Re: [ATM] Ross null test - would this surplus shed lens work?

[Ric Rokosz <radicell2@yahoo.com>]

--- Gil McFarlane <gilboastro@yahoo.com> wrote:

> I would like to try the Ross null test - but
> spending
> $500 for a lens is out of my budget.  I found this
> lens at Surplus Shed ($22.50) - looks about right. 
> What do you think?  Is there a problem that it is
> fused silica rather than BK7?  (I am unlikely to
> work
> on mirrors larger than 12").

Sounds alright,but you need to play with the software
and get diameter numbers of the lens for the mirrors
you plan on making.I say this because the focal lenght
may or may not be too long.The longer the better but
not if the lens is too small to cover the face of the
mirror under test..If you get a very hazy image in the
test setup just use a hard pitch on the convex side
and that may give a better "spherical" shape to the
the convex side.If not just regrind the convex side a
hair,polish and measure the R value  again.

Ric



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