Alpine Astronomical Baader FR-4 Focusing Ring Collar (1.25")

Part of their Astro T2 modular accessory system, you can use the Alpine Astronomical Baader FR-4 Focusing Ring Collar to set and lock a custom insertion depth for just about any 1.25" eyepiece. By choosing a specific insertion depth, you can make the eyepiece parfocal with other eyepieces or gear, such as with imagers.