The specification for the ASA 4CAKORRFL 4” field flattener (http://www.astrosyst...er/?wpdmdl=2977) says that the field flattener should be placed so that its centre is 124.5mm from the CCD.
The adapter supplied to me by ASA puts the centre of my field flattener 127.4mm from the CCD, 2.9mm more than the specification suggests.
The filters and camera glass are in the light path so maybe their refractive index affects the calculation, but surely not by as much as 2.9mm.
Is this difference likely to be critical to the performance of the field flattener? Should I insist ASA provide a revised adapter?