Re: [ATM] A two way null test for convex hyperboloids

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Mauritz Andersson" <mauritz.andersson@gmail.com>


> Regarding the latest discussion on testing convex hyperboloids.
> Maybe someone could comment on the following idea on a null test or
> point to previous identical or similar schemes.
>
> As an example for discussion, consider the secondary for a 400 mm
> diam, f8.4 RC telescope. The secondary has a RoC of 1374.6 mm and a
> conic constant of -5.907.
>
> Assume that the back side of this glass is figured to a convex surface
> of RoC 1277 mm and conic constant of -4.91.

Mauritz,

That's a pretty nifty null, but how would you fabricate it?

Assuming

#1 You found some Quartz
#2 and you ground it convex on both sides to just the right RoCs
#3 and in doing so you created your 20mm center thickness,
#4 and found yourself in the fortuitous position of not having any wedge to 
contend with
#5 and while polishing both sides out, you didn't change the ROC of either side
#6 and finally, after polishing both sides out, both sides ended up spherical.

How do you proceed from here?

You have to manipulate two convex surfaces to known Conics, which means you have 
to test both sides individually by some other means.

On a positive note, if you achieved the desired prescription, this null test 
would make for a nice Sanity check.


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
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