We were extremely impressed by the 4K video on the iPhone 6S Plus, so would the Z5's 4K footage stack up? Actually, it does. Our first attempts were shaky but a check of the menus revealed the cause – the stabilizer wasn't activated.
Without an exposure lock function, it's not possible to fix the exposure for the duration of a clip, so a moving subject against a changing background could cause problems – the exposure will change, even though the lighting on the subject is the same – but in most situations the Z5 is going to produce very good results. It's easy to lose sight of the fact that this is a phone, and yet it's shooting 4K video at a time it's only just starting to appear on professional cameras.
Make sure you switch on the stabilizer. This video (above) was shot with the stabilizer off.
And now see the difference with the stabilizer switched on. The 4K video quality looks good (pity about the wind noise, though).
Here's the iPhone 6S Plus version (above).
Timeshift
The Timeshift mode (slow motion, in other words) is also impressive, but only until you look a little more closely at the results.
The resolution is the same as the iPhone 6S Plus's at 1280 x 720 (standard HD) but the Z5 can only achieve half the frame rate – 120fps versus the iPhone's 240fps. This means you only get a 4x speed reduction rather than the iPhone's 8x reduction.
Even so, that's slow enough for an attractive and impressive slow motion effect, and at first glance the video footage is sharper than the iPhone's.
But there is a problem. In our shot of Dan's car sweeping through autumn leaves, hard edges in the car's body panels or details show clear imaging artifacts.
"DP: The Z5 is clearly interlacing the footage to achieve its 120fps Timeshift frame rate – the result is that straight edges take on a jagged appearance and some fine detail appears to shimmer."
Interlacing is a way of maximising resolution with limited bandwidth by interweaving odd and even rows in the video frames. It's an old-school fix and it's disappointing to see it in such a cutting edge device.
It's not just hard edges that show this interlacing effect. Small details like individual leaves on the road can be seen flickering in and out of existence between frames as they slip between the interlaced rows.
The Z5 treats Timeshift videos in the same way the iPhone handles Slow-mos, producing a movie that runs at normal speed at the start, slows down to slow motion speed in the middle and speeds back up to real time at the end. This gives a much slicker effect than a movie that's in slow motion from start to end.
This is the Z5's Timeshift mode in action (above). The interlacing effect is clearly visible.
However, while the iPhone 6S handles this in a straightforward way – you can change the normal/slow transition points later – the Z5 makes it a little more complicated by prompting you to choose your settings as soon as you've stopped recording your movie, and you have to sort this out before you can shoot another one.
