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12-21-2010, 07:17 AM   #16
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Location: Ames, Iowa, USA
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You present a very difficult question because the range of possible "darkness" is huge.

There is usually a subject in the scene you'd like to be properly exposed. In this cased, center weighted exposure metering may be sensitive enough to get you close to the correct exposure.

If not, do not try to creep up on the correct exposure by making small adjustments (until you get a histogram you can estimate from). Bracketing requires far fewer test shots unless you are a really good guesser.


Here's a manual bracketing scheme (set the camera mode to M, choose an f-stop & ISO):

Guess at an exposure time that's too fast - take a photo to be sure.
Guess at an exposure time that's too slow - take a photo to be sure.

Try an exposure time that's midway between too fast & too slow.
- if the result is too fast (slow), try an exposure midway between it and the previous too slow (fast) exposure.
Repeat the previous step until you are satisfied.

This routine will quickly get you into the correct exposure range.

If you want to adjust multiple parameters to adjust exposure, the relationship is:

Exposure = Brightness*time*ISO/F-stop_squared

Since brightness is constant for a particular scene, time, ISO, or F-stop can all be adjusted to affect exposure.

Dave


Last edited by newarts; 12-21-2010 at 07:23 AM.
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