Reducer / Corrector f/6.3 - with 2-inch internal thread (not for Edge-HD) This practical lens correction system hits multiple targets at once: The 4-element focal reducer shortens the focal length of all Schmidt-Cassegrain telescopes by a factor of 0.63. The aperture ratio changes accordingly from 1:10 to 1:6.3. This results in a significantly larger field of view and exposure times that are three times shorter. The optical correction system flattens the slightly curved image field of all Schmidt-Cassegrain telescopes, providing a fully corrected, vignette-free "richfield" view with a diameter of 24 mm. The focal lengths of the Celestron SC telescopes change as follows: C-5: from 1250 to 788 mm / f 6.3, C-8: from 2000 to 1260 mm / f 6.3, C-9: from 2350 to 1480 mm / f 6.3, C-11: from 2800 to 1764 mm / f 6.3, C-14: from 3910 to 2457 mm / f 7.3. The Celestron focal reducer can also be used effectively for visual observation. It features Celestron SC threads on both sides and is directly screwed onto the telescope tube. It can also be used in combination with the Radial Guider for photography and CCD cameras.