About the TeleVue 3-6mm Nagler Planetary Zoom Eyepiece...
According to "Sky & Telescope" magazine: There have been zoom eyepieces in the past, but none quite like the Tele Vue 3mm-6mm Nagler Zoom. Since the time of Galileo, short-focal-length (hence high-magnification) telescope eyepieces have been notoriously difficult to look through. That has changed in recent years, especially with the introduction of the TeleVue Telescope Radian Eyepiece line (a 1999 Hot Product).
The Tele Vue 3mm-6mm Nagler Zoom is small, lightweight, and offers the same magnifications (with click-stop settings) as four Radians while maintaining a constant focus and 50 degree apparent field. It also lets observers choose in-between focal lengths, thus giving them the ability to tune the magnification to atmospheric conditions, which is very critical for high-power viewing. Although the 10mm eye relief isn''t long enough for eyeglass wearers, it is enough to make this a very comfortable TeleVue Telescope Eyepiece to look through.
"I did not set out to design a zoom telescope eyepieces, per se. David and I were discussing characteristics we''d like in a superior "planetary" TeleVue Telescope Eyepiece, and the zoom feature answered one of the major goals; how to obtain the highest possible useful magnification on a given night considering the ever-changing atmosphere. There were other aspects of equal importance and only the combination of all would satisfy our ethos in creating a "planetary" eyepiece: full field sharpness for any speed telescope, high contrast and transmission for natural color rendition, low scatter, and comfortable eye-relief. Being a zoom, we also concerned ourselves with making sure it was parfocal through the zoom range as well maintaining a constant apparent field of view. The one aspect we were not too concerned with was giving the TeleVue Telescope Eyepiece a wide AFOV.
Limiting the AFOV to 50 degrees and the eye-relief to 10mm, we were able to create a compact physical design employing only five elements to reach the TeleVue Telescope Eyepiece optical goals. Like other "Naglers," it utilized a negative lens group ahead of the focal plane. This permitted relatively long eye-relief for very short focal lengths. By independently moving the upper and lower lens groups, we achieved 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 and instantaneously choose the optimum magnification for the given observing conditions.
I was sufficiently confident in the TeleVue Telescope Eyepiece design and purposely decided to attach my name to the zoom, despite the common association between "Nagler" and 82 degree AFOV. I felt it was more important to stake our reputation on overcoming the "degrading zoom reputation" than maintaining the 82 degree assumption for "Nagler" designs." --Al Nagler
Be sure to check out our line of TeleVue Telescopes, TeleVue Telescope Mounts and TeleVue Telescope Accessories. Don'''t forget TeleVue Telescope Eyepieces, TeleVue Dioptrx and TeleVue Eyepiece Filters, too!
TeleVue 3-6mm Nagler Planetary Zoom Eyepiece Features...
- Small, lightweight, and offers the same magnifications (with click-stop settings) as four Radians while maintaining a constant focus
- Comfortable and consistent 50 degree field of view
- This model has click stops every mm
- Lets observers choose in-between focal lengths, thus giving them the ability to tune the magnification to atmospheric conditions
TeleVue 3-6mm Nagler Planetary Zoom Eyepiece Specifications...
Focal Length (mm): 6 - 3
Barrel Size (in.): 1.25"
Apparent Field of View (deg.): 50
Eye Relief (mm): 10
Weight (lb / oz): 0.33 / 5.3
Field Stop (mm): 5.1 - 2.6
Warranty: Limited LifetimeTeleVue Product Number: ENZ-0306