Part of their Astro T-2 modular accessory system, the Alpine Astronomical Baader VariLock 46 Extension Tube allows you to set your perfect extension length and lock it in for the precise focus distance of 29-46mm. An engraved scale on the tube lets you note the selected length for future repeatability. Both sides have standard T-2 threads to make it completely compatible with all rings, tubes, holders, and other parts of the Astro T-2 system for creating custom visual and imaging rigs.