 In April 2007, Tele Vue Optics introduced the 13mm Ethos,the first eyepiece to offer a 100-degree apparent field of view (see SkyNews, Nov./Dec. 2007). An 8mm model was soon added to the lineup. This spring, three new focal lengths have been released—6mm, 10mm and 17mm —and Tele Vue supplied SkyNews with a 10mm and 17mm Ethos for review.
When I first read that Tele Vue had created a 17mm Ethos, I was immediately intrigued by the focal length. With its 100-degree apparent field of view (AFOV), the 17mm would provide a true field of view very similar to that of the Tele Vue 24mm and 27mm Panoptic eyepieces I own (the Panoptic Series has a 68-degree AFOV). Much of my testing revolved around comparing the 17mm Ethos with the two Panoptics.
I used three telescopes for the tests: a 12.5-inch f/4.8 Mag 1 PortaBall; aTele Vue 76mm f/6.3 apochromatic refractor; and an 11-inch f/10 Celestron Schmidt-Cassegrain. Since short-focal-ratio scopes offer a more stringent eyepiece test, most of the testing was done with the PortaBall. On this scope, the 27mm Panoptic provides a 1.1-degree actual field of view at 56x, while the 24mm Panoptic achieves a 1.0-degree field at 64x. This is enough to frame several galaxies in the same field of view in the galaxy-rich constellations Leo and Virgo, including part of Markarian’s Chain, where I can view nine galaxies at once. Through both the 24mm and 27mm Panoptic, the view was as expected—superbly sharp to the edge. But with the 17mm Ethos providing a 1.1- degree field at 90x, it was instantly much easier to examine each of the galaxies because of the added magnification and the extra contrast and darkened background.
While galaxies present a pleasing image, a bright open star cluster is a better target for testing eyepiece sharpness. With stars filling the entire field of view, it is easy to discern aberrations at both the centre and the edge of an eyepiece’s field of view. M44, the Beehive Cluster, is perfect for this test, and the 17mm Ethos passed with flying colours. I was very impressed at how sharp the entire field of view was in the 12.5-inch telescope. After I placed the 10mm Ethos in the PortaBall’s focuser, it quickly became a favourite, performing just as well as the 17mm. While observing both Saturn and the globular cluster M13 through the 12.5-inch, I also noticed that the 10mm Ethos showed slightly more contrast than a 10mm Tele Vue Radian.
Both the 10mm and 17mm Ethos eyepieces have 15mm of eye relief, which I consider to be just perfect, but the 10mm felt more comfortable than the 17mm. Although I could see the entire field of view through each, I had to press my eye slightly harder against the eyeguard with the 17mm. Two other observing companions experienced this same effect. The 10mm can be used in both 1.25-inch and 2-inch focusers, while the 17mm can be used only with a 2-inch focuser. Do you really need a 100-degree eyepiece? Owners of Dobsonian telescopes or observers who use an altazimuth mount will definitely value the extreme wide field of view. The “spacewalk” sensation when observing with these eyepieces must be seen to be appreciated. But, of course, there is the cost—around $830 for the 17mm, $675 for the 10mm, at Canadian telescope shops—making this one of the most expensive eyepieces ever offered to the backyard astronomer. Weight may be an issue for small telescopes. The 17mm, the heaviest in the Ethos lineup,weighs in at 1.6 pounds.; the 10mm is 1.1 pounds (for additional specifications, see www.televue.com).
After reviewing the 13mm Ethos in 2007 and now the 10mm and 17mm models, I admit to being a full-fledged Ethos-aholic. These are simply the very best eyepieces I have ever used. The 10mm and 17mm Ethos have become permanent residents in my eyepiece collection. If you crave supreme optical perfection, you will no doubt find an Ethos a must-have for your equipment case.
Todd Carlson is an enthusiastic observer and astrophotographer living under pristine skies near North Bay, Ontario
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