Re: [ATM] diagonal flat testing

[Dale Eason <atmpob@yahoo.com>]

A friend just showed me a similar test but the
diagonal is placed very close to the mirror.  Place
both mirrors at the test stand location.  Rotate the
spherical mirror away from the tester so that it faces
the diagonal which is at 45 deg to the spherical and
the tester.  Imagine it as a very short newtonian with
a very long eyepiece.  The distance from diagonal to
tester should be about the ROC minus the distance from
mirror to diag.  Use the ronchi at 45 deg from
vertical.  As you shift the ronchi from inside to
outside COC the image of the lines should not rotate. 
If they do the diagonal is not perfect and has some
astig.

I tried it with one bad and one good diagonal. It
works.

Dale Eason
--- "Jerry B. Hillman" <JBHillman@ev1.net> wrote:
> Hi All,
> At the suggestion of Ken Hunter, I set up my
> Foucault Tester with the
> spherical 5" primary from my Meade scope.  After
> getting everything aligned
> I did the Foucault null test for a sphere and also a
> Ronchi test.  As
> expected, both tests showed a decent spherical
> surface.
> Then I added the diagonal flat into the light path
> about 12" away from the
> light source.  Of course this required turning the
> tester at right angles to
> the mirror, and angling tester and both mirrors to
> get everything back into
> alignment so I could see the reflected light.  Now
> the light is passing
> across the diagonal flat twice.  Once on the way to
> the mirror and again on
> the return path.This wasn't an easy task to get set
> up.
> Results however seem to confirm that the diagonal
> flat is indeed polished
> flat.  At least I still get the same results when
> doing the null test and
> the Ronchi test.  I would assume that if the
> diagonal was not correct I
> would be able to detect problems in one of these
> tests.  Incomplete nulling
> of the sphere or crooked or twisted Ronchi lines. 
> By the way, the Ronchi
> lines were straight, edge to edge, both sides of
> focus with as many or as
> few lines as I cared to display.
> I would like to be told if my testing method was
> invalid or incorrectly
> done, as I have never attempted this type of test
> before and I intend to get
> this flat and the 16.5" coated next week provided
> that the 16.5" passes the
> set of Foucault tests I am about to run on it.
> I'll check my e-mail again before I send these
> mirrors off Saturday just in
> case.
> Clear skies, Jerry
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/



	
		
__________________________________
Do you Yahoo!?
Win a $20,000 Career Makeover at Yahoo! HotJobs  
http://hotjobs.sweepstakes.yahoo.com/careermakeover 
_______________________________________________
ATM mailing list http://www.atmlist.net/