hi all,

I have a classical cassegrain mirror set that I've been meaning to set
up. I only have approximate numbers for the spacing and no indication of
mirror orientation (rotation). I was thinking of using a Ronchi grating
and a web cam and look at a bright star to get fringes. Then do some
tweaking. I suppose a Hartmann mask would also work. Is there any
(inexpensive) software out there to do this kind of calculation ? I've
found the SBIG software and Cyanogen has Quickfringe.