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5mm Shootout Using a New Standardized Approach

Posted by William Paolini   10/01/2006 12:00AM

5mm Shootout Using a New Standardized Approach
This test pitted 3 eyepieces against each other for performance on a variety of celestial objects. While they were all of same focal length, many of their other attributes varied significantly: AFOV ranged from 30 deg to 60 deg, eye relief ranged from 5mm to 16mm, optical design ranged from 3 to 6 elements, and street prices ranged from $79 to $250. Many thanks and appreciation are due to AstroMart member Steve Couture for his generous loaning of the Radian, TMB, and University Optics eyepieces used to conduct this test.

For this test, several evenings of lengthy observation were conducted using a pre-established plan of celestial targets and testing approaches. The first evening all tests were conducted, and during subsequent evenings the observed notes were confirmed and Lunar observations were added. Stars of magnitudes 1, 2, and 5+ were used for evaluation of optical aberrations (CA, SA, coma, astigmatism, etc.) and spot size, 1st magnitude stars and Jupiter was used for evaluation of scatter; nebula (M57), globular clusters (M13), and random star fields with dim stars requiring adverted vision to detect were used to evaluate light transmission, background contrast, and spot size. Jupiter and the Moon were used for evaluation of sharpness. The telescope used was an Orion 10” f4.7 Dobsonian in a fairly typical suburb setting where light pollution results in a typical limiting magnitude of 4. Therefore, test results, as always, should be considered in light of these environmental and optical factors, and should not be considered as necessarily extensible to other than fast Newtonian instruments or performance at significantly darker observing sights.

For this evaluation, a newly developed Eyepiece Evaluation Form was used to document the optical performance of each eyepiece as used under the stated environmental conditions with the stated equipment. This form is an attempt to bring some standardization and “control” to the eyepiece evaluation process. The form is still in the process of development and refinement, and this first use of the form was to serve as an initial shakeout of its usefulness as currently designed. Many thanks and appreciation are due to Floyd Blue and other members of the AstroMart Eyepiece Forum for their assistance into the development of this initial Eyepiece Evaluation Form.

Overall, as I have discovered in many years of observing, eyepieces have a niche where they really excel. And often, this niche is quite unpredictable. This test bore this out well. This test also bore out that a better optically corrected eyepiece, does not necessarily mean it will be better for observing, as the many other ergonomic factors of the eyepiece and observational qualities of the celestial target, weigh heavily into the pleasure and reward of the observing experience.

From an optical correction perspective, in the central 50% of the AFOV, all eyepieces performed the same. In the 50% off-axis portion of their AFOV, the Radian had the least amount of off-axis issues, with the UO HD coming in 2nd, and SuperMono 3rd. The SuperMono showed some CA off-axis, but a rather significant softening due to bloat making the off-axis image less than desirable in my fast Newtonian. So the lesson learned here is that a single significant off-axis issue amounts to more of a performance degradation issue when observing than a multitude of issues that are only negligible in their presentation.

While the form presents the colder “facts” regarding how each eyepiece performed optically, these did not translate well into the overall impression left by the eyepiece from the observing experience. However, the quantification of individual optical performance characteristic, as this form captures, does enhance the evaluation process by giving us a more standardized baseline for reference. The benefits of standardization and uniform recording processes aside, the separate quantification of optical and usability factors, still does not seem to easily translate into a determination of which eyepiece may be characterized as “best.” The qualitative “narrative” still seems to be the best approach for communicating overall performance or niche performance of an eyepiece. This being the case, the evaluation form records both, the quantified results for each optical criteria according to set standards, and the very qualitative and subjective impressions of the observer. Section #6 of the form is probably the most valuable section of the evaluation for those seeking to know which eyepiece is best overall as it asks the evaluator to rate each eyepiece on how it performed on specific celestial targets. Below, therefore, are listed each eyepiece evaluated in this comparison, along with a narrative of its strengths and weaknesses, and it’s Section #6 score.

5mm TeleVue Radian (Section #6 Score = 4; 1st Place for Planets, Globulars, Nebula):
Clearly a well corrected eyepiece! Star images remained intact to almost the extreme edge. Star point size was only average compared to the rest. On Jupiter it suffered from some internal reflections and many eyeball glint reflections, to the point of being not annoying but very noticeable. Eye positioning was also sensitive, giving partial blackout if not correct. This again was not annoying, except on the Moon where it happened more than I liked. It also suffered from some fairly significant CA off-axis. This showed as very noticeable on Jupiter and 1st magnitude stars. On 2nd magnitude stars it became much less detectable. I did not see any CA on stars dimmer than 2nd Magnitude -- for normal viewing of clusters CA was not apparent. On Jupiter is also showed quite a bit of CA, but again, the extra detail it showed on the surface negated that problem. Overall stars also had a warmish or yellowish cast. This was especially noticeable when switching to any of the other eyepieces in the comparison. Therefore, for the majority of celestial objects, the CA, although sometimes significant, was not much of an issue in practical use. However, despite all these issues, and while the Radian was not the sharpest eyepiece in the bunch, it clearly put up the most detailed on-axis view of Jupiter. So of the bunch, it came in #1 for Planets showing much more details in the bands and festoons of Jupiter, so much so that it diverted ones attention from the CA on Jupiter’s fringe. So as far as planetary performance is concerned, of the bunch I was getting the best resolution of fine detail on Jupiter with the Radian 5mm – however, the Siebert 5.9mm Star Splitter was only ever so slightly behind showing detail and further behind showing atmospheric shadings due to its neutral coatings. The others fell well behind, even the SuperMono which for me was performing only a very slight tad better than the UO HD.

On Globulars the Radian also came in #1 for both an expected and unexpected reason. As expected, its wider AFOV at the 240x magnification in my scope, and therefore wider TFOV, put the Globulars (M13 for this test), and nebula (M57 for this test) in more context with the surrounding star field making them more pleasing and interesting to observe. Unexpected was that it’s average star spot size seemed to work as an advantage for Globulars , accentuating the larger brighter stars while still showing finer points for the dim stars. The effect overall was that it gave the globular a more 3 dimensional look. So the Radian was #1 for high power views of nebula, Globulars and planets. It’s performance on the Moon and general star fields was not as well as some of the contenders. Star colors also did not seem to translate as well as they did in the other eyepieces. White stars had a bit of a warmish tint, red stars did not come across as red, and yellow stars seemed overly so. So for color contrast doubles or multi-color stars in Open Clusters, the Radian was not the best choice; it does however have a definite high-power niche excelling on Planets, Globulars, and Nebula.

5mm TMB SuperMono (Section #6 Score = 3.3; 1st Place for Lunar Detail):
The SuperMono’s reputation precedes itself as the ultimate for resolution and contrast. I had never used one before so had many great expectations. Unfortunately, for the majority of objects observed, it did not perform well in my fast Dobsonian. On Jupiter it showed minor CA even on-axis. The biggest issue however, was the outer 50% of the AFOV was very soft, too soft for serious observing and evidenced as bloat on star images. And while the central region was sharp, this was small given its total AFOV of only 30 degrees. On stars it was also a less well corrected lens and with my fast f-ratio mirror coma appeared starting at the 50% mark from center and got quite moderate the last 25%. So while this eyepiece may be a great performer in optical designs without coma (APOs, Achros, SCTs, etc.) it is apparently not a good choice for fast Newtonians.

On Jupiter, it’s performance fell between the UO HD and the Radian. As a high power planetary eyepiece for a Mid-sized aperture Dobsonian I would therefore not recommend it. The UO HD’s on-axis performance was very close, its off-axis performance was much better, had a wider AFOV, and only half the street price – overall the better choice. The small AFOV was also a hindrance for performance on Globulars and nebula because of the resulting very limited TFOV just did not give enough context. True it did have the darkest background FOV, and if it did have better light transmission it was not apparent on stars but only showed up in nebula where the Ring Nebula (M57) appeared just slightly brighter compared to the others eyepieces. While its performance seemed to be lacking on most objects viewed, I found its niche on the Moon. Lunar observing was just spectacular, showing incredibly more detail on-axis than any of the others. It was also very apparent that it showed more contrast as what appeared as delicate shading differences on the lunar surface in the other eyepieces popped out as significantly dark shadings through the SuperMono. While the restrictive AFOV made re-navigating back to a spot on the Moon more difficult, and the 50% off-axis image was much too soft, the reward of the extra fine detail and high contrast shades on-axis made up for that several fold! Definitely a #1 Lunar performer in Newtonians. I spent quite a bit of time examining the very rich fine details in and around Crater Clerke (Longitude: 29.8° East; Latitude: 21.7° North).

5mm University Optics HD ABBE Ortho (Section #6 Score = 3.5; 1st Place for Stellar Color Rendition):
While the UO HD ABBE did not excel as #1 on any celestial object, it came in as a good to very good performer on everything! If I had to characterize this eyepiece, I’d say it is a generalist and a very good one, worth every penny if not more so than its street price. It’s lunar imagery was more detailed than the Radian’s and it’s star point size seemed to be a tad smaller. Background darkness was good, but still exceeded by both the Radian and the SuperMono. A special characteristic unique to this eyepiece over the others though, is that it seemed to put up a slightly brighter star and had the most neutral effect relative to stellar coloring – red stars appeared redder, whites whiter, blues bluer, etc. When circumstances are such that one needs to focus critically on stellar colors, this is where I’d reach – so its niche is very specialized as #1 for Stellar Coloring.


Overall (and price differences aside), of the three eyepieces I would have to give the nod to the Radian as the clear overall winner. Even though it has issues with Chromatic Aberrations and reflections, it’s superior contrast, comfortable eye relief, generous AFOV, and level of detail presented on planetary atmospheres made it the winner. So for all categories of celestial objects, the Radian is the winner. If, as an observer, you have very specialized tastes such as Lunar details and shadings, then the Radian would not be the first choice. For specialized uses, each observer needs to read the qualitative narratives provided on each eyepiece to determine which would be best for their specific application. As always, readers should pay attention to the telescope used in eyepiece comparisons, and observing site conditions to determine if the results of any comparison would be applicable to their situations. The results of this comparison indicate how these eyepiece perform in fast production Newtonian telescopes at typical suburban sites. When conditions vary, such as if you are using premium quality refractor at extremely dark observing sites, then the results may not be extensible to those situations.

If you are interested in obtaining a copy of this Eyepiece Evaluation Form for your own use, send me a message through the AstroMart messaging system and I’ll be happy to supply you with a copy.

Click here for more about the 5mm Radian. -Ed.