The VC 200L Reflector is an 8" f/9.0 highly corrected, highly specialized telescope for gastro imaging. Vixen"s unique cat dioptric design features a high precision sixth order spherical primary mirror, a convex secondary mirror and triplet corrector lens. VISAC is an abbreviation for Vixen"s Six-Order Spherical Cass grain. The primary mirror is held by a retaining ring, instead of hooks, to decrease flare and enhance contrast. The VISAC System provides high-definition star images to the edge of a wide viewing field and offers exceptionally outstanding performance in astrophotography. Even at the edge of the 35mm film format (larger CCD chips) stars are sharp (smaller than 15 micrometers). This is smaller than the resolution of fine quality CCD cameras, which means that the telescope does not limit the image quality. With its elaborate spherical optical design, it achieves excellent image correction throughout the large illuminated field. (42mm diameter fully illuminated) Astronomy Technology Review states: "The VC200L focuser is one of the smoothest I"ve ever tested...overall the visual image quality of the VC200L was quite impressive...and is a step up from the typical Schmidt-Cass grain" Optical Design: VISAC Spherical Mirror Reflector Aperture: 200mmFocal Length: 1800mmFocal Ratio: f/9.0.