[ATM] Banishing the secondary

[artbianconi@blast.net]

Last winter I attended the Mid Atlantic Mirror Making event in 
Delaware. This is the annual 3 day workshop hosted by Don Sarles 
and other equally enthusiastic members of the DelMarva Star 
Gazers.

David Groski was there as was Bill Cheng. Bill brought with him a 
lovely 4.25 Schiefspiegler telescope, carefully crafted from Luen 
(Sp?) Mahogany and which employed lenses corrected by David. I 
forget the F/L but I suspect it was something in the order of 
20". Aside from the small aperture, I fell in love with it only 
to learn that the corrections were only good for a mirror up to 
4.25 Inches after which the image is said to go to Hell. 

Dave has worked on the numbers since then, and appears to have 
solved the cause of the spherical aberrations for a 6 inch 
mirror. I can live with that and have promised myself that as 
soon as the other projects around here get completed, I will 
build a 6 inch Schiefspiegler carbon fiber variant. 

If it performs as well as the previous models suggest, this whole 
conversation about secondary obstructions may well be moot.

Art Bianconi


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