Jump to content




Search Articles


- - - - -

Eyepieces: Performance of Simple Vs Complex types


Voice your opinion about this subject in our forums
I recently purchased a set of Meade Series 4000 Plossl eyepieces for use in a telescope comparison on planetary performance between a Meade 152 ED and Celestron NexStar 11. I wanted a full range of good quality planetary eyepieces of the same brand to make my comparisons as fair as possible. The focal lengths of these telescopes (1370mm vs. 2800mm) meant that with my existing inventory, I would not have similar design eyepieces that could be utilized to provide similar magnifications. As a side effort, I also decided to do comparisons between these simpler design eyepieces and the premium 2” eyepieces I currently own. This inventory consists of a 35mm Panoptic, and 22mm, 17mm, and 12mm T4 Naglers. The goal would be to see if the simpler design would outperform (in absolute terms) the more complex design on a variety of observing targets.

Prior to the purchase of the (used) Meade eyepiece set, I owned 3 Plossls: A Televue 15mm, and Orion HighLight 12.5 mm and 10mm eyepieces. I started with a 15mm Televue because the resultant 185x magnification in my N11 is the most I can utilize on most nights, due to seeing conditions. Because there is no 15mm T4 Nagler, I could not do an exact comparison using the same magnification, however the TV 15mm Plossl was without doubt, my most used planetary eyepiece. This is partly due to the fact that it hit the magnification sweet spot for my seeing conditions, and partly due to the fact that it just seemed to performed better than the 17mm Nagler in my box on planetary targets. The Naglers are incredible eyepieces for what they do, but in fact, I felt that the TV 15mm Plossl was slightly, but perceptibly sharper and more contrasty when doing planetary observing. It also didn’t ghost or bloom, as the Naglers sometimes do on bright objects.

The Meade Series 4000 Plossl line has been described by one reviewer as being an entry-level for premium planetary eyepieces. In fact, using my Televue 15mm Plossl as a reference, I found the 15mm Meade to be practically indistinguishable from the TV 15mm in absolute performance. When I would look through one I would think that it was a tad sharper than the other, until I swapped them. Then I would think, no, I am seeing the same thing here… There was some difference in color tone, but it didn’t really affect performance. I also compared the Meade 12.5mm and 9.7mm eyepieces to the Orion 12.5mm and 10mm Highlights. This was harder because seeing conditions started to affect the ability to make really critical comparisons. Unfortunately, it appears that I live under a 200x sky.

I could not do exact magnification comparisons. Such is life. Still, I was able to get within 3mm in every case. In most cases, the magnifications were close enough that I think comparisons were valid (35mm Panoptic @ approx. 80x vs. 32mm Meade @ approx. 87x).

I viewed three types of objects: Planet, Nebula, and open cluster. I will limit my in-depth text to three specific cases: Saturn, M42, and M35.

Saturn:

In terms of absolute performance The 17mm Nagler was bested by both the Meade 4000 15mm and Televue 15mm Plossls. Views were simply sharper with both Plossls. Both Plossls showed a crisp ring division, and 4 very faint, tiny moons. The details were just more distinct with the Plossls. One of the four moons was not visible in the Nagler using direct vision, and only faintly detectable using averted vision. In terms of contrast, both Plossls also exceeded the big glass’s performance, showing a bit more subtlety in the banding, blacker background, more distinct planet shadow against the ring and the Crepe ring stood out just a bit more prominently against the blacker background between the rings and the planet’s disk. The difference between the Plossls themselves was almost impossible to see, while the difference between the Plossls and the Nagler were subtle, but distinct. Finally, the Nagler tended to show a faint halo around the planet/moon area. This was also noticeable in the Plossls (Large SCT central obstruction is the cause here, I am sure), but not to the same degree. In fact, I attribute this halo to be the main culprit in the Nagler’s inability to pick out the 4th moon that was visible with the Plossls.

Results were similar when comparing the 20mm Meade Plossl to the 22mm T4 Nagler, though the lower magnification made it difficult to compare absolute performance because everything just looks so much sharper at lower powers. In numerous comparisons, and after much changing back and forth, at every viewing, I judged the Plossls to be superior to the big Naglers in all aspects of planetary performance, at least on this one target. I expect that the difference will be noticeable on other solar system targets to the same degree, and perhaps more so on Jupiter because of its greater brightness.

The great Orion Nebula, M42:

Here it is harder to do a direct comparison because of the aesthetic quality imparted by the ultra-wide fields of view being provided by the premium eyepieces. It is easy to look through a 35mm Panoptic or 22mm Nagler and be awed by the majesty of this magnificent nebula. In a recent viewing experience while on a trip out west under the pitch-black sky over the Nevada desert, M42 over-ran the field of view of the 35mm Panoptic and provided such an intense 3D like presence, that I almost didn’t want to look at it when I returned home!

Still, in terms of absolute performance, there is detail available in M42 that doesn’t require ultra-wide fields of view. I have used high powers to poke around this nebula many times. Using really high powers, you sometimes start to see knots of granularity and wisps that don’t stand out under lower powers. And there are stars in there… I’ve seen them. Here and there, you will find extremely faint stars shrouded in the gossamer veils.

I’ll start with the 35mm Panoptic vs. the 32mm Plossl. Here the difference was very, very small. Mostly it was related to the field of view provided by wider apparent field of view in the 68 degree 35mm Panoptic. But judging absolute performance, I would say that the 32mm Plossl did extremely well. While I could see the E and F stars in the Trapezium in both eyepieces, the F was only barely detectable in the 35mm Panoptic. The F component was a bit more separated from the glare of its primary in the 32mm, and therefore, a bit more noticeable. I don’t attribute this to the small difference in magnification. In fact, all for of the primary stars seemed a tiny bit tighter in the 32mm Plossl. I had never seriously considered that anything could really match the 35mm Panoptic in terms of absolute performance because the eyepiece seems so perfect. And yet I am convinced that the 32mm Plossl was sharper. Just a tiny bit, but in the end, sharper is sharper. It was more difficult to judge contrast differences because of the low powers involved. In this area of comparison, on this one object, I could draw no conclusion in terms of contrast performance.

Moving up the magnification ladder provided much the same outcome with respect to sharpness. Viewing the trapezium with the 22mm and 17mm Naglers, and then changing to 25mm, 20mm and 15mm Plossls, the primary stars always seemed to be a tiny bit better focused in the Plossls. Because of this, the E and F stars were more cleanly separated from their primary stars, but E and F were visible with direct vision in all eyepieces. There are several field stars around the Trapezium however, and the Plossls seemed to pull out more of them. Here and there, using the Plossls, I could detect faint stars with averted vision that were not visible in the Naglers.

I was able to use the 12.4mm and 12.5mm Plossls against the 12mm Nagler, but seeing conditions made it more difficult to draw a conclusion on sharpness. However when roving the nebula itself, this magnification starts to show distinct variations in the intensity of the nebula; kind of like a puffiness of a fluffed sheet. I detect knots and wisps at this magnification that are not visible using lower powers. Here, the 12mm Nagler was perhaps equal. Once again, the much larger field of view of the Nagler provides a challenge to making a valid comparison. You are seeing more background sky glow in the bigger field of view, which hurts contrast, but at the same time, the scale of some of these knots and wisps makes them overrun the smaller field of view of the Plossls. Consequently, they tend to be more recognizable in the 12mm Nagler. In ABSOLUTE performance, I would say that the simpler eyepiece did show better contrast, but the 12mm Nagler is probably the best eyepiece for me for this particular application.

Open Cluster M35:

Once again, the Plossls bested the more complex Naglers and Panoptic in absolute performance. I could detect stars in the simpler design that were only visible using averted vision in the more complex eyepieces, and I could see stars using averted vision in the Plossls that were not visible at all in the Naglers. In all cases, the stars were a bit sharper in the simpler eyepieces.

A single Planetary Nebula:

In faint, fuzzy observing, I have not done as much of a comparison. Just last night, I did slew my N11 to a faint planetary in the Orion area (I can’t remember which one, sorry). In summary, once again, the Plossls seemed to show a brighter nebulosity against a darker sky background. I could also use more power with the Plossls on this target. In fact, I could barely detect the nebulosity in my 17mm Nagler. I had the Nagler eyepiece in when I slewed, and when the scope stopped, I didn’t detect the nebulosity at all. When I changed to the 15mm Meade Plossl, I just barely caught it to the northeast of the center of the field of view. When I put the Nagler back in, I was able to see it with the Nagler as well, probably because I knew where not to look (averted seeing joke, get it?).

Conclusion:

In almost every comparison I made, the simpler eyepieces delivered better absolute performance than the MUCH more expensive Naglers and the lone Panoptic in this test. I don’t want to comment on the less tangible, more subjective attributes of the incredible Nagler design. Let it suffice to say that I am not going to sell any Naglers as a result of this comparison. If I just want to stumble around the sky, or when some objects sit in a particularly beautiful field, I still think that the Naglers provide a stunning experience. The ability of the Nagler to frame objects in longer focal length telescopes makes them particularly desirable, and while it may ultimately be marketing hype, the spacewalk affect is quite seductive in terms of its contribution to the overall observing experience.

Summary:

I will have to say that I can no longer ignore the difference in performance between the simpler Plossl design and the big, premium eyepieces. In fact, in the time since I have acquired this set of Meade Super Plossls, I find myself selecting them for more critical examination on many objects. Now more than ever, I am find that the better detail and contrast I can see using the simpler design DOES make it easier to just not notice the more restrictive field of view, as compared to the premium eyepieces I own. In terms of absolute performance, I now realize that it is tuff to beat a good Plossl.

Also, in the past, I have recommended that everyone should try at least one premium 2” eyepiece. Now I am not so sure. At their increasingly high costs, the difference between a FULL SET of quality Plossls and a single Nagler starts to look less appealing. Also, a bigger or better telescope, with a smaller selection of quality Plossls would perhaps be a better use for the money. Really. Especially when you consider the additional cost for high quality 2” diagonals!

PS.

Almost all of the differences in the observations I made in this comparison are probably greatly exaggerated because of my local seeing conditions and by my telescope’s large central obstruction. I believe that the affect of these two factors is magnified by each successive refraction or reflection in the optical train, collimating in an orgy of reflections and light scatter in the numerous air-glass surfaces of these complex eyepieces. Yes, these eyepieces use the finest optical multi-coatings available, but nothing eliminates these reflections; they just reduce them. Multi-coatings on the three or four extra PAIR of air-glass surfaces in these ultra-wide view eyepieces aren’t going to help them escape from the laws of physics. Popular books on the subject of star-testing and telescope design tend to treat everything in terms of optical aberrations in the primary optics, or in theoretical examinations of ray tracing. It is my theory that the successive light scattering of all of these surfaces in the complete optical train all add up to make the differences in eyepiece performance more detectable as apertures increase. Under steady sky conditions, the differences I noted in my observations may be less readily apparent as stars can be more closely focused into airy disks, also resulting in much less contrast reducing scattered light.

Large apertures with large central obstructions are probably going to show the differences between these eyepieces more conclusively than doing this test with smaller aperture, high quality refractors. I recently purchased a Televue Genesis, and I am eager to see how the Plossls stack up to the more expensive eyepieces when used with a premium 4” refractor. It is my guess that the differences won’t be quite as noticeable on the small, unobstructed aperture.

Do you want me to tell you how it turns out???




0 Comments



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics