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Tele Vue Ethos 13


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Tele Vue Ethos

Tele Vue Ethos 13 - A hundred degrees of perfection


22.4.2008 Miroslav Petricek

External characteristics



Perhaps the first thing anybody realizes when seeing Ethos for the fist time is its size. It really is a big thing, even in comparison with other 2" eyepieces, like longer Panoptics or Nagler 31 type 5. On the other hand, when you take it in your hand, you might be surprised that it is not so heavy. Thus, if you are afraid that Ethos might break balance of your scope, calculate carefully. Maybe you find out that the Nagler 13 type 6 (as shown on the comparison picture below) complemented by sturdier 1.25 to 2" adapter, is not much lighter than Ethos. Most likely there is not just a glass inside...



A good news for all bino-lovers is the fact that in March 2008 there was a small update to the Ethos's physical dimensions. In fact, only one person out of a dozen has a sufficient inter eye distance to be able to use a pair of original Ethoses in a binoviewer. That's why a barrel is now a few millimeters narrower than before. Now, nothing can prevent you from enjoying 200-deg in the binoviewer (except for a premium price for such a setup, of course).

As far as the physical appearance and features are concerned, the eyepiece does not stick out of the other Tele Vue eyepieces. Craftsmanship is precise. The body is made from an anodized aluminum with a rubber grip. The upper skirt is chrome-plated, and has filter thread and safety undercut. All important surfaces are precisely blackened. Unfortunately, the foldable eye guard is simple and not adjustable, unlike the type 4 Naglers, for instance. The diameter is hybrid - both 2" and 1.25". This setup has as many lovers as haters. As for myself I tend to prefer 2" over 1.25" as I consider it safer, given by dimensions of the eyepiece. Maybe it is just a feeling. Optical-wise Ethos is a 1.25" eyepiece (measured by the diameter of the field lens). The filter thread is 1.25" only, so if you want to use 2" filters you need to get hold of the optional EBX2120 skirt that turns Ethos into a regular 2" eyepiece.



Unfortunately, no clamp method can fit Ethos to any standard parfocal group. It means you have to refocus when changing eyepieces. As regards the standard Tele Vue lineup, Ethos is quite close to the Nagler 26 type 5, but not exactly. This is unfortunate as up to now it has been possible to create a complete eyepiece set that would be almost parfocal.

The happy Tele Vue customers have learned not to be afraid of the engraved label “TAIWAN R.O.C." revealing the country of origin. In fact, all the products have to make it through very strict tests in the headquarters of Tele Vue Optics in New York, USA. Only then they are passed to the standard distribution. Five years of warranty and quality of after-market service where you can send a product to the factory for repair, adjustment, cleaning and even retrofit upgrades, have become legendary in the amateur astronomers' community.

Optical performance


I am not a professional optician, so don't expect any lab measurement, resolution tests, etc. Everything mentioned below are just my subjective observations emerging from my comparison with the Nagler 13 type 6 I used before.

The eye relief is 15mm. This is one of the parameters that everybody feels differently about. Although I would not declare the eyepiece to be “comfortable", I do not think it is too close. It is not possible to comfortably observe with glasses on. On the other hand, those with astigmatism can use a Dioptrx correction lens without any adapters. I would compare the easiness of use to the Naglers type 6. They have the eye relief even 2mm closer, but it is compensated by the narrower field of view. As far as I am concerned, I think that 15mm is just OK, but I would not be happy if it was even a millimeter shorter. Also, I often fold down the eye guard to feel more comfortable.

It is not surprising that, given by its performance class, all optical parameters are excellent. However, is it better than Nagler of similar focal lengths? Yes, perhaps. The common rule is that the newer the eyepiece, the better the quality of anti-reflex coatings. This is definitely valid also for Ethos. I have noticed different tints of colors in Ethos. For example, Saturn is slightly whiter than in Naglers, where it is more yellowish. Contrary to other reviewers, I don't think I can see more details or observe more easily than in the Nagler 13 type 6. As for optical performance, I consider the Naglers 13 type 6 equal to Ethos. Only some lab measurement or greater experience along with a possibility of comparison would provide the true answer.

Pincushion distortion at the edge of the FOV is surprisingly well corrected. On the other hand, Ethos definitely does not have a rectilinear image. That's why there are better eyepieces for daytime observation than Ethos. The well known fact is that it is the intention of its optical designer, because it is not easy or even possible to correct both the rectilinear and angular magnification distortion at the same time. The optical designer of the Ethos eyepiece, who is, by the way, not Mr. Al Nagler himself but Tele Vue employee Paul Dellechiaie, has decided to focus on the angular distortion, dictated by well known logic that sharpness at the edge is more important than preservation of the exact shape of the observed object. One can see that the distance between two stars may change according to the position of the pair in the field of view, or that straight things like walls can appear bowed. To my eye there has been some improvement from the Naglers type 6, though I consider the Naglers type 4 even better corrected for pincushion.

Rectilinear distortion in the center, middle and at the edge of the field of view

(photos by Zdenek Rehor)


At the extreme edge just around the field stop I can see a tiny blue color ring. Perhaps it is just diffraction from the field stop. It is apparent when a planet or bright star crosses the field stop. I have already seen a similar issue with different eyepieces. But I would not say it lowers the impression of the image. Most people would not probably notice that at all.

100-deg


There is no dispute about the best-selling feature of Ethos - its huge apparent field of view of 100-deg. Since the original Nagler days, it has become a good tradition to alleviate the purpose of such a wide field of view. Many people say that no eye can handle such a field at once. Usually, the greatest skepticism comes from people who have never looked through it and, thus, make presumptions based on their experience with other wide-angle eyepieces they are happy with.

Certainly, the field of view of Ethos is very wide. It is also true that most people, if not all, can not look over its field stop in all directions at the same time. However, is it really a bad thing? Definitely not! A view where you can see nothing else but stars in all directions as if they were surrounding you is very appealing and significantly improves enjoyment from observation. I would compare that to looking through binoculars, or just with naked eyes. It almost wipes out the instrument through which you look, hence you can focus just on the space. It is such a strong feeling that I find myself moving my head, trying to see more. Of course, one can say that you can experience that also with Naglers, especially 2" models, but I suggest everyone to try and compare this with Ethos. But be warned - there is no easy way back.

Does such a wide field also have other advantages than just “better experience"? Be sure it does! The effective field stop of Ethos eyepiece is 22.3mm, which is the same as Plossl 26 and better than Nagler 16 or Panoptic 19. It means that in the given telescope you can see exactly the same real field of stars like with these eyepieces and, what's more, with much bigger magnification. It is well known that higher power reduces brightness of ambient background, which becomes darker and makes the observed star objects more visible. Very impressive is the advertisement published by Tele Vue, showing the comparison between Plossl and Ethos.

Experiences from the field



If you considered Ethos as just another 13mm eyepiece and have doubts about the way it could fit in your current eyepiece set, don't be mistaken. The real field of view makes it a champion that could replace almost every other eyepiece between 13-20mm, especially if you don't use wide-angle models. If there is something I don't like about observing, it is changing the eyepieces. You know that it is a hassle. First you have to take the eyepiece out, safely store it, find the new one, put it to the focuser, locate the object if it has meanwhile disappeared from the field, refocus, rebalance the scope if necessary, etc. It all takes time. And most people want to observe, not fight with the equipment in the dark. I think that Ethos draws closer the days when it will be sufficient to have just one eyepiece + maybe a decent barlow. Personally, I found some of my beloved focal lengths redundant when I bought my Ethos. While with regular eyepieces it is common that you start at low power, find the object, put more power and observe, Ethos is different. Having both high power and wide field of view readily available is tempting. You can just leave Ethos there and “starhop" to the new target. I can not agree more with opinions that Ethos may change our habits of observing.



I can confirm the expectation that Ethos works well with barlows. There is no difference whether you use a standard or telecentric (Powermate) design. In fact, any decent barlow can make Ethos a perfect planetary eyepiece. Despite the fact that the setup looks a bit odd (as you can see on the picture), I have noticed neither any image degradation nor vignetting when using my Tele Vue 2x barlow. However, given to the size of its barrel, be careful when using Ethos with short versions of barlows, coma correctors, diagonal mirrors or similar stuff, as it could damage the optical elements. The risk is even higher with filters.



I could mention here many specific objects I successfully observed with Ethos. But, I don't think it is really necessary. If I look apart from that “added value" mentioned above, there is nothing special about the image - it is perfect in every single aspect as expected. No wonder that in my well-corrected Tele Vue Genesis refractor the stars are focused to points across the whole field. Still, if I were to mention at least some spectacular sights, it would be M13 in Hercules, double clusters in Perseus and Cassiopeae, stunning M42&M43, well-known Leo galaxy triplet, Pleiades, etc. - in fact, almost any other object I pointed my scope to. Focusing the barlow on the moon was beautiful, as well as the planets. There were no flares and ghosting. And again, there is that hardly reproducible “immersion" effect.


Telescope

Magnification

Field of View

Newton 250 f/5

96x

1-deg01'

Newton 300 f/5

115x

0-deg51'

Refr. ED80 f/7.5

46x

2-deg07'

SCT 8" f/10

156x

0-deg37'

Tele Vue NP101

42x

2-deg21'

Parameters of Ethos in some popular scopes

Conclusion



Just like original Nagler 28 years ago, Ethos is probably the most advanced eyepiece on the market, if not ever made. Furthermore, it creates a class of its own because there is no other wide eyepiece like this. Its ideal focal length of 13mm makes it a sweet spot eyepiece in most telescopes, especially in fast Newtonians where it really excels.

If Ethos has some weaknesses it is, apart from its price, its size. Someone could find 15mm of eye relief a bit short, others might miss adjustable eyeguard or non-parfocalness.

Taking the above into account, I warmly recommend you to buy one, either as a new addition or as an upgrade to any existing eyepiece. However, for those already Tele Vue addicted, no suggestion is necessary - they most likely own one already.

Pros

Cons

+++ 100-deg AFOV

dimensions, weight

Very good optical performance

price (almost $1000 in Europe, don't ask me why)

Both barrel sizes

non-parfocal with other eyepieces




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