From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: "Mike and Sara" 
>
>Hello!
>
>    After the previous posts, I've reground my secondary to the correct ROC
>(65mm diameter secondary with ROC=310mm).  I have a tile tool.  I've
>polished both the secondary and the tile tool.  The tool seems to have
taken
>polish well, and looks fine on foucault testing.
>   I've treid the interference test with a green laser and red laser
>pointer.  I used tissue paper to diffuse the light, and tried the source
>with and without a lens.  The lens did not seem to help, so I am not using
>it.

Hi
 Why would you want to use a paper diffuser? I thought the
idea was to use light with all the same phase. To spread the light, you
should be using a small bead lens. At least that is what I understand.



>    Without paper shims, I can get fringes - Usually a bull's eye pattern
>with some aberation around the corners of tiles at the center.  The spacing
>between the fringes is farthest apart ner the center, and get closer
>together toward the edge.  There are many fringes, but easily seen.  I
don't
>see any change in the pattern near the edge.
>    I didn't see any fringes when using paper shims.  Finally, I got the
>thinnest tissue I could get, and I started to see fringes.  Again, there
are
>a lot (more than when I simply mated the the curves together without
shims),
>and the fringes seem to be straight, and the edge looks fine, though with
so
>many fringes, I loose the pattern easily.  Pressing down on the secondary
>around the thick shims seems to space out the fringes, though the pattern
>changes obviously.
>    Is the difficulty in seeing fringes using shims because of the short
>ROC?  Or do the two curves differ substantially?  Since the ROC isn't as

 It is more likely that the shim is too thick.
 Dwight

>important as the sphericity of the secondary, even if the radii differ
>significantly, does this result indicate good sphericity?
>    Thanks and best regards.
>
>Michael Heald
>
>
>

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