How to use SERVOx_FUNCTION as "camera focus (91)" to do focus control on Sony cameras?

Hi,

I am using a Sony camera for aerial mapping and the camera takes two inputs to trigger: focus and shutter release. The common practice according to Camera Trigger Setup for Pixhawk is to ground the focus pin all the time and only trigger the shutter. This works, but has it´s own problems, like sometimes the camera slowly reacts to light changes and not being able to interact with the menu while the trigger cable is plugged in.

I saw, that you can set up SERVOx_FUNCTION to camera focus (91), but there is no documentation about this feature at all.

I would appreciate any further information about this topic.