I removed the AG16 telescope for maintenance and search for the cause of the collimation issue – the telescope was more then 3 year i use without any clenaing of the mirrors. Also the collimation isn’t stable at all, this gives me no round stars in the corners of the CCD-images, but this is always changing. After removing the primary mirror from the mirror-cel i noticed that the 3 bolts on the side of the 3 mirrorholders are loose and a lot ! . So this gives as result that the mirror is moving when the telescope is changing of position, no wonder that i have a unstable collimation. This is easy to fix. Now removing and cleaning the mirror and mount all again. I’ll replace the 3 fans of the telescope because they are about 7 years old and better now to change then in a couple of months when there is a problem with one of the fans.