I picked up a second hand 50mm f/1.2L lens recently with not a scratch on it.

I've noticed that when the lens is set to MF, the autofocus on the camera (6d) still works. As a workaround I have enabled the AF button on the back of the camera, and removed AF from the shutter button, but it seems odd to me that I had to do this. Isn't the MF position supposed to disable AF?

Is this just "how it works" or is the af/mf switch on the lens busted?

2 Answers 2


I suspect the switch is busted. You should be able to disable AF to give yourself full control over the focal point without AF changing it on you. Additionally the body should not (well, can't) override whatever is set on the lens.


Yes, the MF position is supposed to disable AF (I suspect you're not actually surprised by this) - sounds very much like the switch is broken.

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