Unlike conventional zoom eyepieces, whose apparent field of view narrows at lower powers where you’d normally prefer a wider field of view, the TeleVue Nagler zoom eyepieces maintain their 50° field of view at all magnifications.
Unlike conventional zooms, they also maintain the same eye relief at all magnifications. And they remain parfocal at all magnifications – no refocusing needed as you change powers.
The Nagler zooms give you an almost infinite selection of magnifications – the equivalent of getting dozens of individual eyepieces for the price of one. They let you can match your medium power to high power observing to the seeing conditions without having to change eyepieces as the seeing conditions change.