Question for 600mm f4 IS II owners

I'm having an issue with my 600mm f4 IS II, and wondering if anyone else has experienced this too. When using the lens with either version III teleconverter there is a small amount of play in the connections. If the camera and lens are rotated to portrait orientation a light pull backward on the top of the camera will cause the lens and camera to lose their connection. If IS is engaged it will stop with a sudden "clunk" and you will see a significant shift in the image if you are looking through the viewfinder, it appears to me that the lens is losing power. As soon as you stop pulling on the body the connection is restored and the IS kicks back in. In theory the same thing should happen in landscape mode by pulling back on the right hand side of the camera, but in practice I'm not able to duplicate the failure that way. I'm probably not pulling hard enough, in portrait mode gravity is assisting to break the connection.

I've tested this with multiple bodies (1DXII, 1DX, 1DsIII, 7DII), two copies of the 1.4x III, and a single copy of the 2x III and it is consistent across all of those variables. When mounting the body directly to the lens there is no issue, there is no play and I can't cause a break in the connection. Also, I have not been able to replicate the issue when mounting the TC's on other lenses (100-400 IS II, 70-200mm IS II).

Under field conditions I've only encountered this as an issue a few times. Most often when shooting from a vehicle at a downward angle with the lens cantilevered over the windowsill such that gravity is working to pull the lens away from the body. The other time I ran into this was shooting perched eagles off a tripod where the lens was aimed up, in this case it was gravity pulling the camera away from the lens. As mentioned above, in either case this only happened with the camera in portrait orientation.

Once I figured out the cause it became pretty easy to avoid the issue, but I'd like to know if anyone else has experienced this? Even if you haven't run into this under field conditions, maybe a couple people could test their lens and try to duplicate the issue? The part that confuses me is why it only happens with the TC's, if the mount on the lens is out of spec it seems like it should be an issue even when mounting just a body on its own. If it's an issue unique to my 600mm I'll send it to Canon for repair, just trying to figure out if it really is just my lens.

Check all the small Phillips head screws holding the mounting rings in place on both the lens and your extenders. I had a similar issues last year while shooting at Bosque and could not believe how loose some of the screws had got one was to the point of almost falling out. Actually borrowed a kit from Artie that he apparently carries everywhere because of issues he's had tightened everything back up and it was good as new.

I double checked all the screws and they are tight. While doing so I noticed that there is some wear on one of the flanges on the back of the lens, and the last 1/4" or so of the flange appears to have a very slight curve up where it should be straight. I have a feeling this may be the source of the play, and might be what is allowing the TC's to pull away from the lens enough that they loose their connection. I also looked at the contact pins on the TC's and on my 1DXII and it appears that the pins on the body are slightly longer, which might explain why the body doesn't lose contact with the lens when it is mounted on its own. It looks like the solution may be a trip to Canon to have them replace the mount.

Hi Ryan, I would definitely take your lens to Canon, these are precision parts, not something you can fix at home

I can get minimal minor play in different body/TC/lens mounts....some are like rocks...most have play but none of them disconnect the electronic connection......off to Canon for sure on this one.

I did have an issue for awhile with my 2xTCIII where the pin wouldn't always click in....dangerous for sure!!....so I taught myself to give it an extra wiggle until it clicked. It has now self corrected after about 6 months of the issue and now clicks into everything just fine. But that doesn't seem to be your issue and that never broke the electronic contacts with the lens or body.