13mm Ethos

A Triple-Digit Field of View Tele Vue’s new 13-mm eyepiece is about to transform deep-sky observing. S&T RATINGS Optical Performance Sensibly perfect. No meaningful improvements possible. Just as the original 13-mm Nagler set a new standard for deep-sky observing in 1981, the Ethos sets a new standard today. Owning one will guarantee long lines at your telescope during any star party. [I]f I were dropped on a desert island tomorrow with the 12-inch scope and only one eyepiece, I’d want it to be the Ethos. Some of the views were simply stunning. The globular cluster Messier 13 in Hercules appeared as a sprawling sphere with thousands of resolved stars, many sweeping outward in sinuous arcs. Even under the most critical examination, bright stars look sharp and round across the entire field. The Ethos hasn’t sacrificed one bit of on-axis performance in achieving its 100° apparent field. [T]he view of a starry sky with the Ethos and TV-NP127is is nothing short of breathtaking. Besting the fields of other astronomical eyepieces by more than 20% in diameter and more than 50% in area, Ethos is a stunning optical achievement.

Read Complete S&T Review!

After showing Ethos at a number of events since April 2007, we can safely conclude it brings the observing experience to a new level. This is based solely on user's reactions to views of familiar objects, not on any prejudgments, publicity or hype on our part. While we were quite confident of success, we wanted, and still want, to explore all the ramifications of what a sharp 100° field really represents.

Right after NEAF in April, Rodger Gordon, the acknowledged "eyepiece junkie" of all time, wrote me "Definitely the finest wide-angle eyepiece I've ever seen. If God is an astronomer, this is the wide-angle eyepiece he'd choose. You can quote me." Thanks, Rodger. I waited until now to avoid "priming the pump", so to speak before quoting your unbridled enthusiasm publicly.

For some time, I've been pondering just why the response has been so overwhelmingly positive. And if I really understand why, is it possible to quantify? My views of the Double Cluster at Stellafane pointed the way.

The 1991 article I wrote for Sky and Telescope on magnification provides the key. A major conclusion for low power states: "The best view occurs with the highest power that comfortably includes the target object. Higher powers darken the background sky, reveal fainter stars and show more detail. The resulting smaller exit pupil also minimizes the effects of eyesight defects."

Considering the potential of Ethos, let me posit a more general conclusion:

It's clear that the largest possible apparent field for a given true field yields the most magnification for greater resolution, with a darker sky background for more contrast as a result of the smaller exit pupil. I believe this combination of contrast, power and field causes the typical "wow" reaction — the Majesty Factor. I think Tom Trusock said it most succinctly in his Starfest (Canada) report: "The same true field at higher magnification means that you'll see blacker skies and more detail." Dennis di Cicco in his 5-star review of Ethos in his October 2007 Sky & Telescope review noted something similar: "Observing with the 12-inch scope, I typically bounce between a wide-field eyepiece for star-hopping and a high-power one for detailed views. But the Ethos gave me both. The field was large enough to star-hop, and the magnification was high enough to bring out faint stars and resolve details in galaxies and star clusters." (He coincidently also illustrated field sizes using the Double Cluster.)

Let's try to quantify the so-called Majesty Factor. While we cannot quantify the majesty of a great symphony, work of art or edifice, I think a meaningful Majesty Factor is quantifiable for those great deep sky views. Here's how:

— Al Nagler