Aperture and shutter time determine how much light reaches the sensor for a given scene. ISO influences how that recorded signal is represented in the finished image. Increasing ISO does not send more light into the camera.
Your camera’s meter is a starting point
A bright snowy scene and a dark woodland do not need to look the same. The meter estimates a setting; you decide which tones matter. Check the photograph and histogram, especially when bright and dark areas appear together.
Try it
Photograph one subject against a bright background and then a dark background. Watch how the meter reacts. In an automatic or semi-automatic mode, try exposure compensation and compare the results.
By Joseph Hubbard, photographer and artist at Hubbard.ART.
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