[MF3D.FORUM:1156] Re: Camera design

[Richard Rylander <rlrylander@xxxxxxx>]

Greg Erker wrote:

> ... 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).
>
> ...
>
>   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.
>

Tilting the film plane rather than the lens plane might be more
mechanically complex, but it allows you to satisfy the Scheimpflug
condition without requiring the lens to have an extended image circle
(but the top and bottom of the image have slightly different
magnifications - which shouldn't matter much in most real-world image
situations).  The Rolleidoscope (Heidoscope) keeps the horizontal L/R
lens separation small by a vertical offset of the viewing lens/reflex
mirror (like the Spud), but properly previewing the effect of tilting
the lens plane will require the viewing lens to share the same tilt axis
as the taking lenses - creating a fairly long stereo base as you say.

On the other hand, if you could somehow manage to couple film plane tilt
to ground glass tilt (or reflex mirror tilt [by half as much] ), you
could get a  proper preview in a horizontally compact camera (i.e., one
with an offset viewing lens) all without the need for lenses with
extended image circles.  But the more I think about it, getting the
depth of field you want by using f/32 apertures is sounding better and
better.

Richard Rylander