Maximize your "spacewalk" experience with the 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 100º of stars, however wherever you chose to concentrate your attention you’ll see sharpness and richer contrast.
The optical performance of the 21mm is the work of Ethos lead designer Paul Dellachaiae, who achieved a level of optical aberration correction right in line with his other Ethos designs. Contrast and transmission have been maximized using the same advanced coating techniques and further aided by the internal mechanical design techniques used in all Tele Vue eyepieces.
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, has no significant vignetting at the edge of the field, and is parfocal with the 31mm Nagler Type 5.
The 21mm focal length completes the logical set of 21mm/13mm/8mm and nicely juxtaposes the 17mm/10mm/6mm combination. 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.
Like all Tele Vue eyepieces, every 21mm Ethos goes through our optical and cosmetic quality control procedure in Chester, NY and should your eyepiece ever need service we can do everything from replacing a dented barrel to replacing a scratched eyelens.
Since all Ethos models accept Dioptrx, you now also have the “final frontier” – the ability to compensate for your own eyesight astigmatism with a superb multi-coated lens providing your exact correction, rotation orientation and centration over the eyepiece. This is the culmination of our quest to not only bring you observing experiences “…even better than you imagined,” but a 30-year recognition of being “tops in the field.”
|Focal Length (mm)
|Barrel Size (in.)
|Apparent Field of View (deg.)
|Eye Relief (mm)
|Weight (lb / oz)
||2.25 / 36.0
|Field Stop (mm)