Designed specifically for planetary viewing, and to enable the user to easily find the highest possible useful magnification on a given night with constantly changing atmospheric conditions, the Tele Vue Nagler Planetary 3-6mm Zoom Eyepiece is built with a 5-element/3-group lens configuration. This allows it to maintain a relatively long 10mm eye relief despite the short focal lengths, while being parfocal, through the entire zoom range. Maintaining parfocality allows the user to run through the focal length range without the need to refocus after each new magnification is set.

Built to Tele Vue's exacting standards, the eyepiece features anti-reflection fully multi-coated optics to improve brightness, color rendition, and contrast. Click-stop positions at every millimeter through the focal length range allow users to track settings and calculate magnification without having to take their eye away from the eyecup. A fold-down rubber eyecup allows for easy use with or without eyewear, and a textured collar allows for sure handling in the cold or while wearing gloves.

The Planetary Zoom has a barrel diameter of 1.25" to fit into the most common sized focusers and accessories, and is also parfocal with all Tele Vue group 'B' eyepieces, allowing you to change eyepieces within the group without having to refocus every time - saving time and limiting vibrations.