Size and usefulness of 'viewing' pinhole

I am interested in putting a pinhole on a large format (5x7) camera in
order to utilize rise/fall to change perspective. I would like to be
able to see the results of the pinhole shift on the ground glass of a
conventional LF camera, but of course the actual 'taking' pinhole does
not allow enough light through to see anything. I have heard tell of a
'viewing' pinhole, presumably for exactly my purpose. I presume it is
oversized enough to provide a visible image.

Has anyone used a viewing pinhole? If so, do they actually work? Is
there a formula or starting point for finding the correct viewing hole
size, say for 125mm taking hole? Would I be way better off using a
comparable lens for composition?

I am assuming that be the viewer a pinhole or a lens, the coverage of
the taking pinhole would have to be determined by trial and error.

TIA,
CXC
Received on Sun Mar 3 14:05:44 2002