RE: [ATM] Ross null test?

[Ric Rokosz <radicell2@yahoo.com>]

--- lou krajci <loukrajci@comcast.net> wrote:

> OK, you have to pay for a mirror coating for
> Waineo/Maksutov null, but to
> make the Ross lens...you need to work two surfaces,
> control wedge, check the
> glass for striae/inhomogeneities?  Doesn't that make
> the Ross lens more
> expensive?

If you are doing the work yourself,I don't see how it
can be more expensive.The plano side just has to have
an even surface so a quick grind with say 12 micron
and a hard polish should work.
 On the wedge issue,I'm not sure how much freedom one
has,but in most cases one would "design " the lens so
only the more central areas are used so wedge there
would not be a big issue,but I could be wrong on this
point.
 Checking for straie isn't a problem,just a bit of
time if you're making the lens yourself.If you're
buying a lens,I'd think the vendor would use the best
glass to aid their profit margin...


> >to null out the reference element (hyperbolic) when
> >making Cass secondaries ,be it the normal Cass or
> the
> >Ritchey - Chrieten type.A big plus in my view..
> 
> Do you mean the Ross null test can test concave
> aspheres, other than
> paraboloid?  If yes, then the Waineo/Maksutov can do
> the same, if I
> understand it correctly.

The Ross and Waineo can both test a wide range of
conics,but the Waineo needs a central hole to access
the return beam. So in testing the reference element
for a Cass secondary that area of the reference is
lost to testing and for most atm sized secondaries the
central hole in the Waineo mirror is as large or
larger than the secondary itself.

Ric







		
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