7. ISO

Pictures by Neil Douthwaite
Modelled by Theresa the Ceramic Owl

ISO means exactly the same in digital photography as it did in film. In film the higher the ISO number the more sensitive to light the film was. This meant that with higher ISO films it was possible to take pictures in lower light conditions – e.g. Indoors.

In digital photography ISO is exactly the same. A higher ISO means that the sensitivity of the digital sensor has been increased and less light is needed to take a picture. So why not simply increase the ISoto it’s highest and know you will always be able to take a picture? We cna not do this because higher ISOs come at a cost. In film higher ISO films tended to be grainier. In digital photography the same is true, but we call it noise.

Camera manufacturers are in an arms race to create cameras that have less and less noisey film sensors even at very high ISO values. Despite this, there is a big difference in the quality of the picture below, even though it was taken on a £700 camera.

Example:

In the picture of Theresa the owl below the quality is good, it was taken indoors at an ISO of 400, which is a good level to start from in a lot of circumstances. However, this is not especially sensitive and the shutter speed is 1/6th of a second, which is very slow. If the camera had moved even a tiny amount the picture would have become blurred. A tripod was essential and even then small vibrations could have been a problem. For taking pictures of anything other than a ceramic owl it would have been a problem.

ISO 400 6th f4.5
ISO 400 1/6 f4.5

The next picture was taken at an ISO of 1000. Still fairly good quality. The shutter speed can increase to 1/20th of a second which is more practical but still pretty slow.

ISO 1000 20th f4
ISO 1000 1/20 f4

Now at an ISO of 3200 and the image below was taken at 1/60th of a second, we need less time and less light to take a picture. 1/60th of a second means that with a steady hand we could avoid using a tripod. Even though the image is zoomed out you may begin to detect a fall in quality of the image, especially in the background.

ISO 3200 60th f4
ISO 3200 1/60 f4

Now at 6400 the ISO is very sensitive, youwould have struggled to finda film this sensitive. But there is definitely a little fuzziness appearing around the top of Theresa’s head.

ISO 6400 100th f4
ISO 6400 1/100 f4

Finally at 16000 the ISO is very high (although this camera will go higher!). There is definitely now a trade off. The shutter speed is very managable at 1/160th of a second but the quality of the picture has suffered. Not convinced? Well see below.

ISO 16000 160th f4
ISO 16000 1/160 f4

If we were to print these pictures the effect would be much more pronounced than we can see in small images on a screen. So to demostrate the effect more clearly in the sequence below we have zoomed into the left side of Theresa’s head. The decline in quality is now more obvious. Even in the shift from an ISO of 400 to 1000 you can see extra “noise” in the darker areas of the eye.

ISO Collage

In most cases then you will always want the lowest ISO possible to get the highest quality. However, As you become more familiar with your camera you will find yourself making tradeoffs between shutter speed, aperture and ISO to get the best balance for the conditions you are shooting in. Like all areas of photography artistic impression is really important too. You may want a grainier, noisier photo to create a more mysterious or even spooky atmosphere to your picture.

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