Almost every fifth post in the relevant photography forums reads something like this: “My pictures are always too light / too dark. What am I doing wrong?” And by the third answer at the latest, someone suggests using spot metering. Then the exposure is correct. At least that is the opinion of many writers in the forums.
Exposure metering
Whoever holds such an opinion is either negligent (at least towards a photography beginner) or has not understood the principle of in-camera light metering.
Since the camera’s exposure meter does not measure the actual brightness, but only the light reflected from the subject, the measurement result depends (unfortunately!) on the nature of the subject. For an average subject, consisting of roughly equal parts of bright, dark and medium-bright subjects, the usually set matrix metering will come to a (more or less) correct result. The photo then corresponds to our expectations:
In the image above, we have exactly this situation. Thanks to the mixture of differently bright image elements, the exposure metering easily leads to a medium and thus largely correct exposure.
Most subjects are such that the exposure metering works without any problems. However, there are always subjects where this is not the case. Whenever the photographed scene consists of predominantly bright or predominantly dark image areas, a false exposure will occur.
The photo of the white flower against a white background is one such example. Since the exposure meter cannot, of course, “know” what the subject is like, it interprets the light reflected from the subject as if light and dark picture elements were equally present in the image. The result is that the photo is too dark (white tends toward medium gray, image on the left) and exposure compensation is necessary (image on the right).
In this case, spot metering would not have yielded a better result, since the flower itself is almost white and spot metering only measures the light reflected from the subject.
In some cases, however, spot metering is even counterproductive. For example, in the photo of the black panther:
Spot metering on the black fur of the animal would inevitably lead to a significant overexposure of the image. Matrix metering has a much better chance of success in such a case, since it also includes the (brighter) background in the metering and thus comes closer to at least a medium exposure.
So when to use spot metering?
Of course, there are cases in which spot metering can be used sensibly, e.g. in backlit situations. In the photo of the masked person at the carnival in Venice, the exposure metering was influenced by the sun in the picture and the photo is therefore definitely too dark.
A spot metering on the mask or the person’s lace collar will remedy this:
However, you should make sure that you do not measure very dark objects like the costume. That would naturally lead to overexposure.
Conclusion
Spot metering is certainly not a panacea against incorrect exposures. In some cases it is even counterproductive. In most cases, matrix metering in combination with an occasional look at the histogram leads to a more reliable exposure.
As usual, I’m looking forward to your thoughts and comments.
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