Re: [APML] Sort of OT: New Meade Ritchey-Chretien

[Chuck Vaughn <aa6g@aa6g.org>]

Paul,

I have a custom designed field flattener/astigmatism corrector/off axis 
guider for my 12.5" RC. I'd have to have my friend dig up the spot 
diagrams for color correction (if he can) but overall, the field is 
much better with the corrector than without it as seen on 35mm 
negatives. I've never tried TP tricolor with such a slow system but 
since my filter set is not parfocal I wouldn't notice any difference 
caused by the corrector anyway. ;-)

Chuck

-----------------------

> Dear Colleagues,
>
>      Ritchie-Cretien designs are designed to be free of coma and 
> astigmatism at the sacrifice of a flat field.  R-C's become astigmatic 
> if the primary is misaligned.  Because of the curved focal plane, film 
> (or the thin glass plates I used to use on the Yerkes 41" reflector) 
> has to be curved to conform to the shape of the focal plane.  Since 
> curving glass plates under a vacuum was always fraught with breakage, 
> Boller and Chivens introduced field-flattening lenses in their 
> meter-class R-C's in the 1960's.  I used such a system at the now 
> dynamited Lindheimer Astronomical Research Center at Northwestern 
> University in the late 1960's.  The compromise here was that the field 
> flattener could not be perfectly achromatic, requiring separate 
> focusing for each filter.
>
> Paul

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