With the constant bad weather, it was propbably a good idea to collimate the 180mm F/15 Maksutov properly.
This involved a quit afternoon, a long inside raneg in the house free of obstacles, and a Geoptik artificial star (fixed brightness).
The collimation took place in bright daylight, however in the house, with the curtains closed. I positioned the star on a photo tripod, and the Maksutov on a HEQ5, allowing good positioning, and also re-positioning of the scope after tweaking the mirror.
The first image that came out looked as follows:
It may look like the collimation is already ver good. However, on closer inspection (using Sharpcap and a ASI2600MC camera) with a bullseye ring overlay, it was clear that the Poisson point (the little dot in the center) was not dead center in the middle of the diffraction rings.
Quality assesment of the diffraction pattern: smooth mirror surface, no ponched or deformed optics.
The de-centering is also visible in the in-focus diffraction pattern. It’s obvious that the rings on top of the star are closer together then the rings on the lower side. The upper side almost touches, where there is a clear gap on the lower side!
So the next step was to tackle this de-centering by using the push/pull bolts on the OTA backside. I used visually with a 4mm (675x) and 7mm (385x) eyepiece the in-focus pattern to slightly move the point towards the center. Ofcourse, everytime I touched the bolts, the star would move out of the field, so there it came in handy that I used the HEQ5 which allowed me to correct electronically using the mounts stepper motors.