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I have a feeling that my camera isn't metering as well as it used to, and I think it is now over exposing by about a stop. Whilst this can be counteracted by using exposure compensation, it's not a critical issue; but how can I check the calibration of the inbuilt metering?

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up vote 3 down vote accepted

I'd suggest to take an image of evenly lit area without details (wrong focus is a great way to reduce details) and check the histogram. You should see a peak in the center or just a bit left from the center if your meter is correct (left image on the example below, default exposure) and more to the right if your camera overexposes as you suspect (right image on the example below, overexposed 1 stop).

alt text

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Are you sure? My impression was that meters aim for a 18% or 12% gray, and that's not right in the middle, is it? – Reid Sep 19 '10 at 20:04
@Reid - this is an actual example from my camera. 18% is the middle gray, 12% is a little to the left. – Karel Sep 20 '10 at 6:44
Cool, thanks. . – Reid Sep 20 '10 at 18:23

If you have control the light, the easiest way to do it would probably be to compare the camera meter against a hand-held meter and see if they agree or not. Your other option would be to take it in for servicing and have them check it with their computerized gear.

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Another camera is also an option to check. Just be sure you're metering from evenly lit area. – Karel Sep 12 '10 at 18:49
I've only film bodies to go against, although I guess I don't have to actually fire the shutter... – Rowland Shaw Sep 12 '10 at 19:06
@Rowland: For meter testing? Probably not, it's simply seeing what the camera has decided is the best exposure. If you did want to fire the trigger to fully check, you could do one with the camera choice and one with the meter choice and compare the result. – John Cavan Sep 12 '10 at 19:40

You could try following the "Sunny 16" rule to determine the correct metering during bright midday sunlight. The rule generally follows as such:

1/ISO shutter @ f/16 aperture = bright daylight, distinct shadows, midtoned subject

If your ISO setting is 100, you would use a shutter speed of 1/100. Take a shot, then compare that shot to one metered by your camera under the same conditions. Under aperture priority mode, your camera should choose a shutter speed of 1/100, maybe 1/125. Under shutter priority mode, your camera should choose an aperture of f/16, or maybe +/- 1/3 of a stop.

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Well, the "sunny 16" belongs to a time when BW film with wide latitude was shot (and also with possibilities to compensate during enlargement). I wouldn't trust it to verify my calibrated meter. – Karel Sep 12 '10 at 18:46
I don't think the rule is restricted to BW film. Plenty of the modern digital landscape photography books I own still discuss "Sunny 16". It is by no means a highly accurate method of verifying the built in meter calibration, but if you don't have an additional incident meter, it might give you a starting point to determine if you should get an incident meter and do a more accurate comparison. – jrista Sep 12 '10 at 21:28

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