Thanks for the hints. I am busy to find these informations about lenses to be adapted. The image cicle will be O.K. when the lens to be adapted is designed for a larger sensor than the Pentax Q-sensor, which is a 1/2.3inch-sensor (6,2 x 4,6 mm). But not for a too large sensor, since my interest is to have a camera with minimal physical dimensions. Lenses for larger sensors, or with bigger image circles will pysically be bigger than necessary.
See sensor sizes:
Glossary: Sensor Sizes: Digital Photography Review, or:
Image sensor format - Wikipedia, the free encyclopedia
So, lenses from 8mm analogue movie cameras will have a too small image circle. See examples in the above link, example pictures have black corners. I have won a camcorder for 1 Euro (delivery costs more). I will see if I can adapt the lens to the Q. Unfortunately I could not find technical information about this vintage camcorder. To me it is interesting to have a wide range zoom which is standard to those camcorders (mainly 8x, sometimes even 10x zoom).
If there are new results I will post them.