Tele Vue 21.0 Ethos (ETH-21.0)
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.
TeleVue is known for its in-house eyepiece and telescope designs by Al Nagler; our latest eyepieces brings new meaning to the term "in-house." The concept for this eyepiece series was proposed by TeleVue President David Nagler, with performance parameters giving it the fundamental characteristics (the ethos) of a TeleVue 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 TeleVue's philosophy of pushing the state of the art, long-time TeleVue 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, TeleVue once again broadened the amateur astronomer's perspective on the universe with: 100° of pure TeleVue quality. The field area of this new eyepiece is more than 50% larger than an 82° field. The TeleVue 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.
|Apparent Field of View||100 degrees|