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From: amr@rti-sel.UUCP (Alan Roberts)
Newsgroups: net.rec.photo
Subject: Re: filters
Message-ID: <585@rti-sel.UUCP>
Date: Wed, 18-Dec-85 09:29:30 EST
Article-I.D.: rti-sel.585
Posted: Wed Dec 18 09:29:30 1985
Date-Received: Fri, 20-Dec-85 03:31:02 EST
References: <307@tellab3.UUCP> <814@sfmag.UUCP>
Reply-To: amr@rti-sel.UUCP (Alan Roberts)
Organization: Research Triangle Institute, NC
Lines: 30
Summary: 

In article <814@sfmag.UUCP> howard@sfmag.UUCP (H.M.Moskovitz) writes:
>  . . . 
>Since the TTL metering system measures light intensity as it hits
>the film plane, adding filters is compensated accordingly. Metering
>systems do not know anything about color so this has no effect.
>  . . .

True enough (at least in my experience, which doesn't include any
critical scientific photography or the like), but one type of filter
which CAN trip up the TTL metering of SOME cameras is a polarizer.
It doesn't happen to all cameras (I think it is related to use of a
half-silvered mirror to direct light to the metering sensors).  I
also think a summer issue of some mag. (Peterson's ?) had a fair
list of which 35mm bodies were sensitive to the problem and which
were immune.  You can also purchase a "circular" polarizing filter
which doesn't cause the problem (they are more expensive). 

					Cheers,

					Alan Roberts
					Research Triangle Institute
					(decvax!mcnc!rti-sel!amr)
-- 


					Cheers,

					Alan Roberts
					Research Triangle Institute
					(decvax!mcnc!rti-sel!amr)