This accessory is necessary because refractors provide a curved focal plane; stars are not point-like near the edges in imaging. It provides a corrected image up to the edge of the field. A specific adapter will allow you to attach the reducer/corrector to the eyepiece holder of your telescope. It is rotatable to optimize your framing and accepts 50.8mm filters. Optimized for the Sky-Watcher Evolux 62ED f/6.45 (Doublet) telescope, this screw-on reducer/corrector reduces the focal length of the telescope by a factor of 0.9x (induced focal ratio of f/5.8 - apparent field of view 5.09°). Using a focal reducer in astrophotography also allows for reduced exposure time. A dedicated M48 wide T ring for your camera is necessary, available for Sony, Nikon, or Canon.