Originally posted by Royce Howland Put the 645Z into Live View mode, and see if you can autofocus the lens using the contrast detect AF function of the camera. (As opposed to the phase detect AF function that's used when you're shooting optically, no Live View.) I'm on my second 645Z because my first one was faulty. The camera worked fine in every regard, but it would not AF with any of my FA 645 lenses in phase detect mode -- trying to engage focus just did nothing at all, as if the lenses were all manual focus. (I knew the lenses were all fine from shooting with them for years on a pair of 645D's.) But in Live View contrast detect mode, all the lenses would autofocus fine. I exchanged the body for a different one 24 hrs later with my dealer, and the 2nd body worked perfectly.
Depending on your results testing the two AF modes, it may tell you whether it's more likely the lens or the camera body that has a problem.
Thank you for your information, I just tried again with this lens on the LV mode, but it is the same, cannot AF. The camera show it is "MF" all the time, so, obviously, there is something wrong inside the lens that cannot communicate with the camera to tell the camera it is in AF mode. So I will return the lens to the seller after the holidays. I will buy another one later, as the price of this 35mm f3.5 is much lower than the 25mm f4, and lighter weight to carry.