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Origins of Ploessl Eyepiece

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#26 SteveTheSwede

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Posted 17 January 2013 - 05:07 PM

When a foreign word is pronunced incorrectly often enough and long enough by native speakers of English, it will become a de facto English word. Is Plossl one of ours now?

:grin:
Mike


Oh, you mean as opposed to foreign words pronounced correctly, like for example... um.... eh...
:grin:

Steve

#27 Sarkikos

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Posted 17 January 2013 - 05:15 PM

Hmmm.... :scratchhead: Not so much around here, I guess, except mostly by the foreigners.

:grin:
Mike

#28 RogerC

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Posted 17 January 2013 - 05:23 PM

Hi, Don.

My paper attempts to trace the developments back to Ploessl himself, using all original documents. The earliest are all in German, a few in French, and the most recent in English. I have translated the German and French into English where needed. It is for readers of the article to decide whether it is convincing.

GS Ploessl himself certainly designed no eyepieces in the modern sense. He was a fabricating optician, mainly focused on building microscopes. Rather, he replaced the plano-convex singlets of the Wilson-type eye-loupe with cemented plano-convex achromats. That is, he built in essence achromatized Ramsden eyepieces. But they still had a large air-gap, as far as I can tell. A few of these eyepieces exist in Europe, but I have not had an opportunity to examine any. My information is derived from 19th century descriptions/illustrations as indicated in the paper. They were low-power microscope eyepieces.

It was Albert Koenig, apparently, the great Zeiss designer who around 1915 in seeking for a better eyepiece for military sighting instruments, removed the unneeded airgap and began experimenting with use of high-index of refraction glasses and "bending" of the lens doublets to achieve higher performance. Similar developments happened at Goerz and elsewhere.

Many eyepieces of similar performance (and various usable field sizes) were developed between about 1890, starting with the Abbe Ortho, leading through WWI, with Erfle's various designs, and on to WWII. Koenig's own designs as shown by his American & German patents, and German publications (cited in the paper) centered on binocular or gunnery eyepieces of large eyerelief (as understood then). The most advanced 2-2 eyepiece of Koenig was patented in the years around 1940 in Germany and the US. Koenig began calling the design "the orthoscopic according to Ploessl" as a way to distinguish it from "the orthoscopic according to Abbe." All this is discussed and documented from orignal sources in the paper.

Many many eyepieces of this general type (2-2) were developed and used in military equipment such as tank telescopes, dial-sights, binoculars, etc. in WWII. They can be seen clearly in WWII documents in my collections. The most advanced, such as one devised by Chester Brandon, where asymmetrical 2-2 forms similar to Koenig's most advanced type. This is the type of the Brandon still today, I'm told. Other forms were simpler, symmetrical 2-2 types.

It was after the war that the "Ploessl" as we know it for amateur astronomers took off, through the work of Brandon, Jean Texereau/Clave, and finally Al Nagler. But the details and documentation are best seen in the article itself.

In the 50s and 60s in the US, since the name Ploessl was still very unfamiliar, people such as Edmund sold WWII surplus eyepieces (derived from military equipment) under such names as Kellner Type 3, etc. But they were Ploessls of various types, and some indeed were Brandons, I'm told.

I will be very glad to see Bill's book soon.

Cheers,
Roger

#29 Starman1

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Posted 17 January 2013 - 06:57 PM

Roger,

Will you be suggesting changes to all the Wikipedia pages about Plössl?
Because there are innumerable pages that are then incorrect if what you assert is true.

If you send me an email address in a PM, I can send you Chris Lord's email address, too. I think he and some of his cronies would like to be updated since they are responsible for many "documentations" of Plössl's work.

Clavé's literature accompanying their eyepieces (I bought several in the '70s) mention Plössl, but never mention König as a source for the closely-spaced 2:2 design.

I guess the entire world has been wrong for well over a century.

#30 Svezda

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Posted 18 January 2013 - 01:35 AM

I read in one blog that himself pronounces Nagler somewhere between an "ah" as in "Bach" and an "a" as in "bat." That would be about right. But "Plahsl" is just plain wrong.:grin:


Haven't we had this argument err, discussion before on CN? I've asked Al at NEAF exactly how to pronounce his name and his response was NAY-gler. I thanked him for clearing that up for me since our astronomy club members were curious. We had one of our members who constantly pronounced it as NAG-ler which Al said is not the way his name is pronounced. It's a name and the holder of the name gets to pronounce it the way they want. Al chooses to pronounce it NAY-gler. Who are we to say he's wrong? :grin:

Not being a German language expert but having studied it for four years for my first bachelor's degree, I'd bet that Al's pronunciation indicates that the surname originally used an a-umlaut but got anglicized to be spelled without it (just using the 'a').

Regarding 'Ploessl', sure, no one can force you to pronounce it correctly, but considering it is a surname and, as the poster quoted above pointed out, the owner of said surname has a right to say it as he likes, well, Mr(Dr.?) Ploessl would have pronounced his name as was indicated earlier - 'Plerssl'. This is as close as you can get, I think, with the English alphabet.

#31 cjc

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Posted 18 January 2013 - 02:59 AM

Roger, I appreciate that you cannot reproduce the article so many thanks for your summary.

#32 BillP

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Posted 18 January 2013 - 10:02 AM

...König as a source for the closely-spaced 2:2 design.


Look at figure 4 from this 1915 Konig Patent -- http://ip.com/pat/US1159233

Look at figure #2 from this 1940 Konig Patent -- http://www.google.co...&dq=ininventor:"A...

**Sorry for the long paths...the URL function seems to not be working for me.



#33 RogerC

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Posted 19 January 2013 - 10:39 PM

Hi, Don.

It is not for me to "correct" other people's work. It is for other people to decide if I am correct, after reading the article and carefully weighing the evidence that I have tried to bring to bear. And there is much evidence from original documents.

Cheers and all the best,
Roger

PS We have tried to be similarly careful in the writing of our book, Telescopes, Eyepieces, and Astrographs (Willmann-Bell, 2012). All the best.

#34 Mak2007

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Posted 21 January 2013 - 11:20 PM

...König as a source for the closely-spaced 2:2 design.


Look at figure 4 from this 1915 Konig Patent -- http://ip.com/pat/US1159233

Look at figure #2 from this 1940 Konig Patent -- http://www.google.com/pate nts?id=gflYAAAAEBAJ&pg=PA2&dq=ininventor:&...

**Sorry for the long paths...the URL function seems to not be working for me.



Hi Bill,
So, are Brandons actually Konig's design?
Just wondering in good faith

#35 BillP

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Posted 22 January 2013 - 05:00 PM

I would say that there is no way to know (without lab tests). I hear lots of claims made about the eyepiece, like glass types used and such, but can get zero confirmation on it. I have asked Don to comment on if indeed the eyepiece uses several glass types, if it is non-symmetrical, and such, but no response. All that is on record from the manufacturer about their eyepieces is that they incorporate the original optical designs of Chester Brandon and have 4 elements. Kindof vague.

I have an 8mm at home. Not obvious how it comes apart. Has anyone taken a Brandon apart?? All this can validate is the arrangement, # elements, and the surface curves...not the glass types.

From a behavioral perspective, the off-axis of a Brandon acts more like a Konig than it does like a Plossl. Takes a much longer focal length scope to clean up its off-axis entirely...just like a Konig. Plossls clean up at much shorter focal ratios than do Konigs or Brandons.






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