Re: [ATM] Is There a Difference

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

James Lerch wrote:

> ----- Original Message -----
> From: "Richard Schwartz" <richas@earthlink.net>
>
>
>> In optics we have the Ray-Lee criterion:   if the optical path 
>> difference is
>> less that 1/4 wave, the optical system is indistinguishable from 
>> perfect.
>
>
> Isn't this only true for On-Axis image?
>
> My most recent post showed a 1/4 P-V wavefront 6" F/8 (@550nm) was 
> only diffraction limited for a measly 1/20 degree field of view.  
> Where as a 1/10 P-V wavefront 6" F/8 (@550nm) was diffraction limited 
> to nearly 1/2 degree field of view.
>
> Did I make an error somewhere?

Not directly. You did, however, appear to restrict the discussion
only to the performance of a paraboloid/conic.  While the principle
may be similar in most cases, I have seen refractive cases where the
introduction of a field of view requirement optimized to a different
solution than a system with an infinitesimal or small field -- in
the larger field cases, the performance in the field center was
compromised.

>
> Take Care,
> James Lerch
> http://lerch.no-ip.com/atm (My telescope construction,testing, and 
> coating site)
> http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

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