Re: [ATM] 8" Diagonal- More info

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> It appears Scott will be at 0.7 arc seconds/pixel with his 28" f3.7 and
> STL-11000 combination.  Correct me if I'm wrong Scott.

> > > Holding 1/10 wave or better is the priority and I know that the
> > > edges are going to fade from this value.

> >Pardon me for being blunt, but why the emphasis on surface accuracy for
> >an instrument to be used at prime focus with a ccd camera?  Your
> >resolution is going to be nowhere near diffraction limited, instead, it
> >will be pixel size limited.  I'll bet, a calculation would show you can
> >tolerate wavefront errors that would horrify a planetary or double star
> >observer and still produce ccd images not even measureably below
> >"perfect" quality.


If you feel that you need sub-wave accuracy, then by all means, don't let
anyone talk you out of it.  However, I just went through a similar design
exercise, and given your 0.7"/pix requirement, and given typical broad
errors as found in real life optics, you can use a secondary that's only
accurate to several waves.  In other words, a good shaving mirror will work
fine, provided that it is front surface silvered.

Mel Bartels


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