Re: ATM tube length

[Ari <Ari@birmingham-us.crosswinds.net>]

Tim wrote:
> Ok for and 8" f/6 mirror is better for planetary views and splitting
> double stars...
> and 8" f/8 is better for deep space viewing... Right.

WRONG (as I understand it)
For planetary, you want longer focal lengths because that has higher
magnifications for a given E.P. f.l.
For Deep Space, you want a low focal ratio (and thus f.l.) because these
yield wider-field views.

2. Do people make f/7 mirrors. I want to do all around viewing, or is
f/6 just fine?

f/7 mirror is fine, just it's not commercially available. This should be
no problem if you are making the mirror. John Dobson recommends (if I
remember correctly) f/6 or f/7 for all around viewing. f/8 is also
considered a good general choice.

Ari Friedman
        There's light at the end of the Sonotube.