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Even if it weren't the world's first 4K phone, the Sony Xperia Z5 Premium has a lot going on

It's waterproof, it has a fingerprint scanner and the screen will melt your eyeballs. But is 4K on a phone a waste of time?

Now Playing: Watch this: Sony Xperia Z5 Premium has a pixel-packing 4K screen

4K or not 4K -- that is the question. Sony has revealed what it claims is the world's first smartphone with a 4K display, the Sony Xperia Z5 Premium. But can our eyes even cope with such an eye-popping screen at such a pocket size?

Before we get into the 4K debate, it's worth pointing out that even without the 4K screen the Z5 Premium is a heck of a phone. Going on sale in November, the Z5 Premium is a slightly larger and classier version of the new Xperia Z5 and its smaller sibling the Z5 Compact. It's certainly a slick proposition: the 5.5-inch Premium is packed with features and wrapped up in a luxurious mirrored glass package.

The glossy mirrored finish looks lovely, but attracts fingerprints. Rich Trenholm/CNET

The case comes in gold, black or mirror-like chrome. The shiny, reflective casing looks great but it's quickly marred by fingerprints, so keep a cloth handy. Alternatively, you can hose it down -- like most of Sony's recent smartphone lineup, the Z5 Premium is waterproof. Drop it in your Martini and it will continue on like nothing happened. Take it in the shower, and your only worry will be the water going cold.

It's also very thin and light, and the screen fills most of the front face to keep the overall size down.

See how it compares other large-screen superphones, like the Samsung Galaxy Note 5, iPhone 6 Plus and LG G4.

A new feature on the trio of Z5 phones is a fingerprint scanner, but it might take you a minute to spot it by looking at a picture. Give up? It's in the power button. Instead of a sensor in the home button ( like the iPhone) or on the back where you can't see it ( like the Samsung Galaxy S6) the Z5 phones boast a more subtle sensor in the button on the side. It looks great, but does it work? We'll find out when we spend more time with the phone for our forthcoming full review.

The fingerprint scanner is elegantly hidden in the power button. Rich Trenholm/CNET

Inside is a Qualcomm Snapdragon 810 processor, powering Android Lollipop software. That gives you access to Google's vast emporium of Android apps, Google Play and all the usual Android goodies like Gmail and Google Maps.

Features specific to Sony include PlayStation Remote Play, which allows you to play games from your PS4 games console on your phone.

And it's got a whopping 23-megapixel camera, which we'll be testing thoroughly in our full review. But enough of all that. What about the screen?

Putting the 4K in phones

The Z5 Premium's claim to fame is that it has an eye-scorching 4K screen. 4K is the next big thing in display technology, promising loads of extra detail packed into movies, games and videos whether you're watching on a 4K television or filming on a 4K camera. It's so new, there's still a shortage of things to watch: Netflix has some shows in 4K and a few live events are filmed in 4K for broadcast.

Some phones already shoot 4K video -- including the Samsung Galaxy Note 5 and Sony Xperia Z3+ -- that you can watch on your 4K TV. But the Z5 Premium is the first phone that allows you to shoot 4K video and then watch it back at full resolution on the same device. The Z5 Premium also upscales less detailed video from Netflix or YouTube or other sources to 4K.

The big question is whether there's any actual benefit in having a 4K phone. A vast amount of extra detail in a huge TV is one thing, but it's open to debate whether at this smaller size you'll actually be able to see the difference between 4K video and high definition video, which is already pretty pleasing to the eye.

We'll try and answer that question when we've spent more time with the phone in our full review, coming soon. During our limited time with the phone so far, we certainly found that Sony's sample 4K footage looked gorgeous...but so does the full HD video. Ultimately, trying to work out whether video is jawdropping or just eye-popping is quite a nice problem to have.

Sony's Xperia Z5 Premium packs a 4K display -- a pixel count which blows rival mobiles out the water, but whose benefits are still open to debate. Rich Trenholm/CNET

One of 4K's selling points is that it future-proofs you for when 4K becomes the industry standard. This is certainly true when buying a TV, as you're likely to keep a TV for a few years and you want to know it will be able to keep pace with advances. But it's less relevant when buying a phone, which you're likely to change in a year or two.

The extra detail in a 4K video means much bigger file sizes. To deal with that, the Z5 Premium will take a memory card up to a monstrous 200GB. Even if you never store any 4K content, that's still roughly 16 hours of full HD video...if you have a spare couple of hundred bucks to by the card, that is.

The other potential issue of such a powerful screen is that it will eat through your battery. Sony still promises the same two-day battery life as the Z5 and Z5 Compact despite the power-hungry screen, thanks to a hefty 3,600mAh battery. The software also wrings out extra juice from the battery by waking the CPU only when there's something moving on the screen; when there's a still image, such as a lock screen or a static menu or home screen, Sony says the processor runs slower and so uses less power.

That should also solve a problem that plagued the Xperia Z3+. That phone overheated when shooting video, crashing the camera app. Sony reckons the Z5 Premium won't heat up any more than other phones, but again we'll believe it when we see it.

Sony reckons the hefty 3,600mAh battery will last for two days. That doesn't mean 48 hours; it means you'll be able to have two normal days of using the phone to make calls, watch some 4K video, browse the Web and other typical use before you have to charge it. Again, that's a bold claim and one we'll be testing in our full review.

One area where 4K would be a definite advantage is in virtual reality. VR works by splitting the image in two and showing a slightly different version to each eye to create a 3D effect. Instead of one detailed image you have two images, one for each eye, each with half the amount of detail. So if you ramp up the overall detail to 4K levels, when the image is split in two each image is still Full HD. That means if you download a VR app on your Z5 Premium and strap the phone to your face, you'll see a much crisper view than in other phones.


A lot will depend on the price of the Sony Xperia Z5 Premium: a lack of content, danger of overheating and doubt over whether you can see the difference at this screen size mean it wouldn't be worth forking out extra for 4K. In Australia it's AU$1,299 versus AU$999 for the regular Z5. As such, you might prefer the regular Z5 and its full HD display. But even without the 4K screen, the Z5 Premium is still an awful lot of phone.

For more of the best of IFA 2015, see CNET's complete coverage.

Where to Buy

Sony Xperia Z5 Premium (black)

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