Re: ATM More Spheroidalage

[Anthony Stillman <atmer@flash.net>]

>I have been considering the case of the
>1/10th wave parabolic primary combined with a spherical
>versus hyperbolic secondary in a classical Cassegrain design.

Dominic,

A year or two ago there was an article in S&T which presented an ultra-high
magnification cass.  It used an f/typical paraboloid and a ball bearing
sized secondary.  As I recall there was some controversy over a patent
application.

This over-corrected Dall-Kirkham design works as a slow system but suffers
tremendously, as you would expect, from off-axis stig and field curvature.
As a result, tiny tiny tiny fields are useful.  Like, 3 arc minutes and
less with magnification ratio's in the 100s and barely more that this with
magnification in the 10s.  Still in a Nasmithe configuration, a ball
bearing convertible might be interesting.

As for more conventional magnification ratios, I afraid you're stuck with
either a true cass or a true Dall-Kirkham.


Anthony