Re: Pressure Plate Info

[John Bercovitz <bercov@xxxxxxxxxxx>]

> I thought that the 'pressure plate' kept the film flat against
> the rails for proper focus.  Not true?  If I found or built a
> camera without one, I would still be OK?

In most of my cameras it is just the back plate of a rectangular
tube through which the film slides.  There are rails which the
pressure plate hits and rails which the film hits:


------------------------------------ press plt rail
------------------------------------ film rail




------------------------------------ film rail
------------------------------------ press plt rail

I do have one camera wherein the pressure plate fits between
the pressure plate rails and so pushes the film against the
film rails.  Can't remember which one.  I think on the later
cameras the pressure plate is just a "safety valve" that
opens up to make the tube large in case there is a kink in
the film or something.  The tube is a few thousandths of an
inche bigger than the thickest film.  Seem to me it would be 
more accurate if the pressure plate always pushed against the
film but I suppose the film might get scuffed or something
sometimes.

John