Designed with a fully multicoated 8-element/5-group lens configuration, the Celestron Ultima Edge 15mm Flat Field Eyepiece produces bright and clear views with crisp and sharp resolution across the wide 65° field of view—even at the extreme edges. The eyepiece's focal length produces a medium magnification that strikes the delicate balance between being able to see details without the appearance of distracting vibrations that can ruin a view. This Ultima Edge has a 1.25" barrel that makes it compatible with popular diagonals, Barlows, and visual backs with standard threads for filters. This version is parfocal with the 10mm and 18mm models in the Ultima Edge series, requiring little or no refocusing when changing between them. A textured collar makes inserting and removing the eyepiece easy, and the combination of comfortable 16mm eye relief and fold-down rubber eyecup make it comfortable to use with or without eyewear.