Alan Stankevitz wrote me:
Thought I’d pass this along for your 4/3 site. I do nature photography and videography using both the Sony and M4/3 systems. (Sony A1 + 200-600) / (GH6 + Panasonic 100-400 and the Canon 60mm f/4 II lens)
Although I much prefer the Sony system for stills, I have been enjoying the Panasonic GH6 for filming wildlife. With the 2X cropped sensor I find this as an advantage for getting close-in while filming in 4k. Add the Canon 600mm f/4 to the mix and now you’ve got an effective focal length of 1200mm. This comes in handy when there’s a need to get closer to your subject. Film in 5.6k and you can crop down to 4k without any resolution loss. It’s hard to beat!
Here’s a video that was taken with the GH6 and the Canon 600mm f/4. There is no autofocus but for this kind of shot, there was no need for it.