Will the Canon EF 24-105mm f3.5-5.6 IS USM lens autofocus with the Canon EF12 II extender? How about with the EF 50mm f1.4 and EF 16-35mm f4L IS USM lens?
Will they autofocus with the Mount Adapter EF-EOS R?
It may depend upon which specific camera body.
I do not see any reason why it should not work. The macro extenders do not contain any active electronics. You’re just going to wind up with an cumulative set of mount adapters and extensions that may not stay in perfect alignment. Due to its own weight, it may begin to sag when held horizontally. I would recommend only using such a configuration when the camera is pointed straight down at the subject.
The EF12 contains contacts to allow the lens and camera to communicate. So, you should be able to set the aperture and autofocus.
However, autofocusing may prove to be a little cantankerous, due to the higher resolution and control demands that will be placed on the AF motors. You will most likely discover that your AF system will get it close, but you may still need to fine tune it manually. Use of a tripod is highly recommended.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.