Re: ATM 11.2" F/2 Primary testing questions :)

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Dennis Nikitin" <ndenis@sarkor.com>
> 
> Hi, James
> Don't warry about coma. You can stop down the aperture at the point of
> curvature radius just like in Schmidt camera. It will kill coma +
> astigmatizm. You will get a strange Schmidt with no corrector and with
> parabolic primary. Anyway f/2 mirror has big field curvature. I don't know
> what is the resolution of your CCD chip but it seems that you will have to
> include Piazzi-Smith lens.

Do I have to stop it down at the ROC, or can I do it at the FL?  Will doing it at the FL, still allow of-axis light to make it the edge of the mirror?  

The goal of the project is an Astometric worthy camera with a resolution of 2 Arc Seconds per pixel, based on recomendations from the Minor Planetary Center.  With the Sony CCD chip I'm using, that neccisitates a Focal Lenth of 570mm.  From discussion on this list, as well as results from software, a diameter resulting in F/2 was chosen..

The Piazzi-Smith lens you spoke of, is this some type of Coma-Correcter?  If so what type of figure is it?  One of the hopes for this instrument, were to avoid any lenses in the optical system, but if it's a must, then so be it ;)

> >>>
> I'm just looking for some guidance on which might be best/easiest ;)
> <<<
> 
> Focault test is hopeles for f/2 parabola. Wire test will work but its
> sencitivity and acuracy won't be satisfactory. For my  RC cassegrian with
> f/3 primary I used Spherical Null Test. SNT gives a lot of fun while testing
> such a fast paraboloid. I'm sure that it will work with f/2 as well.

When you did your Spherical Null Test, Did you construct a Full size spherical Lens, or did you use a sub-diameter lens and just move it around?  
 
> Happy New Year!!!
> Dennis Nikitin
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