Limiting the AFOV to 50° and the eye-relief to 10mm, TeleVue was able to create a compact physical design employing only five elements to reach the optical goals. Like other "Naglers," it utilizes a negative lens group ahead of the focal plane. This permits relatively long eye-relief for very short focal lengths. By independently moving the upper and lower lens group the eyepiece has constant focus (parfocality), constant apparent field of view, and essentially constant eye-relief. Just by rotating the upper barrel, you can zoom through the power range. Click stops offer known power points for reference without needing to look at the barrel so you can instantaneously choose the optimum magnification for the given observing conditions.
Despite the common association between "Nagler" and 82° AFOV, Al Nagler has said that he felt it was "more important to stake our reputation on overcoming the degrading zoom reputation than maintaining the 82° assumption for 'Nagler' designs."
|6 - 3-mm|
|Focal Length (mm)||6 - 3|
|Barrel Size (in.)||1¼"|
|Apparent Field of View (deg.)||50|
|Eye Relief (mm)||10|
|Weight (lb / oz)||0.33 / 5.3|
|Field Stop (mm)||5.1 - 2.6|