What is ISO and how to use it?
Photo Tip Friday January 10, 2014
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 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), then 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 give some guidelines for choosing your ISO setting.
Here are photos for comparison. I shot the first one at ISO 100 and the second one at 6400.
As you can see the lower ISO image is sharper, has better colour and more dynamic range in highlight and shadow. If you enlarge these photos up to 8″X12″, they are quite similar and presentable. So if you have to shoot in faster ISO try to keep the print or display size smaller.
Here is a comparison at 100% view, or if you enlarge the photos larger than 8″X12″.
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 have everything sharp, for instance 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 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.
Ted and the Omnilargess Team