Youtuber HillbillyGripTruck helped out a friend with a pre-production Panasonic GH5 and immediately set about executing one of the first tests any filmmaker does with a new camera: how does it handle higher ISO settings and low light? This helpful video shows a direct comparison between the GH4—which tops out around 800 or even 500—for nice clean footage, and the brand new GH5.
The upside is that, when set up correctly, even video shot at 12,800 ISO seems like it would be useable in certain situations. The biggest surprise in the video is that the 10bit footage is significantly noisier than the 8bit footage. 10bit was one of the features that has been most heralded about the new camera, with the higher bitrate supposedly leading to less artifacting and easier to color correct footage in post.
However, as is clearly shown in the tests, the 10bit is actually noisier than the 8bit. This is likely do to with bandwidth limitations in the camera, since the low noise isn't the result of changes in the sensor but instead the result of internal noise correction. With more internal bandwidth going to the 10bit processing, less is available for noise correction, leading to more bouncing video dandruff.
The 10bit footage is still wildly more useable than the GH4, and there are of course a ton of tools for post noise correction including Red Giant Denoiser and Neat Video, which could be applied to the 10bit footage and would likely give as good, or better, results than the realtime noise correction we see on the 8bit footage. But for those of you considering the GH5 for fast turnaround jobs where there might not be time for post noise correction, it's good to note you should be testing 8bit just as much as 10bit for your low light work.