Image quality
The matter is simplified by the fact FZ1000 has got pretty much only two modes: 4Kp25@100Mpbs and 1080p50@28Mbps. GH4 matches at 4K, but 28Mbps is where it starts off with bitrates for HD.
In 4K (3840x2160) mode both cameras use crop of their sensors: in case of GH4 it results in extra 1.2 factor magnification (horizontal, 1.15 diagonal), but for FZ1000 it ends up in initial focal length becoming very moderate 37mm, not wide angle 25mm! To some extend it is compensated by proportional gain at longer end, but it is not the setting for most of the scenes...
Since sensor resolution is capped at the same level, it is only down to the lens and here again FZ1000 shows slight edge, additionally helped by the fact of using mostly the central part of the lens.
In HD mode the story is different: both cameras offer full sensor readout with binning/downsampling to achieve final frame size. But result is the same: sharper lens and more pixels to start with, FZ1000 comes slightly ahead of GH4 in acuity department. In both cases downsampled 4K shows slight advantage, so even this full sensor readout method is a bit lossy - still way above traditional line skipping though. Mind that I compare static scene - when dealing with movement, available higher bitrates of GH4 will benefit that camera. But what really makes it a winner, not only against FZ1000, is the amount of in-camera pre-grading controls. Remember, the output is 8-bit only, so any shifts outside of that range will end up as clipping - additional dynamic range together with master pedestal adjustment will help to squeeze as much of useful image information as possible. In skilled hands of course - if red button is enough to make footage, that won't matter much...
Google gallery limits long end to 2048px so 4K frames were squashed, click below to download files:
FZ1000 4k25p 100Mbps
FZ1000 HD50p 28Mbps
GH4 4K25p 100Mbps
GH4 HD50p 100Mbps
GH4 HD50p 200Mbps
GH4 HD50p 28Mbps
GH4 HD50p 50Mbps
Focus
There are reports that GH4 struggles with autofocus at 4K (due to lower sensor readout rate) more than in 50p HD and I would expect the same to apply to FZ1000. When slowly panning, that wasn't very noticeable though - again, more dynamic tests would be needed. Regardless racking speed, it seemed gradual in both cases and only when pressing shutter button, (I use that for start/stop of movie capture) AF kicked in and showed hunting.
GH4 4K
FZ1000 4K
GH4 HD
FZ1000 HD normal zoom speed
FZ1000 HD slow zoom speed
Zooming
FZ1000 is equipped with power zoom lens. It is very noisy, and although it seems to be suppressed when recording, still is audible. The zooming action happens at exactly the same speed as for stills: 2.4s to cover the whole 25-600 range at fast speed, 6 s at slow speed, which results in very rapid image angle change, with AF not catching up. Disappointment. Also the slower speed makes for more audible (lower frequency) noise being recorded
14-140 mm lens zooming is jerky, but even when going through a smoother range, focus changes in big jumps. It is a bit strange, as when manually focusing the effect seem to be fluid (even if the mechanism is based on stepper motors, the steps aren't noticeable). Useless.
Nobody would expect those lenses to be parfocal, but they could definitely behave better.
Stabilisation
Like for stills, so this time Power O.I.S on FZ1000 produces better result than its equivalent on 14-140mm lens, but I wouldn't say the outcome was completely shake free. FZ1000 offers additional digital stabilisation and levelling, but only in HD mode and that additionally crops the output.
Read next: Panasonic FZ1000 vs GH4 with 14-140mm f/3.5-5.6 (5): winners and losers
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