re:ATM 10" F/4

[Howard.Banich@nike.com]

A well made f/4 will give you (or your parents) tremendous views. I suspect 
the problems mentioned were coma along the edge of wide field views, and that 
can be taken care of with a coma corrector lens (i.e. Tele Vue's Paracorr). 

The size of the diagonal is also often mentioned as a problem with f/4's - 
they lessen contrast at high power on the planets compared to less obstructed 
systems. However, in my experience the detail is there to be seen, it just 
isn't quite as obvious.

Several people I know with f/4 systems (or f/5) don't mind the coma and don't 
have a coma corrector lens. I use one with an 8" f/4  - and an 20" f/5 - 
because I like sharp stars to the edge of the field at low power. However, at 
medium to high powers a corrector lens isn't needed. And yes, a good f/4 will 
give truly excellent high power views.

IMHO, the only problem with f/4's is that there aren't more of them - a short 
optical assembly goes a long way toward ensuring a very manageable scope 
that's easy to take out and actually use. Good luck with yours, I'll bet your 
parents will love it.

----------------------[Reply - Original Message]----------------------

Sent by:Mike Pence <mpence@avalon.net>
 Recently I've seen some people talking about problems with the faster
10" telescopes.  I am having a 10" F/4 polished right now and wasn't
aware of needing a corrector lens or anything of that sort.  What
problems will arise from the short focal length that I will need to
correct and what problems are there going to be that won't be a big
deal?  And, since I am hoping on giving this 10" scope I am building to
my parents and then building a 12.5" for myself to keep, is it going to
make things ever worse if I go with an f/4 or f/5 on the 12.5"?

Thanks.

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