Baader FR-4 Focus Ring Collar
The Baader FR-4 Focusing Ring Collar slips onto your 1.25" eyepiece barrel and enables you to adjust and lock a reference stop for repeatable eyepiece focus. The FR-4 allows you to set an eyepiece to be precisely parfocal with another eyepiece or piece of equipment (i.e. setting an eyepiece parfocal with a CCD camera for visual framing and focus). Multiple collars can also be useful in pre-setting Bino-Viewer eyepieces for repeatable focus (to compensate for eye-to-eye focus differences). The focusing collar is 0.23" (6mm) thick, and incorporates two nickel plated brass lock screws, which are spherical-tipped to minimize eyepiece barrel damage.