Re: [APML]: Coma correctors

[Steve Bell <sb635@delphi.com>]

Peter Ceravolo wrote:
> 
> I bought a stack of the Celestron coma correctors a while ago. I took one
> apart and reverse engineered the thing and pluged the lens's parameters in
> my optical design code. Basically it is a Ross type corrector (Ross back in
> the 30's designed one for the 200"), there was an article written about
> building one in S&T about 10 years ago or so.

Wallis and Provin also discuss these type correctors in AMOACP.

> 
> I have no knowledge of the Lumicon unit but the TeleVue model uses two
> doublets, probably of high index glass, to keep spherical corretion in check
> but still correct the coma.
> 
> The problem with all of these units is their size. I suspect, please correct
> me if I'm wrong, they would introduce more vignetting, especially with an
> f/4 beam.
> 

The 2" TeleVue ParaCorr also introduces a slight 1.1-1.2x Barlow effect. This helps 
counteract the vignetting, but it is still noticable.

-- 
Clear skies,
Steve Bell
sb635@delphi.com
http://people.delphi.com/sb635 - Astrophoto page