IT Pro Verdict
Multiple problems doom Sony’s 4K phablet to expensive gimmick status
Water resistant design; Sturdy and attractive; Fast fingerprint reader
Limits on use of 4K screen; Overheating issues
Most flagship smartphones are capable of shooting 4K, but viewing the footage as it was supposed to be seen typically means using a 4K TV. Not so with the Sony Xperia Z5 Premium, which is the first (and only, still) smartphone to have a 4K Ultra HD display. It's an impressive stat to lead with and makes the handset one of the most interesting. But, is 4K anything more than just a gimmick and do you really need this many pixels in a device this small? After all, once you reach a certain pixel density, it's a case of diminishing returns when it comes to image quality. Now, eight months after the phone was launched, we find out if the 4K screen still holds up and if it's worth having, and look at the new Android 6 update to see if it brings much to the handset.
Measuring 5.5in diagonally, the screen has a whopping 3840x2160 pixels, which is far more than most TVs and monitors - especially ones found in most offices - and results in a staggering pixel density of 801ppi.
However, the catch is that the screen only displays 1920x1080 pixels in the vast majority of apps. The only exceptions currently are Sony's own video and photos apps. There's no way that we know of to force the Z5 Premium to display any other app at the screen's full 4K native resolution. Even if you could, we doubt that would be a good idea - squinting at minuscule controls and content in an unoptimised app would be counterproductive.
We've been sceptical of the ever higher pixel densities that smartphone manufacturers like to boast about as it's now very much a case of rapidly diminishing returns the higher up you go, but this takes the cake.
Sony claims this arrangement is in place to preserve battery life (more on this later). In any case, we were hard pressed to discern any substantial difference in quality when viewing 4K video clips in Sony's app compared to 1080p versions without literally holding the phablet centimetres away from our faces. Sony claims lower-resolution content can be upscaled to near-ultra HD quality, but we couldn't see much difference here either.
Given Sony's meagre influence over Android app developers, we don't hold out any hope that third-party apps will be updated to display content at 4K resolution on the Z5 Premium or that upscaling quality will improve. This might change if and when Google adds official 4K support to Android, but that's a big if.
Given its almost constant downscaling to 1080p, we naturally didn't notice much difference in text sharpness. Regardless of the resolution, images and videos did look good with natural looking colours, good contrast and reasonably high brightness.
If you're nonetheless dead set on shooting 4K video, then at least the camera is up to the job. Videos were full of detail with pleasing colours and surprisingly effective digital image stabilisation, although we had to watch videos on a big 4K TV to appreciate them.
Stills were more of a mixed bag. The 20-megapixel resolution of the relatively small sensor is excessive as the resulting noise, especially in low-light shots, was excessive and ugly. Autofocus wasn't as fast or as sharp as we were expecting either, especially compared to other similarly-priced flagship phones. There's little we can do about the latter, but changing the camera app's settings from 20 megapixels to eight megapixels resulted in much better looking shots on par with the iPhone 6s as well as the Samsung Galaxy S6 and Nexus 5X and Nexus 6P, although the automatically applied sharpening was a bit too aggressive. There's a good camera lurking in the Z5 Premium, but it needs better software to bring out its best.
Battery life and Performance
Battery life was something of a mixed bag. We used Sony's video player app, which automatically upscales non-4K video, in our video playback test. While not awful at just over nine and a half hours, this is far behind non-4K phones.
Battery life was much better when displaying 4K wasn't involved. When connected to EE's 4G network in London and used for browsing, GPS, calls, photography and video recording, the battery lasted just under 27 and a half hours which is much better and in line with what we'd expect from a phablet at this price. Clearly and unsurprisingly, a 4K screen working at its native resolution has a substantial effect on battery life.
Another unfortunate example of give and take is performance. The eight-core Snapdragon 810 processor and 3GB of memory sped through our benchmarks and we didn't see any problems with the responsiveness of the touchscreen. Unfortunately, the processor was sometimes prone to overheating with the rear of the phone becoming much warmer than usual. There was no rhyme or reason to the occurrence of this problem - it occurred more often during web browsing and emailing than it did when recording 4K video - suggesting that it might be fixable via a software or firmware update.
Waterproofing and casing
Although Sony no longer claims that its Z-series phones are waterproof enough to survive complete immersion, the Z5 Premium is still water resistant enough to survive rain, spilt drinks, puddles and other aquatic hazards. There's no longer a protective flap over the micro USB port as on previous Z-series phablets, though, so you'll have to remember to dry it out thoroughly before plugging it in.
Sony has carried over the same general aesthetic from older Z-series phones. Available in chrome, black or gold, the reflective glass rear felt a tad slippery in the hand but the phone still felt evenly weighted and very well-made too. The plastic rim looks a tad cheap, but it doesn't spoil the generally classy look of the phone. The rear on the chrome variant is especially shiny and reflective - it can almost be used as a pocket mirror and picks up fingerprints very easily too.
Last, but by no means least, is the fingerprint built into the home button. This is located on the side of the Z5 Premium, rather than on the front or the rear as with other smartphones. Despite our fears, this writer didn't have any problems using it either left or right handed, although certain fingers obviously work better from a comfort point of view. Recognition was fast and generally free of false negatives. We do wonder whether this side-mounted fingerprint scanner will pose any ergonomic problems when using the phone with Android Pay if and when that tap-to-pay service ever launches in the UK, but that's a theoretical concern for now.
The Sony Xperia Z5 Premium currently comes pre-loaded with Android 5.1.1 Lollipop, but the Japanese giant has now released the Android 6.0.1 update for all Z5 phones. Although you should have been prompted to upgrade, you can force your phone to check for an update by going to Settings, About phone, Software Update. If a software update is available, you can tap Download and, then when the software has downloaded, tap Install.
The initial update ran into problems with users reporting that the Google Play Store would crash upon opening or that they would get the "System UI has stopped" error message. Fortunately, it appears as though these issues have been fixed, with the update once again available to all phones. There aren't a lot of stand-out new features, with Android 6 more of a subtle upgrade than Android 5 was, but the update promises better battery life and has a few other important tweaks. See ourAndroid 5 vs Android 6 guidefor more information.
The Sony Xperia Z5 Premium has a lot going for it and that 4K screen certainly grabs attention. But, scrape a little below the surface and it's clear that the 4K screen is little more than a gimmick, with the phone running at a Full HD resolution for most of the time, as it's a massive battery drain and, on this screen size, it's hard to the see the improvement over 1080p displays.
On top of that, the Xperia Z5, with its 5in 1080p screen, has pretty much all of the same features without the needless 4K screen. You're better with the regular Z5 if you really want a Sony handset. However, if you can live without water resistance, then the lure of theNexus 6P and iPhone 6s beckon.
This review was first published 1/01/2016 and has since been updated, most recently on 23/05/2016.
Multiple problems doom Sony’s 4K phablet to expensive gimmick status
Processor: Octa-core 2.0GHz Qualcomm Snapdragon 810
Screen Size: 5.5in
Screen resolution: 3,840x2,160 pixels
Rear camera: 23 megapixels
Storage (free): 32GB (22.5GB)
Wireless data: 3G, 4G
Operating system: Android 6 (via upgrade)
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