From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: "Tom Krajci" 
>
>As scopes get larger, secondary mirrors get larger.
>
>Up to now, mechanical edge clips, supporting the secondary mirror, have
>worked well for the amateur.  But as secondary mirrors get larger, and
>probably thinner to keep weight down...edge support of a large secondary
>mirror will distort the mirror too much and image quality will suffer.
>
>What then?  Upside down 'flotation cell' design for large thin secondary
>mirrors...with RTV bonding to the secondary?
>
>What does PLOP say for edge supported mirrors?...at what size/thickness
>does image quality begin to degrade?  (I know, secondary mirrors are
>elliptical, but PLOP would give us a first approximation.)


Hi Tom
 Maybe we need to modify PLOP to find the best support for a
secondary that allows the mirror to sag a little so that it always forms
one of the family of hyperbolic off axis shapes that keeps the image
correct. This way, a thinner mirror can be used and the only disadvantage
is that the focal point moves slightly as the telescope is moved about.
 We might find that the normal three point mounting is not
really the best for a secondary. It might be that a beam 4 point was actually better.
Dwight

--- BBBS/NT v4.00 MP