[ATM] Re: Hugs and Kisses II

[vladimir sacek <vladis.2@juno.com>]

Richard,

Thank you for additional information. I run the "Hugs"
and it is exceptionally well corrected: beautifully small spot
both on axis and far off axis. The only drawback I see is a need to make 
double meniscus. I used TDesign to get a single-meniscus corrector, 
for comparison. For some reason, the software comes up with designs
way off correction-wise, but it is easy to get it down to acceptable, or
better.
The corrector is also silica (n=1.46 in e), the system 500mm f/16. You
may 
want to check it out:

R1: -700mm
Thickness: 26
R2: -714.6
Corrector-to-Primary: 1560
R3: -4000
Primary-to-Secondary: -1540
R4: -1286

Its spots are not nearly as neat, but it is corrected to better than 1/10
wave
as it is (I didn't spend much time optimizing, so it likely can be made
better).
Color correction doesn't seem considerably inferior. 

I also checked out the Schmidt version. Corrector thickness seems to be
fairly
irrelevant, which is to expect with flat first surface. An all spherical
design (except
the corrector, of course) would look like this:

R1: infinity
Thickness: 59mm
 n=1.46
R2: Schmidt surface, Power 0.743, neutral zone @ 0.866 radius
Corrector-to-Primary: 1600
R3: -4000
Primary-to-Secondary: -1556
R4: -1178

Spherical aberration is cancelled, astigmatism very low, and coma exceeds

"diffraction-limited" (0.80 Strehl) at ~11mm off axis. Coma can be
cancelled 
either by moving the corrector nearly twice farther away, or aspherizing
the 
secondary (approx. -1.1 conic). Chromatism is at a similar level to the
other two 
systems. 

As Dominic-Luc suggested, the curve needed for Schmidt corrector would be
very 
shallow: ~1/25mm at the 0.866 zone, and less than that everywhere else.
Is it really
much harder to make such a slight curve, as opposed to Maksutov
corrector, which also 
requires very tight tolerances?

Vlad



 
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