| This Celestron zoom eyepiece is fully multicoated, with an 8mm to 24mm focal length range and a soft rolldown rubber eyecup for eyeglass use. The rubber eyecup can be removed to expose T-threads that permit direct connection of a camera T-ring and camera body for variable power imaging. As with all zooms, the apparent field of view of this Celestron zoom decreases as the focal length increases. This generally results in a 20% narrower field of view at low powers and a 10% wider field at high powers than you can achieve with similar focal length single magnification eyepieces. This is just the reverse of what most people expect from eyepieces – which is a wider field at lower powers, where you’re usually observing larger objects that don’t need as much magnification to fit in the eyepiece field, and a narrower field at high powers. Likewise, this Celestron zoom’s usable eye relief decreases slightly as the focal length decreases, from a specified 18mm at a 24mm focal length to 15mm at an 8mm focal length. Contrast is also generally a little lower than you’ll find in single magnification eyepieces of similar focal lengths. If these minor anomalies are not a problem for you, however, a zoom offers the convenient ability to precisely match the observing magnification to the seeing conditions, as well as offering a virtually infinite number of magnifications in a single reasonably-priced eyepiece. The eyepiece has a safety groove cut into its chrome barrel that will catch the thumbscrew of your focuser or star diagonal and keep the eyepiece from falling to the ground should the thumbscrew accidentally loosen during use. The power change band on the eyepiece uses a broad knurled rubber gripping surface that makes it easy to make small power changes, even in cold weather when wearing gloves or mittens.
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