Fast-Focus Eyepiece
A quick-adjust ocular ring that lets a shooter sharpen the reticle to their own eye in a turn or two rather than a long threaded barrel.
A fast-focus eyepiece is a rear ocular housing with a short, knurled ring that focuses the reticle for your individual eyesight. Older designs used a long threaded eyepiece and a lock ring that took many turns and was awkward to set, while the fast-focus version reaches sharp focus in roughly one turn. The control adjusts the diopter so the reticle snaps into crisp definition against a blank, distant background.
It is important to remember that this ring focuses the reticle, not the target, so you set it once for your eye and then leave it alone. Because the adjustment sits on the ocular lens at the very back of the tube, a correct setting also helps you find a consistent, full picture within the scope’s eye relief.