The Optical Design of the Orion 6" f/9 Ritchey-Chretien Astrograph allows you to capture spectacular, detailed images of deep-sky objects like never before. In contrast to conventional Newtonian reflector and Schmidt-Cassegrain systems that are susceptible to coma away from the center of the field, the Ritchey-Chretien utilizes hyperbolic primary and secondary mirrors to achieve superb flat-field images that are truly coma-free. In the 6" model, mirrors are made of BK-7 optical glass with enhanced aluminum 94% - 96% reflectivity coatings, to provide diffraction-limited performance. Since there are no lenses involved, images are also free from chromatic aberration, which affects all but the finest, most expensive apochromatic refractors. The Orion 6" Ritchey-Chretien Astrograph is ideal for use with small-format CCD cameras like the StarShoot line, as well as DSLR cameras, for deep-sky and solar system astrophotography. The telescope's wide, fully illuminated flat field produces pinpoint star clarity all the way to the edge of the camera's sensor. The Orion 6" Ritchey-Chretien Astrograph features a machined, dual-speed (10:1) Crayford-style focuser with an engraved millimeter scale on the drawtube. One 2-inch and two 1-inch extension rings are included for adjusting the focus position for various cameras. The secondary mirror is precisely center-marked to facilitate collimation. The 19-inch enameled steel optical tube weighs only 12.3 lbs. and features