A high ISO value? Or corrected underexposure?

Saturday 27 April 2024, 14:28 by Nando Harmsen | 3,641 views | 1 comment

This article was translated from Dutch with the help of AI. Read the original.

Sometimes you need to use a fast shutter speed. This may mean increasing the ISO value to achieve it. Is it better to take an underexposed photo and correct it, or should you simply choose a high ISO value?

A high ISO value causes noise. This is well known, and is why many people never use a high ISO value. But what if the shutter speed still needs to be faster? Then they take an underexposed photo and correct it later.

Which is better? A photo with a higher ISO value or a corrected underexposed photo? It really comes down to the following question: what causes the most noise?

Brightening dark areas causes extra noise. Sometimes this is worse than using a high ISO value.
A high ISO value produces noise. But a corrected underexposed photo does too. It is very easy to test which works best. Take a photo with a high ISO value, then take the same photo again with underexposure.

Do this in steps, keeping the shutter speed and aperture the same and only lowering the ISO value. Then correct the underexposed photos and compare them. You will immediately see which produces the most noise.

Is it the same? Then your camera is ISO-invariant. In other words, correcting underexposure produces just as much noise as using a comparable high ISO value. In that case, you can simply use high ISO values, because there is just as much noise as in a corrected underexposed photo.

ISO invariance test of a Nikon Z fc
However, it can also turn out differently. Often, correcting an underexposed photo will show more noise than using a comparable high ISO value. In that case, the camera is not ISO-invariant. But this does mean that you are better off setting the ISO value high for the best result.

In almost all cases, it is better to set the ISO value high and expose correctly than to use a low ISO value and underexpose. Of course, this also depends on the degree of underexposure. The best thing is to try it out for yourself.

Are you a photographer who often underexposes to avoid using a high ISO value? Share your experiences in a comment below this post.

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