Goofy project idea

[Greg Erker <erker@xxxxxxxxxxxxxx>]

  I've been admiring a Pentax screwmount
fisheye lens that is on consignment at
a local store. It is a full frame fisheye
rather than a circular fisheye. This
is both good and bad. You don't get the
"see half the world" effect of a circular
fisheye. It is only 180 degrees of view
across the diagonal.

  The good is that it means the image
circle of the lens is at least 43mm
(the diagonal of 24x36mm). So I'm thinking
maybe it could be rigged up to produce
a 40-some mm circular fisheye image on
120 film.

  The rear element of the lens is pretty
small so you could potentially put
a leaf shutter behind the lens and still
project the full circle onto the film.

  My first thought is to destroy the
non-working diacord that I have. But
cutting far enough back to get the
lens close enough to the film would
ruin the bottom film spool holder.
After a bit of thinking I decided that
maybe a 6x6 folder type camera would
be best. The spools are off to the side
out of the way. And by removing the
bellows etc it should be possible
to get close enough to the film plane
to get infinity focus from the screwmount
len.

  The second aspect is the shutter.
The shutter that came with our Tominon/
Polaroid 127mm lenses looks like it might
do the job. So I unscrewed the lens
elements. The clear aperture of the shutter
is good, but the front thread is only 40mm
diameter or so. Pentax screwmount is 42mm.
Darn!

  I could machine down the fisheye's M42
threads but that's kind of drastic. I'd still
like to use it for 35mm photos too.
So I guess I need a bigger shutter, unless
the lens could mount in front of the Tominon
shutter, rather than thread into it, and still
be able to project the full circle.

  Some of you have seen my semi-fisheye stereos
taken with my Bronica with 75mm lens and a 0.42x
fisheye adapter. I liked the effect but wasn't
happy with the sharpness away from the center.
The Pentax lens is much sharper so I think it would
make some very interesting shift type stereo
shots.

  So, does anyone have any ideas about a
camera body that might work, and/or a shutter
to place behind the fisheye lens?

Thanks - Greg