Understanding ISO

There are 3 things that affect your image quality in photography; ISO, aperture and shutter speed. All 3 of these things depend on one other factor which is light. A photograph is basically a chemical process in which light is exposed to film, or a sensor in digital cameras, and registers an image. On this artical we will be talking about ISO


What Is ISO?

ISO stands for international Standards Organization; ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots.

The one on the left is taken at 100 ISO and the one of the right at 3200 ISO

Use ISO Strategically

It’s a good idea to always shoot with the lowest possible ISO you can get away with. On many cameras, that means dialing in ISO 100 and leaving it there unless you have a good reason to increase it.

What kinds of reasons? Imagine you’re outdoors late in the day trying to take some photos and your flash won’t illuminate the scene because it’s too large or far away. In that case, crank up the ISO until the camera stops giving you a slow shutter warning. I’d suggest going with the lowest ISO that’ll give you a satisfactory photo in order to avoid introducing too much noise in the image. But don’t fret too much about this: It’s a lot better to capture a sharp photo with some noise in it than a shaky photo that was shot too slow for the available light.

You might also be able to rely on your camera’s Auto ISO setting. Check your camera’s user guide for details. On many cameras, you can set the ISO to Auto and it’ll dial the ISO up and down on its own when you shoot in certain modes (like Automatic exposure mode). I’m not a huge fan of Auto ISO because I don’t know exactly what the camera is doing, but it’s a convenient way to ensure you get the sharpest results without sweating over the settings.

ISO Math

It’s also worth pointing out what the ISO numbers mean. What, for example, is the difference between ISO 100 and ISO 200? Thankfully, cameras use a fairly consistent set of conventions, so that doubling the ISO doubles the light sensitivity. So in this sense, ISO is like shutter speed or aperture. If you go from ISO 100 to ISO 400, that’s two stops of exposure change (doubled and then doubled again), so that’s equivalent to changing the shutter speed from 1/60 second to 1/15 second.

Put another way, suppose your camera is currently trying to take a photo at a shutter speed of 1/15 second at an ISO of 100. Change the ISO to 400, and the camera will now be able to take the same photo at 1/60 second, which is probably good enough to take a sharp photo. Change the ISO to 800, and the shutter speed will be 1/125 second.

This blog is designed to provide photography tips and tricks and post processing tips

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Posted in Tips And Tutorial
One comment on “Understanding ISO
  1. Mirjam says:

    Thanks for your post. It was interesting reading.

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