Re: ATM 3.5" Secondary Sources?

[Bill Marriott <btk@pacbell.net>]

Herb Kasler wrote:
 
> I just got a 3.5" secondary, spider, and holder from Discovery Telescopes in  SoCal. They charged me $169 for the mirror, which I think is pretty
> reasonable. They claim 1/10 wave accuracy.

PV? Surface? RMS?

> No evidence yet of how good or  bad it is, but folks around here seem to think that for the most part, flats is flats. I got a couple of replies to my initial questions about
> secondaries to that effect. Their URL is
> http://www.discovery-telescopes.com.
> 
> Later,
> Herb.

Herb;

If you go through all the work to get your 16" to the point of a good
overall figure, there is no way you want that wave front bouncing off a
piece of glass that is less flat than your primary, you should try to
have the secondary not be the limiting factor in the system.

Over the years, I have seen some 'interesting' figures on supposedly
'flat' ellipticals.

One reporters opinion...

Bill
--
Bill Marriott
http://www.starlightoptical.com
telescope/optical stuff