The SkyWatcher f4 Aplanatic Super Coma Corrector is Optimised for f4 imaging Newtonians and delivers stunning wide-field views with pinpoint stars to the edge of the flat field. Magnification remains unaltered. Features a 4 x element design with one element made from FPL51 ED glass. Requires 55mm back focus. Image height 28mm. Outside diameter 50.8mm. A suitable M48 x 0.75mm adaptor is required to match your Canon or Nikon camera.