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TeleVue Delos Eyepieces
TeleVue is pleased to introduce the 10mm and 6mm Delos eyepieces, the first available focal lengths in a new mid-to-short focal length eyepiece line of 20mm eye-relief, 72 degree apparent field of view eyepieces. Every optical, mechanical, and ergonomic aspect was rethought to achieve reference standard performance for any visual application. Both of these first members of the Delos family are suitable for use in binoviewers.
TeleVue Delos Concept:
It was natural to take lessons learned from the tremendously successful Ethos project and apply it going forward. In the fall of 2008, Paul Dellechiaie was tasked to investigate a long eye-relief eyepiece design in the 70° AFOV range, retaining the key performance goals met with Ethos. My father named Paul's design, "Delos." Delos is a beautiful Greek island which happens to be the mythical birthplace of Apollo, god of light. More importantly the name was chosen to give recognition to Paul, principal designer of both Delos and Ethos. - David Nagler
Introducing TeleVue Delos
The Delos was conceived as a narrower field Ethos. Reducing the field to 72 degrees allowed freedom to increase eye relief, while controlling pupil aberrations, all without making the eyepiece too large. With Ethos performance standards as benchmarks, the Delos design achieves full field sharpness, virtually perfect theta distortion mapping, and color neutrality.Image fidelity is maximized utilizing glass matched multi-coatings and anti-reflection surfaces throughout the eyepiece.
Contrast is further enhanced with a new, continuously adjustable height eyeguard system that can be locked in any position. Since the Delos eye-lens measures a quite large 35mm in diameter, preventing stray light from reflecting off the first surface and extraneous light from entering your eye pays off in a nice increase in perceived contrast. The eyeguard's sliding action allows for positioning the soft rubber eyeguard at the ideal height to suit the observer's preference. Indicator marks on the eyepiece body are handy reference guides for setting your perfect position. The eye-guard can also rotate for Dioptrx users.
Delos First Light - May 2011
We received our demo Delos eyepieces in early May. Naturally it rained most of the month. The first thing we noted in the daylight was that the 10mm Delos snaps into and out of focus within a very narrow range of focus travel. This behavior was far less noticeable on the 6mm Delos. A quick call to the designer, Paul Dellechiaie confirmed that this was not our imagination.
We chose to observe Saturn for our first light using a TeleVue TV-102 refractor and the 6mm Delos in a side by side comparison to the 6mm TeleVue Radian eyepiece. The first thing we noticed was that the difference between the 72 degree apparent field of the Delos and the 60 degree apparent field of the Radian seemed much larger than the numbers might suggest. The second thing we noticed was that the Delos had a definite edge in terms of contrast, producing a much more enjoyable image of Saturn. One thing we did not notice was any tendency to black out or "kidney bean," which is often a problem in eyepieces with longer eye relief.
Deep Sky Observations - June, 2011
Our demo Delos eyepieces took a field trip to Cherry Springs State park in early June. A group of seasoned observers armed with 17 to 25-inch Dobsonian telescopes and Paracorr Type 2 coma correctors put the Delos eyepieces up against Nagler Type 6 and Ethos eyepieces of similar focal lengths. This group found they preferred the Delos to the Nagler Type 6 because they thought it offered higher contrast. On the other hand, as they put it, "the Delos is no Ethos." A/B testing of the 10mm Delos and Ethos demonstrated that the Ethos was capable of revealing fainter stars.
Our test group also noted some tendency for the 6mm Delos to black out or "kidney bean" if the eye cup is not extended. We discussed this observation with Paul Dellechiaie at TeleVue, who explained that the eyepiece would start to black out if the eye is placed too close to the eye lens. That is what the rubber eye cup with twist up adjustment is for. There should be no problem if the rubber eyecup is extended, and this has been our own experience.
