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

["David Harbour" <scarab2@cox.net>]

Yes, John!!

While I have been wracking my tiny pea brain, John has come up with the
idiot proof test.

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

Very excellent thinking, John.

Dave

P.S.- I knew an atm who bought (I do not know for what purpose) an opthalmic
blank, very steep, very short R.O.C. (when I said very steep, I meant the
blank was strongly "reflexed"- i.e., "meniscied", if I may be allowed to
invent a term. He had it aluminized; a tiny, very short focus, bery bright
and shiny little mirror. I wonder how accurately they are figured? Probably
not very accurately. Still, might be worth looking into (of course they
won't be figured at all; what I meant was, I wonder how close to spherical
they are). Opthalmic blanks still come in glass as well as plastic.


----- Original Message ----- 
From: "john sherman" <atm@mail.johnspics.com>
To: <atm@atmlist.net>
Sent: Wednesday, June 15, 2005 4:52 PM
Subject: Re: [ATM] Re: Figuring the little dinky sphere


>
> Hi guys,
>
> >1.25" negative meniscus.
>
> >2" f/2
>
> Wow, such small surfaces! You will probably have to use a beam-splitter,
but use a pellicle. Forget the cube. Here's a way.
>
> Use a pinhole light source and an eyepiece. A pellicle will keep you
on-axis. Now you are doing a normal star test. With a perfect sphere, the
star will focus perfectly.
>
> You can also put up a spot instead of the eyepiece, for a different view.
>
> You can also just polish away merrily. At the end make sure you have good
contact with the lap, in different positions. That will make you believe you
are very close to a sphere. I don't know how close you have to get the f.l.
and errors. Testing may be necessary. Good luck,
>
> John
>
>
>
>
>
>
> _______________________________________________
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>


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