RKE eyepiece

[aerohound73]

Hello, Ive noticed in buy and sells rke eyepieces.They always sell fast.Is there anything special about them and how are the optics ?What your opions.Thanks

[John]

They are a fairly simple design that were marketed by Edmund Scientific quite a while back. I believe they are a 3 element, 2 groups design with the eye lens being a singlet and the field lens being a doublet.

They are reputed to be good eyepieces in slower scopes.

[Merlin66]

The RKE 28mm is a very nice good eye relief eyepiece for any scope above say f7.

They are still available from Edmund Optics.

http://www.edmundoptics.com/microscopy/eyepieces/edmund-optics-rke-precision-eyepieces/2075

http://www.edmundoptics.com/microscopy/eyepieces/edmund-32mm-rke-wide-angle-erfle-eyepiece/2074

[michael.h.f.wilkinson]

RKE stands for reverse Kelner, I believe. Simple designs like these can be good, but they would not beat a Plossl of similar fit and finish.

[Merlin66]

No,

Edmund Optics- indicated that RKE stands for Rank, Kaspereit, Erfle, the three designs from which the eyepiece was derived.

[E621Keith]

No,

Edmund Optics- indicated that RKE stands for Rank, Kaspereit, Erfle, the three designs from which the eyepiece was derived.

Interesting, I thought it stood for Rank Kellner Eyepiece.

[John]

Interesting, I thought it stood for Rank Kellner Eyepiece.

I've heard all sorts of views on what it means - which is why I didn't venture an explanation in my post above !

[michael.h.f.wilkinson]

No,

Edmund Optics- indicated that RKE stands for Rank, Kaspereit, Erfle, the three designs from which the eyepiece was derived.

Interesting. Looking at the design it is a bit hard to see how this derives from the Erfle, or the 6-element version due to Kaspereit.

[Merlin66]

Michael, I agree....but the Edmund quote from Wiki I've seen elsewhere.....

http://en.wikipedia.org/wiki/Eyepiece

See section 2.11

[John]

Here is the Edmund Optics web page on the RKE eyepieces:

http://www.edmundoptics.com/microscopy/eyepieces/edmund-optics-rke-precision-eyepieces/2075

The technical images tab shows a diagram of a 3 element, 2 group design.

[michael.h.f.wilkinson]

Given that price list I would say: overpriced by a large margin. I mean 80.75 euro for an 8mm EP with 45 deg FOV (and a reverse Kelner design, whatever they say). I cannot see this beat an orthoscopic (which mysteriously is cheaper from EO). EO also have a weird idea of specs if they say orthoscopics have "very wide, flat fields" (44 deg in their spec). The RKE might have desirable properties for certain optical instruments, such as lack of distortion (but so has the ortho), but I would go for a TV Plossl (4.25 euros more than the 8mm RKE) or a BGO/BCO any time. The RKE is not better than the ortho in terms of eye relief either: the 21 mm sports only 13mm eye relief.

[Ohmless]

This is a short blurb on RKE eyepieces from Phillip Harrington's Starware(awesome astro gear guide BTW)

RKE

From Edmund Optics (not to be confused with Edmund Scientific Co.) comes

this twist on the Kellner eyepiece. Instead of using an achromatic eye lens and

a single-element field lens, the RKE (short for Rank-modified Kellner Eyepiece

after its inventor, Dr. David Rank) does just the opposite. The computer-

optimized achromatic field lens and single-element eye lens combine to out

shine the Kellner in just about every respect. However, images are not gener-

ally as sharp as through orthoscopic or Plössl eyepieces.

in the states, there is a bit of a following for the 28mm lens

[michael.h.f.wilkinson]

This is a short blurb on RKE eyepieces from Phillip Harrington's Starware(awesome astro gear guide BTW)

RKE

From Edmund Optics (not to be confused with Edmund Scientific Co.) comes

this twist on the Kellner eyepiece. Instead of using an achromatic eye lens and

a single-element field lens, the RKE (short for Rank-modified Kellner Eyepiece

after its inventor, Dr. David Rank) does just the opposite. The computer-

optimized achromatic field lens and single-element eye lens combine to out

shine the Kellner in just about every respect. However, images are not gener-

ally as sharp as through orthoscopic or Plössl eyepieces.

in the states, there is a bit of a following for the 28mm lens

I thought I had heard it was a Kelner adaptation in an ancient EO catalogue (still get one each year). Rank-modified or Reverse Kelner Eyepiece: Same difference . I have no objection to acknowledging the inventor of course. I do wonder why they state that the Ortho is sharper, and offer those for less. Why buy an RKE, in that case (45 deg vs 44 deg FOV is hardly a selling point).

[E621Keith]

I thought I had heard it was a Kelner adaptation in an ancient EO catalogue (still get one each year). Rank-modified or Reverse Kelner Eyepiece: Same difference . I have no objection to acknowledging the inventor of course. I do wonder why they state that the Ortho is sharper, and offer those for less. Why buy an RKE, in that case (45 deg vs 44 deg FOV is hardly a selling point).

May be the RKE was made in the USA while the Abbe ortho was made in Japan. Some people on CN cares A LOT where an item was made and believe everything made outside USA is substandard. Just look at some comments about Takahashi vs Astro-physics or TEC apo.

[crazyjedi]

This has been a very interesting (if confusing in nomenclature) thread. The only comment I've heard about the RKE's was that they were an old design that has been superceded by the plossl design.

Is there a concensus on what RKE stands for? there seem to be many opinions that have web based evidence to back them up.

[crazyjedi]

Ok here's my ten pence worth... (well actually Terence Dickinson and Alan Dyer's)....

RKE ---Rank modified Kellner for Edmund.

They were apparently not true Kellners (having the lens arrangement reversed) but did offer an improvement over original Kellners. They don't measure up to plossls though.