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Have an Acromatic doublet needing mounting

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#1 Skywise2

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Posted 21 September 2019 - 12:12 AM

I have a 4" Achromatic pair that are not coated or mounted.  It was suggested that they were to be cemented together.  Where could I send them to be cemented (if they are supposed to be) and reflection coated?   



#2 sg6

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Posted 21 September 2019 - 02:15 AM

If they are not cemented then they are very much not meant to be - they have to have 2 faces of identical radaii and they would have been cemented initially.

 

Post reads of 2 achromats, wording reads of 2 lens that have been suggested you cement. Which is it ?

 

I guess you have 2 lens from something, if so then likely they are 2 lens that should be air spaced in a lens cell. In which case you need to find (guess) the seperation at the edges and add a spacer ring of that thickness.

 

Likely means determining the lens order and orientation - positive lens at the front, flatter surface towards the front again. Then working out a sensible seperation - the rear surface of the front lens and front surface of the rear cannot touch.

 

Usually seperation is small, so could try say 1mm between the centers and see what that is at the edge and go for that.

 

Search out Fraunhoffer Doublets - reasonable chance that that is the construction/orientation you need - it should allow you to get them the right way round, but no guarantee as thereare other options.

 

Get lens cleaning fliud as you will have finger prints over every surface. Eventually you will have to clean and assemble in whatever chosen arrangement.

 

Do you have a lens cell?



#3 dan_h

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Posted 21 September 2019 - 10:50 AM

If they are not cemented then they are very much not meant to be - they have to have 2 faces of identical radaii and they would have been cemented initially.

 

 

Not so long ago Surplus Shed was clearing a number of unfinished lenses. SS indicated some of these were meant to be cemented. 

They still have a bunch of smaller uncemented pairs and they do sell cement if you want to try it yourself. 

 

If the OP has a set from the Shed. it may be they need to be cemented.

 

dan


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#4 Skywise2

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Posted 21 September 2019 - 09:32 PM

These were from a member of our club, who ground lenses.  Donated the grinding equipment to the club and it is currently in storage, as no one knows how to do it.  Anyway, his estate donated most optics to the club members and I came away with a 4" mounted achromatic and this pair that said "for cementing," which led me to believe they were meant to be cemented.  Really not sure what I have.  Nifty if I could send them to someone who knows what they're doing.



#5 BGRE

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Posted 21 September 2019 - 09:44 PM

You could try oiling the elements of the doublet together and then test it. Then you can decide whether its worthwhile cleaning it and having it coated.

N.B. the cemented surfaces should not be AR coated only the outer surfaces should be AR coated.


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