"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 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 maginfication 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.Surprise! 3mm-6mm Planetary Nagler Zoom! This high performance, high-contrast, high power eyepiece is ready to take its place among the best planetary eyepieces available,... but with a ""Nagler"" twist. Tele-Vue incorporated its proven ""Nagler"" concept into a zoom, while optimizing for the performance factors critical to planetary observers; contrast, resolution and comfortable eye-relief. The Nagler Zoom is ""tack-sharp"" across its constant 50� apparent field, and throughout its 3mm-6mm focal length range, even in fast APO scopes. The 3mm-6mm Nagler Zoom is parfocal throughout its zoom range, parfocal with other Tele Vue 11/4"" eyepieces and has a constant 10mm eye-"