ABSTRACT
The key to understanding how all light-sensitive materials work whether film, a digital sensor or a child's sun print is the law of reciprocity. As each new generation of digital camera has incrementally improved noise performance across a wider range of sensitivities, ISO sensitivity can finally come into its own as part of the exposure setting. As with autofocus, there is nothing inherently wrong with automatic exposure, but the photographer has to understand how and when to choose to override the suggested settings. The aim is always to get a good exposure with detail in the highlights and shadows if appropriate, but one where there are no surprises. Photography 101 is simply learning how to make a piece of well-browned toast. While amateurs choose so-called exposure scene modes, cameras used by professionals feature auto-exposure modes and semi-automatic modes that allow the user to choose one exposure variable and have the other variables, including sensitivity, adjusted accordingly.
