Product Description
The new 17mm TeleVue Ethos 100° field eyepiece is designed for no-holds-barred medium power deep space use with telescopes having focal ratios down to f/4. It is exceptionally effective on nebulas with fast f/ratio reflectors, such as Dobsonians, giving both an immense field and a bright exit pupil (nearly 4mm with the typical f/4.5 Dob). Its very wide field also makes it convenient for moderate power lunar and planetary observing with Dobsonians, as you have much longer to observe before the planet drifts out of the field and the scope has to be repositioned. That said, it is worth noting that the new 17mm TeleVue Ethos is marvelous for open clusters, nebulas, galaxy clusters, and globular clusters with any telescope.
The 100° apparent field of this new 17mm Ethos eyepiece is nearly 50% larger in area than the 82° field of a "space-walking" 17mm Nagler. You could get a similar true field with a longer focal length (but narrower apparent field) eyepiece, but the 17mm TeleVue Ethos has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length. You can use the field of view calculator below to see just how much sky the Ethos can reveal with your telescope.
There is a soft rolldown eyecup to shield the eye from ambient light (from a neighbor's security light, for example) and improve the image contrast. At a usable eye relief of 15mm, the 17mm Ethos would normally somewhat vignette the field of view for eyeglass wearers. However, since the 100° field is so wide that you can't see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem.
The 17mm Ethos has all the virtues that professional and amateur astronomers have come to expect from a TeleVue eyepiece: high contrast, comfortable eye relief, and full field sharpness - with well-controlled astigmatism, field curvature, lateral color, angular magnification distortion correction, and low pupil sensitivity (kidney bean effect) for daytime use. While sharpness is inherent to the optical design itself, the contrast is maximized through the intelligent use of flat finished baffles and ultra low reflectance, high efficiency coatings that are tuned to the glass composition of each lens element.
The 17mm Ethos fits 2" focusers only. A safety groove is machined into the 2" chrome barrel to engage your focuser thumbscrew. This will help prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing.
The 17mm TeleVue Ethos eyepiece will accept TeleVue Dioptrx eyesight astigmatism correcting lenses.
Please note the weight of this eyepiece if you have a Dobsonian telescope. Its use may require some temporary rebalancing of your scope, or the use of a TeleVue #TVEQC equalizing adapter with your 1.25" eyepieces to avoid balance problems.
Tech Details
| Barrel Size | 2" |
|---|---|
| Eye Relief | 15mm |
| Field of view | 100 |
| Focal Length | 17mm |
| Weight | 24.8 oz. |
| Warranty | Limited Lifetime |
Reviews
On the 102mm f/8.8, the 17mm Ethos is a 53x magnification, 1.89 degree TFOV (True Field of View), 1.98 mm exit pupil eyepiece. Having a TFOV just under 2 degrees in a scope of this length is quite a large area of the sky, and is quite good for large objects such as M42 (Orion Nebula) and M44 - I use it quite often on M42. It's a bit too small for M45 (Pleiades) - you cannot see the entire cluster at once, nor can you get a nice border of sky around it for the best view - you need a lower focal length telescope or a wider view eyepiece for objects that huge. The exit pupil is very useful for the medium magnification it generates in a 900mm focal length f/8.8 telescope.
On the 235mm f/10, this is a 138x magnification, 0.72 degree TFOV, 1.7mm exit pupil eyepiece. A TFOV of 0.72 is too small for all of M42, but it's great for objects like the moon or M11 (Wild Duck cluster) or M6 (Butterfly cluster) - in the longer scope, this eyepiece serves as a good still sky planetary eyepiece as well, generating a magnification just higher than my 7mm Ortho does in the 102mm refractor above. In a scope this long, it's far too small a field of view for the larger clusters and nebulae, but it's a good planetary performer.
In all cases, it's a heavy eyepiece, so if you switch back and forth with 1.25" eyepieces (like my high-magnification Orthos), you should use a heavy 2" adapter to preserve your scope's balance. The 15mm exit pupil is quite good; while wearing glasses, I can see most of the FOV with the cup turned down; with the naked eye I'm fine after a little refocusing - either putting my eye closer or moving my head just a little lets me see edge to edge.
For comparison, the TFOV is about 9% more than a 1.25" 32mm Plossl, or 20% smaller than a 2" 42mm Plossl - but with the magnification of a 17mm eyepiece. Essentially, the 17mm Ethos has a slightly higher TFOV than the maximum possible 1.25mm eyepiece could have due to field stop limits, and will have a much higher magnification. The apparent size of objects is even larger, due to the 100 degree AFOV (apparent field of view). (Posted on 8/4/2017)
The 17mm is heavy (around 1.5 pounds, according to Tele Vue) but the weight is not at all detrimental. I have it in a William Optics 2" diagonal on my 8 SE with the standard mount and the views are solid. The motor does not struggle a bit and the balance is fine. The Ethos eyepieces are pretty expensive but they are worth it to me. I am buying eyepieces in order to (hopefully) keep them around for life, so I view it as a good investment for any telescope that I will get in the future as well. This eyepiece is a joy to use and I am very happy to own it. (Posted on 8/4/2017)
