From: "Richard F.L.R. Snashall" 
CC:  atm{at}shore.net
Reply-To: "Richard F.L.R. Snashall" 




John Sherman wrote:
>
>
> Okay. I will accept your much greater knowledge of the stuff. You have
> probably forgotten three times as much as I have ever learned. So is there a
> way to design a scope using refractive elements, and getting a perfect,
> color-free image? Or are reflective elements the only way to achieve
> perfection?
>
> Thanks,
>
> John

First, define "color-free".  If what you mean is diffraction
limited, then, for example:

        http://users.rcn.com/rflrs/zflat1-67x.len

is "color-free" in that it is lambda/4 from 345 to 2050 nm, but
you'd have to design your own AR coatings to match the reflective levels of
your mirror through your band of interest.

--
Rick S.
http://users.rcn.com/rflrs

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