We tried the new Fujinon MK 50-135 Lens on the Sony FS5, recording 4k via RAW to the Atomos Shogun Inferno, 50 fps. The lens works really well and offers a neutral, yet sharp set of images. This is using the latest FS5 firmware, shot at ISO 2,000 in SLog3. Did some basic grading but did not apply any noise reduction in post.
No evidence of focus breathing, and the Inferno screen helps to set the manual focus right. There is no electrical connection between lens and camera. These tests were recorded with the lens right open, and the depth of field in quite narrow. But that of course is the point!