Archived posting to the Leica Users Group, 2001/06/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]My M3 (927xxx) has four rails, but only three appear to do something. The top rail is very high. The top of the plate hits this rail as you shut the back (it slides toward the top of the camera). That rail is not visible when the back is open. You have to look up and in to see it. As far as I can tell, it has no function. The second and third rails are what the film rests on. The pressure plate appears to push the film hard against both of these when you have the shutter open and the bottom screwed on. The fourth rail (at the bottom) seems to be a guide. It is higher than the third rail. Dante On Wed, 6 Jun 2001, Marshall Hunt wrote: > 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/ > > > >