ATM: Coma corrector for large fields

[Bratislav Curcic <epabcc@epa.ericsson.se>]

Mauritz Andersson wrote 

> coma corrector for ... 6x6 cm film
> 17.5" f/4.5 Newtonian
> We want a simple design with no more than two elements. (I guess two is
> needed in order to correct chromatic aberrations.)

No. Ross corrector for example is made from same glass, and has zero
power, so chromatic aberration is no issue.
With only 2 elements and paraboloidal mirror you don't have much
choice. Ross corrector is the only option (the one in S&T requires deep
hyperboloid). Depending on image size you can put up with in the corner
of 6 by 6, two element Ross may not be good enough. Who's going to make
lenses ? With 3 lenses AR coating is compulsory.
Consider how big your secondary needs to be to cover 6X6 format.

Examples of two and three element Ross are in Wallis/Provin book.

Bratislav