[rollei_list] Re: Film tight on rails? - formerly: Planar 2.8 coverage
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Thu, 4 Oct 2007 12:12:52 -0700
----- Original Message -----
From: "ERoustom" <eroustom@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, October 04, 2007 5:27 AM
Subject: [rollei_list] Re: Film tight on rails? - formerly:
Planar 2.8 coverage
Thanks for pursuing this further Richard, and thanks for
that amazingly thorough explanation Dennis.
I have to tell you that not only was I using Rodinal for
the first time for this roll of film, but it was
processed in a tank a little shorter than what I usually
use, and filled to brim (I had to mix 520 ml for the 1+25
and the tank takes about 450). Unwittingly, I stacked
some odds against myself. This was very helpful. Mostly
I'm relieved that it's not my Rolleiflex lens that's to
blame.
However, Richard, I'm not so sure I'm ready to leave it at
that. I'm suspicious of the reflection off the roller
theory, without it also being loose film. Any idea how to
test it? Is it possible that as the film is spooled off
the bottom roller it looses tension?
Elias
The spring which bears on the supply reel can become a
bit loose, just bend it up a bit. However, I don't think
this is the problem. Slight buckling of the film might
affect uniform focus but not illumination. The darker edges
of the film would not be produced by the lens since lenses
tend to have reduced illumination away from the optical
center and that fall off is uniform in all directions.
I also think the tension from the spring is mostly to
keep the supply spool reasonably tight rather than for film
guidance. I've studied the film gate in the Rollei and
concluded the the film is located in the focal plane by the
back plate and that the film and paper combination is
supposed to relax against it. This would hold the
combination in a fixed position and reasonably flat. Too
much tension on the film would tend to make it buckle inward
along the longitudinal axis because it is guided at the
edges by the film rails but not at the top and bottom of the
frame. The rollers are inset a bit from the plane of the
guide rails and I think excessive tension would tend to pull
the film inward against them.
I am not sure I am right about the film guidance but a
lot of other opinion is also just guess work. One could tell
for certain by taking the lens out of a camera and using an
interference laser set up to measure the actual topography
of the film. I think it would be very interesting to measure
a number of cameras this way to find out how flat and how
close to the focal plane they hold the film.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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