I want to use my sony pl mount lens that I use on my motion picture camera on my 5d mark iii...can this be done with just an adapter or do I have to lock the mirror?????
AFAIK, you'd have to get the camera modded to be able to use PL glass. These guys do it, but it ain't cheap: http://hotrodcameras.com/cameras/cameras/custom.html
Some lenses are designed to let you change the mount. Zeiss CP lenses are set up to do that, and some high end Canon cinema lenses (North of $40K). I doubt if Sony lets you change to a EF mount.
If its a savings to you, you might get a different lens and sell the Sony.
There are pl to ef adapters for a limited number of lenses. Some buyers indicate that the adapter worked on their Sony pl mount lens, but I expect that not all will work.
This is from one of the comments on the B&H web site:
"It should work with any PL lens, but I can say from personal experience that it works with my RED 50-150 zoom, RED 300 prime, and Sony PL primes, Zeiss PL zooms, and many others.