Does D60 REALLY underexpose?

Started Apr 22, 2002 | Discussions thread
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Keith Lommel
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Does D60 REALLY underexpose?
Apr 22, 2002

All these complaints about "underexposure" make me wonder whether we need to reconsider what "proper exposure" is for a digital camera.

I think that "proper" exposure for digital is DIFFERENT from film. A properly exposed, unprocessed digital photo will often appear darker than a properly exposed film photo. With film, the goal is to get, for example, something that is 18% gray in real life to be recorded as 18% gray on film, and let everything else fall into place. Thus many film photographers will carry a gray card and use spot-metering to get proper exposure.

This is not appropriate for digital, however! Sometimes, recording something that is 18% gray as 18% gray will result in the highlights being pushed beyond white. The resulting clipping means that ALL DETAIL in the highlights is IRRETRIEVABLY lost. Thus a different standard for “proper exposure” is needed.

The goal when setting the input levels of any recording device is to make the most efficient use of the dynamic range offered by the recording medium. Different recording media have different dynamic range characteristics, and therefore different strategies for making optimum use of that dynamic range.

Photographic film (especially negative film) is said to have a relatively wide dynamic range. However, not all of this dynamic range is equal. Film offers the highest quality image reproduction in the center of its dynamic range. Detail can still be pulled out of areas that are exposed significantly above or below this center, but you lose contrast and color accuracy, and there is often an increase in noise or “grain.” Thus, with film you want the most important part of your scene to be recorded in the middle of the emulsion’s dynamic range. Since most things people are interested in (other people’s faces, flowers, etc…) tends to be neither black nor white, but rather gray (or with color film, mid-tones), it is usually best to set the exposure to get the grays in the middle, using a spot meter and gray card, if necessary. The highlights and shadows, respectively, will end up being exposed above and below the optimum middle of the dynamic range, so there will be some inevitable loss of detail, although it is usually not very pronounced. But anyway, as these parts of the picture are not the most important, losing a little detail is okay. The important thing to making optimum use of the dynamic range of film is to get the mid-tones exposed properly, and then generally everything else will take care of itself.

Digital sensors are very different from photographic film. Dynamic range is somewhat narrower, but there is an even more important difference. As long as you keep between maximum exposure (pure white) and minimum exposure (pure black), digital sensors will more or less deliver their optimum image reproduction at any level. Should you exceed the maximum or minimum in a region of your scene by even a little bit, however, you instantly and irretrievably lose all detail in that area. Thus, with digital, it is not so important to keep the main parts of your scene at a certain exposure level, because optimum image quality can be obtained at almost any level. Instead, what you have to worry about is keeping as much of the scene from exceeding the maximums at either end. Because in most scenes there is a much greater chance of clipping in the highlights, the best way to make optimum use of the sensor’s dynamic range is to expose so that the brightest highlights are just at, but below, the brink of clipping and let everything else fall into place. In cases where the highlights are really bright, this can often result in the majority of the scene being recorded quite a bit darker than the 18% gray that is optimum on film. But that’s okay, because the apparent brightness/darkness of the subject, as well as the highlights and shadows, can be quickly and easily adjusted with the Curves Tool in Photoshop.

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