I just thought I would add a tip about an issue I was having with the BF setting on my PMW-350. After aerial shooting in Virginia, and my camera being shipped in a hard case on the jet, I decided to BF the camera....you know what flight vibration can do to a camera. To my alarm, the BF sequence would always give a message "BF No Good:Timed Out". After a dozen tries in different light, different cards, and different distances, I gave up. The Sony Service Center didn't have an answer over the phone either. So I sent the camera in, and after a couple weeks, heard from the senior technician via phone (this was during the holidays).
Long story short, in the OPERATIONS menu>AUTO-IRIS, I had the "Clip High Lights" switched on for some damn reason. (I thought I had gone through my menus looking for just such an "on" switch, but missed this one.)
Unfortunately, when going through the BF electronic procedure, this setting is NOT over-ridden, and the lens cannot through it's acrobatics during the procedure. (I would dare say that other settings in the auto-iris submenu turned on might cause a problem as well.)
So there it is, turn this setting OFF and leave it off! This is NOT in the manual, so you might make a note of it (page 106).