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Fluorite scope lenses costly due to time to grind?

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#1 RichA

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Posted 02 June 2020 - 12:47 AM

According to Canon (they use fluorite in more expensive lenses)

 

"-another challenge since fluorite is so fragile. The engineers at Canon developed a new grinding technique to ensure flawless fluorite lens elements. The downside is that it takes four times longer to grind a fluorite element than a glass element −"

 

https://cpn.canon-eu...nd_ud_lenses.do


Edited by RichA, 02 June 2020 - 12:48 AM.

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#2 TOMDEY

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Posted 02 June 2020 - 03:38 AM

Yes indeed; if anything, they are understating the difficulties. This comes under the heading of ~exotic optical materials~. For example, we made these giant optical prisms for IR spectrometers, to exacting optical standards. The material was single crystal NaCl aka common table salt! Just imagine trying to grind and polish that, without being able to get even a single drop of water, your breath, or even slightly humid air in it, ever! After production, each and every prism assembly is stored in its own dedicated, desiccated, evacuated bell jar, under vacuum... and toted around like that. Breathe on it and you've just destroyed a $10K prism. Accordingly, exotics cost whatever it takes to manufacture and maintain them.

 

[I worked at B&L back when it was a full-service optical shop. Now they just make contact lenses and bottled water. There is precious little precision production in the USA anymore.]    Tom


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#3 daquad

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Posted 03 June 2020 - 07:24 PM



Yes indeed; if anything, they are understating the difficulties. This comes under the heading of ~exotic optical materials~. For example, we made these giant optical prisms for IR spectrometers, to exacting optical standards. The material was single crystal NaCl aka common table salt! Just imagine trying to grind and polish that, without being able to get even a single drop of water, your breath, or even slightly humid air in it, ever! After production, each and every prism assembly is stored in its own dedicated, desiccated, evacuated bell jar, under vacuum... and toted around like that. Breathe on it and you've just destroyed a $10K prism. Accordingly, exotics cost whatever it takes to manufacture and maintain them.

 

[I worked at B&L back when it was a full-service optical shop. Now they just make contact lenses and bottled water. There is precious little precision production in the USA anymore.]    Tom

So in what instruments was this NaCl prism used if it could not be exposed to air?

 

Dom Q.



#4 RichA

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Posted 03 June 2020 - 07:38 PM



Yes indeed; if anything, they are understating the difficulties. This comes under the heading of ~exotic optical materials~. For example, we made these giant optical prisms for IR spectrometers, to exacting optical standards. The material was single crystal NaCl aka common table salt! Just imagine trying to grind and polish that, without being able to get even a single drop of water, your breath, or even slightly humid air in it, ever! After production, each and every prism assembly is stored in its own dedicated, desiccated, evacuated bell jar, under vacuum... and toted around like that. Breathe on it and you've just destroyed a $10K prism. Accordingly, exotics cost whatever it takes to manufacture and maintain them.

 

[I worked at B&L back when it was a full-service optical shop. Now they just make contact lenses and bottled water. There is precious little precision production in the USA anymore.]    Tom


Interesting.  I'd seen salt crystals used as scintillation detectors in geiger counters, but high optical quality wasn't a criteria.



#5 TOMDEY

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Posted 03 June 2020 - 09:21 PM

So in what instruments was this NaCl prism used if it could not be exposed to air?

Dom Q.

Interesting.  I'd seen salt crystals used as scintillation detectors in geiger counters, but high optical quality wasn't a criteria.

I think it was for laboratory spectrophotometers. They were about three inches on a face, which implies that spectral res was paramount, so they would have had to be tenth wave PV wavefront all the way through! I just saw them sitting in one of the meticulously-maintained cabinets in one of the labs. There was so much optics stuff around that I didn't get a chance to research everything... but sure noticed and pretty much memorized everything I saw. My global mem is deficient... but when it comes to technical stuff, especially optics... I seem to remember everything... and forever!    Tom

 

The closest ~similarity~ picture I have is this thing I use for objective prism on my 4-inch scope >>>

 

~click on~ >>>

Attached Thumbnails

  • 86 original Fraunhofer objective prism 1899 and Toms.jpg


#6 Alrakis

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Posted 05 June 2020 - 08:25 PM

Sounds like the optics for a Nicolet FT-IR spectrometer (Fourier Transform infrared ) or FT-Raman. 



#7 Rollo

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Posted 05 June 2020 - 08:48 PM

According to Canon (they use fluorite in more expensive lenses)

 

"-another challenge since fluorite is so fragile. The engineers at Canon developed a new grinding technique to ensure flawless fluorite lens elements. The downside is that it takes four times longer to grind a fluorite element than a glass element −"

 

https://cpn.canon-eu...nd_ud_lenses.do

Fluorite is much harder to work with than glass.   It's very delicate and breaks and cracks more easily too.  



#8 JohnH

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Posted 06 June 2020 - 09:41 AM

According to Canon (they use fluorite in more expensive lenses)

"-another challenge since fluorite is so fragile. The engineers at Canon developed a new grinding technique to ensure flawless fluorite lens elements. The downside is that it takes four times longer to grind a fluorite element than a glass element −"

https://cpn.canon-eu...nd_ud_lenses.do


Fluorite has to be grown, and larger elements take around a YEAR.

Also a very fragile material with excellent cleavage
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#9 JohnH

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Posted 06 June 2020 - 09:43 AM

I remember in chemistry class in college we were analyzing little pieces of steel alloy to see how much manganese was in the material. We dissolve the steel and acid and then any specialized instrument we measured the colour of the solution that resulted. Are Professor warned us not to touch the crystal through which the light shine as it would be damaged by humidity of our fingertips. So I imagine it was some material that was transparent in infrared.


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