This full-frame photographic field flattener is designed for the Stellarvue SV80ST. It threads directly onto the Stellarvue or Feather Touch 2.5" dual speed focusers. Simply remove the 2" adapter on the focuser and thread this on. This flattener significantly improves flat field performance when imaging with DSLR or CCD cameras. With its over-sized 48 mm t thread it has far less vignetting than the SFF6 flattener which uses a smaller and more restrictive 42 mm t-thread. Optically, it is designed for any size ccd chip up to full frame size.