[MF3D.FORUM:1154] Camera design

[Greg Erker <erker@xxxxxxxxxxxxxx>]

  Now that my SR225 (twin TLR) is 99.5% working
my engineering mind is planning my next better
MF stereo camera. I ran some of these ideas past
Sam on our day trip to the mountains but maybe
someone here would like to comment also.

  My goal with the SR225 was to get more shutter
speeds, better viewfinder, better lenses and f32
(compared to my Sputnik). I managed to get everything
I wanted plus a few bonuses like crank wind/ auto
shutter cocking etc.  I do have to set the apertures
separately but I suspect they could be linked if
I tried hard enough.

  My next camera should fix two problems I currently
face: It's hard to get everything in focus in MF
(due to 80mm lenses) without shooting at f32 all the
time. Secondly my SR225's mechanincal shutter speeds
are consistent but not super accurate. So I have
a cheat sheet on the back of the camera and have
to stop down or open up various amounts (1/3 or 2/3's
usually) for various speeds compared to the meter
reading.

  To solve problem 1 I'd like to make a camera with
the finder lens in between the taking lenses like
on a Rolleidoscope. I'd build the camera to have the
ability to do lensboard tilt which would let me
control where the plane of focus is. Often just the
ground in the foreground is the near object so
a degree or three of lens board tilt should allow
you to bring it into focus along with infinity.

  I've long thought that Mamiya TLR lenses would
be ideal for making a MF stereo camera. They are
readily available, high quality and come in a
range of FLs. So a bellows focusing camera could
have interchangable lensplates to go from 55mm to
75mm up to 180mm (I think).

  I have heard that Mamiya used the same elements
for the finder lens and for the taking lens. So
perhaps getting a matched pair for left and right
would be as simple as using the top and bottom lenses
(on two different shutters). Getting a matched finder
lens would still require some work.

  Another idea I have is to use a dead shutter for
the finder lens (shutter blades removed) and then
have the ability to preview depth of field using
the aperture control.

  To solve the shutter speed linking and speed
accuracy problem I wondering about using modern
35mm electromechanical vertical travel focal plane
shutters. I believe the two curtains are tripped
with separate solenoids. So an electronics guy like
me could easily come up with a timing circuit
(with 1/2 stop speed steps from 30s to 1/2000s) to
trip the two in perfect sync and near-perfect
accuracy.

  The focal plane shutters would be used behind
the lenses (assuming their diameter isn't too
large).  There are some concerns about light leaking
thru the FP shutter between shots (the new Cosina/
Voigtlander rangefinder camera has an extra shutter
curtain to prevent this). But I have some ideas
about that.

  Assuming I used FP shutters then the Mamiya lenses
could all come from dead shuttered ones as long as
the aperture controls work.

  There is also the question of whether the Mamiya
lenses have a large enough image circle to allow
a useful amount of lensboard tilt.

  Also fitting three lenses in a row might require
a fairly large stereo base. With horizontal film
travel that might mean 5 stereo pairs per 120 roll
rather than the Sputnik's 6. Or I could go with
two vertical travel rolls like my SR225.

  Comments and ideas appreciated.

Greg E.