The 28mm RKE in action

February 20, 2017

Still cloudy here, but we got a gap earlier this evening, a persistent sucker hole right over Orion, and I got a whole 10 minutes of observing in. I was using the Bresser AR102S Comet Edition and for eyepieces the 20mm 70-degree that came with it, and my new 28mm RKE from Edmund.

Both eyepieces will just fit in the belt of Orion, with Alnitak and Mintaka in the last 5% or so of the field on either side. So the belt turns out to be a good test of edge characteristics. The 28mm RKE is way sharper at the edges, by the way. You might think that its 45-degree apparent field of view would feel positively claustrophobic after the 70-degree field of the Bresser eyepiece.

But it doesn’t, because of the magical floating stars effect. It’s real! It’s one of the most arresting things I have experienced in almost a decade of observing. As your eye gets closer to the eyepiece, you begin to be able to see the image. As you move in until you can see the entire field, the point where the eyepiece barrel disappears from view coincides exactly with the point where you are far enough to see the field stop of the eyepiece. If you hold up right there, you see the image created by the eyepiece floating in space, with a thin ring of unresolved darkness around it, which if you back out a bit will be the eyepiece barrel, and if you move in a bit will be the eyepiece field stop. In either case, the eye relief is great enough that you can still see the rest of the scope in your peripheral vision, past the thin ring of darkness at the edge of the field.

I have never, ever seen anything like this. It is exactly as cool and immersive as the legends have it. I can imagine building a whole observing kit consisting of this one eyepiece and a series of Barlows of various magnifications.

Anyway, if you have been on the fence about this eyepiece like I was, just get it. It’s amazing.


  1. Wow, very cool! Great report. Looking at the website, they sell the EP “mounted” for $85 and “unmounted” for $62.50. What the heck does that mean? Which one did you get?

  2. Mounted means a normal, complete eyepiece, ready to observe with. Unmounted means just the glass, so you can mount the lenses in a tube of your own if you like. I notice that they also sell tubes. I assume this is for people who like to tinker. I got the mounted one.

  3. Matt,
    Thanks for the timely field test and glowing review. Deal sealed. I am ordering one today.


  4. Matt,

    The specifications for this eyepiece are actually:

    Focal length 28.7 mm
    Field Stop: 23.3 mm

    With these specs., the apparent field is actually 46.5 degrees. My 28 RKE bears this out.

    What I really think would be interesting, but not cheap, is to try the 32 mm, 2″ Erfle: http://www.cloudynights.com/page/articles/cat/user-reviews/a-review-of-the-31-nagler-versus-the-32-edmund-erfle-r2422

    As much as I love my TeleVue Naglers and 13 Ethos, strangely, if I had to give them all up and go back to older wide field designs, I could still find contentment.

    While not wide fields the RKEs deliver sharp views that I think (some disagree) are on par with any eyepiece.

    John O’Hara
    Oil City, PA

  5. I’ve had a couple more short sessions with the 28mm RKE, including one doing some daylight spotting. My findings are as follows:
    – the Bresser AR102S Comet Edition really plays well with this eyepiece. It shows a LOT less distortion than the came-with 20mm 70-degree. I think it’s a hair sharper on-axis, and way sharper near the edge of the field. Makes sense that an eyepiece designed to ship out with 4″ f/4 AstroScans would perform well in a 4″ f/4.5 unobstructed scope.
    – the eyepiece does the magic floating image trick during the day. Just as mesmerizing.
    – I need more Barlows of different magnifications. I was totally serious when I wrote that you could design an observing kit around this eyepiece. Especially for the AR102S, which doesn’t like high powers, the 28mm RKE plus a 2x and a 3x Barlow would be a superb and compact travel kit. Although I’d probably bring at least one other just in case – taking only one eyepiece on a trip seems like unnecessarily tempting the gods of payback.

    It’s no exaggeration to say that I plan on having this eyepiece out with me at every observing session for the foreseeable future. It’s that good.

  6. […] word about the 28mm RKE. It is simply the most comfortable eyepiece I’ve ever used. There are several factors that […]

  7. […] Plossl, which in the XT4.5 yielded 28x, 32x, and 75x, respectively. Once I was rolling, I used the 28mm RKE almost exclusively. The reputation of this legendary eyepiece is well-earned; for the kind of […]

  8. […] to grab gear for a Messier Marathon or they’d shoot me, I’d grab that scope, the 28mm RKE, a folding chair, and a water bottle, and be out the door with minutes to spare. You can find the […]

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