This combination focal reducer and field corrector lens accessory works with all Celestron 5", 6", 8", 9 1/4", 11" And 14" Schmidt-cassegrain telescopes. This clever accessory makes it possible to have a dual focal ratio instrument, without sacrificing image quality. The reducer/corrector is F/6.3 for C5, C6, C8, C9¼ and C11 telescopes and F/7 for the C14 telescope.if offers wide fields of view with any Schmidt-Cassegrain telescope. Used for astrophotography, it reduces exposure time by a factor of 3.celestron doesn’t offer a F/6.3 Schmidt-Cassegrain telescope, because the design is impractical, with a large central obstruction, and resulting loss in contrast. This, added to the inability to utilize longer focal ratios for certain objects, LED Celestron to design the four-element, fully multi coated f/6.3 reducer/corrector. Results are amazing both visually and photographically.