Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

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realflow100 United States of America
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Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

#1

Post by realflow100 »


Says plossl 17mm on the side. but the field of view is fairly wide. and the focal length very well matches a 24mm eyepiece. (4mm approximately exit pupil with a 70mm F6 refractor)
but the design internally is more like a singlet and doublet. like a kellner. but backwards. The doublet is facing the objective. and the eye-lens singlet is facing the eye.
The more convex side of both the singlet and doublet are on the inside.
The singlet is only completely flat on the eye-lens side so its plano-convex
and the doublet is slightly convex on the side facing the telescope objective.
Eye relief is low but not too low. Need to get uncomfortably close to see the full field of view. eyelashes occasionally touching parts of the edge/rim around the eyepiece. though I might just have spectacularly long eyelashes.
Had to replace the rubber eye-guard because it was disintegrating and falling apart. and a disassembly and clean of the inner lens surfaces (Grimy and some spots visible inside) now its clean enough to be usable at least.
Field of view is not too bad. average. its decent. maybe 50-60 AFOV not sure exactly.
Field sharpness is lacking at the edges.. Not great at the edges. though I dont see any additional CA caused by the eyepiece. just some blurring/out of focus look at the edges. Center is sharp though.
Only see CA from my telescope being an achromat/doublet refractor.

Here are some pictures of it. Any idea what this mystery eyepiece is supposed to be And its best use cases? Its DEFINITELY not a plossl. and DEFINITELY not 17mm.
Image
Image
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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realflow100 United States of America
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Re: Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

#2

Post by realflow100 »


any ideas? I measured the exit pupil to be right about 4mm approximately. so its definitely either a 24mm or 25mm eyepiece. but im not sure exactly which. since im using a 70mm F6 telescope.
but what is the eyepiece actually supposed to be? whys it got a 17mm plossl label when its clearly not a plossl?
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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WilliamPaolini United States of America
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Re: Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

#3

Post by WilliamPaolini »


IME the label on the eyepiece is not a guarentee of the optical design. I have taken apart labeled Kellners that were Plossls inside, Orthos that were Plossls, even a Modified Achromat that was a Plossl. Also took apart a vintage Celestron Erfle that was what looked to be Goerz design of 1-3-1. So you cannot really depend on the name on the eyepiece.
Exposed Celestron Erfle.jpg
-Bill

U.S.A.F. Veteran - Visual Amateur Astronomer since 1966 - Fully Retired since 2019
8" f/5 Newt - Lunt 152 f/7.9 - TSA 102 f/8 - Vixen 81S f/7.7 - P.S.T. - Pentax 65ED II - Nikon 12x50 AE
Pentax XWs - Baader Morpheus - Takahashi LEs - Edmund RKEs - BST Starguiders - 6ZAO-II/5XO/4Abbe
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DeanD Australia
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Re: Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

#4

Post by DeanD »


I had a couple of eyepieces with similar markings that were (oddly) included in the box of an EQ-4 mount that I bought ages ago. Not sure where they are now (they weren't top quality)...
There are a lot of oddly named, cheap eyepieces out there and often included with entry level telescopes. I have even seen Ramsden or Huygenian designs (heaven only knows why!) included with basic Celestron scopes. Some have plastic lenses too.
I suspect you are right and it is some sort of reverse Kellner. In any case it would not have been designed for, and will probably struggle with an f6 scope like yours, and it would be better suited to (say) f8 or even longer.

All the best,

Dean
Telescopes: 12" f5 dob, Celestron CPC800, 150mmf5 Celestron achro, Tak TSA102, TV76, ETX125...
Binos: Steiner Wildlife XP 10x26, Swarovski 8x30 Habicht, Zeiss SFL 8x40, Vanguard Endeavour 10.5x45, Fuji FMTR-SX 10x50, Tak 22x60, Orion Resolux 15x70
Eyepieces: way too many (is that possible?), but I do like my TV 32mm plossl, 13mm Nagler T6, 27mm Panoptic and 3-6mm Nagler zoom, plus Fujiyama 18mm and 25mm orthos and Tak 7.5mm LE
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realflow100 United States of America
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Re: Mystery 1.25" 25 or 24mm reverse kellner/RKE eyepiece?

#5

Post by realflow100 »


Thats a bummer. its not a particularly useful eyepiece :(
the eye relief is too short to be comfortable for me (I really need very long like 20-25mm eye relief or more to be comfortable even without glasses) and unusably short if I use my glasses.
My astigmatism is too severe to use any large exit pupils without wearing my glasses. its essential for me to wear glasses at large exit pupils (over 1.5mm) but 1.5mm or smaller exit pupils i dont see a noticable difference.
The field of view is average/ok but the edges are very blurry and not particularly usable.

I have a 20mm svbony goldline clone eyepiece and the edges of that are even worse. Unusable. Horrible vomitingly disgustingly bad blurry edges. the 25mm reverse kellner eyepiece isnt nearly as bad. but its still pretty poor. stars get blurred to non-existence past the central like 50% of the image. and dim stars disappear past the central 25% of the image.

No point in a wide field of view when its horribly blurry and unusable.

but my 40mm plossl gives me fantastic almost perfect edges. Perfectly acceptable and usable. stars still look like stars to the very edges. its very good to use with a barlow too. especially with the exceptionally long eye relief its comfortable with glasses so I have a sharp view of the stars.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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