I always wanted to build a controller for Canon Telephoto lenses to use them with c-mount cameras and control the focus from a PC. Might be helpful for that.
A couple of universities built a telescope called Dragonfly, that utilizes 48 Canon 400mm lenses to photograph the skies of New Mexico. The kicker is they don't use camera bodies. Instead, they designed and built mounts that directly connect the lens to a sensor. A PC controls each lens through some custom electronics using commands they reverse-engineered from the Canon control software. These commands control focus, aperture, and triggering a photograph. Images from the 48 lenses are then combined in the computer into a highly detailed final image. This was done back in 2013 so its possible Canon has released an API by now but I suspect they still keep it proprietary.
I visited some similar telescope in Australia at https://www.sidingspringobservatory.com.au/ run by Macquarie University ... the students explained the lens system could not be too new and could not be too old. Basically it sounded like someone had partly reverse engineered one generation of the lens interface only.
I guess the camera and lens manufacturer wants their lenses to be used with their cameras and to have better results than other manufacturers, whereas random companies want to clone the interface and sell cheaper lenses that also work with the cameras. Realising how awesome the lenses are, the students want an array of them, however they don't have the budget to buy a similar array of top end manufacturers' cameras.
A number of machine vision camera vendors have higher-end variants that support active EF-mount lenses. They tend to be quite expensive models with larger sensor, since you tend to lose a lot adapting full-frame lenses to tiny C-mount sensors.
If you want a computer-controlled lens, one of the cheapest options is to use Blackmagic cameras that support SDI and/or USB control. You can then control either native M4/3 active lenses (focus, aperture, zoom) or supported EF-mount lenses if you use one of the EF->M4/3 active adapters.
