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Panoptics and Naglers and Paragons - Oh My!
A Widefield Shootout
Tom Trusock
7/07
To go by discussions on the net the Burgess / TMB Paragon 40 is certainly one of the years hottest eyepieces. So when the opportunity came to put the Panoptic 41 and Paragon 40 through a critical, side by side evaluation, how could I turn it down? And since I happened to have a Nagler 31 on hand, I thought it might be instructive to add some comments about that as well - and so, here's a side by side of three of the finest wide field eyepieces on the market.
Testing Rationale, Optics and Methodology
Over the last year, I've come to realize that when trying to discuss eyepiece performance, you need to be careful NOT to compare the systems. If you want objectivity, you must separate performance of the scope from performance of the eyepiece. This isn't as easy as you might think. Nearly every telescope design contributes something to the system, the most common element being field curvature - an aberration which is all too often taken for something else. The best systems for objective and critical judgment of eyepiece performance are the Tele Vue NP systems. These 4-element Petzvals are the successors to Tele Vue's original MPT telescope - which is still used for testing eyepieces at Tele Vue today. They present the most perfect field of any commercially available telescope, and therefore are an ideal optic for eyepiece evaluation.
In many cases I suspect there is entirely too much blame placed on the eyepiece when in reality the owner/user is actually commenting on the performance of the system as a whole (telescope, eyepiece, atmosphere and eyesight). In my opinion this is a rather important distinction.
Once the scope induced aberrations are eliminated from the evaluation process, if the telescope owner is aware of the specifics of their own systems (relative field curvature, coma, astigmatism, individual visual accommodation etc...), they should be able to take a better educated guess as to what type of performance they should see.
Although my primary optic for evaluating these eyepieces was an NP101 (for the reasons given above), I did use them in a variety of other telescopes; an NP127 (f5.2), an FS102 (f8), a TMB 130mm (f7) and an 8" Celestron SCT (f10). I also took a look in a couple of different fast Dobsonians (f4.5 and f4), but I'll say at the outset, I don't feel the 40 Paragon or 41 Panoptic is really an optimum match for a fast Dob. The combination of greater magnification and smaller exit pupil of the 31 Nagler is well worth the price difference here.
Test targets involved daytime resolution photos and tests, as well as twilight and nighttime views of Luna and various wide field, deep sky objects. Comparisons were conducted over a period of 6-8 weeks under a multitude of seeing conditions.
Top Views: 9 o'clock - Nagler, 1 o'clock - Pan, 5 o'clock - TMB
The specifications as listed by the manufacturers:
| 40 Paragon | 41 Panoptic | 31 Nagler | 6 element 4 group design
AFOV 69 deg
1lb 1.5 oz
ER 16mm | 6 element 4 groups
AFOV 68 deg
2.1 lbs
ER 27mm
46mm field stop
| 6 elements 4 groups
AFOV 82 deg
2.2 lbs
ER 19mm
42mm field stop |
**The field stop of the 40 Paragon has been measured at 45.7 (just under 46mm).
My initial daytime comparison took place with an NP127. Using a terrestrial target (a photo with some text) placed at the edge of the field, I noted that while there was some pincushion distortion in the Panoptic, the field of the Paragon was relatively free. The Paragon showed some flat field defocus compounded by minor astigmatism. This resulted in edge sharpness not on a par with the Panoptic.
Extended night time comparisons generally confirmed my initial daytime observations.
There is minor, but noticeable astigmatism in the Paragon once you get out to the outer portions of the field. It's much less than what I've seen in other eyepieces like the Konigs and such, but it's obviously worse than the Panoptic. I suspect the Paragon's field is slightly curved as well, but the inherent astigmatism in the eyepiece makes it hard to accurately determine the amount. Stars aren't coming to points - rather they show trade mark signs of eyepiece astigmatism - a tiny cross at best focus. Because of this and the flat field issue, tt's somewhat difficult to find a critical best focus in the outer portions of the field. The inner field shows targets quite nice, sharp and very contrasty.
The Panoptic isn't perfect either. There is some minor loss of edge illumination - while this isn't much of an issue for most observations (I didn't notice it at all during the day, and doubt I would at night - but at twilight it seems to come out). I can maybe see how that might make things difficult if you were trying to judge respective true fields at night. Some critical observers have commented that they feel the Panoptic shows some lateral chromatic aberration at the very edge of the field. In my opinion, when the eye is properly placed on axis, it's an insignificant amount. The Panoptic certainly does have pincushion distortion, but it does not bother me in the slightest - each to their own. It's a trade off, and personally if everything else is equal, I'll take edge of field sharpness.
As I increased focal ratio, the view through the Paragon improved. At f7, images seemed tighter than at f5.4. At f10, the Paragon was better yet but edge performance still wasn't quite to the level of the Panoptic.
So, how would I sum these up?
The 40mm Paragon:
I found the Paragon to be axially very sharp with a cooler tone. I didn't note any lateral color (although this may be swamped by astigmatism), nor did I see pincushion distortion, but I perhaps glimpsed a touch of barrel distortion - however, there's not much - if any. I also noted some minor astigmatism towards the outer portions of the field of view - the affected portion being dependent on the focal ratio of the telescope. It's not anywhere near as pronounced as it is in something like an MK70, but it's noticeable in direct comparisons with the Nagler 31 and Panoptic.
The AFOV was slightly smaller than that of the Panoptic. I'd put it as closer to 64 deg AFOV than 70 - in line with the lack of pincushion distortion. The TFOV seems to be about the same as the Panoptic, consistent with the field stop measurements. The Paragon is well baffled and provides very good contrast, great transmission and an excellent on axis view. When viewing luna, it was apparent that the field lens is in focus - any dust on the field lens is noticeable when viewing against a bright background.
I should point out that although they may be used as such, neither of these are what I'd call a Lunar eyepiece, being too long of focal length.
I found the coatings excellent and fit and finish to be first-class.
The 41mm Panoptic:
I found Panoptic 41 to be axially very sharp. In fact, it maintained that across of the field of view. I found the color tone to be neutral, and the level of pincushion to be overall rather minor. In my opinion, it's effect is negligible except when viewing an extended object (such as luna) at the edges of the field. I found it to be moderately sensitive to eye placement - until I utilized the adjustable eye guard, at which point it became as comfortable as the Paragon to view through. I didn't note any significant field curvature.
Throughput and coatings are excellent. Fit and finish is top notch.
Although its vastly different focal length and apparent field of view puts it in a different class altogether, I thought it might be of value to include some comments about the Nagler 31.
The 31mm Nagler:
The 31 Nagler is most definitely not a daytime eyepiece (and was not designed as such) due to its spectacular "ring of fire." (For those not familiar with this effect, it's a band of color - appearing brown, red or blue - that surrounds the outer part of the field when one is viewing a bright scene, the degree is related to critical eye placement. On DSO's, it's not noticeable and thus is a complete non-issue.) Because of the "ring of fire" I'd prefer either the Panoptic or the Paragon for lunar or daytime viewing. I found the 31 Nagler's color tone on the warm side. While the eyepiece yielded a much larger apparent field of view, the true field of view was noticeably smaller, about 10%. I also found the Nagler 31 to be sensitive to eye placement during dayime use - but far less so under the stars. While not for lunar or daytime use, the Nagler 31 would be my choice for DSO's. The greater magnification allows for greater apparent contrast, I find the larger AFOV far more immersive, and I generally prefer smaller exit pupils over larger ones whenever possible.
Throughput and coatings are both very good, as is fit and finish.
Conclusions:
While none of them are perfect (my spontaneous definition of perfection requires a total lack of aberrations, AND an insignificant hit on the pocketbook), all three of these eyepieces are excellent. If you're looking to buy, as always, a proper choice will depend on your specific circumstances.
Of the three, I preferred the Paragon for lunar glimpses because of the paucity of pincushion in its design. On the other hand, I found the Paragon's minor astigmatism to be more noticeable on stellar fields, and thus preferred either the 41 Panoptic or 31 Nagler for star fields and DSOs. Overall, I also found the field a bit flatter in the Panoptic than in the Paragon, and the Panoptic definitely had more pincushion. However, to many observers - myself included - pincushion is simply not an issue on star fields, and personally, I prefer that to astigmatism if everything else is equal.
The Paragon is an excellent eyepiece, and while it does boast a lack of pincushion, critically speaking, it's not equal to the Panoptic 41 in terms of edge and outer field performance. If you: 1) are only going to use the focal length occasionally, 2) have a slower scope, 3) need a light weight eyepiece, or 4) if you can't or simply don't want to drop $500+ then the Paragon is an excellent choice. To my eye, the 40 Paragon is perhaps the best 40mm wide field on the market for its price point.
However, those who: 1) want the sharpest stellar fields, 2) aren't bothered by pincushion, and 3) simply want the best edge performance available in a 40mm (ish) wide field eyepiece should look to the Panoptic.
Finally, if you: 1) don't need a widest true field eyepiece, 2) don't plan on doing any lunar / daytime viewing with a long focal length, or 3) want a smaller exit pupil, you should really consider the 31 Nagler type 5 - especially for deep sky. It's simply a superb eyepiece.
In shootouts, it's somewhat expected that something or someone has to be declared "the best" or "the winner" - so I guess we've come to that point.
Therefore, I'm betting you really want to know who the winner is here, right?
It's simple really.
We are.
Kudos to both TMB and Tele Vue. We're a long way from Erfles and Konigs. It's a good time to be an amateur astronomer. |
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