Week 2 - Exposure: Shutter Speed, Aperture, ISO & Depth of Field

Exposure is the act of exposing the image sensor to light. 

It is the combination of a particular aperture and shutter speed that results in a specific amount of light entering the camera to be exposed to the image sensor

Shutter Speed: The amount of time the shutter on the camera is open. This is shown in seconds or fractions of a second. If the shutter speed is set fast, then this allows a shorter amount of time for the image sensor to be exposed to light. When more time is required for the image sensor to be exposed to light, then a shorter shutter speed is required.

f/3.5 - 1/60 sec - ISO-2000

Pity Sex Live @ Sticky Mike's Frog Bar
5/10/2016

f/3.5 - 1/25 sec - ISO-2000

Pity Sex Live @ Sticky Mike's Frog Bar
5/10/2016

As shown above, by using a slower shutter speed allowed the image sensor to exposed to more light, making the image seem brighter rather than darker. 

Motion Blur

f/5.3 - 1/40 Sec - ISO-1250

I noticed in the photograph above that the drum sticks in the hands of the drummer are blurred. This was due to the fact the drum sticks were moving while the shutter was open. As I did not desire this motion blur in the photograph, I would have had to increase the shutter speed. This would have, in turn, made the image become darker. Therefore, adjustments to the aperture and the ISO setting would have to have been altered to ensure optimal exposure.

Aperture: This is the ability to control the brightness of the image that passes through the lens on the image sensor. These are expressed as f-numbers or f-stops.



   
        LOW                                                                                                                       HIGH

The f-stop of a lens is determined by dividing the focal length of the lens by the diameter of the size of the lens opening. 

I shall note here that the lower the value of the f-number then the wider the iris of the lens.

We can understand aperture as we understand the human eye. When we are in dark lighting conditions, our pupils dilate (become wider) in order to allow more light in. When in bright lighting conditions, our pupils contracts. This allows less light in. 

Changing the aperture on a camera from f/4 to f/2.8 increases the amount of light that falls on the image sensor by half. This is known as stopping aperture up a step. If we were to do the reverse this will decrease the amount of light that falls on the image sensor by half. This is known as stopping aperture down a step.

f/9 - 1/500 Sec

f/3.5  - 1/1000 Sec

The example above shows how both the aperture and shutter speed interact to produce either a darker or brighter image. If a high shutter speed is required (less time the image sensor is exposed to light), then using a low f-number may compensate for to make the image brighter.

 Depth of Field

Changing the aperture changes depth of field.

Depth of field is the distance in front of or behind the focus point of the photograph.

If increased depth of field is required, then a high f-number needs to be chosen.

f/11 - 1/3 Sec

If decreased depth of field is required, then a lower f-number needs to be chosen.

f/4 - 1/25 Sec

Depth of field can be used to bring focus on the subject in foreground and blur our anything appearing in the background.

ISO: Changing the ISO setting adjusts the DSLR camera's sensitivity to light.

In digital cameras, light that falls on the image sensor is converted into electrical signals for processing. By raising ISO sensitivity, you raise the amplification of the signal. By decreasing the ISO sensitivity, you lower the amplification of the signal.

F/5.6 - 1/50 Sec - ISO-1600

I encountered a few issues when taking photographs at the Pity Sex gig. The room was dark, but had different types of unnatural lighting all around the room, this meant I would have to use a low aperture to allow in more light. The subjects were also moving around the stage a lot, this meant I would have to use a fast shutter speed into to 'freeze' the subjects movements. To increase the brightness of the image above, I could have used a higher ISO setting, increasing the amplification of the converted signals.

Noise

The implementation of a higher ISO sensitivity allows for reducing blur caused by motion of the subject (or the camera itself in some cases) and higher shutter speeds in low lighting. However, this does come at a price.

Example taken from Google Images

 Note how the image on the right appears 'grainy' as opposed to the one on the right that used a lower ISO setting. Raising the ISO sensitivity introduces what is known as 'noise' into photographs. As a higher ISO sensitivity amplifies the converted electrical signals, this means that it will also amplify any 'noise' in the signal as well - producing a poorer quality image (unless such an effect is desired, of course).


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Finding the 'sweet-spot' between the having the correct aperture, shutter speed and aperture I found quite difficult to master. But I have come to understand on reflection that a higher ISO sensitivity compensates for high shutter speeds to give my images the desired brightness. Also, taking a photograph that could require a decreased depth of field (as in the photo above) means that I could have increased the aperture (allowing more light to come through the iris) and decrease the ISO sensitivity.