Bruce Girrell on tue 29 sep 98
One thing that I haven't seen mentioned in this discussion of polarizers and
exposure adjustment is the type of camera in use. Or maybe somone already
mentioned it and I didn't read it.
Everything[1] that has been contributed regarding the correction of exposure
for polarizers is valid if a view camera, range finder, or similar
non-through-the-lens-metering camera is used. But _no_ filter correction
factors should be applied when using an SLR. The amount of light reaching
the meter in an SLR has already been reduced by the filter(s).
One final note. The polarizer, repositioning of the lights, etc. should be
able to remove most reflections or at least leave only a pleasing "eyecatch"
sort of reflection. But if you have a really, really stubborn reflection and
you can't move/diffuse those lights, it is possible (but a little pricey) to
use polarizers over the lights with a polarizer on the lens as well.
Bruce "sunglasses" Girrell
[1] I have to quibble with Tom Wirt's comments regarding the polarizer's
effect.
Tom, you are correct in saying that the light from tungsten or stobes is not
polarized. But your statement that the polarizer only appears to cut glare
because it simply reduces the incoming light by two stops is incorrect. When
light reflects from a nonmetallic surface, a good bit of the light becomes
polarized. It is that polarized portion that the polarizer is able to block.
To see the effect get a polarizer filter or a set of polarized sunglasses.
Find some water with a nice reflection on it. Now look through the polarizer
and rotate the polarizer. The reflection will decrease and increase
depending on the position of the polarizer. If the polarizer were only
decreasing the light, like a neutral density filter, you could not see the
effect.
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