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[OM] mirror/shutter camera design

Subject: [OM] mirror/shutter camera design
From: William Sommerwerck <williams@xxxxxxxxxx>
Date: Mon, 07 Jan 2002 11:54:26 -0800
"Ground-glass back, see the lens straight through, and the film FLIPS DOWN, in
place of the mirror, there is no mirror, and there is no need for curtains
either, the mirror [sic] duration would be it..."

Which is it? Does the mirror flip or the film flip? (I assume it's the film.)

Viewing a direct ground-glass image has problems, including image reversal and
inversion. (If view cameras didn't offer superb image quality and total image
control, their inverted viewing would put off most photographers.) There's a
good reason reflex cameras have mirrors!

Having the film flip is, indeed, crazy. In order not to rip the film (!!!),
you'd also have to flip the spools. Given their mass, the maximum achievable
shutter speed would be low.

In this design the ground-glass focal plane and the film focal plane are offset
by the thickness of the film. Even if this were compensated for, moving the
_film_ would produce a total blur. Not to mention that, throughout most of the
exposure, only the film nearest the "hinge" would ever be even _remotely_
in-focus!

Because the film flips through the same arc a mirror would, the lens cannot sit
significantly closer to the film. Sitting closer does not guarantee a smaller
lens, either, except _possibly_ for extreme wide angles. (Note that all those
tiny Zuikos were designed for a "conventional" SLR -- 25 years ago!)

How do you propose to keep the film flat during exposure? (I suppose pulling it
against the ground glass would work.)

There _have_ been reflex cameras in which mirror movement controls exposure
time, eliminating the focal-plane shutter. (A "cap" on the back of the mirror
prevents fogging.) I'm certain a few 35mm SLRs used these "mirror shutters,"
but I forget brands and models. The best-known camera of this type was the
Pentax 110, an incredibly tiny interchangeable-lens SLR for 110 film.

The conventional SLR has largely replaced other types of professional hand-held
cameras because its greater bulk and weight are more than compensated for by
the advantages of viewing through easily interchanged lenses. If compactness
and light weight are more important, you can still buy a Leica 35mm or Fuji
rollfilm camera.


"Am I smoking crack, or has something like this been thought of/done before?"

You're not doped-up, you just haven't thought through the huge number of
problems and zero advantages of your design. There has only been one truly
"clever" non-conventional SLR, the Polaroid SX-70. Believe it or not, its basic
design was invented by Nelson K. Cherrill -- in 1907! (See Brian Coe's
"Cameras," page 138.) That's two years before Dr. Land took his first breath of
Russian air.


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