5D mark iii with Sigma EX 70-200 f2.8 dg macro

[Stephen-Blair]

Hey y'all,

I recently purchased the 70-200mm lens and am trying to use it on my canon 5d mark iii. The lens won't autofocus no matter what settings change or no matter which firmware I use. I'm currently on firmware 1.3.6. I have also ensured that the lens is set to auto not manual. Is there anything that I am missing to be able to use this lens? the autofocus works on my M50 with an adapter, but not on my 5D.

[Stephen-Blair]

That is the lens I am trying to use. I can’t find any forum posts or similar issues with the same body and lens. I am assuming it’s an issue with the lens. It functions on my m50 kinda. The camera doesn’t have an issue with any other lens. I have cleaned the contacts on the lens and the camera and it didn’t make a difference

[deebatman316]

What do you mean by it works on your other camera kinda. Is it slow to AF or have any other issues.

-Demetrius

40D, 5D IV, EF 16-35mm F/2.8L III, EF 24-70mm F/2.8L II, EF 28-135mm, EF 50 F/1.8 STM

430EX III-RT, 600EX II-RT

[Stephen-Blair]

On the m50, it is constantly focusing even when not engaging back button focusing. Holding down the focus button doesn’t make any changes

[Waddizzle]

Cleaning contacts rarely fixes anything, not unless you can see visible debris or discoloration.  The mere act of mounting and dismounting the lens creates sufficient friction on the contacts to keep them clean.

Make sure the camera body contacts are springy and not getting stuck.  Otherwise, I do not know what else to do about it.  They just do not want to play together.

[Waddizzle]

Mirrorless cameras work a little differently compared to a DSLR.

[deebatman316]

Does OP have BBF (Back Button Focus) setup on their 5D III. Since the shutter and AF Start buttons have been decoupled now.

-Demetrius

40D, 5D IV, EF 16-35mm F/2.8L III, EF 24-70mm F/2.8L II, EF 28-135mm, EF 50 F/1.8 STM

430EX III-RT, 600EX II-RT

[Stephen-Blair]

Yes I do. I put the camera to factory settings and it didn’t help. I also tried to have a few different buttons operate the AF and it didn’t change anything

[deebatman316]

A factory reset does not always clear (CF) custom functions. Try the camera in A+ Mode (Full Auto) overrides all custom functions.

-Demetrius

40D, 5D IV, EF 16-35mm F/2.8L III, EF 24-70mm F/2.8L II, EF 28-135mm, EF 50 F/1.8 STM

430EX III-RT, 600EX II-RT

[Stephen-Blair]

No luck with that either. I have chalked it up to a failure of communication with the lens and body

[deebatman316]

Usually a faulty communication will cause an error code of some kind. It also seems strange that it works when its adapted to an EOS-M/ EF-M series body.