If lost or damaged, you can replace the Rubber eyecup for Celestron, Acuter spectra.
Compatible with the Celestron Ultima and Acuter 65, 80 and 100 zoom eyepieces for spectra, as well as the Celestron 8-24 zoom eyepieces for astronomy, the rubber eyecup fits the T2 thread of the eyepiece. It is designed for comfortable viewing and to exclude distracting side light. In order to quickly mount your camera on the T2 end of the eyepiece with an adapter, the rubber eyecup is easily removable, so unfortunately it's easy to leave it behind, but the good news is that it can be replaced!