Determining Base ISO

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Today’s Question: How do I determine the optimal ISO for my camera? I don’t remember anything like that in the manual or specifications when I bought my camera.

Tim’s Quick Answer: As a general rule the “base” ISO for a camera will be the lowest ISO setting available using the normal control for the camera. The special “low” ISO options available on some camera models would not generally be the base ISO.

More Detail: As noted in a recent Ask Tim Grey eNewsletter, in most cases you can expect the least noise and best overall image quality by using the “base” or “native” ISO setting for your camera. In most cases, that base ISO will involve the least amount of amplification to the signal being gathered by the image sensor, which translates into less noise and greater dynamic range.

There are, of course, some exceptions in terms of how specific cameras function or the results you can achieve at various settings. And, of course, as many photographers have found, it isn’t always easy to find out which ISO setting is the “base” setting.

For most digital cameras you will find that an ISO setting of 100 (or sometimes 200) represents that base ISO. As noted above, in most cases the lowest setting you can set with the normal ISO adjustment control on the camera will typically be the base ISO that will provide the best image quality. The “extra” settings with a lower value that are typically found on a separate menu control for cameras with such an option are generally not the base ISO setting, and won’t necessarily provide improved image quality.

Again, there are many variables involved among the different camera manufacturers and models. That is why I always recommend performing some testing of your own to get a sense of the impact various ISO settings have on noise levels for your camera. In particular, this type of testing can help you get a better sense of how high you can raise the ISO setting before you start to see problematic noise in your images.