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[OM] polarizers

Subject: [OM] polarizers
From: Joseph <joseph@xxxxxxxxxxx>
Date: Tue, 18 Jan 2000 14:13:32 -0800 (PST)
=========================
However, assuming you tried the experiment with a linear polarizer, I'd
be interested in the results of repeating the experiment with the filter
at different rotations.  The half-silvered part of the mirror is
=========================

not carefully.  exposure is supposed to change as you rotate the
filter when pointing it at a scene with polarized light.  when
the filter has little or no effect, it reduces exposure by 1 stop,
and at maximum polarization, it reduces it by 2 stops.  you should
see that variation when using a circular polarizer.

I guess I've just never noticed this effect before because I don't normally
spotmeter through a polarizer, and when I want to do an average 
metering I use OTF exposures anyway.  With my medium format cameras,
I use a  pentax digital spotmeter so I'm used to just applying filter
factors when using a polarizer.  I use my Olympus cameras for
macro work and when I want to carry a lighter load (hence I use Olympus--
an EOS system wouldn't be enough lighter than medium format).  In the latter 
case, I consider the savings in bulk of not having to carry a handheld 
spotmeter to be a benefit, but I usually miss having a precise 1 degree spot.  
The spotmeters in cameras measure too wide an angle to properly meter some
scenes.

Joseph


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