The Takahashi reducer RD-QB 0.73X is the newest reducer for the FSQ-85EDX telescope. It features 4 elements and 2 groups and provides a 0.73X reduction factor. When used with the FSQ-85EDX, it provides an effective focal length of 330 mm and a focal ratio of f/3.9. The correction provided to field curvature is similar to that provided by the FSQ-85 flattened 1.01x. The resulting image circle is 44 mm in diameter.
OTA side mounting thread - M72 P=1.0
Camera side mounting thread - M55.9 P=0.75
Metal Back - 72.2 mm
Internal thread for 58 mm filter
It is also advisable to obtain the CA-35 (SKY-90) TKA35201 to aid in mounting your camera at the correct backspace.