RE: [ATM] diagonal flat testing

["Robert Turner" <rbturner@charter.net>]

Jerry,

Here is a link to an article that would describe the test. I have not tried
this yet. Look close to the bottom it talks about the knife edge test. Read
about telling if the surface is concave or convex.

http://bobmay.astronomy.net/johnpierce/part8.htm

Robert

> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
> Of Jerry B. Hillman
> Sent: Thursday, April 29, 2004 10:00 PM
> To: The Amateur Telescope Makers List
> Subject: [ATM] diagonal flat testing
>
>
> 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
>
>
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