The point of this polarizer-as-a-substitute-for-neutral-density-filter
discussion has gone astray as this thread has gone on. A polarizer has
little, if any, effect in many, if not most, photographs - other, that is,
than to serve as a neutral density filter.
Where no significant glare exists, there will be no significant variation in
light transmission or metering regardless of how the polarizer is
positioned.
Unless one's photographs are almost exclusively of large bodies of water,
landscapes with lots of sky, or windows with lots of glare - assuming all
sources of glare that *can* be minimized by a polarizer are at the correct
angle.
For every other subject and photographic situation, a polarizer is basically
just a neutral density filter with a rotating element. There should be no
change in metering as the element is rotated when the lens is pointed toward
any subject without a significant source of glare. If there is any change
in metering, the polarizer and camera's TTL metering are a mismatch.
Even in situations where a properly matched polarizer/camera used on a
subject heavy with glare indicates a metering change, such exposure
modification isn't always appropriate. For example, when a polarizer is
used to minimize sky or water glare to the extent that the meter calls for
1/2 a stop more exposure, this may not be the best choice since the
surroundings may be overexposed - an important consideration with films like
Kodachrome and Velvia.
The best reason I can think of *not* to rely on a polarizer is that the
effect often looks false - skies so heavily affected at the corners it
resembles vignetting; flat, muddy looking water with no highlights. For
many situations where I see polarizers used a graduated ND filter - or no
filter at all - may have been better.
Lex
===
From: "Terry and Tracey" <foxcroft@xxxxxxxxxxxxxxxx>
Subject: Re: [OM] What lens to carry (again)
Date: Sun, 6 Aug 2000 17:51:56 +1000
With minimal polarisation, light loss is 1 1/2 stops. With maximum
polarisation, light loss is two stops. As per manufacturers data and
experience with linear polarisers and OM-1n
Foxy
----- Original Message -----
> Shouldn't be any difference in light transmission regardless of how a
> polarizer is rotated. What can vary is the light meter reading when a
> linear polarizer is used on a camera that requires a circular polarizer
> (like the Can-not-an-OM-on FTbn).
>
> I *have* one polarizer that is darker than my others, thus reducing
light
> transmission more than the others - but it does so uniformly regardless
of
> rotation.
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