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Kellners - an underrated eyepiece design?


F15Rules
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I've been going through my eyepieces recently and trying to sort out which are keepers and which are surplus to my needs..do you ever feel that you over complicate things by having too many eyepieces? Surely that just means we spend more time swapping them in and out of our scopes and less time looking through them! :rolleyes:

Anyway, in having this sort out, I "re-discovered" a couple of Circle T volcano top Kellners, in 9mm and 12mm focal lengths. I don't know how old these eps are, my guess is at least 20 years old.

They are both very solid, with chromed brass barrels and matt black painted bodies, in the traditional (and very comfortable) volcano top design, a la late lamented Circle T ortho series. In fact they look very like the orthos.

Kellners are a very simple, 3 element design that has been around for years and years. In these days of exotic glass, multiple elements (of 7 or 8 different lenses sometimes), it seems that the humble Kellner has been grown out of, overlooked or just not considered.. and they  are CHEAP! - could there be some inverted snobbery here, whereby we don't consider something because it is SO cheap? :confused:

I also came across this thread from earlier this year..http://stargazerslounge.com/topic/178622-circle-t-kellners/ which I found interesting.

A Kellner is a quite simple, 3 element design. As such, there are fewer glass surfaces to absorb light, so light transmission is very good. Modern coatings also reduce internal reflections, and the field of view is normally around 40-50 degrees, maybe a little more, so they compare well in this regard to orthos.

I've tried out my 9mm and 12mm recently up against some good quality orthos I have, and to be quite honest I have been gobsmacked by how well they perform in my F10 and above refractors..very hard to see much difference versus some of the orthos.

I like them so much I've just bought a 40mm to use as a finder ep, and intend to fill in the gaps (I believe they are available in 18mm and 25mm lengths, probably others too.

Don't be put off by their low prices..the simple design means they do seem to do well on fainter stars and in fact I have a set of TS Optics 2" barrel RK (reverse Kellners) with 55degree fov in 26, 32 and 40mm which give lovely quite wide field views of clusters etc..the 32mm especially, is a peach.

So, next time you're tempted to pull the trigger on a high cost ep (and I'm talking to myself here too :p ), consider whether that old Kellner you have not used for years, if ever, isn't actually worth dusting off and giving a whirl..you might be pleasantly surprised -especially if your scope is F7 or longer.

cheers

Dave

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+1 on keeping it simple. I try to go out and manage with 3 EPs, and sometimes just 2, one in the focuser, the other capped and in my pocket.

What 2 ?   With my Dob, that's a 22mm Vixen LVW, and a 10mm Radian. Perhaps a bit restricted with only 55x and 120x at my disposal, but for DSOs, is ok, but not for planets on a good night of course.

What 3 ?  Again with my Dob, a 27Pan, 14 & 8mm Radians, for 44, 86 & 150x.

I suppose there's no 'simple' designs mentioned, because my Dob is F4.8.

But with my little Mak, almost anything works fine.

I've had loads of EPs over the years, way too many bought and sold, and a few regrets that I did sell.......and if Kellners are good for you, why not, best not to be swayed by 'fashion' but by what works for each individual, not others.

I do find that for 'outreach' like my clubs public events, people struggle with short eyerelief.  (Some of 'em struggle with 20mm ER  :huh: )

Note to self - check out stuff I've had stashed away for years.....

All the best, Ed.

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I agree with Ed on this, whatever you get on best with is what you should use :smiley:

I normally have 3 eyepieces with me for each session, one in each pocket and one in the focuser. 31mm Nagler, 17.3 and 12mm Delos. :smiley:

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I'd be interested in trying a quality 25mm Kellner on the Horsehead Nebula. Getting a few extra photons through would not go amiss with that object !

The other simple "oldie but goldie" design I've always wanted to try is the RKE which seem to get lots of enthusiastic praise from USA astronomers.

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John, the Reverse Kellners I have in 2" barrel by Teleskop Service really are good eps for the money. You can find them here:http://www.teleskop-express.de/shop/product_info.php/info/p2254_GSO-2--RK-eyepiece---32mm---55----maximum-transmission.html I have the set and really like them. I think the 32mm is the pick of the bunch, seems to have the best contrast, and sharp across about 75% or more of the field in my refractors. In my 6" achromat they deliver superb views of the Double Cluster for instance and the field seems wider than 55degrees to me, more like perhaps 58?

These are made by GSO who know their stuff and although the build cannot compare with TV for example, they are soundly made with good materials.

I remember observing M13 with a barlowed 26mm from this set to give me about x100 in my big frac and being pleasantly surprised at how many very faint stars "popped" into view :-)

cheers

Dave

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First of all, the Kelner is a very nice EP for a modest price. We use a 28mm Kelner from a defunct pair of Russian 7x50 bins as wide field EP in our kids' min-Dob, and it performs nicely, even in that fast scope (F/4.3 !). Regarding the numer of elements I would like to point out that it is the number of groups that determines most of the scatter (far more than the number of elements). Orthoscopic, Plossl or Kelner all share the same number of groups, and should score very closely in terms of transmission. A colleague of mine bought a scope with two Kelner EPs (10 and 25mm) on my recommendation ( Bresser 100mm F/9 achromat on EQ mount). When I started replacing my Plossls (10, 26 and 36mm Vixen) with Naglers and a TMB Paragon, I suggested he try my old Plossls with his Kelners, and if he found them to be significantly better, he could have them for a reasonable price. He always found the differences very significant. Kelners are not bad at all, but a good Plossl is better, I have always found.

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I think it is the cheap nasty kellners that give them all a bad name. I have a Vixen 20mm Kellner, and it's truly lovely, sharp across the field of my F/6 6" Newt (the one it came with), just a limited FOV when compared to a plossl.

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Michael, I take your point about the light scatter being related to the number of elements. Mine was more to do with the simple 3 element design meaning that transmission is good for such a cheap eyepiece design. The more pieces of glass in a light path, the more some of the light is absorbed by each additional element: on brighter objects this is not noticeable, but it's at the very limits of visibility that this kicks in, I feel. Of course, this can be to some extent compensated for in modern eyepieces by the improved coatings which are available.

And of course, the quality of the actual eyepieces vary tremendously. I have the 10mm and 26mm Vixen plossls you mention and they are indeed very good and "superior" to the Kellners in that they have a wider field of view which tends to enhance the overall view..but on axis, my old circle T Kellner 9mm appears to my eyes just as sharp as the 10mm Vixen plossl- but with a smaller field so that, aesthetically, I think most people would say the Vixen was "better" - but of course, the Vixen would cost 2 or 3 times the price of the Kellner on the used market.

I think that given the modern mutli coatings which are now used on good quality eyepieces such as the BGO Phantom coatings etc, it's remarkable that these old Japanese Kellners put up such a good show as they do! I agree with Jonathan that it's not wise to generalise but to look at brands with these eps - in general a good brand, such as Circle T or Vixen, don't offer poor eps, they were/are too jealous of their reputation..

I do know that some of the modern cheaper eyepieces are utterly useless, typically those found on "department store" 60mm refractors. But the older ones as discussed in this thread are worth seeking out. The other advantage is that, since they are so low cost, you don't have to be precious about taking them out loose in the pocket, or using them for other people to get a first view of the moon etc - something I wouldn't be so keen to do with my Fujiyama/Nagler/Panoptic eps! :eek:

Two other small observations I've noticed (pun fully intended :grin: )..have any of you noticed 1) The older eps can seem to perform better with a good quality Prism diagonal? (this can also apply to older achromatic refractors...I've seen more than one report that CA is noticeably less when using a good prism - I use a Takahashi 1.25" one and it works really well with all my older eps). 2) Using a good dielectric 2" diagonal can also bring out the best in older 1.25" eps.. my theory (not scientific) is that the "sweet spot" of the larger dielectric mirror is in the centre of the mirror and so the 1.25" light path is only using the "best" of the light available, bouncing of the most reflective and smooth part of the diagonal mirror - does that make sense?

Dave

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I have a 25mm circle t kellner Dave, I can't describe it fully but it is so sharp and bright compared to anything else I own. I love looking at M42 with it through a f12 mak. I can tell the difference between using it and a 25mm ortho which surprised me. So I know what you're getting at!

I will never sell it, even though I have other 25mm.

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I have a 25mm circle t kellner Dave, I can't describe it fully but it is so sharp and bright compared to anything else I own. I love looking at M42 with it through a f12 mak. I can tell the difference between using it and a 25mm ortho which surprised me. So I know what you're getting at!

I will never sell it, even though I have other 25mm.

Jim, did i sell you my 25mm kellner ?

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Jim, did i sell you my 25mm kellner ?

Yes Jules. I did buy it from you. It's a lovely eyepiece, which you told me at the time. I was just starting out in astronomy with my first good scope and knew from reading that a kellner would be ok in my long fr mak. But wow! It made me start seeking out vintage Japanese optics I was so blown away by it.

I forgot to mention earlier that it's also my favourite eyepiece for framing the moon in my scope. I often use just that rather than go higher mags.

Edited by username
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