Orion 08267 Ritchey-Chretien 8 inch F/8 Optical Tube Assembly (White) 8 inch (200mm) aperture Ritchey-Chretien optical tube ideal for use with DSLR cameras and small-format CCDs to produce wonderfully flat, virtually coma-free astrophotos Hyperbolic primary and secondary mirrors made of low-expansion quartz glass with enhanced aluminum coatings boast 96% reflectivity for bright imaging performance, and the secondary mirror is precisely center-marked to aid in collimation A rotatable, machined dual-speed (10:1) Crawford focuser equipped with a sturdy linear-bearing provides precise focus adjustment without slippage or flexure with heavy astrophotography accessories attached Three included focus extension rings (one 2 inch and two 1 inch) allow focus position adjustment for use with various imaging cameras and astrophotography accessories Features two dovetail finder scope bases and a unique, Orion-exclusive slotted narrow dovetail bar along the top of the tube for easy accessory attachment