The Baader 7.5 mm T-2 Extension Tube is part of the Varilock T-2 System for setting the exact focus at intervals * Determining the preload by adjusting the extension tube"s millimeter scale to the desired length * The Baader 7.5 mm T-2 Extension Tube incorporates both male and female T2 threads * Helps to set H-alpha solar filters and image field correctors with critical focus position