Focusing issue with my 24-105mm L lens for Canon 5D mkiii

[cynicxl]

My lens stays in AF regardless of whether it's in AF or MF mode, I've tried switching them back and forth and noticed that occasionally the lens does go into MF but sometimes it happens when it's in AF as well as MF mode, so it's very random. 

I've tried taking off the lens a few times but nothing is working. Any tips?

[Anonymous]

You could dampen the cloth with isopropyl alcohol. Are you having this problem with another lens on this camera or only the 24-105mm?

[cynicxl]

Hi there,

I've now tried properly cleaning the lens and camera contacts, but the problem persists. My other lens works perfectly fine. Any ideas on what I could do?

[Anonymous]

The problem seems to be in the lens then. It will need repair. 

[kvbarkley]

Send it to Canon for repair.

[ebiggs1]

"I've now tried properly cleaning the lens and camera contacts, but the problem persists."

This seems to be something that new or inexperienced folks suggest all the time. It rarely to never works or even helps. And if done incorrectly it can permanently damage the contacts. The act of mounting and removing a lens is usually sufficient to keep the contacts in good working order. That's why cleaning hardly ever helps.

There is a very thin, I mean very thin, layer of gold plating on the contacts. It can easily be rubbed off. If it is, the contacts can not be repaired. They must be replaced and that ain't cheap!

You solution was given by Mr. Barkley, "Send it to Canon for repair."

[amfoto1]

It makes sense that your lens is the first version EF 24-105mm f/4L IS USM, if it was provided as the "kit lens" on your camera. The 5D Mk III was intro'd in 2012 and that version of the lens was in wide use at the time. In fact, the "II" version of the lens didn't superseded it until 2016, when the 5D IV also was being introduced. 

It sounds as if the lens will need to go in for repair.

But...

As this is a first version EF 24-105mm f/4L lens, it has "full time manual override" of the USM ring type focus drive. In other words, you can adjust focus manually regardless where the AF/MF switch is set. And it's mechanical (not focus by wire). 

It should only autofocus when the switch is set to AF.

The problem may be in the switch itself. A little corrosion in there might prevent it from engaging or disengaging. It MIGHT help to simply operate the switch 10 or 15 or 20 times. Those switches are typically a "self cleaning" design that "wipes" away any oils or oxidization that might be on the metallic contacts inside the switch.

No guarantee this will work... But it's something you can try yourself before looking to get the lens repaired. I seem to recall a common problem with that version of the 24-105mm was a "ribbon cable" that would come loose or break wires internally, simply from the repeated flexing that occurs with normal operation. I don't know if that can cause the lens to be "stuck" in AF mode.

If you do need to get the lens repaired, contact Canon before sending it. Since that lens was discontinued around 7 years ago, they may or may not still work on it.

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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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