[ATM] RE: [atm_free] A model of the Hindle Sphere test of a convexHyperboloid

["James Mulherin" <jcmulherin@opticalmechanics.com>]

James:

> Greetings All,
> 
> I've been working on an OSLO model of a Hindle sphere null
> test for a convex hyperboloid (a some day RC Cass, maybe)..
> 
> Anyway, If I modeled it correctly, starting with the assumption that all
> the
> optical properties are known, It would appear that the spacing between the
> concave sphere and the convex hyperboloid are impressively sensitive to a
> change
> in distance.  If I modeled it correctly, it would appear I have to get the
> spacing between the two mirrors to within +/- 0.01mm (how exactly would I
> accomplish that?)
> 
> In addition, things get catastrophically worse if by chance I don't KNOW
> the
> exact RoC of my poor Convex optic, nor it's current Conic Constant.
> 
> I am starting to come to the conclusion the Hindle sphere test may be near
> impossible to implement with quantifiable results, however I hope I'm
> overlooking some rather obvious fact
> in my blissful ignorance.. :)
> 
> Here's a  link to an Oslo Screen shot, as well as the Oslo file on my web
> site:
> http://lerch.no-ip.com/atm/Hindle_Null.gif (112KB)
> 
> http://lerch.no-ip.com/atm/Hindle_Null.Len (2KB Oslo Len file)
> 
> Just looking for ideas :)

The back focus is very sensitive to mirror/Hindle sphere spacing. A good
technique for achieving the proper spacing is to place your tester at the
desired back focus position and adjust the mirror separation to put the back
focus where it belongs. As you figure the secondary mirror and approach the
null you can check your back focus position and make minor adjustments in
spacing to put the null focus position where it belongs. Figuring a
secondary against a Hindle sphere is an iterative process in this regard.

 

James

James Mulherin
Optical Mechanics, Inc.
jcmulherin@opticalmechanics.com
www.opticalmechanics.com
Tel: (319) 351-3960
Fax: (319) 351-3943



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