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From: howard@sfmag.UUCP (H.M.Moskovitz)
Newsgroups: net.rec.photo
Subject: Re: \"Match-needle\"
Message-ID: <577@sfmag.UUCP>
Date: Wed, 22-May-85 13:09:54 EDT
Article-I.D.: sfmag.577
Posted: Wed May 22 13:09:54 1985
Date-Received: Fri, 24-May-85 02:11:12 EDT
References: <2029@decwrl.UUCP> <10473@brl-tgr.ARPA>
Organization: AT&T Information Systems, Summit, NJ
Lines: 36

> > The term "match-needle" was applied to cameras where you matched a needle
> > against a single index mark long before there WERE cameras that displayed,
> > for example, a shutter speed scale in the viewfinder with a green bar
> > indicating the "recommended" exposure.  I suppose this newfangled innovation
> > could legitemately be called match-needle, but it ain't what the term
> > originally meant.
> > 
> I always thought it was originally applied to the center the needle on
> the bullseye paddle that some camera used because the correct exposure
> position on the meter varied.  I don't know what moved the bullseye. I
> never had one of these.  My old PENTAX took the film speed into account
> and you always cenetered the needle rather than trying to match it.
> 

The way a match-needle metering system works is as follows:
	The camera meter measures the incoming light with a wide-open
	lens. By adjusting the aperture (f-stop) the camera gets a
	reading of the amount of light reaching the film-plane and
	sets the needle accordingly. The film speed (asa) sets a 
	relative position for the target (bulls-eye, ring, etc...),
	and by changing the shutter speed the target is moved. When
	the target is lined up with the needle, the camera now will
	have an exposure time that is adequate to get a pre-calibrated
	amount of light on the film that is required for the proper
	exposure of the film speed that the camera is set for.

	If the aperture is changed, the camera will get more or less
	light in thru the lens and will require a shorter or longer
	exposure, accordingly, to properly expose the image.

					Howard Moskovitz
					AT&T Info. Systems
					attunix!howard
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