Re:Re: ATM Aplanatic 4-mirror telescope system /2

[kwhitefire@juno.com]

One problem with 3 mirror designs like this (the flat doesn't count) is the 
3rd mirror is looking at the sky and unless you baffle for it you'll end up 
with two sets of images at the focal plane. Realistic designs have 50% or 
larger effective central obstructions once you baffle them properly.

I'm wondering if the 50% rule is carved in stone or not.  I have a half a degree with my numbers as they sit, which is plenty for almost any deep sky viewing.  If I were to use my primary alone with a diagonal flat (f/3.125) I would need a large diagonal to get all the light I can to the eyepiece.  Why not go to the small obstruction, use the primary itself to baffle the tertiary with the help of a little cardboard, and compromise the huge FOV with a bigger useful aperture?  I figure the opening in the primary will be about equal to the diagonal.  I have an old 8" paraboloid from Orion that I can refigure for the tertiary, and quarter inch window glass will work for the secondary.

If it doesn't work in reality, I can still make a decent Cass from the primary, even with the huge hole.  Or a Newt.

Mechanical structure may be a challenge.  Collimation will be a nightmare.  But, as far as nightmares go, I write them when I'm not a telescope maker.

Kevin of Eastern Iowa
Seeker of the Darkness




________________________________________________________________
Sign Up for Juno Platinum Internet Access Today
Only $9.95 per month!
Visit www.juno.com