Most digital still cameras have the ability to display a histogram–a graphic display of brightness levels in a scene. Photographer Michael Reichmann calls it “the greatest invention since the built-in light meter.” If you’re not using your camera’s histogram function, you should.
A histogram basically lets you know whether your image is properly exposed. The graph runs from dark to light, left to right. If the graph has a peak at one edge or the other, you may have a problem. A peak on the left signals underexposure. A peak on the extreme right and your image may be overexposed.
Reichmann says one rule of thumb many photographers follow is to “expose to the right.”
…bias your exposures so that the histogram is snugged up to the right, but not to the point that the highlights are blown. This can usually be seen by the flashing alert on most camera review screens. Just back off so that the flashing stops…This will accomplish a number of things. The first is that it will maximize the signal to noise ratio. The second is that it will minimize the posterization and noise that potentially occurs in the darker regions of the image.
There are a couple of caveats, however. To make this work, you have to use a RAW converter like Camera RAW. And because this technique requires slower shutter speeds and wider apertures, you may not want to try it if you’re shooting hand-held or shooting moving objects. For more detail on histograms, check this “how to” article in Professional Photographer Magazine.