The Tele Vue philosophy (ethos, if you will) has always been about inspiring "spacewalk" vistas by creating both the finest "rich field" refractors and wide angle eyepieces. With their minimum 100-deg apparent field of view, full-field sharpness, and exceptionally high contrast, the Ethos eyepiece line is another step in that direction.
Maximize your "spacewalk" experience with the TeleVue 21mm Ethos. Transform your passage through the Milky Way with the 21mm's nexus of contrast, power and field. Larger deep sky objects and rich star fields are its natural playground. Looking on-axis your field-of-vision is filled with 100 degree of stars, however wherever you chose to concentrate your attention you'll see sharpness and richer contrast. Extending the Ethos focal length range to 21mm while maintaining the original performance goals of the rest of the series brings the eyepiece up against the mechanical limits of the 2" barrel and focus constraints. The 21mm provides the maximum true field of view, and has no significant vignetting at the edge of the field.
The 21mm focal length completes the logical set of 21mm/13mm/8mm and nicely juxtaposes the 17mm/10mm/6mm combination within the Ethos Series. Each step within these two sets approaches a 3x field area gain. The 21mm's effective field stop diameter is 36.2mm, bringing its true field close to the 35mm Panoptic (38.7mm Field Stop diameter). Its true field is also larger than the 26mm Nagler with its 35mm effective field stop diameter. In an f/4 Dobsonian, the exit pupil is just 5.25mm using the 21mm Ethos instead of 8.75mm with a 35mm Panoptic, or 6.5mm with a 26mm Nagler.
All Tele Vue Ethos eyepieces have proprietary tuned full multi-coatings, blackened lens edges, high index glasses, fold-down eyeguards, rubber grip rings, cover for the eyeguard, an undercut in the barrel for extra locking security, and filter threads. All Tele Vue eyepiece lines are proprietary, in-house designs manufactured to their specifications and tolerances. Every eyepiece is individually tested at Tele Vue to ensure it meets high optical and cosmetic standards.
Ethos Series Development History
Tele Vue is known for its in-house eyepiece and telescope designs by Al Nagler; their latest eyepieces brings new meaning to the term "in-house." The concept for this eyepiece series was proposed by Tele Vue President David Nagler, with performance parameters giving it the fundamental characteristics (the ethos) of a Tele Vue eyepiece: high contrast, comfortable eye relief and full field sharpness. Control of astigmatism, field curvature, lateral color, angular magnification distortion correction, and low pupil sensitivity for daytime use were specified criteria.
Following Tele Vue's philosophy of pushing the state of the art, long-time Tele Vue employee and optical design protégé Paul Dellechiaie took up the challenge and designed the basic eyepiece form. Under Al's guidance, Paul tweaked his design to fulfill the original goals.
While sharpness is inherent to the optical design, contrast is maximized through the intelligent use of flat finished baffles and ultra low reflectance, high efficiency coatings tuned to the composition of each element.
Introduced at the 2007 Northeast Astronomy Forum, Tele Vue once again broadened the amateur astronomer's perspective on the universe with: 100° of pure Tele Vue quality. The field area of this new eyepiece is more than 50% larger than an 82° field. The Tele Vue Ethos is essentially multiple eyepieces, delivering the true field size of a longer focal length, narrower apparent field eyepiece with the benefits of higher power and darker sky background.
|Barrel Size||2" (50.8mm)|
|Apparent Field of View (Mfg Specified)||100°|
|Eye Relief (Designed)||15mm|
|Filter Threads||Standard 2" Filter Thread (M48 x 0.75)|
|Blackened Lens Edges||Yes|
|Barrel Safety Recess||Yes|
|Barrel Type||With safety undercut|
|Protective Plastic Storage Container||Yes - Free Agena Eyepiece Container|
|Protective Plastic Storage Container Size||Agena 85x120mm|
|Maximum Width||2.95" (74.9mm)|
|Field Stop Diameter||36.2mm|
|Rubber Eye Guard||Yes|
|Warranty||Limited lifetime warranty|
- Suitable for use with Tele Vue Dioptrx / digiscoping