Re[2]: [ATM] Re: Figuring the little dinky sphere

[Richard <cnc@cncservo.co.uk>]

Hi David,

Thursday, June 16, 2005, 2:26:02 PM, you wrote:

DH> I would recommend using a 5X apochromatic telenegative amplifier in front of
DH> a long eyepiece; comfort translates into accuracy. Yes, forget the knife
DH> edge.

It may well be OK, but I see two problems. Firstly, you have to
know how to interpret a star test - to the point of knowing
where to remove material from the mirror by how an (out of
focus?) star image looks. While I don't dispute that such skill
could be obtained to some degree, I don't think anyone could
achieve reference element optical standards by it without half
a life times experience. Secondly, we are talking about F/2 here
folks!. No eyepiece or barlow is possibly going to handle such a
fast beam well enough to achieve a reference surface. Well, OK,
if we are COC then I guess we are talking F/4, but it's still
damned fast.

Now, I've had one thought that is probably nonsense, but I'll
state it anyway for opinion please. I remember reading, here
probably, about a series of tests to produce known good
flats without a reference flat. It involved some sort of round
robin with three flats. test A against B, B against C and C
against A. It occured to me that I have four of these dinky
little mirrors, all polished and ready to test. Does anybody who
knows the three flat test know if I could apply it to my little
mirrors. I could test them in the interferometer, each one
taking a turn as reference while another is the unknown. Three
interferograms, three equations in three unknowns.

Possible?

-- 

Best regards,
  Richard in the UK



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