Archived posting to the Leica Users Group, 1999/01/27

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Subject: Re: [Leica] Polarizing Filter
From: Doug Herr <71247.3542@compuserve.com>
Date: Wed, 27 Jan 1999 22:33:49 -0500

On Wed, 27 Jan 1999, Bill Christensen write:

>Leica R camera also require a circular polarizing filter.  For some
reason,
>linear filters may produce an inaccurate meter reading.

It's because of the partially-silvered mirror that lets some of the light
reach the meter cell.  A linear polarizer in the light path will block
light waves which are not aligned with the polarizer.  The semi-silvered
mirror also acts as a polarizer to a certain degree and if the polarizing
filter and the mirror's polarizing effect are not perfectly aligned the
meter cell will "see" less light than the film will.  In the extreme case
where the polarizer and mirror are mis-aligned by 90 degrees the meter will
get no light at all.

You'll get the same effect with the polarizing filter and polarized
sunglasses (or, I suspect, with polarized sunglasses and any Leica SLR
viewfinder aside from the Leicaflex Standard).

Doug Herr
Sacramento