In this slideshow, we look at exposure theory and how it applies to our manual camera settings of aperture, shutter speed and ISO.

1. Exposure Theory

2. Exposure Defined
Exposure: the quantity of light reaching a photographic
film/sensor, as determined by shutter speed and lens
aperture.
Exposure based on a scale where 0 = Proper Exposure
- Negative number indicates underexposure
- Positive number indicates overexposure

3. How a Camera Sensor Works
Similar to an array of buckets collecting rain water, digital camera sensors
consist of an array of "pixels" collecting photons, the minute energy
packets of which light consists. The number of photons collected in each
pixel is converted into an electrical charge by the photodiode. This charge
is then converted into a voltage, amplified, and converted to a digital value
via the analog to digital converter, so that the camera can process the
values into the final digital image.

4. Exposure Triangle
The “exposure triangle” is a term used to reference the relationship
between the three elements that control the quantity of light entering the
camera: aperture, shutter speed, and ISO/Gain. A
photographer/videographer can use many combinations of the three
settings to achieve the same exposure. The key, however, is knowing
which trade-offs to make, since each setting also influences other image
properties.
The three key elements of the exposure triangle are:
- Aperture: Controls Depth of Field
- Shutter Speed: Controls Motion Blur
- ISO/Gain: Controls Noise/Grain

5. Aperture Defined
A camera's aperture setting controls the area over which light can pass
through your camera lens. It is measured in terms of an f-stop value, which
can at times be counterintuitive, because the area of the opening
increases as the f-stop decreases. In photographer slang, when someone
says they are "stopping down" or "opening up" their lens, they are referring
to increasing and decreasing the f-stop value, respectively.
Aperture: the unit of measurement that defines the size of the opening in
the lens.
Iris diaphragm: a thin opaque structure with an opening (aperture) at its
center.
F-number: the ratio of the focal length of a camera lens to the diameter of
the aperture being used for a particular shot (e.g., f8, indicating that the

6. Aperture Process: F-Number Ratio
Aperture is represented by an F-Number or F-Stop (f/n). F/n represents the
ratio of the focal length of a camera lens to the diameter of the aperture
being used for a particular shot. The lower the F-number, the more light
that’s let into the camera, but it also means the less depth of field for
focusing on a subject.

7. Aperture Control: Depth of Field
Depth of Field: the distance between
the nearest and farthest objects in a
scene that appear acceptably sharp in
an image.
Lower f/n = more light/less depth of field
Higher f/n = less light/more depth of field

8. Shutter Speed Defined
A camera's shutter determines when the camera sensor will be open or
closed to incoming light from the camera lens. The shutter speed
specifically refers to how long the light is permitted to enter the camera.
The lower the shutter speed, the longer the light is exposed to the sensor,
resulting in the more light that is accumulated by the sensor. A lower
shutter speed also results in more motion blur seen in an image or video.
Shutter speed is measured in
seconds/fractions of seconds.
This is usually represented as
1/30, 1/60, 1/80, all the way up to
1/4000 and above.

9. Shutter Speed Process: CMOS vs. CCD Sensors
Generally speaking, CCD sensors utilize a Total Shutter and CMOS
sensors utilize Rolling Shutter. While there are many reasons for camera
manufacturers to choose one type of sensor over the other - processing
speed, power consumption, cost, complexity and more, CMOS sensors
(which use the rolling shutter method) tend to deliver the image faster, thus
clearing the sensor for the next shot. This may not be an issue with stills,
but is a huge factor when selecting a sensor type for video - the sensors
needs to take 24,30 or 60 frames a second. This is why almost all our
DSLR and Smartphones sensors are using rolling shutters.

10. Shutter Speed Control: Motion Blur
Motion Blur: the apparent streaking of rapidly
moving objects in a still image or a sequence
of images such as a movie or animation.
-Lower shutter speeds = more light/more
motion blur
-Higher shutter speeds = less light/less
motion blur

11. ISO/Gain Defined
In Digital Photography ISO measures the sensitivity of the image sensor to
light. The lower the number, the less sensitive your camera is to light and
the finer the grain. Higher ISO settings are generally used in darker
situations and/or to get faster shutter speeds, but results in a more grainy –
or noisier – image.
Gain is typically used interchangeably with ISO, but works a little differently
to increase sensitivity. Gain increases the sensitivity by removing
information from the underexposed background. As a result, the
background loses detail.
Common ISO speeds include 100, 200, 400 and 800,
although many cameras also permit lower or higher
values. Gain is measure in decibels (dB), and usually
range between +0 to +24.

12. ISO/Gain Control: Image Noise
It’s important to note that ISO and Gain DO NOT control the amount of
light entering the camera, but rather take the existing amount of light
entering and amplify the sensor’s sensitivity to it.
- Higher ISO/Gain = “more light”/more noise
- Lower ISO/Gain = “less light”/less noise

13. Review: Exposure Theory
Aperture (measured in f/n):
- Lower Aperture = More Light, Less Depth of Field
- Higher Aperture = Less Light, More Depth of Field
Shutter Speed (measured in 1/s)
- Lower Shutter speed = More Light, More Motion Blur
- Higher Shutter Speed = Less Light, Less Motion Blur
ISO/Gain (measured in 100’s/dB)
- Higher ISO/Gain = “More Light”/More Noise
- Lower ISO/Gain = “Less Light”/Less Noise

14. Sources: