ATM Calculating Secondary Offset

["Anderson, Jay" <andeja@mail.va.gov>]

Okay.  I think I understand this... the diagonal is offset away from the
focuser and down toward the primary somewhat (say no more than 1/8" inch
for a 12.5" f/4.5 scope).  The benefits are: You can use a slightly
smaller diagonal mirror and so a very small benefit in image contrast
and brightness.  Does anyone know if there is a standard formula for
calculating proper offset for various primary sizes and focal lengths.
I understand that offset is more necessary in faster and larger aperture
scopes.  Thanks.

Jay D. Anderson, KF4LLZ