This full-frame photographic field flattener is designed for the Stellarvue SVR90T. 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 less vignetting than a flattener using a 42 mm t ring.
This field flattener requires 55 +/- 0.5mm (standard DSLR) back focus. When using a CCD camera, the remaining back focus required can be made up with 48mm extension tubes.