Here is a test of the most relevant features of the Panasonic Lumix DMC-GH4. All workflow was in 4K (UHD) 3940x2160@25p, shooting, editing, delivery. I think it may help you to understand the real potential of this camera and of 4K shooting. No effects were applied on clips, no Color Correction, grading, stabilization, etc.
The location is Minori, one of the pearls of Amalfi Coast, the closer town to the more famous Amalfi and Ravello.
Two and half years ago I tried the GH2 (I never used the GH3), and I was surprised by the low quality of the camera body while this time my feeling was the opposite. The ergonomics and the materials are almost perfect. The body is small and lightweight (compared to a 5D MK III). In manual mode two rings allows to adjust in realtime, during recording, shutter and IRIS. The ISO button, small but with a different surface for easy finding, allows to adjust the ISO using the same ring, Another ring allows to choose between "Creative Video" mode, and different Picture modes (that allows to record video clips too using the video rec button on the back of the camera). Creative video exposure modes (Manual, Auto, Program, etc.) can be changed in the internal menu, that is well navigable. The 3.0" touchscreen LCD screen is versatile, it is articulated allowing to move it in any direction. The quality of the display is good but not like the latest I used on some other competitors. The touchscreen often helps to save time in camera customization. The camera has several buttons than can be customized by the user.
I tested the camera with the bundled lens, the Panasonic Lumix G 14-140 F4-5.8 Mega OIS, that has a very good focal range (28-280mm in the 35mm), has a good price/performance ratio (in the bundle its price is about 300,00Euro) and provides a good quality but manual focusing isn't always easy and F4-5.8 is too "dark" for the ISO performances of GH4. I got the best at 800 ISO, but in the night I was often compelled to use 6400 ISO, where lots of noise affects the image. At 6400ISO noise is similar to +32dB on HD handheld camcorders.The noise is not so annoying on whites and greys. I liked very much the shots I made at the twilight at 800ISO (some are not in the upload video), although the Youtube compression introduced a lot of noise and compression artifacts not present in the native clips and in the exported movie.
Rolling Shutter & Depht of Field
Rolling shutter effect is bigger than on other competing products (like Canon C100) or modern camcorders (like JVC GY-HM600/650). Flash banding is not a big problem, but skew is relevant. As you can see, the images are very nice, but their look is more closer to a camcorder than a full size DSLR. Images are clean, with lots of details, but there is always a big depth of field; using the 140=280mm focal lenght it is easy to get a nice bokeh effect even if IRIS aperture can't be lower than 5.8 (Alessandro on the pier).
on a "camcorder" I'm not very interested in autofocus, but when light is good, GH4 autofocus seems to work very well+, also in AFC (AF continuous). I can't say the same in low light situations, where it was bad, but probably it required some menu items to be set in a different way.
White balance has a lot of options, and the Auto one worked very well in all tested conditions. There are presets for any condition, as well as fine tune of Kelvin degrees and several memories of manual WB.
the camera features a good stereo embedded microphone, with the capability to handle audio levels, and features two 3.5mm jack plugs, one for a stereo Mic and another one for headphones. In the headphones you can choose to hear the direct MIC input or, with a small delay, what you are recording, and this is very nice. Moreover, if you'd need more inputs and features, you can add the optional 4K docking station DMW-YAGHE that adds 2xXLR Inputs with 48V Phantom power, 4x3G SDI Out and Timecode IN. It provides audio monitoring, an HDMI connector and 12V power input, but, unlike a battery grip, it doesn't host extra batteries (to swap battery you have to remove it).
Video Codec: video recording was made at 3940x2160@25p, with a data rate of 100Mbps. Like on the best HDV camcorder of some years ago, the datarate and codec is good if the camera is still and steady. When you move it for pan and tilt, the recorded clips are slightly blurred, the same thing that happened with the best HDV camcorders. The clean HDMI output allows to use an external recorder when needed. HDMI 4K out has two options 8bit and 10bit. When enabling 10bit, it is not possible to record into the internal SD card.
I had the camera for very short time, and I was mainly interested into the video features, but I made some pictures and they are very good.
GH4 is able to capture true 4K images that show more details than you could have imagined. It has a very good body and ergonomics, and, unlike many camcorders, allows you to make excellent pictures too. It would be perfect for me if it would get a wider ISO range with less noise, a built-it optical ND filter, and an additional ring for ISO, it is better for me to not to share commands. About the bundled lens, it could be better, but you know, you can change it anytime, this is why most of us like DSLR and mirrorless cameras. I hope to be able to try the GH4 with other lenses soon.