A short presentation on photography - understanding the camera basics

1. 2nd May 2015, Partha Ray

2.  Our Eyes vs the Camera
 Variable aperture vs fixed aperture
 Sensor – The soul of the camera
 Sensor as Electron Bucket
 Bucket filling by adjusting time and water flow
 Color Blind Sensor with colored sun glasses
 Sensor size example of some modern camera – different sensor sizes
 If Sensor is a field, the sensels / pixels are bucket collecting rain water (photon rain)
 Filling buckets (with electrons) ~ charging a batteries, ISO
 Exposure – a function of overcharged, under charged and optimally charged batteries
 Bucket sizes in Professional, semi professional and amateur cameras
 Interplay of Aperture, Shutter Speed and ISO
 Nature’s gift – Shot Noise and who handles better
 Pitfalls of high ISO – which type of camera is more susceptible
 One-upmanship between sensor and ADC
 Q&A – too tired, prepared this between 9PM to 7 AM(today)

3. Camera has same type of components
as in our visual system.
The ADC (Analog to Digital Converter)
is an extra which does not have
biological equivalent (we are analog).
The still camera has shutter (our eyes
are video camera) which is also an
extra.
In our retina, we have cone cell to sense
light intensity and rod cells to sense colors
(most sensitive to Green, Red and Blue).
Camera sensor is “color blind”. They have
colored glasses on top to see color. There
are double the number of Green glasses
compared to blue or red.
Why ? (clue – we were monkeys).
Note that nature “des not have color”. It is
a simulation of human brain. (Big topic,
not part of this course).
As human brain is million times more
powerful that any image processing chip,
professionals always process image
outside camera using tools such as “Light
room” and their brain /imagination.
(separate topic, not part of this workshop).
Aperture control ~ Iris Shutter Sensor ~ Retina
Wire ~ Nerves
Image
Processor ~
Brain
Lens ~ Lens
A
D
C

4. VARIABLE VS FIXED
APERTURE – DYNAMIC
RANGE
1. Our eyes are variable aperture
scanner.
2. Hence, we can see very dark to
very bright – nearly 24 stops
(224).
3. The camera has fixed aperture.
The best camera can only have
a maximum dynamic range
(darkest to brightest) of only 14
stops (limited by ADC,
explained later).
4. The sensel (bucket) size and
quality, the ADC determines the
dynamic range (explained later).
5. The picture is build in our
brain: we see through our brain,
not our eyes.
Variable
Fixed

5. SENSOR, SENSELS OR
PIXELS
The sensors consist of many
sensing cells and they are known
as sensels or pixels.
Modern cameras have between 16
to 24 Million sensels (with a few
high mega pixel exception).
These sensels collect photons or
light particles and store them as
electrons.
This is very similar to collecting
rain in millions of buckets which
are stacked side by side in a field.
However, in this case the rain can
be started and stopped by a
curtain which is called a shutter.
Filling these buckets optimally is
the key to proper photography.
36 mm
24 mm
The Sensor – Soul of the camera
Photons / Light particles
Sensels/ Pixels
The Sensor

6. FILLING THE BUCKET:
HOW LONG X HOW BIG
Exposure is all about filling the
buckets to the max (when
possible).
If the water pressure is high
(strong light), we can either use
smaller opening (aperture) or
shorter duration (higher shutter
speed).
Ideally, a dry bucket (dark,
shutter closed, no exposure)
should have no water (electrons).
There is no ideal bucket (sensels)
and real buckets always have
some dirty water (stray electrons)
sticking around.
These are called dark noise
(sensor noise).
How big?
t = 1/60 second
How long?
Ideal dark
bucket
Actual dark
bucket
Electrons
Fully Exposed
Minimally
Exposed

7. MAKING COLOR BLIND
BUCKETS TO SEE COLOR
The sensels are color blind –
they just store electrons.
Therefore each pixel is covered
by a colored glass or filter. This
allows specific pixel or bucket
to count photons / electrons of a
specific color.
These filters are of primary
colors – R, G, B. There are 2x
Green for each Red and Blue.
Why?

8. THE SOUL OF THE
CAMERA
The sensor is the soul of the
camera.
Professional cameras have bigger
sensors.
The biggest sensor size is 36 x 24
mm (35 mm format camera). This
is same size as 35mm film.
The sensors consist of many
sensing cells and they are known
as sensels or pixels.
Modern cameras have between 16
to 24 Million sensels (with a few
high mega pixel exception).
Higher the pixel count, lower the
pixel or bucket size.
The sensor is like a football field
that has got millions of buckets
(sensels) for collecting rain water
(photons – electrons).
The bucket /
Sensel / Pixel
The colored
glasses or
filters
The football field or Sensor – Soul of the camera
Type 1/2.33" / Q M 4/3s APS-C APS-H 35mm Full frame
Sensor w x h 6.16 x 4.6 mm 17.8 x 10 mm 22.2 x 14.8 mm 28.7 x 19 mm 36 x 24 mm
Sensor area 28 mm2
178 mm2
329 mm2
548 mm2
864 mm2
crop factor 5.84 2 1.6 1.26 1
Pentax Q System Olympus OM-D E-M1 Canon 7D II Canon 1D IV Canon 5D III
Panasonic Lumix Panasonic Lumix DMC Nikon D7200 Nikon D750
Canon Powershot Sony a77 II Sony a99
~ body cost U$ 200 - 500 U$ 1000 U$ 1000 - 1500 U$ 2500
discontinued
(~ U$ 5000)
Camera
Models

9. HIGHER THE NUMBER OF
PIXEL, LOWER THE PIXEL
SIZE AND VICE VERSA.
Even with in the same sensor
size (e.g. full frame 36 x 24 mm
or APS-C 22.2 x 14.8 mm), the
number and size of buckets /
sensels / pixels vary.
Within a same sensor size, if
the pixel count goes up, the
pixel size has to come down.
The combination of bucket size
and numbers (mega pixels)
results in different capabilities
(explained later).
36 mm
24 mm
15 mm
22 mm
3.42 mm
4.54 mm
Smaller Field – APS-C
Big field with
big buckets –
Full frame
with
relatively low
mega pixel
Big field with
many small
buckets –
Full frame
with
relatively
high mega
pixel

10. Filling Buckets ~ Charging
Battery
When buckets or sensels are full of
electrons, it is a fully charged battery.
Sensels recording brightest part of the
photo is fully charged.
When buckets or sensels have just a few
electron, it appears as a discharged or
empty battery. Sensels recording darkest
part of the photo is charged at its
minimum.
In a properly exposed photo, most of the
sensels are properly filled or charged.
In a poorly exposed photo, most of the
sensels are not properly filled or charged.
In low light situations, when pixels or
batteries cannot be charged optimally, a
voltage multiplier (amplifier) is applied. It
is very similar to increasing volume of
your music system.
This amplification gain is referred as ISO
(increase). The ISO definition came from
chemical film (1934) and has no direct
meaning in Digital Camera.
Higher ISO simply means higher gain of
the amplifier.
- e
0
10
20 30
40
50
xN
N = 1
(i.e. ISO = 100)
Analog
to
Digital
1
0
1
1
0
1
0
0
1
1
0
0
1
0
Image
Processor
- e
0
10
20 30
40
50
xN
N = 8
(i.e. ISO = 800)
Analog
to
Digital
1
0
1
1
0
1
0
0
1
1
0
0
1
0
Image
Processor
ISO

11. Over exposure means that the
buckets or sensels are over flowing
(of electrons) – all white.
Under exposure means that the
buckets or sensels have minimal or
no electron.
In a optimally exposed
photograph, the brightest area of
the photograph fills the bucket of
sensel to brink without overflowing
while the darkest area has some
minimum electrons to dominate
over the stray electrons (enough
clean water to dilute the dirty
water).

12. 1. Full frame camera has very
high Signal to noise ratio. They
are also the costliest cameras.
2. Camera with smallest sensors
have lowest SNR. They are also
the cheapest .
3. Newer cameras have better
SNR.
4. Some cameras have very large
bucket, relatively lower SNR
but still very costly (e.g. D4s, U$
6000)
5. What is the advantage of bigger
buckets or sensels?
6. A new trend: Cameras such as
the Leica X2,Fuji X100S, Nikon
COOLPIX A, feature an APS-C
sensor (23.7 x 15.6 mm) along
with a fixed-focal-length lens.
Sony RX1which does the same,
but with a Full Frame sensor
(36 x 24 mm). These are ultra
high end compact cameras.
Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2
Pixel ISO Read Noise Sat Cap SNR QE
Nikon D3s 2009 2844 4288 11.63 24 36 8.4 14 100 26.0 84,203.4 3,243.5 58%
Nikon D600 2012 4028 6080 23.36 24 35.9 5.9 14 100 7.4 76,443.6 10,334.2 54%
Nikon D800 2012 4924 7424 34.86 24 35.9 4.7 14 100 4.6 48,818.0 10,724.0 51%
Nikon D800E 2012 4924 7424 34.86 24 35.9 4.8 14 100 5.2 54,923.9 10,636.8 54%
Nikon D4 2012 3292 4992 15.67 23.9 36 7.2 14 100 18.8 118,339.0 6,284.8 53%
Nikon Df 2013 3292 4992 15.67 23.9 36 7.2 14 100 21.7 134,567.1 6,208.3 60%
Nikon D610 2013 4028 6080 23.36 24 35.9 5.9 14 100 5.7 74,971.2 13,116.3 50%
Nikon D810 2014 4928 7380 34.68 24 35.9 4.9 14 100 4.5 49,553.7 11,012.9 48%
Nikon D750 2014 4032 6032 23.19 24 35.9 6 14 100 5.5 81,607.7 14,851.3 52%
Nikon D4s 2014 3288 4936 15.48 23.9 36 7.3 14 100 14.0 125,596.7 8,973.6 55%
Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2
Pixel ISO Read Noise Sat Cap SNR QE
Nikon D3000 2009 2868 4310 11.79 15.8 23.6 5.5 12 100 14.6 29,246.4 1,998.4 29%
Nikon D5000 2009 2868 4310 11.79 15.8 23.6 5.5 12 100 5.6 28,283.6 5,076.9 35%
Nikon D300s 2009 2868 4352 11.90 15.8 23.6 5.4 14 100 6.5 26,154.2 3,993.1 32%
Nikon D3100 2010 3084 4672 13.74 15.4 23.1 4.9 14 100 15.7 29,504.7 1,877.2 34%
Nikon D7000 2010 3280 4991 15.61 15.6 23.6 4.7 14 100 3.1 38,317.8 12,233.0 45%
Nikon D5100 2011 3280 4992 15.62 15.6 23.6 4.7 14 100 4.1 39,022.4 9,537.9 46%
Nikon D3200 2012 4012 6080 23.26 15.4 23.2 3.8 12 100 4.7 28,773.8 6,102.4 44%
Nikon D5200 2012 4020 6036 23.14 15.7 23.6 3.9 14 100 2.7 27,429.1 10,295.6 39%
Nikon D5300 2013 4016 6016 23.04 15.6 23.5 3.9 14 100 3.4 33,924.7 9,869.6 54%
Nikon D7100 2013 4020 6036 23.14 15.6 23.5 3.9 14 100 3.3 29,441.6 9,000.9 42%
Nikon Coolpix-A 2013 3280 4992 15.62 15.6 23.6 4.7 14 100 3.6 40,408.4 11,220.7 46%
Nikon D3300 2014 4016 6016 23.04 15.4 23.2 3.9 12 100 8.5 35,988.8 4,246.1 58%
Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2
Pixel ISO Read Noise Sat Cap SNR QE
Nikon Coolpix-P70002010 2742 3664 9.58 5.7 7.6 2.1 14 100 4.4 7,535.6 1,723.5 51%
Nikon 1-V1 2011 2606 3904 9.70 8.8 13.2 3.4 12 100 12.5 22,826.6 1,825.3 45%
Nikon Coolpix-P71002011 2744 3664 9.59 5.7 7.6 2.1 12 100 4.5 7,271.0 1,613.4 56%
Nikon 1-J1 2011 2606 3904 9.70 8.8 13.2 3.4 12 100 12.2 23,681.0 1,933.7 47%
Nikon 1-J2 2012 2604 3904 9.70 8.8 13.2 3.4 12 100 14.7 24,808.0 1,686.1 46%
Nikon Coolpix-P77002012 3024 4032 11.63 5.6 7.4 1.8 12 100 3.4 8,781.9 2,608.7 73%
Nikon 1-V2 2012 3082 4620 13.58 8.8 13.2 2.9 12 160 7.9 11,602.7 1,466.3 53%
Nikon Coolpix-P3302013 3024 4032 11.63 5.6 7.4 1.8 12 100 3.4 8,367.8 2,440.4 82%
Nikon 1-AW1 2013 3082 4620 13.58 8.8 13.2 2.9 12 160 7.2 10,712.0 1,497.2 52%

13. 1. A major differentiator between
higher end and lower end
camera.
4.7µm4.7µm
= 22.09µm2 (e.g. D800)
Pixel Size / Pixel pitch

14. All Camera settings or modes (auto,
manual, aperture priority, shutter
priority, etc.) plays around with
these three basic settings.
Auto: Camera decides al three.
Manual: Photographer decides all
three.
Aperture Priority (A, Av):
Photographer decides aperture,
camera decides the rest two.
Shutter Priority (S, Tv):
Photographer decides shutter speed
or time value, camera decides the
rest two.
X
Time value / Shutter speed
Aperture size or f stop number
X
ISO or gain
1) Moving object?
Need higher shutter
speed.
2) Open up aperture
to fill the buckets?
3) Buckets still not
full? Increase ISO.1) Doing landscape,
need higher DOF,
smaller aperture
2) Reduce shutter
speed to fill up the
sensels / exposure.
3) Low sun light,
insufficient exposure,
increase ISO.

15. SHOT NOISE, PHOTON
NOISE
Even under uniform illumination,
there is small variation of light or
photons reaching each pixel or
bucket.
This variation manifest as grains in
the photograph. This is called shot
noise. It is measured as,
Small
variation
in level
With smaller
bucket, the
variations are
more
pronounced.
√ √
125,597
125,597
= 354.4
√ √
81,608
81,608
= 285
D4S
D750
Bigger Bucket win in handling Shot Noise, useful in low light photography
(Poisson Noise)

16. SENSOR NOISE
There are noise (stray electrons) in any
sensel. They get amplified at higher
ISO.
The noise also increases with
temperature / long exposure (thermal
noise). Hence keep your camera cool.
Modern high end camera (high SNR),
this problem is now minimal. They can
operate at high ISO.
Semi-professional and in compact
camera, this problem is profound as
they tend to use smaller sensels.
Shot noise is any way relates to “well”
bucket capacity. Thus, any smaller
sensel camera is susceptible to shot
noise.
For example, latest full frame high
mega-pixel cameras – Canon 5DS
(50MP), Nikon D810E (36MP) cannot
operate at higher ISO. These cameras
are targeted for high resolution
landscape photography (note that the
lens should also be capable of resolving
higher resolutions).
Minimally
Exposed
= X =
The Stray also
get multiplied

17. WHEN SENSOR KNOCKS
THE ADC’S DOOR.
• 12 bit ADC (earlier)
• Improving Sensor
• 14 Bit ADC (now)
0
10
20 30
40
50
xN
Analog
to
Digital
1
0
1
1
0
1
0
0
1
1
0
0
1
0
Image
Processor
Ideal sensel, Zero sensor Noise.
Well capacity 100,000.
Hence the dynamic range is
100,000 as far as the sensor is
concerned.
However, the ADC is 14 bit. It
means it can count from 0 to
214, which is 16.384.
Hence, this is the limit to
dynamic range even if the
sensor is ideal.
Hence, with improving sensor,
we will see >14 bit ADC.

18. Keep all your questions for the other three.