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Anyone ever tried this?

ATM
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11 replies to this topic

#1 Ed Jones

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Posted 12 August 2019 - 09:35 PM

I've never tried this or seen it done but can you press a pitch lap against a polished convex lens you would like to test with just water (no channels), take it off and do a Ronchi on it.  If it truly matched the lens it should also show any surface errors reversed.  


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#2 Pinbout

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Posted 12 August 2019 - 09:38 PM

Interesting, just a tad cerox to act as seperator?


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#3 Pinbout

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Posted 12 August 2019 - 09:40 PM

How about shoot thru to a flat and bounce back against a perforated flat

 

so basically dpac off a flat. 



#4 Ed Jones

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Posted 12 August 2019 - 09:42 PM

What ever works, getting it off without deforming or sticking might be the tricky part.



#5 dave brock

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Posted 13 August 2019 - 03:06 AM

How much light does pitch reflect?

#6 BGRE

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Posted 13 August 2019 - 04:11 AM

How much light does pitch reflect?

 

Should be more than sufficient, the reflectance increases with the absorption (imaginary part of the refractive index). Thus the reflectance should be higher than that of transparent glass.

The high absorption of metals like aluminium and silver results in a high reflectance even though the real part of the refractive index can be relatively low for a metal.



#7 Mark Harry

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Posted 13 August 2019 - 04:20 AM

Put some drops of surfactant detergent in the water. They do it all the time with convex stuff at the shop. It should separate fairly easily, if not too large. 
I think you're defeating the purpose with a ronchi test. You have a Zygo Ed, why don't you use that?



#8 Ed Jones

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Posted 13 August 2019 - 06:23 AM

 

You have a Zygo Ed, why don't you use that?

Yes I have a Zygo but I was thinking in terms for what an ATM might be able to do.



#9 Matthew Paul

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Posted 13 August 2019 - 07:51 AM

I recently cast a pitch lap without channels to use polishing pads on. It came off the mirror without any sticking issue. It would be interesting to see how the shape changed from casting to casting, or press to press I guess... I cast the lap with Gugols 73 about 1/8 to 5/32 thick. 


Edited by Matthew Paul, 13 August 2019 - 07:52 AM.


#10 Pinbout

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Posted 13 August 2019 - 08:07 AM

Yes I have a Zygo but I was thinking in terms for what an ATM might be able to do.

shoot a ronchi thru the lens [pcx] and off a flat... a water flat... and compare the curves in diffract. it will look like a -1 conic so...

 

for an f4 you could judge better than 1 wave.


Edited by Pinbout, 13 August 2019 - 08:08 AM.


#11 davidc135

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Posted 13 August 2019 - 12:20 PM

Or perhaps smooth a plastic film over the lens and press the pitch to that? Maybe the irregularities within the film would be absorbed into the pitch leaving the outer film surface true to the lens. And if that surface was aluminised as in 'one way' mirror film (or solar film) could it work?   David


Edited by davidc135, 13 August 2019 - 05:06 PM.


#12 luxo II

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Posted 14 August 2019 - 06:00 PM

Ed, that you ask suggests to me you haven’t actually polished something with a pitch lap. If you had you’d know the answer ;)

And no it doesn’t work.

Edited by luxo II, 14 August 2019 - 06:01 PM.

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