I bought a Sharpstar 2.5" Flattener to use with my Altair 102mm f7 (712mm according to a plate solve!) triplet refractor.
Setting it up at the correct spacing with my ASI294MC Pro camera, the stars are anything but 'sharp'. I have attached images of both coming to focus with the flattener in place, and coming to focus without the flattener in place from near the centre of the frame.
I cannot re-iterate enough, the spacing is correct. I have:
6.5mm to ASI294 sensor from camera body face
11mm ZWO coupling ring
21mm ZWO filter drawer
16.5mm ZWO spacer
= 55mm total
then 36.5mm from Sharpstar flattener to endface of M48 adaptor
55mm + 36.5m = 91.5mm TOTAL
The supplier is kindly sending me another one to try in the meantime.
Edited by vk2gom, 12 April 2021 - 11:50 AM.