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Reged: 09/03/05
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BT100-45 Eyepiece Comparison new
      #830681 - 02/18/06 01:59 AM

BT100-45 Eyepiece Comparison: Siebert Ultra 24mm vs. Televue Panoptic 24mm vs. Meade Series 4000 Super Plossl 26mm.

This is a lengthy post, really more of a mini-review. I hope some will find it useful.

The 23.9mm eyepieces that came with my Oberwerk BT100-45 binocular telescope provide good images and a generous apparent field of view. Unfortunately, they don’t work well for me as a binocular pair—I can’t get my nose between them to see an adequate portion of the field, even with the rubber eyecups removed. I need a pair of eyepieces with a narrower outer diameter, or longer eye relief, or some combination of both.

Based on Ed Zarenski’s testimonial in the binocular forum, I acquired a well-matched pair of Japanese-made Meade 26mm Plossls. They were inexpensive, and I found them comfortable to use, with excellent image quality. However, I desired wider apparent and real fields of view than the Meades offered. I wanted to maximize the real field, and also maximize the “wow factor” with the widest possible apparent field.

Research suggested that the gold standard to achieve my goal was the Televue 24mm Panoptic. In the BT100, it offers the widest possible real field in a 1.25” eyepiece of binocular-usable outer diameter, along with an excellent apparent field of 68 degrees. The 24mm Panoptic is also expensive, about $600 a pair. Worth it? Maybe—the cost is not out of line compared to the price of the BT100—we all know that good eyepieces can substantially leverage the value of any telescope.

Research in the Cloudy Nights binoviewer forum showed a lot of positive buzz around the Siebert Ultra 24mm. The advertised 65mm apparent fov is close to the Panoptic’s 68mm. A number of users compared the Sieberts favorably to the Panoptics. At $258/pair, less than half the cost of the Panoptics, they seemed worth trying.

After one night of intensive comparison, the differences seemed clear. I’d like to have more time with them, but our weather this time of year is fickle, and it could well be another month before another clear night comes along. So, with the caveat that this is based on a couple hours of comparison, here is what I found.

Executive Summary: the Panoptics are the best. The Meades compare favorably to both the Panoptics and the Sieberts. The Sieberts are also good, but came in third, all things considered, at least for my personal preferences in the BT100.

First I tried the Sieberts. The Siebert Ultra 24mm is a three-element design, offering 20mm eye relief, and a maximum barrel diameter not much larger than 1.25”. These are very lightweight eyepieces, potentially a plus. Harry Siebert recommends the 24mm Ultra for f/7 and slower optics, so I was pushing the spec by using them in my f/6 BT100. The Ultra has a flared stiff rubber eyecup which does not fold down. With the eyecups in place I was not able to see the entire field of view—what I could see looked like maybe 45 or 50 degrees—however the entire eyecup pops off easily and can be placed back on the eyepiece in reversed position, still providing a couple mm of protective rubber ring above the eyelens which means you don’t have to push your eyeglasses or eye sockets against bare metal. With the eyecups in the reversed position there was more eye relief than I needed and I could see the entire field. I did not notice any kidney-beaning.

Each Ultra came from the factory with a small white dot on top of the barrel just outside the eyelens. Mr. Siebert provided a note with the Ultras recommending that the eyepieces be oriented in binocular pairs with the dots facing each other for best collimation. Because the BT100 focusers rotate the whole eyepiece, and the eyepieces fit very snugly into the focusers, I gave up on even trying to comply with this recommendation. Possibly if I had paid more attention to this I would have had better results.

Observing impressions: The field stop was not sharply defined. I had some difficulty achieving good focus with the Sieberts. This seems to be a characteristic of the BT100, with its extremely finely-threaded helical focusers. Possibly part of the problem was sensitivity to on-axis eye position. In any case, with the Sieberts, as with some other eyepieces I have tried in the BT100, I found myself fiddling with the focus a lot, never really being satisfied. Good round or pinpoint stars are important to me. Off-axis stars showed spread in the outer 10 percent or so of the field; overall the sharpness of the field was more consistent closer to the edge than with the Oberwerk 23.9mm eyepieces, or typical Erfle designs. It was really pretty good, especially for this wide an apparent field. Contrast and light transmission were excellent, with the sky background showing a black black. The Trapezium showed three stars most of the time; once, when everything lined up just right, I could see all four.

Next I put in the Panoptics. My first impression was, “wow!,” along with an immediate feeling that these were worth whatever they cost. The apparent field appeared substantially wider than the Sieberts—although this was a subjective impression and I can’t confirm it with any measurement—with a sharply defined field stop well out of the way. I achieved better star images immediately, which was most important to me. Stars were sharp pinpoints or round dots right to the edge of the field, with an interesting twist—viewing straight into the center of the field, stars at the edge appeared blurry. However, if I moved my eyeball, or my head, to point my eye towards the stars at the edge of the field, those stars became sharp. Possibly this is an example of “curvature of field?” (When I tried the same technique with the Sieberts, there was no difference in the appearance of the stars at the edge—their blurriness did not change.) Contrast and blackness of background were not quite as good as with the Sieberts. Trapezium showed four sharp stars immediately. Despite the Panoptics’ relatively wide barrel, I had no problem with my nose or eye sockets getting in the way—I think the tapered upper barrel, non-intrusive flexible eyecup, and sufficient eye relief get the credit here.

At this point I felt the evidence was clear, but just for thoroughness I decided to try the Sieberts one more time, and that’s when things became a bit murkier. This time, I got some nice sharp star images, including a no-problem view of four Trapezium stars. Had the seeing suddenly improved? Had I just lucked into better focus in the BT100? Were the eyepieces oriented slightly differently? Were my eyes warming up?

I went back to the Panoptics. Wow again. Yet, the stars did not seem as sharp as the first time I looked through the Panoptics. They seemed about the same as they had looked in the Sieberts. I fiddled with the focus, moved my head around; sometimes the stars would ‘pop.’ I went back and forth between the Panoptics and the Sieberts multiple times. Overall, I achieved better focus more frequently with the Panoptics, but each time it seemed like luck as much as anything. Possibly my eyes were getting fatigued.

Finally, I thought I’d try the Meade 26mm Plossls. This was a casual lark. I had written off the Plossls in my mind, assuming they couldn’t possibly be as good as the Panoptics or Sieberts. After all, they only cost 40 bucks apiece, and price correlates to performance, right? Time for more re-education.

First, interestingly, the Meades were perfectly parfocal with the Sieberts. This was convenient for comparisons. Second, I was newly impressed with the optical quality of the Meades. It was easier to repeatedly achieve well-focused star images with the Meades than with either the Sieberts or the Panoptics. Yes, the apparent field was substantially narrower, but the all-important star images were as good or better, most of the time, than either of the more-expensive eyepieces’.

This seems like an exaggerated illustration of the old “80-20” rule. In this case, the Meade gives arguably 80 percent of the performance value of either of the other eyepieces, for 20 to 10 percent of the price. Even compared to the Panoptic, the Meade 26mm Plossl remains a respectable choice for the BT100. Depending on what is important to any individual observer, could well be the best choice to use in that instrument.

Really, my biggest problem with the Meade is that it seems more prone to fogging than other eyepieces. I think it’s because their eye lenses are deeply recessed, so your eye against the barrel forms a moist enclosed chamber above the eye lens. When your eyepieces fog up, the sky might as well be cloudy.

For all of the eyepieces, I had no problem fitting them into the BT100 focusers. They were snug but reasonable. The Panoptic inserts into the BT100 focuser with a satisfying and positive “snap” due to the recessed ring on the barrel. Also, for all of the eyepieces, color correction seemed fine, not an issue. I don’t get real excited about color correction so others who care more might notice more on that front.

At this point I have returned the Sieberts, and am leaning towards keeping the Panoptics based on my trusty and well-exercised rationalization that “I can always sell them.” My intention with the BT100 is to settle on one pair of eyepieces to use, and not switch around changing power. It’s a philosophical and esthetic choice. It also helps in justifying relatively expensive eyepieces—if I wanted a selection of powers, price would be a more important consideration.

I want to put in a good word for Siebert Optical—even though the Ultras did not work out for me in my application, I was impressed with their quality. Harry talked to me personally when I ordered them and offered helpful advice. The company gives great service and has an interesting web site.

I’ll be happy to correspond with anybody who would like to compare notes on the BT100.

Kurt Meyer

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The British Flash

Reged: 04/27/03
Posts: 20139
Loc: Lancashire UK
Re: BT100-45 Eyepiece Comparison new [Re: kdmeyer]
      #830715 - 02/18/06 03:24 AM

Thanks for that great input Kurt , the result of which may well be worthy of TRUE CN " REVIEW status " accessible from the main page .

Regards , Kenny


Milton Wilcox R.I.P

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Carpal Tunnel

Reged: 07/28/05
Posts: 1873
Loc: Melbourne, Australia
Re: BT100-45 Eyepiece Comparison new [Re: KennyJ]
      #1097092 - 08/16/06 02:14 AM

just stumbled on this review looking for info on siebert EPs. Very informative. Thanks Kurt!

Steve H --- Dobs: Saxon/SW 10" f/4.7, GSO 8" f/6, custom truss 8" f/4 | Intes MK-65 (6" Mak) + EQ | binos: Pentax PCF 8x40, AOE 10x50MX Ultra, AOE 12x60.

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professor emeritus

Reged: 07/09/05
Posts: 645
Loc: Ampthill, UK, 52:02N 0:30W
Re: BT100-45 Eyepiece Comparison [Re: Stephonon]
      #1097230 - 08/16/06 08:00 AM


Thanks for that review! My wife and I settled on 24mm and 17mm Ultras for our BTs and are delighted with them. Together they cost us less than a pair of Pan 24s! We did not have the advantage of being able to readily compare any pairs of EPs, so finally bought blind (that's not a good choice of words!).

While I guessed the Pans would work out best of all the alternative 24s, the Sieberts make a great economical upgrade. The real WOW for us came with our 17s, which blow the socks off the 15mm originals, which we found unusable.

What was important for us was better eye relief, for use with eye glasses. Pans are marginal and very expensive, especially when compared with the price we paid for our BTs. I could also argue that BTs are really not up to the quality mark for that level of expense on a single pair of EPs. A second pair, of shorter FL Pans, would be way too much!

We wrote a Review on our experience with BTs for bird watching and I am about to update it with our experience of choosing EPs, so look out for it.


"one eye good, two eyes better...the more I look, the more I see"

BT100-45 degrees, plus 35,24,17,13,9mm Sieberts
15x80, 7x50 Steiners
12x50, 10x42, 8x20 Leica Trinovids
7x35 Minolta

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