DESC: This optical tube assembly includes parabolic mirror optics, center marked for easy collimation. It has an upgraded 2" Crayford-style focuser (with 1.25" eyepiece adapter), quick-collimation cap, dust cap, and a dovetail base that accommodates any Orion finder scope. Pre-tapped holes in the rear cell allow attachment of an Orion Cooling Accelerator Fan (sold separately).