Canon 100-400 EF 4.5/5.6 not focusing (auto or manual)

[SethHarrison]

I had to tighten a screw on the lens mount of my 100-400 lens because it was loose and not coupling completely with the camera. After tightening it (and now getting a good fit with the camera), the lens is not focusing, either in autofocus or manual focus) In autofocus, I can hear the motor working when I depress the shutter halfway, but it doesn't focus, and as I said, it also does not focus in manual focus mode. This is happening on two different 1Dx bodies, so I know it's not the camera. Any ideas?

[Tronhard]

My first thought is to slightly back off the tight fit you got and see if that makes a difference.

[SethHarrison]

I was thinking the same thing. I'll try that. Thanks!

[ebiggs1]

"I had to tighten a screw on the lens mount of my 100-400 lens because it was loose and not coupling completely with the camera."

I think unrelated and just coincidence. It needs service. Call Canon 1 (800) 652-2666

[Tronhard]

You may be right Ernie, but getting the OP to simply take some of the pressure off the lens screw might be a resolution that will be a lot cheaper and more convenient that sending it in for Canon to do the same and charge for it.  If that doesn't work, then absolutely invest in a service.

[jrhoffman75]

Hi guys. 

If that works Trevor it would still recommend the OP send it in for service. The lens mount is a rigid piece. It is held in by four screws. If everything is to factory spec completely removing one screw shouldn’t make a difference (I just tried this on an old lens that I have on my display shelf). 

[jrhoffman75]

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@SethHarrison wrote:

I had to tighten a screw on the lens mount of my 100-400 lens because it was loose and not coupling completely with the camera. After tightening it (and now getting a good fit with the camera), the lens is not focusing, either in autofocus or manual focus) In autofocus, I can hear the motor working when I depress the shutter halfway, but it doesn't focus, and as I said, it also does not focus in manual focus mode. This is happening on two different 1Dx bodies, so I know it's not the camera. Any ideas?

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When you say “not coupling” do you mean the loose screw prevented full rotation of the lens so it wouldn’t click into position?

[ebiggs1]

"If everything is to factory spec completely removing one screw shouldn’t make a difference..."

Of course but if it makes him feel like he did something go for it. Than send it to Canon!

[SethHarrison]

Thanks all, CPS has the lens and is taking a look at it.