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Last night I spent some
quality time with one pair each of old Vixen/Celestron 25MM and 17MM
Kellners in my DenkII binoviewers.
First, these early 1980's vintage eyepieces are very well made. Machine work is excellent and ergonomics first rate. Even the good old MagFl coatings were excellent. With a blue sky above, looking down into the eyepieces, which had black end caps on, I saw very little reflection back thru the lenses. Only a deep rich, very dark blue/black.
The scope was my 11" F12 D&G achromat, at first stopped down to 8.5", which yields an F16 stop size, and then later, when the glass and seeing had settled down, I used the full 11" at F12. I also had the Chromacor color corrector in tow all the time. Subjects were the moon for high contrast and sharpness and Jupiter for low-level contrast.
I must say, at least at these slow scope speeds, these guys gave up nothing to the more expensive orthos and Plossls I've got.
I used them as the first eyepieces of the evening to get a feeling for their performance without comparisons. The viewing was superb. The moon was extremely sharp with that "etched" or chiseled appearance. The subtle variations in browns and tans of the surface were readily seen. On Jupiter the planets body stood in sharp relief against the background blackness of space with a minimal scattered light "glow" around the planet. The very subtle, low contrast structuring in the poles and between the equatorial belts were no challenge really.
Importantly, I felt no urgent need to swap them out with the other eyepieces. I was enjoying the view as is. Why bother?
But being a compulsive eyepiece junkie I did do comparisons with my Vixen/Celestron 26 & 17 MM Silver Tops and my Denk 14 & 21 MM's. The Silver Tops are of similar vintage but one price point up from the KE's and from the same OEM while the Denks represent the state of the art 25 years later....at a 10X (!!) price point.
The 26 MM Silver Tops did have the wider AFOV than the 25 MM Kellners but, even after taking into account the subtly lower magnification of the 26 MM Silver Tops there were no readily noticeable differences in sharpness/contrast. The 17MM Silver Tops and Kellenrs both had about the same AFOV and I felt the Silver Tops were a bit sharper at the field stop but it's really splitting hairs and I had to do several swaps to make sure.
Only the Denks displayed why you might be able to justify spending more for eyepieces on such slow F ratio scopes. Both the 14 and 21 MM displayed NO glow around Jupiter and had very generous AFOV’s with even better off-axis sharpness and an “abruptness” or “Tah-Dah” to the image that I find very attractive. However, there is no free lunch as the Denks do weigh considerably more, especially as a set, and the eye positioning on the Denk 14MM was a bit more restrictive. And I already mentioned the price thing. Interestingly, though, the Kellners focal lengths, like those of the Silver Top Plossls, complimented those of the Denks.
So who says you need to spend a pound of 10’s on super expensive eyepieces with a slow refractor? You don’t. You can go retro and get great results. At their price point's (about $40.00 for each pair) I'm keeping these guys and their performance level will keep them away from the public star party crowd.
In this application I got high-end construction and performance with a CHEAP price for admission.
As results may vary by scope design, I will next do some comparisons using my “slow” TEC and Intes Mak-Cass’s.