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

[Aplanatic@aol.com]

James:

A postscript to my last post:

I don't want to discourage you from trying to figure an f/2 parabola, however, it may take you -- how should I say -- an overly long time to accomplish this task, unless you are willing to accept an optical surface that is significantly less accurate than, say, 1/4 wave on the wavefront.  For a camera of this speed, when used with a CCD having roughly 10 micron pixels, the accuracy of the mirror need not be much better than a wave on the wavefront, I think (although I haven't raytraced the situation).  This might just make the project doable, but still a tough nut to crack.

On the other hand, have you considered a Schmidt camera outfitted with a CCD instead of curved film?  I've made three Schmidt corrector plates and can state with great confidence that a spherical f/2 primary plus an 11.5" corrector is a much easier project than figuring an 11.5" f/2 paraboloid.  As an added bonus, the system has no coma.  The down side of this approach is the added length of the optical tube assembly.  I use a light-weight truss-tube structure to hold the corrector at the RoC of the prmary.  Not too onerous, perhaps, considering the other benefits.  Just a thought.

Again, best of luck whatever you decide to do, and keep us posted.

Dave Rowe