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Once upon a time, “underexposure” and “overexposure” described mistakes.
Underexposed negatives lacked sufficient density. Overexposed negatives were too dense. Underexposed prints were too light. Overexposed prints were too dark. Underexposed color transparencies were too dark. Overexposed color transparencies were too light. Underexposure and overexposure were failings, embarrassments, proof of shameful incompetence.
Now the terms have been stood on their heads.
Many photographers use “underexposure” and “overexposure,” to describe a deviation in exposure relative to the reading of a light meter; to describe a technique for determining the correct exposure; to describe how they obtained the effect they wanted. “I underexposed by a half-stop to increase color saturation” is a common report. So is “I added a stop of overexposure to open up the shadows.”
Another variation on the underexposure theme occurred in the days of rating Tri-X at an exposure index of 1600 or 3200 to obtain higher, action stopping, shutter speeds. Pushing film was described as “underexposing and overdeveloping.” But the reduction in exposure, which reduced a negative’s density, was intentional, not a mistake, as was extending the time in the developer to boost the contrast to make printing easier. A similar misuse of “underexposure” occurs in digital photography when a higher shutter speed is obtained through a negative value of exposure compensation, followed by stretching the histogram of the photograph in an image processing application such as Adobe Photoshop.
At The Blogger’s Lens, underexposure and overexposure are mistakes.