Re: ATM Is my blank thick enough!!

[Mark Holm <mdholm@telerama.com>]

Hi Ivan,

Plop doesn't calculate diagonal sizes.  It does the mirror cell support point 
geometry calculation.  Plop uses the diagonal size to ignore that portion of the 
mirror that will be in shadow from the diagonal and not contributing to the image.

A diagonal of about 38mm minor axis (1.52 inch) is about right for an 8-inch f/6 
or f/7.  The program Newt and the program SEC (from Sky & Telescope web site) 
can help determine correct diagonal size.  The 1.52 inch minor axis size is 
common in the U.S. (Don't know why it is such an odd fraction.)  A couple of 
millimeters one way or the other won't matter too much.  Texerau and other ATM 
books discuss how to choose diagonal size.

The Plop analysis numbers I gave you in the previous message will work for the 
f/6 to f/7 range with no adjustment.  If you end up outside this range, let me know.

Mark Holm
mdholm@telerama.com