In your message dated: Tue, 31 Mar 1998 20:47:42 EST you write:
>There seems to be somewhat of difference of opinion on which to use with which
>camera.
>Here is a quote form John Shaws "Landscape Photography" book on page 46.
>"To determine whether your camera's metering system works with a linear
>polarizer, mount one on a lens and take a meter reading off a dull, evenly lit
>area that is all one tonality. If the meter reading changes when you rotate
>the filter in its mount, then that particular camera requires a circular
>polarizer to meter TTL correctly."
This is correct only for spot metering... see below.
>To test John's recommendation, I took my OM4T w/ 100mm f2.8 and an old OM
>linear polarizer outside and metered against my house. In BOTH Average and
>Spot the meter changed when rotated about +1&2/3 stops from 1/125 sec to
>almost 1/500 sec.
Yes, but the meter readings you see in "average" mode in the OM-4 are
only appoximate. When you actually take a photo, the metering is OTF,
so it doesn't matter what you have on the front of the lens (as long as
it transmits light :), the exposure will be correct. The problem is
that when you spot meter, the reading is taken through the partially
silvered mirror, and locked in. And the partially silvered mirror is
what causes the problem with linear polarizers. The mirror is not in
the optical train with OTF metering, and thus doesn't affect exposures.
>I then replaced the Linear polarizer with my Circular polarizer and I did not
>get any change in readings in Avgerage or Spot.
As it should be. So the lesson here is that if you plan to do any spot
metering at *all*, you need a circular polarizer. My advice is to throw
away all your linear polarizers, so you don't make the mistake of using
one by accident.
>I agree with John Shaw quote on page 47 "It makes more sense just to buy a
>circular one that can be used on ALL cameras, including the models that accept
>linear polarizers."
Exactly.
Cheers,
--Lee
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