[MF3D.FORUM:1155] Re: Camera design

[Alan Lewis <3-d@xxxxxxxx>]

Greg Erker wrote:

>   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. 
> 
>   I've long thought that Mamiya TLR lenses would
> be ideal for making a MF stereo camera. 

Since I've just finished the first version of a Mamiya TLR lens MF
camera I can give some basic info.

The largest OD of the finder lens is 1.88".  The body dia. is 1.65", but
the 1.88 dia. is really the determining dia. for spacing the lenses.

The finder lens sticks out 1.25" from the lens plate.

Quick calculations say that the min. stereo base with the finder lens
right inbetween the taking lenses is 4.4".

The angle of view of the normal 80mm Mamiya TLR lens is 50deg.40min.

> 
>   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.

I'm not following exactly here.  But the easiest way is to just buy two
complete lenses and throw away (!) the extra finder lens.
The Mamiya TLR is a professional camera, and the finder lens/taking lens
lenses are well matched for professional use.  I have never heard anyone
complain about these camera systems having focus problems.  I think they
have stood the test of time very well.

The finder and the taking lenses are both 80mm f.l. and f/2.8.

>From the two lenses that I bought for my camera I found that one had
shims under one of the taking lenses, the other did not.  After checking
each for infinity focus once mounted on the stereo camera I could see
why.  They used shims at the factory to make each lens focus at infinity
at the same point regardless of which body it is put on. They must have
controlled the camera body dimensions very tightly.

I put the shims back in and infinity focus was good for both lenses.

> 

>   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.

Are we at the point of technology in shutter design yet to use the LCD
screens that can change density with differing voltage?  It sure would
be nice if this technology could be applied to shutters.

Your description above of the shutter sounds similar to the electronic
shutter used in the Polaroid Color Pack cameras.  Lots of electronics
packed in those Polaroid shutter boxes.

-- 
Alan Lewis  
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