Mastering your Canon camera - ISO setting

October 14, 2013

This is one of the things you should check every time you go out shooting. It will be set to whatever you set it to the last time you used your camera.

On all my cameras, the button to set ISO is close behind the shutter button and dial on the right side. On the 1D it gets its very own button and can be changed using either the wheel or the dial (nice!). On the 5D the button handles both ISO and flash compensation; you have to turn the dial to change ISO. On the 20D the button handles both ISO and "drive" you have to turn the wheel to change ISO (sigh!).

The game here is to use the lowest ISO value possible for the highest image quality. In low light you have to use higher ISO values (or a tripod). If you are shooting action (or flowers moving in the wind), you need fast shutter speeds and probably higher ISO settings. The problem with higher ISO settings is noise. You should explore how high you can push ISO without getting significant noise (or understand that you are going to get noise at higher ISO and put up with it in order to "get the shot").

ISO expansion

You may notice that there is a special function to access some "special" ISO settings. These are tucked away because they are simulated by software in the camera. The low 50 setting is generated by dividing all pixel values by two (and discarding every other value). The high setting is similarly produced by multiplying by two (so every other code is missing). I leave these disabled, especially after I learned the nature of them.

Auto ISO

I have never used this, but the idea here is to let the camera pick the ISO setting. The 20D does not have this feature, but the 5D does (it is the "A" setting at the far end of the ISO selections).
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Tom's Digital Photography Info / tom@mmto.org