PICTURE THIS
ISO - setting the sensitivity of your camera

There are three aspects to what is termed, the ‘Exposure Triangle’ (Depth-of-Field, Shutter Speed and ISO). ISO is the third part.

ISO (International Organization for Standardization) is the third part one of the ‘Exposure Triangle’ (Depth-of-Field, Shutter Speed and ISO).

Using the DoF exercise when we closed our eyes to experience shutter speed, ISO in this scenario would be the equivalent of how sensitive our eyes were to light. How tired we were, or going from a darkened room into daylight.
Our brain automatically adjusts the sensitivity level of our eyes. 

The normal ISO setting for daylight is around 100 - 200, cloudy days could be 400 +, dusk 800 and night anywhere from 1000 to 6400 or higher. So you can photograph in almost any situation. 

But as your ISO is linked to the exposure triangle, each number effectively doubles in sensitivity. 200 is twice as sensitive as 100, and 400 is twice as sensitive as 200 and so on. This makes ISO 400 four times more sensitive to light than ISO 100, and ISO 1600 sixteen times more sensitive to light than ISO 100. When it is sixteen times more sensitive to light it needs sixteen times less time to capture an image! If you need one second to capture a scene at ISO 100, by bumping up to ISO 800, you can capture the same scene at 1/8th of a second, which offers you more flexibility.
It’s still slow but maybe you can handhold it.

But as the ISO gets more sensitive the camera sensor starts to record ‘noise’ a sand like texture. So there is a trade off going on. Yes you can shoot later and later but your images will be noisy and not really capable of enlarging too much. Noise is cool and can be used as an effect, but not if you don’t want it.  (A): This was taken at 1600 ISO on an aircraft at dusk. There was no other light source apart from the darkening sky and the light from the mans phone. It has some noise to it but the ambience has been captured.  The same goes for the shot of the ice ring around the moon (B), taken at midnight. The frame of the Cambridge punts (C) was taken at 05:00 while still quite dark, but taken with a film setting of 1600 ISO. You can see the noise here but I feel it ads to the mood.

All photography and information © Jon Davison 2021.



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