Re: [ATM] 16"RCC mirror

[Ric Rokosz <radicell2@yahoo.com>]

--- Attila Schné <yolo@chello.hu> wrote:


> >>        surface is not quite flat?
> 
> RR> 12 inch cass that used a 2.2" secondary of pyrex
> and I
> RR> just used the back as is.

Should mention that if you use a  hunk of pyrex that
has been cast,such as the larger 4" and up in size,the
straie (or veins) in the glass might be a concern,but
just rotate the "lens" in several differnt positions
to get a feel for what to ignore.Some people do test
the Cass secondary from the back,through the glass and
learn to compensate for the veins.Ronchi works great
here.

Pyrex blank that have been cut from a sheet that has
been rolled at the factory is better for this
purpose.Never tried plate glass,but with the supposed
better quality of the more recent material it might be
worth the effort to at least try it.There is a way to
find the refractive index of the material once the RC
and focal length is known.If anyone wonts the formula
let me know and I'll post it.

Ric
Toronto


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