[ATM] what causes coma?

[alaskawolfjoe at hotmail.com (lance clarke)]

Thanks to everyone for the great input on the subject.  Turns out to have 
been more complicated than I expected, but I have a better idea at least.  I 
guess my next project is to get to a good library and try to get a handle on 
how the other abberations fit in.

Aside from that, I'm particularly interested in the references made to an 
aplanatic gregorian.  One of my original reasons for asking the question was 
that I'm considering my next project, and a gregorian is a definite 
possibility (and I wondered if coma would be horrible on an f3 or faster 
primary)  One thing though...if a classical greg has a parabolic primary and 
an eliptical secondary, how can an aplanatic have both primary and secondary 
that is eliptical?  Different parts of the ellipse?

Thanks again for all the imput!
Lance
Toronto

_________________________________________________________________
STOP MORE SPAM with the new MSN 8 and get 2 months FREE*   
http://join.msn.com/?page=dept/bcomm&pgmarket=en-ca&RU=http%3a%2f%2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarket%3den-ca