ATM Wynne 3-lens corrector

[Aplanatic@aol.com]

I took a good look at the three-lens Wynne corrector that Kevin McCarthy 
posted and it is indeed a beauty.  Two things worry me, the distance from the 
front of the first lens (closest to the mirror) and the focal plane, and the 
sensitivity of the optical performance to RoC variations in manufacturing.

Let's address the first issue.  The aforementioned distance is 278 mm 
(10.9").  That is a lot of glass and metal to be sticking out of the side of 
a telescope, even for a 1M aperture.  In addition, to accommodate the 
corrector, the primary must be moved closer to the secondary by about 5" as 
compared to the design using the more compact 4-element Wynne corrector.  
With an f/3.3 light cone, the secondary must grow in diameter by about 1.5" 
to account for the change in primary position.  In my opinion, diffraction 
effects from the increased secondary size are less important than the weight 
and cost of the larger flat.  Opinions on these two matters are welcomed.

I could use some advice on the second issue, i.e., the manufacturing 
tolerances required of the lenses.  To keep the spot characteristics 
"reasonable" it turns out that R1 must be controlled to about 0.1% (or R2 
must be matched to R1, a similar problem).  The second lens in the corrector 
has an 0.2% error margin, etc.  Does anybody know enough about lens 
manufacturing and tolerances to tell me if this is possible without driving 
the cost through the roof?

Finally, it turns out that the 3-lens Wynne can be re-optimized for a larger 
back focal length with only a small compromise in performance.  This may be 
important for applications involving a CCD camera and tri-color filter wheel. 
 I would be happy to send this modification to anyone interested.  So far, I 
have been able to achieve a 59 mm BFL.

Dave Rowe
Torrance, CA