RE: [ATM] Off-centered Mirrors?

["Donald Good" <donald.good@comcast.net>]

The Yolo design is a schiefspiegler or TCT that uses an off-centered mirror
(secondary in this case) to reduce aberration.  The secondary is either
figured as a centered conic and then placed in an asymmetric warping
harness/cell (a kind of flex mirror) in the telescope or it is placed in a
similar warping harness for figuring and when released, taking on the shape
of an off-axis mirror.

A frequent problem with figuring a large parabola and then cutting 3 or 4
off-axis sections out of it is that cutting after final figuring can cause
permanent deformations around the cut.  This is the reason that a
preliminary (nearly through) cut is made in thru-the-mirror focus designs
(cass, gregorian, etc.) in the polishing/figuring stages such that the final
polishing/figuring removes that distortion prior to the finishing cut.  Such
a procedure for 3 or 4 large area cuts in the off-axis case may weaken the
mirror too much for proper final figuring.  Maybe the best is to make the
cuts after figuring and live with or mask off the distortion.

Clear skies,
Don

> -----Original Message-----
> From: atm-bounces@atmlist.net 
> [mailto:atm-bounces@atmlist.net] On Behalf Of Greg Jones
> Sent: Saturday, October 23, 2004 11:30 PM
> To: atm@atmlist.net
> Subject: Re: [ATM] Off-centered Mirrors?
> 
> The schiefspiegler is a tilted component scope.  Don is 
> describing an off-centered scope and there is a difference.  
> The TCTs use centered conic sections.
> 

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