I have now done some test with the Canon 300 mm lens, very satisfaid with the result. Time to replace it with the Pentax 645 lens. When I did this I got one problem, the focus barrel on this lens runs backwards.
My project report:
http://www.astrofriend.eu/astronomy/...645-300ed.html
It wasn't a clear sky this night, have to wait until I get that and can do some test.
All these tests I do now are done from a very light polluted sky. But I can still see the shape of the stars, vigenneting etc to judge how the lens perform.
Lars