The Celestron Luminos 31mm Eyepiece offers a wide 82º field. It has a seven elements optical design which is fully multi-coated for crisp sharp views. This eyepiece is parafocal which allows eyepieces to be switched out without refocusing. The eyepiece is made of polished and anodized aluminum. A rubber grip runs around the equator of the eyepiece for raising and lowering the retractable eyecup. Just twist the rubber grip to adjust the height of the eyecup. The insert barrel is threaded and can accept filters.