[Leica] Film flatness

[Mike Johnston <michaeljohnston@ameritech.net>]

There is a 35mm camera (the Contax RTS III) with a vacuum back designed
specifically to keep the film flat. There either is, or will be, a
medium-format camera that has a vacuum back to keep the film flat (one
is promised for the Contax 645, which is selling like hotcakes BTW,
and--much to Contax's surprise--doing better in the USA than in home
market [which for Contax is Japan]). I don't know whether this is
actually available yet and I'm too lazy to go check.

Film flatness is indeed a valid technical concern for specialist
photographers. It's just not of much practical concern to photographers
for pictorial photography--except sometimes when a frame with a "memory"
of a "set" curl creates obvious unsharpness in a negative--and sometimes
in large format. Which is why you don't see much effort to correct the
"problem" in the products on offer (Contax excepted, and I have a
feeling this has something to do with the fact that Kornelius Fleischer,
head of 35mm optics at Zeiss, is an aficionado of high-resolution
photography! He uses surveying tripods and has access to the legendary
Zeiss S-Planar process lenses for enlarging, lucky dog!)

The Contax vacuum backs were based on the technology used for 10x10
aerial reconnaissance and satellite photography.

You think medium format is bad, try large format. It's been demonstrated
that the film not only does not lie flat, it can _move_ during
exposures. This can occur because of "sagging" or because of the film
suddenly being exposed to ambient humidity when the darkslide is pulled.
At any rate, measured with a micrometer, 4x5 film lies very far from
flat in a holder. In fact it resembles a rumply blanket.

At least one of our contributors uses a special vacuum 4x5 back, and
another has devised a system whereby he uses five little patches of
double-stick tape on the inside of his 4x5 holder--he carefully loads
the film and then presses it lightly with his fingertips to make the
tape "engage" with the base side of the film. He then uses these holders
for very long exposures, so his film won't move or sag during the
exposure.

- --Mike