Developed for exclusive use with the compact PF-65ED and PF-645EDA spotting scopes, the smc PENTAX XF series offers a choice of three distinctive eyepieces: two unifocal models with a long eye relief and a wide angle of view, and one zoom model with a 20-60X variable magnification range. When the rotatable eyecup is removed, they feature an adapter-mounting screw (30.5mm in diameter with a 0.5mm pitch for the unifocal models, and 43mm in diameter with a 0.75mm pitch for the zoom model).