11 replies to this topic

[BillP]

A fellow observer from Australia was kind enough to loan these Kellners to me for a look-see.  Not sought-after premiums by any means, but good solid build economy eyepieces.  I disassembled one to confirm it is a Kellner design and it is.  On ebay I see these for sale from Australia for a price of about $53 USD for all three, and shipping around $18 USD to the U.S.  So that's a total of $71 for 3 eyepieces, or about $24 each.  Not bad for a well built eyepiece (all metal build except for the rubber eye guard.

 

Marketing specs are interesting in that they only mulitcoated the 25mm whereas the 20 and 10 are single coated.  Being just a 3-element 2-group design not sure multicoating is really necessary although always nice when the eye lens is multicoated to help mitigate eyeball glint and reflections from street lights and such.  Given a 99% efficient multicoating the overall theoretical transmission efficiency of the 25mm should be around 96%, while the single coated only 20mm and 10mm should be around 93%, so in either case very good.  Also interesting in the marketing is they are touting these will work well in sub f/6 instruments!  Not a claim that makes sense given their generous AFOV for a Kellner, but we will see when I place them in the 80mm f/6.25 I have.

 

In the hand they feel quite sturdy.  Holding them up to the eye they show good field stop definition in the 25mm and 20mm, and just a little less than sharp in the 10mm.  Rubber eye guard is a bit thin and naturally folds down nicely and is easily removable if you desire.

 

I did some measures of them on the bench and got the following:

 

K25 -- 51° AFOV; 20mm ER
K20 -- 49° AFOV; 15mm ER
K10 -- 48° AFOV;  7mm ER

 

Will be fun getting them under the stars once the snow storm passes here in Virginia, and seeing how they compare to a vintage Celestron 25mm Kellner as well as the current production 20mm Starbase Kellner.

 

 

Edited by BillP, 01 February 2021 - 12:55 PM.

[Neptune]

Would like to know how they stack up against the vintage Celestron Kelners.

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[BillP]

What is the optical mark on your k.25?  The one I have is the older vintage where "CELESTRON KELLNER 25mm" is engraved on the bevel of the volcano.  Optical Mark Circle-Dash.  So the 25 Kson will be compared to that.

 

25 Kson:       51° AFOV; 20mm ER; 26mm Eye Lens Diameter; Fully Multicoated

25 Celestron:  45° AFOV; 13mm ER; 14mm Eye Lens Diameter; Fully Coated

 

---------------------

 

20 Kson:       49° AFOV; 15mm ER; 23mm Eye Lens Diameter; Fully Coated

20 Starbase:   50° AFOV;  9mm ER; 16mm Eye Lens Diameter; Fully Coated

Edited by BillP, 01 February 2021 - 12:59 PM.

[Neptune]

Mine look like this....

 

I believe these are from about 1977ish.

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[BillP]

And the optical mark stamped on the barrel of your 25mm is what?

 

 

Edited by BillP, 01 February 2021 - 04:38 PM.

[Tropobob]

I have owned the Kson orthos 24 & 16.8mm EPs. They performed differently to most orthos, as they were incredibly sharp at the very center, but almost immediately lost this sharpness away from the center.  (using longer F-ratio, small refractors & an 8" HD Edge.)  

 

I now own a variety of other orthos and they retain their sharpness away from the center. 

 

I have parted with the Kson orthos, but am sometimes tempted to buy a higher magnification Kson ortho to use on planets/double stars with a tracking mount.  The sharpness at the immediate center did seem quite remarkable.  

 

However, I like parfocal EPs, and the Kson ortho EPs are not parfocal with each other.  

Edited by Tropobob, 01 February 2021 - 04:52 PM.

[Neptune]

And the optical mark stamped on the barrel of your 25mm is what?

 

Image-1(2).jpg

 

Image-1(1).jpg

Bill,  similar to the second photo with the exception my text is towards the lower edge of the volcano (not centered). 

 

David

 

Edited, added close up pic.

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Edited by Neptune, 02 February 2021 - 06:55 PM.

[BillP]

That is a Circle-T, Tani in Japan, very prolific and many of the vintage and modern Abbe brandings, like the UO Volcanos, were made by them.

[BillP]

Finally got a chance to get these under the stars in my TSA-102.  Sky tonight was absolutely gorgeous tonight and spent my time in and around Orion.

 

As far as edge correction goes they were all sharp out to at least 75% of the FOV, with some sharp til about 90%.  Ranking of off-axis sharpness was as follows, best to worst.

 

1. Kson 26mm Erfle (very good out to 90%) - not sure I mentioned I had this one also to test.

2. Kson 25mm Kellner

3. Celestron 25mm Vintage Volcano Kellner

 

1. Kson 20mm Kellner (good out to 80-85%)

2. Starbase 20mm Kellner

 

1. Kson 10mm Kellner (good out to 85-90%)

 

Eye relief was really comfortable on all of them, even the 10mm Kellner!  With the Kson 10mm Kellner my brow was just lightly touching the top of the eye guard and could easily see the entire FOV.  With the Kson's longer ER this is a much much nicer eyepiece to use than the standard 10mm Plossls that come with scopes. 

 

Looking at various nebula and clusters the real story came to light as star points in the off-axis took a back seat to the visual contrast of the view.  The Kson 26 Erfle was clearly the shining star here and its views were just wonderful.  M42 was so stark against the background and lots of mottled details in the nebula.  Was really a beautiful view.  The Kson 25mm and 20mm Kellners suffered from some rather large region of EOFB so the result was a very low contrast looking view in comparison.  Then the Kson 10mm did not suffer from this so its views were quite pretty.  Contrast of the view in both the vintage Celestron and the Starbase was very good so no complaints there.  Colored stars looked to be rendered equally in all of them.

 

So for these Kson units the 26 Erfle and 10 Kellner were really nice performers.  This pair would be quite a nice set for a new scope.  Remember though that this nights view was with an f/8 instrument.  Will try the f/6.25 Apo another night.

[BillP]

I took the Kson 26 Erfle, 25-20-10mm Kellners out for a spin in my f/6.25 80mm Apo tonight.  Since I had them out last time I added some better blackening of the interior, specifically the section between the field stop and the field lens.  This reduced the EOFB some were showing quite significantly, to the point that it was no longer distracting.

 

I know everyone likes to give simple 3-element designs a hard time, and when we talk Erfles you would think they were horrible, but these KSON's all performed admirably in the f/6.25 Apo quite nicely across their 50-ish degree AFOVs.  Like my results in the f/8 scopes, they showed nicely pinpoint stars out to 75-80% of the FOV.  Only in that last 15-20% did some astigmatism start to show.  But even there it was mild not deforming the star point of any significance until that last 5-10%.  So really they put up quite enjoyable views! 

 

Of these only the 25 Kellner is fully multicoated, the Erfle just the eye lens is multicoated, and the others are only single coated.  Using Sirius as the test subject I could not induce an ghosting or flare in any of them excepting the 10mm, which showed ghosts and reflections as the star was approaching the field stop and then when outside the field stop for a little.

 

These particular Kellners do not seem to be the typical, having rather large lens diameters when I compared the 25 KSON (26mm diameter eye lens) to the 25 Starbase (16mm diameter) or a vintage 25 Celestron Volcano Kellner (15mm diameter).  So there is that difference, the ER feels a lot more comfortable with the KSONs, and their off-axis was tighter than other Kellners.  So the optical prescription they are using for these 3-element Kellners appears to offer some better overall performance then other Kellner varieties.  Btw I did take them apart and they are indeed 3-element Kellner-like designs.

 

They do not sell them here in the US.  In Australia they go for $70 AD for the 3 Kellners, which is US dollars would be $20 an eyepiece.  Given their oversized lenses, comfortable ER, nicer than cheap Plossl construction, and really nice performance even at f/6, they are quite a bargain IMO and would make a great newbie set with a first scope.

Edited by BillP, 13 March 2021 - 10:28 PM.

[Neptune]

Bill P., 

If I recall correctly, Roland from Astro-Physics found the design of the 3 element Kellner to be wonderful planetary performers due to their minimal optic count.

 

I have not had my set of Celestron Kellners out in a long time due to their competition from Ethos, Naglers and such. I will have to revisit them as soon as we get some clear skies here in GA.

David

[russell23]

I have the 28mm Skywatcher LET. I think it is a Kellner. It is excellent in my 102mm f/11 ED. High contrast and sharp. In my 102 f/7's it is not very good.