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What Is ISO?

Long shutter speed is used to take low-light photographs.

What is ISO?

ISO represents the sensitivity of your camera sensor to light. For those of you close to my age, you might remember the old term ASA. Same thing. ISO can vary from 100 to as high as 25,000 or more on some digital SLRs and mirrorless cameras. The bigger the number, the more light is sensed.


How does ISO affect a photo?

Why not just go for the highest setting and be done with it? Well, just like with film, there is a trade-off for that sensitivity. In film, it was called grain; in digital terms, it is noise. The higher the ISO, the more noise you will get. So you will want to keep the setting as low as possible. Preferably at 100. But what if you can’t? What if it is too dark and you can’t use flash? Well, if you must, use a higher setting. But if you do so, know that you are compromising the quality of your photographs in favor of getting lower-quality pictures versus not getting any. And there is one thing you can do to decrease the noise significantly. There is a camera setting for automatic noise reduction on most digital SLRs and mirrorless cameras. Where it is located varies from camera to camera. It helps a lot. The problem is that, as usual, there is a price, a trade-off. Whatever shutter speed you use, it will take at least that long for the noise reduction algorithm to work. That is because it takes a black picture, with the shutter closed, right after each exposure and looks for false sensitivity readings. It then subtracts out that noise from your photograph. It will be much better, but it will slow things down significantly at times. That slowness could prevent you from using Burst Mode, also known as Continuous Mode.


What is a good ISO range for a camera?

It is important that you do not leave your camera set at the default settings for ISO. The default settings usually include Auto ISO, which means the camera might choose a very high ISO. Yes, you will get the photograph, but will you want to use it for anything? Better to be forced to set it manually so that you can consciously decide how to get the best quality photograph under the existing conditions. Newer cameras also allow you to set a range for Auto ISO, so you can select the highest ISO your camera will choose.


How can I tell what the best ISO for my camera is?

Try this exercise: There have been significant advances in noise reduction in the newer digital cameras. Take several photographs of the same object under the same lighting conditions while varying the ISO settings. Look at these photographs on your computer monitor. But go beyond the size of your monitor. Enlarge them, and look for “grain.” Determine where the quality begins to deteriorate. That will be an important discovery for use in taking low-light photographs in the future. Digital cameras are improving at a fast pace. ISO settings can be set higher and higher without much noise. Find out what works for you. But look at the photographs at high magnification. Consider the results if you get that great shot and want to print it poster size. That option is now very affordable, so don’t rule it out.

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