As both George and Catherine have said, the camera is just a box, and
there is plenty of resource regarding the hole size which is indeed
critical. BTW, in addition to the PJ volume 8 # 1, which contains lots
of useful information, I have an article in volume 3 #2 on making
pinholes, in which I reveal all of my magic.
The problem you have, Brian, is not so much the camera but the holders.
Sure, 11 x 14 holders are available, but they are very hard to find - at
any price. I really wish I had even one. 8x10 holders are easy to find,
and Catherine's idea for a hinged (vs. spring) back is a good one. But
with no holders, of what use is it? It is a problem you share with
everyone who uses an unusual format. A good friend of mine is building
custom film holders for old large format panoramic cameras. In your
favor, you can get by with a good deal less precision, so maybe you can
devise something. If you do, I'd sure like to hear about it, and I'm
sure that Eric and Nancy would be eager to publish any kind of practical
solution to the film transport problem.
Some workers have solved this problem by buying a big old station wagon
and filling it to the gills with cameras, each loaded with a single piece
of film. So cheap and easy cameras are one way out.
Larry Bullis