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Criterion 18mm lenses

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#1 oasmith

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Posted 14 February 2018 - 02:05 PM

Hi All,

 

I have two Criterion 18mm lenses, one says A.R. and the other says H. Does anyone know the difference between them? Also, the H. has a larger lens screwed on to the bottom, and I didn't know if that was an old version of a Barlow? And if so, would it work if I moved it to the A.R. 7mm or 9mm? Thanks for any insight! 



#2 Chuck Hards

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Posted 14 February 2018 - 02:12 PM

A.R. means "Achromatic Ramsden", or a Kellner variant.  H means Huygenian.  The focal plane falls between the field lens and eye lens with the Huygenian design, all others have the focal plane located outside of the field lens.

 

Don't remove or switch eyepiece lenses around.  It is not a Barlow on the H 18mm.  

 

Pictures will help.


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#3 JIMZ7

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Posted 14 February 2018 - 05:32 PM

I had the 18mm A.R. but it was the Bausch and Lomb version which I believe was the same. The fov was 40 degrees but very pinpoint sharp. 

Jim




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