Just a quick update, I 3D-printed a mount for the filter glass (without ring) and placed it into the
holder that mounts directly onto my DSLR (previously the filter was taped to the front of the flattener). This roughly halved the distance of the filter to the sensor, to about 55mm.
The star shape significantly improved. When focused I would say the star shape is almost perfect. I could see a slightly non-rounded shape when slightly out of focus each way.
to everybody for help
