QHY9M flattener spacing

[that_guy (Tony)]

Hi guys, about a month of ago I bought a Hotech SCA flattener for my refractor. Someone lent me a vernier caliper to measure the distance between the sensor and the front of the filterwheel. The flattener requires the usual 55mm spacing for optimal use but when we measured everything, it came up to 58mm between the sensor and the flattener. I couldn't find anything that I could remove to reduce the distance further. The results i've gotten are ok, but there are definitely still some field curvature in the corners. I think my filterwheel is the first generation QHY 2" filterwheel from what I can research. Does anyone have this particular filterwheel/camera combo with a flattener that ran in to the same issue? If so, what was your solution?

Thanks
Tony

[LewisM]

Remember, spacing is METAL BACK distance, so the 55mm is from the very rear most metal of the flattener housing out (NOT the threads).

The distance from the front of the QHY9M face to the sensor is 17.3mm (removing the 2" nosepiece etc, which you don't need). This leaves 37.7mm, which seems SHOULD accommodate a filterwheel and still need a small spacer.