The Z50 II offers a better video mode than the Z50 and is definitely the one to buy if you're predominantly a videographer.
The original model offered 4K/30p and Full HD/120p recording modes.
The new Z50 II offers 4K/60p, albeit with a 1.5x crop, 4K/30p oversampled from 5.6k with no crop, and Full HD/120p.
It also provides 10-bit N-Log for the first time ever on a DX camera, along with the ability to use RED Luts.
There is a red video record light on the front of the Z50 II and a red framing border is displayed on the LCD screen when recording.
The Z50 II has a 2x Hi-res zoom for full HD video with 11 zoom speeds. There is no loss in resolution, unlike a digital zoom, because the camera records in 4K first then converts to 1080p.
Sound is also improved on the Z50 II, thanks to its built-in stereo mic and the option to attach an external mic. It also offers an onboard wind-noise reduction function and a headphone socket.