MFT cameras don't share the same wide field of view as a full frame DSLR. In addition the 4K Video setting on the Panasonic DMC-GH4 is further cropped in when compared to it's own 1080p setting.
One benefit to shooting 4K video is the extra resolution that will allow you to recompose, level a shot, or even zoom in to frame when outputting to 1080p. Seeing how my Rokinon 7.5mm Fisheye lens became less 'fisheye-like' with the 4K crop, I was also curious about using the extra resolution to correct the remaining distortion and finally outputting to 1080p. Nothing new as many users have 'de-fished' the Ultra Wide look from early GoPro cameras. I attempted to DeFish a BlackMagic Pocket Cinema Camera Clip with my fisheye lens that ended up looking great, but 1080p can only be stretched so far.
Here's a video showing different crop factors between 1080p using the Panasonic 12-35mm F/2.8 (@12mm) and the Rokinon 7.5mm MFT Fisheye Lens.
My tests with the GH4 4K Video show that the image is far from perfect, but far better when attempting to defish from a 1080p file. There's an obvious loss of sharpness towards the edges if you're really nit picky, but in many cases where you have to work in very tight situations with a GH4, taking advantage of the extra resolution in 4K is a good option. (BTW no sharpening has been done in post in this video)
Rokinon 7.5mm Fisheye Lens for MFT Cameras
Panasonic 12-35mm F/2.8 Lens
Panasonic Lumix DMC-GH4 MFT 4K Camera
The Panasonic GH3 camera pretty much runs me all day on a single battery. In fact we covered several products at NAB 2014 without ever having to swap out a battery during the conference. Still if you think you need to use the Panasonic GH3 battery grip for extra battery life, you'll quickly find that the Tripod Mounting hole is thrown completely off center with Panasonic's OEM battery grip.
This is problematic when using your cage, rails, and other accessories that require optical alignment with the lens. That's where this new Battery Grip Adapter comes in handy from Marketech.
The Battery Grip Adapter for Panasonic GH3 & GH4 Cameras from Marketech is a slim, rectangular accessory that mounts on the bottom of the Panasonic DMW-BGGH3 battery grip, and provides a 1/4"-20 tripod mount that is located directly underneath the lens. This matches the position of the camera's own 1/4"-20 mount, as opposed to that of the grip's 1/4"-20, which is shifted to the right. The adapter is constructed from durable Delrin acetal resin. It connects to the grip via the attached, free-spinning, standard 1/4"-20 slotted screw, the same type found on many tripod plates.
If the GH3 battery grip is compatible with the GH4, then this product claims to correct the issue with the new #GH4 as well. You can find the Panasonic GH3 Battery Grip Adapter via B&H (click here).
Battery Grip Adapter for Panasonic GH3 Cameras