wdh777 wrote in post #16183633
I was reading the manual and it is a little unclear when you can switch the 1.4 extender on. I'm using it with a 1Dx which is I think a group two camera. It almost sounds like I need to press the shutter half way when the camera is off to flip the switch. Do you need to turn the camera off or as long as it isn't focusing can you flip the switch so you can press the AF stop button on the lens and then feel free to flip with switch and don't have to press the shutter? Thanks
According to Arthur Morris:
I tracked down Rudy Winston, author of the article linked to above, for clarification:
"Thanks for all your insights into the new 200-400mm lens, and for taking the time to not simply work with it, but to invest in it, early-on. You are correct -- the advice about switching the built-in extender into or out of the optical path refers to cameras OTHER THAN the EOS-1D X and EOS 5D Mark III. With this lens, there is additional data communication that has to be pushed into the camera body, and it's done in a way that earlier cameras (5D Mark II, EOS-1D Mark IV, and so on) weren't initially designed to accommodate. Hence, the advice to switch into and out of extender operation carefully. With anything introduced after the 1D X and 5D III (that would include the EOS 6D, Rebel T5i & SL1, and new EOS 70D), you likewise can go into and out of extender operation without significant issues.
Our technical data from Japan included advisories to resist making the change during active camera operations (writing to the memory card, etc); to be honest, we haven't had a working sample in our department to be able to test it to see whether there's any issue with this when using the newer cameras. So the info you read on that on-line piece reflects what we have been told in the technical info from Japan. As a 5D III/1D X user, though, you don't have to worry about shutting down Live View and so on.
TLDR: If you have a camera model from the 5d3 or later, you do not need to worry about flipping the TC while the lens is still in operation (IS engaged/AF on). It is only the camera bodies made prior to the 5d3 where switching the TC while the lens is in operation can cause electrical/EXIF damage.
Hope this clears stuff up