Understanding ISO

Understanding ISO in Photography

Part 1


What is ISO

ISO in photography terms is a measurement unit which measures the sensitivity of our media (film or digital sensor) to light. In simplest terms the higher the number the more sensitive the media is to light.

We’ve seen that we can control the exposure through choices for Shutter Speed, Aperture and ISO. When it comes to low light situations, to maintain a certain shutter speed or to use a desired f-stop, we have to adjust the ISO.

As a rule of thumb, photographers prefer to use the lowest possible ISO to keep the sharpness and dynamic range in their photos, but there are times when you want to capture a moving subject (such as sport photography or taking photos of kids) and there is no other choice than to use a higher ISO setting. After all a noisy (grainy) photo is far better than a blurry one!

In this article I am going to show you some samples of different ISO and discuss some guidelines for choosing your ISO setting.

Here are photos for comparison. I shot the first one at 100 ISO and the second one at 6400 ISO.

Understanding ISO in photography
ISO 100


Understanding ISO in photography
ISO 6400
Understanding ISO in photography
ISO 100 Vs 6400

As you can see the lower ISO image is sharper, has better colour and more dynamic range in highlight and shadow.

Here is a comparison at 100% view.

Understanding ISO
ISO 100 vs ISO 6400. Notice the noise and lack of sharpness in ISO 6400

Generally speaking you want to stay with lowest ISO setting when you shoot landscape, portrait and detailed images such as macro photography. For moving subjects you should consider the lowest possible ISO. As an example if your subject is a bird in flight and you want to keep everything sharp and you are using a 300mm lens at f5.6, your minimum shutter speed should be 1/500s or faster. With your shutter speed set to 1/500s and your aperture at f5.6, check your camera’s light meter for exposure. If your camera cautions for under-exposure (usually there is some kind of warning that tells you the exposure is not correct), instead of reducing shutter speed (which results in a blurry photo) or opening up the f stop (which will give a shallow depth of field), increase the ISO till your camera’s built in meter stops asking for more light!

There is much to learn about ISO and dynamic range which I will cover in future articles. For now, happy ISO shooting!

We have scheduled a Digital Camera workshop for beginners for November 4 and 7. It is a two part workshop that covers the basic settings of a digital camera. Read more about this class and register now.

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