Archived posting to the Leica Users Group, 2001/06/06

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Subject: Re: [Leica] Re: Hexar Back focus
From: Marshall Hunt <huntmc2@fuse.net>
Date: Wed, 06 Jun 2001 18:58:31 -0400
References: <Pine.SOL.4.33.0106061619360.4174-100000@frogger.gpcc.itd.umich.edu>

My Ms (M3, M4-P) have 4 rails.  The pressure plate rests on
the outer rails, and the film travels over the inner rails. 
The film travels through a space defined by the outer rails
longitudinally, and the difference in height between the
inner and outer rails, vertically.  The emulsion side does
not touch anything in the picture area, and the shiny side
barely touches the pressure plate. (On my cameras you can
see the abrasion where the plate touches the outer rail, but
no abrasion in the center of the plate from the film).The
pressure plate does not depend upon the film for support.
Even my Zorki has 4 rails. Did Leica remove them for the M6?
I doubt it. Hunt.

Dante Stella wrote:
> 
> The pressure plate is not flexible.  It rests on the film, which rests on
> the inner guide rails.  When there is no film, it rests on the outer guide
> rails (which are slightly raised).  This is pretty conventional with
> modern motorized SLRs, at least as far as I can tell.  Too much force
> against the film would be hard on the motors, I think.
> 
> My M3 has no outer rails, and the plate rests on the film plane rails with
> no film in it.
> 
> On Wed, 6 Jun 2001, Mark Rabiner wrote:
> 
> > John Collier wrote:
> > >
> > > I can only speculate but perhaps the flange to film distances are the same.
> > > The difference may be in the measuring technique. If Hexar measures from the
> > > bayonet flange to the pressure plate, this would give a greater distance
> > > than Leica's  nominal 27.8mm which is to the front surface of the film.
> > >
> > > John Collier
> > >
> > ><Snip>
> >
> > Is the pressure plate flexible? Under pressure?
> >
> >
> > Mark Rabiner
> >
> > Portland, Oregon
> > USA
> >
> > http://www.rabiner.cncoffice.com/
> >

Replies: Reply from Dennis Painter <dennis@hale-pohaku.com> (Re: [Leica] Re: Hexar Back focus)
In reply to: Message from Dante Stella <dante@umich.edu> (Re: [Leica] Re: Hexar Back focus)