Camera will not autofocus when 200-400mm f4 is connected

[jshfoto]

Hi,

I recently bought a used Canon 200-400 f4 lens and have used it for several hours of sports shooting with no problems. Last night while shooting it stopped being able to autofocus and none of the buttons on the camera would work. I tried switching bodies thinking it was my camera, but the same thing was happening. After lots of experimenting, I could get it to work right if I disconnected the lens from the camera while the camera was powered on and then reconnected. It would only work correctly for a short time though. Anyone have ideas on what might be wrong or fixes I could try?

Thanks,

Jessica

[jshfoto]

The camera does not report MF.

[deebatman316 · Accepted solution]

Then it's likely the AF stop button.

[jshfoto]

Indeed it is. I turned it off with my R5 and worked perfectly. Unfortunately, I cannot turn that button off with the 1DX Mark III.

[deebatman316]

I'm surprised by that. On my retired EOS 40D. A button could be assigned for that function or turned off. But my 5D Mark IV only gives me a choice to remap it to a different button. My retired EOS 40D had the "*" button set to AF Stop. I experienced the same problems you did. After I changed what the button did back to default. I never had that problem again. My uncle used to own that camera before I did. 

[jshfoto]

I can map it to something else (another function) but OFF is not an option for that button when on my 1dx. I was able to do it on the R5... I now have to decide if I want to return it, pay to fix it, or only use it with my r5 since I never use those buttons anyway... That is my least favorite option.

[deebatman316]

Where did you get this lens from does it have a warranty on it. If so it can be returned because the lens is NOT functioning correctly.

[jshfoto]

Yes, I can return it. However, they have no other used ones in stock right now and I need the lens for my business. Hence why I am trying to figure out if it's worth getting fixed or if I need to return it and then hope another one pops up.

[deebatman316]

I would check and see if Canon supports this lens first. If they still do get a quote first before a repair is made.