Re: ATM 6" f/4 or not?

["Gary Seronik" <gseronik@direct.ca>]

Tom:

You could make a lovely RFT with such a mirror.  With a 24mm eyepiece you'd
get a 6mm exit pupil and great wide fields of view.  If this was your
principle use for the mirror, you can afford a bit of uncertainty in the
final figure - low power use is mighty forgiving of figuring errors.  Also,
if you use a low profile focuser, that secondary doesn't need to be any
bigger than 1.5" m.a.  Remember, the light fall off in an f/4 is VERY
gradual.

Good luck1
Gary in Vancouver

----------
> From: Tom.Stock@gsbsc.gensig.com
> To: atm@shore.net
> Subject: ATM 6" f/4 or not?
> Date: Tuesday, September 17, 1996 6:02 AM
> 
>      
>         I recently purchased a partially completed 6" mirror from a 
>      friend.. apparently this being his first mirror, he thought he was 
>      making an f/8 but actually made it f/4...it is almost completely 
>      polished, but f/4 seems a little impractical for a 6" scope...
>      
>         Does anyone have any advice as to what I should do with this 
>      mirror?
>      
>         The secondary would have to be a little over 2" for good 100"
zone 
>      illumination, which then causes vignetting of the 75% zone at the 
>      eyepiece...
>      
>         This seems like a big obstruction for a 6"...I was thinking it 
>      could make a good photographic scope however, except for the 
>      vignetting at the eyepiece....
>      
>         I just hate regrinding this to f/6 or f/8 after seeing all of his

>      polishing efforts go into it...
>      
>      Oh, and there are a couple of scratches as well...
>      
>      
>      -tom