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Anyone recognize this eyepiece? Carton ER20mm

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#1 Lentini

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Posted 12 May 2021 - 10:21 AM

I love this little 1.25" eyepiece... Could never bring myself to get rid of it. Gives super sharp views, But I can't find out any specs (or even a single picture of this model) online.

 

Carton Erfle 20mm

 

What would the AFOV be? Field Stop Diameter?

 

Do all Erfles have the same number of glass elements? 

 

I could guess, estimate or measure those perhaps... But was looking for a manufacturers data sheet.

 

I'm also looking for another one to try it with binoviewers.

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#2 astrokeith

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Posted 12 May 2021 - 11:00 AM

Carton is a long established Japanese manufacturer, or some repute. They make a lot of microscopes but their telescope eyepieces were sold by Apogee at some time.

 

The Erfle is a 5 element design related to the Plossl. Good for comfort due to generous eye relief and diameter. Normally better at long focal lengths (say 40mm) where they excel. At below 20 they can produce nasty aberrations & reflections. AFOV about 65 degrees I would expect.


Edited by astrokeith, 12 May 2021 - 11:01 AM.

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#3 Starman1

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Posted 12 May 2021 - 11:04 AM

1) If you time the passage of a star on the celestial equator from edge to edge and get a time in decimal minutes (e.g. 4min, 12 sec = 4.2 minutes), then divide by 4, you have the field in degrees.

From there, you can derive the field stop:

Field stop = (True field x Telescope focal length) / 57.296

2) The flashlight test is the only easy way to measure the apparent field.

(search for threads on it in the Eyepieces Forum here on CN)

3) Erfles commercially sold have a few different configurations.  Most are 2:1:2, but some are/were 2:2:2.

And some disassembled and shown here on CN weren't even Erfles inside, though labeled as such.

4) That eyepiece hasn't been made for decades, so good luck finding another like it.

It might be easier to find a pair of another brand of 20mm Erfle that was sold in much larger quantities like, say, the Meade Research Grade eyepieces from the early '80s.


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#4 mike bacanin

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Posted 06 June 2021 - 02:48 PM

I love this little 1.25" eyepiece... Could never bring myself to get rid of it. Gives super sharp views, But I can't find out any specs (or even a single picture of this model) online.

 

Carton Erfle 20mm

 

What would the AFOV be? Field Stop Diameter?

 

Do all Erfles have the same number of glass elements? 

 

I could guess, estimate or measure those perhaps... But was looking for a manufacturers data sheet.

 

I'm also looking for another one to try it with binoviewers.

 

PM sent.

 

Mike


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#5 Jon Isaacs

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Posted 06 June 2021 - 05:46 PM

If I were looking for a 20 mm Carton Erfle, I would contact Sheldon Farowski, the proprietor of Apogee Inc.

 

He still has new old stock.. his contact info:

 

https://www.cloudyni.../25634-masilmw/

 

Jon


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