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EP Testing Form Trial Run

Started by wpaolini, 09/08/2006 12:31PM
Posted 09/08/2006 12:31PM | Edited 09/08/2006 12:39PM Opening Post
OK. I've given the form the 1st run thru. There are several problems yet to be worked out IMO.
1 - Judging AFOV in increments of on-axis, central 50%, outer 50%, edge, was odd. If use 25% increments then too small. I think it should be just 3 areas, central 3rd, next 3rd, final 3rd. If you draw a circle and place inner circles at 1/3 and 2/3 measured linearly, then hold it close to your eye, those regions would be reasonable.
2 - While it's great evaling all those edge aberrations, if one is severe, then the rest don't matter since overall it can ruin the view. It was tedious testing for them all. And with them all seperate weighting becomes an issue.
3 - The weighting needs lots of work to find correct balance. Numbers you will see in attached photos (in next 2 threads I posted) are not how I judge the line up. I'm thinking that perhaps all the edge distortion aberrations should be combined somehow into a single aberration factor number then weighted and averaged with the rest.
4 - Moving from the field, to the form, meant lots of going over notes. I'm thinking of adding a tab where you can print out a pictorial diagram and just mark it up so translating back to form is easier.
5 - I know I'll hate this, but adding mid-points beteen each rating category. Let's face it...some just fell between Solid and V.Good. But on current form had to pick one or other.

That's it for now. But it's also clear that Narratives are still very valuable to explain where some of the EPs really excelled observationally. So more work to be done in hashing this out to be more easily usable and as an accurate archive.

What was interesting is that I filled out the form after 1st evening's observations. Then did some additional evenings of verifying, and a few days later filled out the form again anew, then compared 1st impression with memory after a week or so and they were both the same! I gave everyone the exact same marks.

Anyway, in the next 2 threads under this I have the photo of the form filled out. Below is the actual narravive (in draft) that I'll post in review section once I clean it up a bit.

-Bill

ps - You'll note on form the UO non-HD is rated. I need to explain in the narrative yet about this. It was just terrible the entire outer 50% afov and was giving so much scatter it haloed. I can't believe it was good and am thinking it must be a defective unit as the HD version was leaps better.

==========TEST RESULTS NARRATIVE===========
This test pitted 5 eyepieces against each other for performance on a variety of celestial objects. While they were all of similar focal length (four being 5mm, and one 5.9mm), 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 $59 to $250. Many thanks and appreciation are due to AstroMart member Steve Couture for his generous loaning of the Radian, TBM, 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. This latter point should be of particular note as when observing conditions are ideal, the differences between eyepieces become much more apparent. As conditions degrade, these differences narrow or even go away. During my observations of Jupiter this was very apparent. As Jupiter descended, the differences between the eyepieces gradually grew smaller and smaller to a point when they all presented equal imagery when Jupiter was only 20 degrees above the horizon and the atmosphere leveled the playing field.

The pictured 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 objectivity to the eyepiece evaluation process, is still in a 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. For more information regarding the observing conditions, telescope used, and experience of the observer conducting the test, please refer to the 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, Star Splitter 3rd, and SuperMono 4th. It is interesting to note when you look at the form, that the Star Splitter had a variety of off-axis issues, but for the most part they were present only negligibly. The SuperMono showed some CA off-axis, but a rather significant softening due to bloat making the off-axis image less than desirable. 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. Simply stated, the complex interplay of all the optical and usability factors, does not easily translate into a determination of “best.” The qualitative “narrative” still seems to be the best approach for communicating overall performance or niche performance of an eyepiece. Quantification of individual optical performance characteristic, as this form also captures, enhances the process by giving us a more standardized baseline and perhaps a future hope of being able to discern what the exact connection may be between optical performance factor, observing instrument, sky conditions, observing site, celestial target, and overall observing performance of an eyepiece. Therein lays, I believe, the most valuable aspect of having a standardized form to capture critical data points during an eyepiece evaluation. Below, therefore, are listed each eyepiece along with a narrative of its strengths and weaknesses:

5mm TeleVue Radian (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 (1st Place for Lunar Detail):
T----------------------------------------------------
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 XXX

5mm University Optics HD ABBE Orthoscopic (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.

5.9mm Siebert Star Splitter (1st Place for Open Clusters and Double Stars):
----------------------------------------------------
Like the UO HD, the Siebert Star Splitter also performed admirably across the board on all objects. However, it edges out the UO HD often placing in the #2 spot behind those eyepieces that took #1 positions on particular classes of celestial object. For lunar detail it was a #2 behind the SuperMono, and it was only ever so slightly #2 behind the Radian on Jupiter putting up a good fight against both. The primary edge the Radian had on Jupiter was probably due to its warm coatings. While the resolution of the Star Splitter shows excellent details, its cooler/neutral coatings present more of a washed-out view of Jupiter’s clouds compared to the Radian. On Globulars the Star Splitter had the same advantage as the Radian with the larger AFOV, but its extremely small star point size did not work as an advantage for Globulars under these observing conditions. However, for Open Clusters and splitting doubles it did excel over the others, coming in as #1, but not by what I would characterize as an order of magnitude. While it’s focal length was slightly longer than the others, and many will say this could be a factor for any noted differences, I would tend to disagree that it was a significant factor. I did not have a 5mm Star Splitter and wondered myself how much of an issue this might be, so I did a quick compare on a few objects using a 5mm UO HD and a 6mm UO HD to see if this 1mm (240x vs 200x) made any difference in details. Flipping between the 5mm and 6mm UO HDs showed now noticeable difference in image details or quality on-axis. Because of that, I tend to believe that the performance of the 5.9mm Star Splitter is valid compared to the 5.0mm test companions and would hold true if the Star Splitter were also 5.0mm. Finally, in addition to being a better generalist than the UO HD, and almost equaling the Radian on Jupiter, the Star Splitter does have a very specialized niche where it performs #1, this was in star point size. The Star Splitter easily produced the finest star points compared to the others in my fast Dobsonian. An excellent eyepiece for splitting the most difficult of doubles, and #2 in most other categories compared to its competition.

Posted 09/08/2006 12:32PM #1
Posted 09/08/2006 12:33PM | Edited 09/08/2006 12:33PM #2
Posted 09/08/2006 05:49PM #3
Thanks for all the work Bill, it look great ... just wish you had a Pentax XW Series 05.0mm I think thats giong to be my next EP.

Again GREAT WORK.

Bob

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