daily challenge for your lens. Dust and other dirt on the surface of your lens will
create horrible images. One stray spec of dust is probably not going to be noticed but if your
lens is obviously dusty it can cause problems. Dirt causes even more problems as it is more
difficult to remove from your lens surface.
Scratches:
Scratches are a killer of your lens. There is no good way to repair them yourself. The best
thing you can do is prevent scratches. The easiest thing you can do to protect your lens against
scratches is to use a filter. A filter is a small piece of glass that fits in front of your lens.

28. Shock:
Shock is when your camera lens is hit or hits something else with considerable force. If you
drop your lens or if someone slams a car door on your lens it will probably cause damage.
Sometimes this damage can be repaired by an professional repair shop but it is almost
always very expensive. The best way to protect your lens is to carry it (and your camera) in
a padded camera bag, and to be aware of your surroundings. If you have your lens (and
camera) out of the bag, pay attention to what is around you and be prepared to move your
camera, and yourself, out of harm's way.
Water:
Water is a mortal enemy to your lens. The electronic circuits and motors inside most of
today's lenses can be destroyed by water. Also, most lenses actually have several elements,
or other lenses, inside them. If water gets on these internal lenses, it leaves water spots that
you cannot clean yourself.