86 replies to this topic

[elzopilote]

When reading about eyepieces, a lot of people speak passionately about RKE, with many mentioning it in the thread on the 10 best eyepieces of all time (specifically the 28mm RKE).  Can someone explain to me what the big fuss is with this one? And if I'm curious to try one for my 8" Dobsonian, which one would you recommend?

[MarkGregory]

Your post made me laugh. It is true, the 28mm RKE oculars have a stellar reputation and following. So much so that I went out and bought a set for Bino viewing. My analysis after using them.  No big deal. Not as great as what I expected. Nice, but not great. Now, let’s see how many people call me crazy. Lol 

[SandyHouTex]

The 28mm RKE has a peculiar thing where, when using it, the star field appears to float above the eyepiece.  That’s what makes it special.

[N-1]

I got the 28mm RKE for its well-known floating starfield effect, and it's definitely there. I've since come to appreciate this EP's performance in other respects, especially in long f-ratio optics. In those, the view doesn't just float, it's also very sharp and contrasty. The floating effect has been at it's absolute best for me when used in small-ish refractors in straight-through mode, under dark skies. At the right viewing distance, the instrument disappears completely, and the image blends into the background sky outside of the telescope. This has to be one of the very best presentations of a magnified image that are possible with eyepieces. But, you need the right conditions and some practice to really get the most from it.   

[TOMDEY]

AFOV 45 deg 3-elements in two groups. A "reverse-Kellner" computer optimized. Works fine with a slow feed. Otherwise rather ~meh~ Lot of hype when they 1st came out, because of the optimization. Nice for the price $90 still available new from Edmund Optics. They've been around a long time. I just think of them as decent Kellners. The rest seems just mystique. Just so much you can do with three elements.    Tom

[vtornado]

I bought an 8mm RKE for planetary.  IIRC an 8mm televue plossl was slightly better for lunar/planetary.

Tested in a f/5 dob.

 

You have sparked my interest though.  Next time the moon is out I will have another look.

Planets are up too early from me to get out of bed.

Edited by vtornado, 30 June 2021 - 07:04 PM.

[MisterDan]

The "floating" effect is not specific to RKEs.  It seems the requisites include long eye relief (perhaps very long) and large eye lenses with moderately (or significantly) convex outer (eye-facing) surfaces. Nikon's C-W 10x/22 microscope ocular might fit the bill, but I'm just guessing (never tried one).  Moderately/significantly convex eye-lens surfaces aren't very common among eyepieces.

 

Best wishes.

Dan

[coopman]

I bought the 28mm to see what was so great about it.  I was not impressed.  Used it once & sold it.

[N-1]

The "floating" effect is not specific to RKEs.  It seems the requisites include long eye relief (perhaps very long) and large eye lenses with moderately (or significantly) convex outer (eye-facing) surfaces. Nikon's C-W 10x/22 microscope ocular might fit the bill, but I'm just guessing (never tried one).  Moderately/significantly convex eye-lens surfaces aren't very common among eyepieces.

 

Best wishes.

Dan

See here

[naramsin]

Some other EPs have a similar effect. The decloaked Luminos 7mm are quite nice, esp. in binoviewers. The naked EP has a very narrow bezel that disappears when you are close enough to view the field stops. The star field just seems to float in midair as you approach the telescope. It's a really interesting effect, and for me it's a very comfortable way to view since I don't like to put my eyes agains the EPs if I don't have to. I've had limited opportunities this season, but the decloaked 18.2mm Delites seem to have something like this too.

[MisterDan]

See here

Thanks for that link!  I had not seen that thread.  Don's notes make sense.

 

Best wishes.

Dan

Edited by MisterDan, 30 June 2021 - 08:12 PM.

[alancraig]

See here

Yes! Post #17 by Starman1 in the link above seems accurate to me. I just started this hobby a few months ago and got the 28mm RKE early on to see what the fuss was about after reading about it on CN. The floating effect is real and presents a different type of view than I’ve had with other EPs in my small (but growing) collection.

Edited by alancraig, 30 June 2021 - 08:35 PM.

[jeffmac]

The Morpheus eyepieces with the eye cup down have a similar "floating" field of view. The first time I used my 12.5mm Morpheus, it was very obvious and kind of cool. After observing with it for some time now though, it seems like I don't really notice it any more. I guess I've become used to it.

[GOLGO13]

RKEs are better than people realize. But the 28mm is special. It is a bit of a novelty but super cool. I had the whole set and they were really nice

[GOLGO13]

RKEs are especially good for solar observation. They are decent eyepieces.

[Ernest_SPB]

For me "floating effect" looks like a factor when nothing to count from objective advantages.

Actually it is just 3-elements classic narrow angle eyepiece. 

For F5 Newton I'd selected eyepieces from 82-deg. series, depending from budget it can be Naglers or Explore Scientific 

[Jeff B]

This is indeed a very special eyepiece.

 

Need proof?

 

People have been arguing about it for over 40 years.

 

I personally find a pair of them much fun with my bino-viewer friendly refractors.  

 

I also very much like the Edmund 28mm Plossl as it gives a nice fat slice of that "floating effect" (but not quite the same) but handles the barlow elements in my viewers much better than the RKE version, which has excessive eye relief for me when used with barlows.

 

But I always recommend people at least try an RKE 28mm and see for themselves...pun completely intended.

 

Jeff

Edited by Jeff B, 01 July 2021 - 09:02 AM.

[j.gardavsky]

About the RKE

 

The legendary RKE 28mm eyepiece has been decloaked by Hernando in

http://hyperionzooml...3/?view=classic

 

Its lenses ordering is (field stop - 2 - 1), and so it is one of the König designs, like the Pl, W-Pl, E-PL, ZEISS West Germany, and Carl Zeiss West Germany eyepieces for the stereo microscopes (STEMI), and  microscope binoviewers (Axioskop, ...), manufactured since decades.

It is not any sort of reversed Kellner, sorry TOM.

 

The RKE letters abbreviate the names Rand, Rank, Kaspereit, and Erfle, some sources claim.

Dr. Rand Rank is regarded as the initiator of adapting the König design for the astronomy telescopes.

And before, the König eyepieces have been also used in the binoculars. Leica Ultravid 7x42 and DOCTER Nobilem 8x56, are examples.

 

The maximum floating view eyepiece in my collection offers the old "monocentric" Leitz triplet f=42mm. There is a nearly holographic Universe through this eyepiece.

 

The RKE eyepieces certainly belong in the EPs case,

and not only because they are cheaper to get than the Zeiss Pl, W-Pl, E-Pl,

JG

 

PS: Name corrected according to https://stargazerslo...7-rke-eyepiece/

Edited by j.gardavsky, 02 July 2021 - 04:23 AM.

[GOLGO13]

The 28mm has the disappearing diagonal effect, but the 21.5mm is the best of the bunch in my opinion. I had purchased the 21.5mm new from the current company and it was very good. Worth $85? well, maybe not. But it was very good. 

[MisterDan]

About the RKE

 

The legendary RKE 28mm eyepiece has been decloaked by Hernando in

http://hyperionzooml...3/?view=classic

 

Its lenses ordering is (field stop - 2 - 1), and so it is one of the König designs, like the Pl, W-Pl, E-PL, ZEISS West Germany, and Carl Zeiss West Germany eyepieces for the stereo microscopes (STEMI), and  microscope binoviewers (Axioskop, ...), manufactured since decades.

It is not any sort of reversed Kellner, sorry TOM.

 

The RKE letters abbreviate the names Rand, Kaspereit, and Erfle, some sources claim.

Dr. Rand is regarded as the initiator of adapting the König design for the astronomy telescopes.

And before, the König eyepieces have been also used in the binoculars. Leica Ultravid 7x42 and DOCTER Nobilem 8x56, are examples.

 

The maximum floating view eyepiece in my collection offers the old "monocentric" Leitz triplet f=42mm. There is a nearly holographic Universe through this eyepiece.

 

The RKE eyepieces certainly belong in the EPs case,

and not only because they are cheaper to get than the Zeiss Pl, W-Pl, E-Pl,

JG

 

Hello, JG.  I wondered if a long-focal-length monocentric might very well produce the same effect.  It's good to know that your 42mm does, indeed.

 

Best wishes and thanks.

Dan

[Thomas_M44]

I own a complete set of current-production Edmund RKE eyepieces (except for the now discontinued 15mm).

 

These current Edmund RKE eyepieces all use high quality Japanese lenses.

 

The unique presentation of the 28mm is enjoyable, but ironically I feel this distracts attention away from the fact that the Edmund RKE’s in general are remarkably sharp and high-contrast eyepieces which are truly exceptional for high-magnification planetary viewing.

 

During the last Mars opposition, I had several types of quality eyepieces which I utilized with my TV85 refractor, including sets of current production KK Fujiyama Orthos; TV Plossls and Edmund RKE’s.

 

The overall best results I obtained were using eyepieces in the 28mm to 15mm range in conjunction with a TeleVue 5X Powermate, which gave effective eyepiece  FL’s in a range between 5.6mm to 3mm. I also could insert a simple 1.5” long extension tube between the 5X Powermate and the eyepiece which would increase the Powermate magnification to approximately 6.2X,  and so an effective FL of 2.42mm when using a 15mm eyepiece.

 

Surprisingly, the most detailed and highest contrast views I was able to obtain of Mars was via using the 21mm RKE with the 5X Powermate with the 1.5” extension tube (6.2X) and so an effective FL of 3.4mm which gave me 177X in the 600mm FL TV85.

 

I also used various combinations of 15mm to 9mm range KK Ortho, TV Plossl and RKE eyepieces with a TV 3X Barlow,  and the results were VERY good, but this did not seem superior to the results using the longer FL eyepieces with the 5X Powermate, which also gave the considerable benefit of much more comfortable eye-relief.

 

Another nice combination was the 28mm RKE plus 5X Powermate with 1.5” extension tube for an effective eyepiece FL of  4.5mm, producing 133X in the TV85.

 

A few other surprising findings:

 

The *actual* AFOV of the RKE eyepieces is right at 50-degrees, and not the 45-degrees stated by Edmund.

 

The RKE eyepieces tolerate moderately fast f-ratios below f/6 much better than is generally assumed. The RKE is much more versatile in this respect than a Keller.

 

And so, the Edmund  RKE eyepieces in general are surely worthy of respect and serious consideration as high-resolution planetary eyepieces and also purportedly very good for double star viewing, which I hope to experiment with soon in comparison to my Abbe Orthos, Plossls and Keller’s

Edited by Thomas_M44, 01 July 2021 - 02:35 PM.

[asenov13]

I also love my RKE 28mm pair. What I love most about them is the cool tone they produce.Once I saw the Moon through a 28mm bino, I fell in love. In my eyepiece case I have only Zeiss, Leica and RKE.

This eyepiece pair is also the sharpest and brightest ever.

As a negative I will say the difficult eye placement because of the long eye relief.This eyepiece is the best price to quality ratio.

If someone is new to astronomy than they need to try at least once RKE 28mm.

[jeffmac]

According to the book Through The Telescope by Michael R. Porcellino the following info appears on page 70.

"In the 1970's, Edmund Scientific commissioned Dr. David Rank to develop an improved version of the classic Kellner eyepiece. Called the Rank-Kellner-Eyepiece (RKE), it consists of an achromatic field lens and a single double-convex eye lens."

[izar187]

A bit of marketing from back in the day there by Edmunds, from when Kellners were considered higher end.

The glass, curves and configuration really aren't Kellner, rather just 3 element.

 

I also agree that they do work better in faster focal ratios than Kellners.

But not as well as ortho's. IMHO

[Frisky]

One thing I'd add to the conversation is the floating effect is not impressive in a light-polluted environment, as you can see the ground surrounding the image. You need to go out into dark skies and set up on grass. Then, the floating effect looks really neat!

 

Joe