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

["john sherman" <atm@mail.johnspics.com>]

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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