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What Is This Glass For?

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#1 Tom Duncan

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Posted 14 September 2018 - 02:19 PM

Got this pair of glass blanks recently, have a question. At first I thought they were just blanks for Newt mirrors but the red arrow on one and the size (7-1/2" diameter, 1-1/4" thick) is throwing me off a bit. Is there a chance these are blanks for a large refractor? 

 

Thanks

 

Tom Duncan 

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#2 davidc135

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Posted 14 September 2018 - 02:34 PM

They look ground and polished. Are the surfaces curved? Flats maybe?  David



#3 Pinbout

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Posted 14 September 2018 - 02:47 PM

 

Flats maybe?

I usually draw an arrow on th edge pointing to the good side on my flats


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#4 TOMDEY

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Posted 14 September 2018 - 02:48 PM

Almost always, a test-flat has an arrow on the edge just like that. It points to the "good" reference surface. The other side is just polished so you can look through it at the fringes off the other surface. Optics shops have such pieces all over the place. They can also be recognized in that they are pretty beat up from pernicious use on the always-bustling shop floor.

 

Or it could be a work in progress or a non-flat test glass.

 

Take even a small test glass to it under e.g. fluorescent lights. Fringes should be obvious. If they fluff nicely... it's a reference flat... Tom


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