Model TRF-2008 Tele Vue 0.8x Reducer/flattener 400-600mm converts TV-85 to 480mm f/5.6 and TV-76 to 380mm f/5.0 for flat field, fast photography. Fully multi-coated 3-element unit inserts directly into 2" focuser, accepts standard T-rings for 35mm cameras. Whilst designed for use in the TV-76 and TV-85, it can be used with other fast refractors between 400mm and 600mm focal length.
Used in prime-focus imaging, reducers increase photographic speed while flatteners decrease image curvature away from the center.
Important Note: The following products were all designed for an optimum 55mm back focus. (Distance from flange surface to film or CCD plane). If you use a CCD, be sure the spacing between flange and CCD is 56mm +/-2mm for best results.
"This accessory is a must-have for someone planning to use the TV-85 photographically" - review in Sky & Telescope, July 1999. Also it can be used with any 400-600mm refractor.