Re: [ATM] Joe Martin's Mirrors

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

I obviously stand corrected on the matter of the 6" f/8. Tony's numbers are essentially correct. I confess that I was doing that from memory. Perhaps I was confounding the 6" f/10 and the 6" f/8.

tony gondola <acgna@comcast.net> wrote: >
> BTW, if you make a 6 inch f/8 mirror perfectly spherical, the results, 
> according to FigureXP, are more than acceptable; they are great!
>
> Guy Brandenburg

It's always interesting to look at that. When I run the numbers I get a 
wavefront of 1/3.6, a transverse error of 4.2 and  strehl of 0.76.It won't be much of an panetary/lunar scope but yeah, for a beginner and low power deep sky it will seem ok, might even give an older commercial SCT a 
run for it's money. I'll bet that a smooth sphere with a good edge would be better then some of the totally wacked "corrected" shapes that some commercial mirrors have.
Just for fun, consider a 6" F/14 spherical mirror. The P/V wavefront 
appraoches 1/20 and the diffraction limited FOV will cover the full lunar 
disk. With a tube length of somewhere around 6.5' this would not be an 
unreasonable instrument to build or use. I suspect it's performance would surprise a lot of people.
Tony



Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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