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Bertele 6mm eyepiece

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#1 CharlieB

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Posted 17 February 2017 - 09:59 AM

I've had this eyepiece for a while and it's a very good performer, but I was never completely convinced about its design.  I took it apart today and took some photos (which I've enhanced to show its internal structure.  I've also attached a small portion of the C J R Lord eyepiece chart that shows the structure of the Bertele design.  Unfortunately, I could only remove the field lens, which looks like it consists of two cemented elements, but I can't be sure.  The eye lens looks like a plano-convex element, but it's difficult to tell due to the rolled over brass lip that hold it in place. 

To my eye, it looks very similar to the Bertele design - more so than any other design.  In the side view of the field lens, the curved portion faces the eye lens.

If there are any eyepiece experts out there, could you chime in on this.  The B6 eyepiece came with my Monolux-branded Asahi 60/800.

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  • bertele.jpg
  • bertele2.jpg
  • bertele diagram.jpg
  • B6 eyepiece.jpg

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#2 deSitter

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Posted 17 February 2017 - 11:04 AM

There are several Bertele designs - yours is listed here.

 

http://www.quadibloc...ience/opt04.htm

 

-drl



#3 CharlieB

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Posted 17 February 2017 - 11:50 AM

I've seen that very useful chart.  Yes, there are more involved (and wider angle) Bertele designs.  Here is the full chart I usually refer to.

 

www.gorin.it/extra/Oculari.pdf


Edited by CharlieB, 17 February 2017 - 11:51 AM.


#4 bremms

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Posted 17 February 2017 - 11:58 AM

Charlie,  I have the same eyepiece. Mine came with a Asahi 50 x 600mm. It's a decent EP, far better than an H 6mm. Took mine apart and saw the same. Thought it is a type of Plossl or reverse Kellner. the eye lens looked like a singlet or a thin doublet, it looks like two groups. 



#5 CharlieB

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Posted 17 February 2017 - 12:04 PM

It's impossible to tell the structure of the eye lens without destroying the eyepiece.  Heisenberg at his best.

 

It's as sharp, or perhaps a bit sharper, than my . 965 University Optics 6mm orthoscopic



#6 deSitter

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Posted 17 February 2017 - 12:43 PM

If you shine a laser into the eyepiece, you may be able to count the internal surfaces by the scattering of the laser beam at the entry and exit points. Also you can examine the eyepiece in very bright light with a magnifier and get some idea of convexity and concavity of the internal surfaces.

 

-drl


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#7 CharlieB

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Posted 17 February 2017 - 12:55 PM

Thanks.  I'll give that a try.



#8 bremms

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Posted 17 February 2017 - 02:53 PM

It's a very rare eyepiece..  It should fetch as much as the vaunted Unitron tray light...  Oh well, my Tinsley cass cost about the same as a tray light. :lol:


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#9 Bomber Bob

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Posted 17 February 2017 - 03:21 PM

:funny:



#10 deSitter

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Posted 17 February 2017 - 03:38 PM

Charlie how did you come by this eyepiece?

 

-drl



#11 strdst

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Posted 17 February 2017 - 04:04 PM

It's a very rare eyepiece..  

Rare as hen's teeth

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#12 terraclarke

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Posted 17 February 2017 - 04:06 PM

I guess that accounts for why I have never seen any hens with teeth! I obviously have not seen everything. :lol:
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#13 CharlieB

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Posted 17 February 2017 - 04:43 PM

It's a very rare eyepiece..  It should fetch as much as the vaunted Unitron tray light...  Oh well, my Tinsley cass cost about the same as a tray light. :lol:

Actually, it's a well-done eyepiece.

 

This one is rare.

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  • zeiss mono 6mm.jpg

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#14 levidog2

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Posted 17 February 2017 - 04:44 PM

I have a couple of these, they came with my Asahi Pentax 60mm x 800mm and the other with my Asahi Jupiter 60mm x 800mm, very nice eyepieces. I will keep these-

Frank



#15 CharlieB

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Posted 17 February 2017 - 04:44 PM

Charlie how did you come by this eyepiece?

 

-drl

It came with my Monolux branded Asahi 60/800.


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#16 deSitter

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Posted 17 February 2017 - 04:53 PM

Does it have any virtues compared to say a typical Kellner that works fine with slow refractors? One of the Bertele designs has the field stop coincident with a lens surface, which would be hard to stomach! Every little piece of dust would be in sharp focus.

 

-drl



#17 CharlieB

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Posted 17 February 2017 - 05:00 PM

No, it doesn't seem to be an exceptionally fine eyepiece, just a very good one.  There was a speck of flaked paint on the convex side of the field lens that was very noticeable (which is why I took it apart), so perhaps you are correct.



#18 bremms

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Posted 17 February 2017 - 10:13 PM

 

It's a very rare eyepiece..  It should fetch as much as the vaunted Unitron tray light...  Oh well, my Tinsley cass cost about the same as a tray light. :lol:

Actually, it's a well-done eyepiece.

 

This one is rare.

 

We had one in our collection in college. Used it with a 6" F15 Brashear refractor. Very sharp over about a 20 degree field. Like a soda straw.

Really too much magnification for the 6" F15. Tried it in my RV6 and Jupiter looked good. The narrow FOV even compared to an Ortho  made it hard to use.


Edited by bremms, 17 February 2017 - 10:19 PM.



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