Tele Vue Nagler Zoom Eyepieces

Tele Vue Nagler Zoom Eyepieces

Zoomable 50° Constant Apparent Field Eyepieces

Concept / Background: I did not set out to design a zoom eyepiece, per se. David and I were discussing characteristics we’d like in a superior “planetary” 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 eyepiece a wide AFOV.

Limiting the AFOV to 50° and the eye-relief to 10mm, we were able to create a compact physical design employing only five elements to reach the 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 design and purposely decided to attach my name to the zoom, despite the common association between “Nagler” and 82° AFOV. I felt it was more important to stake our reputation on overcoming the “degrading zoom reputation” than maintaining the 82° assumption for “Nagler” designs.

— Al Nagler
 

Nagler 3-6mm Zoom:

Model # ENZ-0306
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
 

Nagler 2-4mm Zoom:

Model # ENZ-0204
Focal Length (mm) 4 - 2
Barrel Size (in.) 1¼"
Apparent Field of View (deg.) 50
Eye Relief (mm) 10
Weight (lb / oz) 0.36 / 5.7
Field Stop (mm) 3.3 - 1.7

The 2-4mm Nagler Zoom is recommended for fast, high performance scopes of 800mm focal length or shorter, such as the Tele Vue-60. It has click-stops every half-mm.
 

Reviews

Excerpts from The Backyard Astronomer's Guide review of the 3-6mm Nagler Zoom.

•An exceptional zoom eyepiece is the 3mm-to-6mm Nagler Zoom, a specialized high-power eyepiece for dialing in the optimum power for planetary viewing with short-focal-length telescopes, such as fast apo refractors.
•Imaging is superb, and - a first - the apparent field stays constant throughout the zoom. Click stops define the 6mm, 5mm, 4mm and 3mm positions, through the observer can select any value in between. Its 10mm eye relief is a bit cramped for those who wear their eyeglasses while observing.

T. Dickenson, A. Dyer. "Zoom Eyepieces". The Backyard Astronomer's Guide (2nd Ed., 2002). 71.

From Sky & Telescope's Hot Products review of the 3-6mm Nagler Zoom.

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) eyepieces have been notoriously difficult to look through. That has changed in recent years, especially with the introduction of Tele Vue's line of Radian eyepieces (a 1999 Hot Product). The new Tele Vue 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 zoom's 10-millimeter eye relief isn't long enough for eyeglass wearers, it is enough to make this a very comfortable eyepiece to look through.

Sky & Telescope, (Editors). "Hot New Products of 2001: Zoom In". Sky & Telescope (Dec. 2001).

Excerpt from S&T's Hot Product review of the Nagler 2-4mm Zoom eyepiece.

Tele Vue's new 2-to 4-mm Nagler Zoom ... features click stops at half-millimeter intervals of focal length, a constant 50° apparent field of view, and an eye relief of 10 mm -- not sufficient for eyeglass wearers, but remarkabley comfortable fro an eyepiece of such short focal length. It's the perfect companion for any of today's popular short-focus telescopes.

— Sky & Telescope, (Editors). "Hot New Products for 2004: Magnification Extremes". Sky & Telescope (Jan. 2004). 34.

You are buying from an authorized Tele Vue UK dealer.