See the latest test by the PF with a roll of film for the $7,000 DA560 lens put onto a MZ-S:-
http://www.pentaxforums.com/news/da-560mm-f56-is-it-a-full-frame-lens.html
The test pictures speak for themselves, there is heavy vignetting at corners at f/5.6. It should be noted that the hood was not extended for these shots. The darker corners can still be seen at f/8, i.e., one stop from wide opened, although it is not as obvious then.
Updated: Compatibility of DA Lenses on Full Frame