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32mm RKE wide angle Erfle?

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#26 BillP

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Posted 30 November 2012 - 12:18 PM

"RKE" stands for "Rank Kellner Eyepiece". It is pretty much a standard Kellner reversed.


Rank, Kaspereit, Erfle, per filing for the RKE trademark ( click on document called UNCLASSIFIED ). Plus, when you look at a standard Kellner design it is a plano-convex doublet followed by a convex-plano singlet. And RKE is a double-convex singlet, followed by a convex-concave doublet. So both groups use different curve directions than the Kellner. When you look at the field doublet in an RKE, it is the same configuration as the field doublet in an Erfle or a Kaspereit design. The Kaspereit was developed from the Erfle. The upper 2 doublets of the Kaspereit are both double convex doublets. So the RKE is like removing one of those doublets, and replacing the other with a same curved singlet. So overall, looks much more like a hybrid of the Erfle and Kaspereit designs than it does at all like a reversed Kellner at all. The only common thing between the RKE and the Kellner is that they both are 3 elements in a 2-1 (or 1-2) configuration. The curves are all wrong between them, unlike the Erfle and Kaspereit.

#27 jrbarnett

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Posted 30 November 2012 - 12:34 PM

Yes, but we didn't know about that document in early 2011, and have discussed it subsequently in a different thread, after the post you're responding to. :grin:

- Jim

#28 Sarkikos

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Posted 30 November 2012 - 12:42 PM

"It is sharper on axis than any plossl, 1RPD, Proxima,etc.."


Damning with faint praise? :thinking:

Mike

#29 Sarkikos

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Posted 30 November 2012 - 12:53 PM

http://www.astromart...?article_id=793

"There is a place for all of these designs. It depends on what you want out of your set of eyepieces."

I wonder if that includes Televue designs as well? :question:

Mike

#30 BillP

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Posted 30 November 2012 - 02:29 PM

Yes, but we didn't know about that document in early 2011, and have discussed it subsequently in a different thread, after the post you're responding to. :grin:

- Jim


OMG...look how old that post was. My bad! I never check the dates and assume posts are relatively recent. Sorry I missed that :rainbow:

btw, you still have the 1 RPD? I need a pic of it :grin:

#31 Mark Swanson

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Posted 30 November 2012 - 09:28 PM

Yes. Televue too. I don't think that you have to pay Televue and Pentax prices to get good glass. However, I am all for free enterprise.

#32 Mark Swanson

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Posted 30 November 2012 - 09:29 PM

I no longer have the 1RPD. No pics either.

#33 Dave Ittner

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Posted 30 November 2012 - 11:52 PM

what is the 1RPD?

#34 jrbarnett

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Posted 01 December 2012 - 12:24 AM

"1 revolution per day"

A rebrander of Chinese eyepieces, sold through Astrobuffet. Basically the same eyepiece as the 30mm BW Optik UWA and others from the same maker. All are clones of a Japanese eyepiece called the "Widescan III".

1rpd ST80: http://www.astrobuff...b/30mm_vert.jpg

BW Optik: http://www.cloudynig...83bw1-large.jpg

Widescan IIIs: http://www.astromart...99/358231-1.jpg

Agena UWA: http://agenaastro.co...b33525d08d6e...

Very poor edge correction in fast scopes.

- Jim

#35 Dave Ittner

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Posted 01 December 2012 - 12:39 AM

thanks. I learn something new every day.






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