This flattener was designed to be used with the fsq-85ED (it may work with other scopes) and will provide a 44mm image circle for full frame sensors.
NB if you have the newer version of the telescope, the FSQ-85EDX I believe this is already corrected for full frame and therefore doesn’t need this flattener.
$280 posted anywhere in Australia. I’ll include the custom adapter I had made for precise distancing to the sensor using the Canon EOS Ra if that’s useful.