[Raytrace] Stevich Paul in OSLO LT

[Henry Feinman]

Thanks Mike for the reassuring note.

The slightly hyperboloidal primary  came about as a result of me playing 
with the optimization routines in search of improvements on the the 
basic design.  This curvature,  according to Oslo, provided very 
slightly improved Strehl ratio,  and better Airy disk containment 
through focus, though the Wavefront analysis and MTF curve at .7 field 
were not as good.

As the 'ideal' curvature according to the tests is so very slightly 
hyperboloid, and the improvements small and isolated to one test over 
another - my target conic when grinding the mirror will still be parboloid.

Thanks again, Henry Feinman


Michael Peck wrote:

> At 19:46 04-05-03 -0400, Henry Feinman wrote:
>
>> I have come up with a design that appears quite good  - going by 
>> wavefront analysis, peak valley / RMS OPD, spot diagram, MTF, Strehl 
>> ratio, but there appears one major problem:  The distortion analysis 
>> shows a huge percentage compared to other  designs -350 Distortion % 
>> at about 2 mm distant from axis.
>
>
> I think that distortion graph is probably wrong. Distortion shouldn't 
> scale that way, although I suppose strange things can happen in a 
> system with tilts. If you look at the estimated Seidel distortion 
> coefficient it's fairly small, which I believe it should be.
>
> An interesting feature of the "Stevick-Paul" that isn't at all obvious 
> when you set it up in an optical design program is that it isn't 
> really a tilted component system at all. What Stevick did was take the 
> basic Paul geometry and *rotate* the two spherical mirrors around 
> their respective centers of curvature far enough to get them out of 
> the way of the light cone. What you end up doing is looking at 
> off-axis light from the primary. The reason that works is because the 
> Paul system is an all-reflective Schmidt - its only 3rd order 
> aberration is Petzval field curvature. I don't know for sure but I'd 
> guess that distortion might be asymmetric around the axis at the focal 
> plane, but it should be very small.
>
> One thing that bothers me about your design is that if you straighten 
> out the mirrors the primary should be exactly paraboloidal. I don't 
> understand why you're getting a slightly hyperboloidal primary in your 
> design. Maybe someone who understands how to set up tilts in OSLO can 
> comment on that - I've never bothered trying to figure out in any 
> detail how to do TCT's.
>
> Mike Peck
>
>
> _________________
>
> Michael Peck
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