Archived posting to the Leica Users Group, 1998/01/12

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Subject: Re: [Leica] Polarizing Filter w/M6 -Reply
From: Jim Brick <jim@brick.org>
Date: Mon, 12 Jan 1998 20:27:47 -0800

At 04:37 PM 1/12/98 -0800, you wrote:
>OK .............. let us empty the whole can of worms onto the table.
>
>I was told by someone ( I really forget who ) that a circular polarizer was
>designed to work with the new  ( 10 yrs.-? ) autofocus lenses and had
>nothing to do with the metering system. Further, that a linear polarizer
>would work just fine on the new lenses but that you might have a focusing
>problem and should probably use them in manual focus mode if using a linear
>polarizer.
>
>Cheers,
>David Medley

David,

For Leicas, it's the fact that a portion of the incoming light is directed
through a partially silvered mirror (the SLR mirror), for exposure
determination. The partially silvered mirror (beam splitter) acts as a
polarizer and will give incorrect exposure readings with a linear polarizer.

If someone told you that circ. polarizers were for autofocus lenses, I
guess it could be true. Perhaps one of the camera makers uses a polarized
beam splitter to extract focus information. I've never heard of this
though. Leica publishes the reason for circular polarizers.

Jim