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The ultimate planetary eyepiece design?

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#51 Jon Isaacs

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Posted 22 January 2020 - 08:09 AM

It is not the case.

 

The comparisons I have run have been between the wide field Leica, Zeiss, Swarovski eyepieces against the EPs from Japan and fromTaiwan.

The one group has been for the focus lengths around f=17mm, and the other for the focus lengths around 10mm.

 

The winners in resolution and contrast have been the spotting eyepieces from Leica and Zeiss, leaving those from Japan and Taiwan behind. The Swarovski have found their honorary place in the middle.

 

So, I have parted with some stuff from the Far East manufacturing, keeping the EPs arsenal below fifty.

 

Best,

JG

 

It's been said a number of times that the best planetary eyepiece is the eyepiece that's in the best planetary telescope.  I calculate that you are evaluating these eyepieces at 44x and 75x. 

 

I am not one who evaluates planetary views at 44x or 75x.. even in a 60mm scope.  

 

:shrug:

 

Jon


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#52 j.gardavsky

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Posted 22 January 2020 - 09:33 AM

It's been said a number of times that the best planetary eyepiece is the eyepiece that's in the best planetary telescope.  I calculate that you are evaluating these eyepieces at 44x and 75x. 

 

I am not one who evaluates planetary views at 44x or 75x.. even in a 60mm scope.  

 

shrug.gif

 

Jon

Sorry, Jon

 

it went away off topic, I can test the short orthos just visually at the moment,

JG



#53 Astrojensen

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Posted 07 February 2020 - 12:25 PM

Yesterday evening was stunningly clear here, with reasonably okay-ish seeing, with occasional moments of very good sharpness. I had my 152/1200mm APM ED outside, looking at the Moon. I didn't do any super serious observing, but experimented a lot with different combinations of prisms, barlows, GPCs, binoviewer and eyepieces.

 

At one time, I took out my Dollonds for a swing. One particular combination stood out: A 25mm Dollond + a long 3x GSO barlow, resulting in a focal length around 8mm (not measured exactly, but in the ballpark). The image was extremely sharp and the field startlingly free from glare and stray light. It was remarkably comfortable to look through. The field was rather small, but didn't feel cramped, perhaps due to the very comfortable ergonomics. 

 

I compared it with a 9mm UO volcano top and an 8.8mm ES82, as well as a 25mm UO VT in the 3x barlow and while all showed essentially the same, as far as I could see in the not so perfect seeing, the Dollond was by far the easiest and friendliest to look through and always seemed to have less glare and the brightest view, although the brightness COULD be an illusion from the small field. Outside the field stop, it was absolutely, perfectly black. 

 

For someone wanting an extremely comfortable eyepiece for prolonged observations of difficult planetary details, a Dollond in a barlow seems to have much to recommend it. As my experiment shows, it works splendidly well in an f/8 telescope. The telescope should ideally be driven, but that's not a major issue today. 

 

 

Clear skies!
Thomas, Denmark 


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#54 TG

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Posted 08 February 2020 - 02:08 PM

I'm not sure minimalism matters if the polish and coatings are top notch. I have compared a Pentax XO 5mm and Pentax XW 5mm and it was very hard to see any difference. I wanted the XO to win but in the end, I just wasn't sure.
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#55 luxo II

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Posted 09 February 2020 - 09:57 PM

Yesterday evening was stunningly clear here, with reasonably okay-ish seeing, with occasional moments of very good sharpness. I had my 152/1200mm APM ED outside ... One particular combination stood out: A 25mm Dollond + a long 3x GSO barlow, resulting in a focal length around 8mm

So... 150X. That's still not a lot for a 150mm refractor...


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#56 lylver

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Posted 13 February 2020 - 07:57 AM

/.../

 

At one time, I took out my Dollonds for a swing. One particular combination stood out: A 25mm Dollond + a long 3x GSO barlow, resulting in a focal length around 8mm (not measured exactly, but in the ballpark). The image was extremely sharp and the field startlingly free from glare and stray light. It was remarkably comfortable to look through. The field was rather small, but didn't feel cramped, perhaps due to the very comfortable ergonomics. 

Just retro-engineered a Huyghens Mittenzwey eyepiece : dismounted and mesured thickness and focal length of lenses.

At f/30, behind a Dakin type barlow on an achromat : +/-25° perfectly corrected with strehl over .95 in achromatic range. (complete system)

hm20.jpg image.png HM20j.png  oc40.jpg

Made with high index/low dispersion baryum/lanthanum, this eyepiece has no coma, no astigmatism but balanced spherical/chromatism that big a f/D lower much.

FOV is limited by construction, a classic barlow matches well.

Liechtenknecker seems to be one one the last instrument designer to create a serie for its Solar/Planetary "AK" refractors and others.

 

Around 1886 Mittenzwey developed a new type of eyepiece as a modification of the Huygens eyepiece, which was later named in his honor. Hartmann & Braun in Bockenheim (now Frankfurt am Main) were the first to manufacture such eyepieces, sent three copies to Nikolaus von Konkoly, in Hungary, and exhibited two such eyepieces during the exhibition of scientific instruments, apparatus and specimens produced in 1886 at the 59th Assembly. A German naturalist and doctors were held in Berlin. Konkoly provided the only contemporary description of these eyepieces: although Mittittenzwey himself published a small work on eyepieces in 1886, he only mentioned their optical theory. Mittenzwey eyepieces are still available today for telescopes (amateurs)


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#57 Mark Harry

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Posted 15 February 2020 - 03:40 AM

A knowledgeable co worker mentioned he was acquainted with David(?) Rank, who was tied in with Edmund somehow, and they came up with the Rankin eyepiece???
He had very high opinion how that eyepiece design worked with long focus scopes for planetary.
I'm relying on memory of a 2 week old conversation, so I might be off some.



#58 Starman1

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Posted 15 February 2020 - 12:56 PM

It was speculated for many years that "RKE", an eyepiece designed by David Herr Rank for Edmund, which resembled a reverse Kellner design, stood for: "Reverse Kellner Eyepiece" or "Rank Kellner Eyepiece".

But then it was revealed by Edmund that it stood for "Rank/Kaspereit/Erfle" pointing to its derivation.

See: https://en.wikipedia...ki/Eyepiece#RKE

However, its design appears to be a slightly re-spaced version of one of König, so a slightly different interpretation could lead to: "Rank König Eyepiece".

It's a design better at f/8 and longer than in faster f/ratios.


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#59 luxo II

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Posted 16 February 2020 - 03:22 AM

I’ve had a set of RKEs ... long gone, replaced by vixen LV’s (also mostly gone).

Back on topic...

A good set of orthos remain the benchmark to beat. A while back I suggested modern glass types may allow an eyepiece with 2 air-glass surfaces and 50 degree AFOV at modest focal ratios, say f/10 or longer.

Initial attempts suggest this is achievable with 4, or maybe 3 cemented elements. Anyone else pursuing this idea ?

Edited by luxo II, 16 February 2020 - 03:26 AM.


#60 BKSo

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Posted 16 February 2020 - 07:21 AM

That means a lens with diameter almost as big as its focal length, which is ambitious. If that could be done I'd like one for hunting DSO :)




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