It's 2015 and there's an argument that the compact camera is obsolete in the face of advancing smartphones. The Sony Cyber-shot RX100 IV is the absolute antithesis to that; a high-end, pocketable compact with large 1-inch sensor and 24-70mm f/1.8-2.8 equivalent lens. It all adds up to arguably the best pocketable camera money can buy.

If, that is, you have a lot of money. Because the RX100 IV is a stonkingly expensive £840. According to Sony's official site its RRP is £918. Whew. That makes even the earlier third-generation model seem like a pocket money purchase.

We've been fans of the RX100 series since its inception, so is the Mark IV worth its significant cover price this time around, should you instead opt for the also-available RX100 III or look to a competitor instead?

That price bump is courtesy of the latest technology being on board, so there's a definite argument that you get what you pay for in the RX100 IV.

First up there's a brand new sensor. It's still a 1-inch 20.1-megapixel offering just like the RX100 III, but in the RX100 IV it's constructed differently, showcasing Sony's Exmor RS stacked CMOS technology. This pushes the circuitry to the rear of the sensor construction as to not get in the way of the pixel layer for the best possible light-gathering properties. So despite it being the same resolution, a cleaner signal should result in yet cleaner images.

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Second there's the built-in electronic viewfinder (EVF). Again, the RX100 III had a pop-up EVF, and while the RX100 IV's is the same by design - which means you still have to manually pull the rear lens outwards by hand (annoying) - it's now much higher resolution. Almost double the resolution, actually, with a 2.35m-dot display (compared to 1.44m-dot) and it looks rather impressive indeed. The fact it can be stowed away when not of use is a space-saving design marvel, even if it comes at the expense of a hotshoe (not seen since RX100 II era) and without a decent eyecup to shield from surrounding ambient light.

Third, there's a push in processing power. Now you might think, why does a compact camera need more processing grunt - but in the RX100 IV it means 16fps burst shooting without delay and the ability to capture 4K clips (up to five minutes) too.

However, there's still no touchscreen controls, and the camera's buttons still feel rather small, but otherwise the RX100 IV feels every bit the high-end compact. Whether the added EVF resolution, subtle image quality boost, 4K capture and faster processing are worth the extra £250 (at the time of writing) is something that you'll have to mull over. Here's what we think:

In terms of build, it's hard to fault the Cyber-shot RX100 IV. That's because it's the very same as its RX100 III predecessor, albeit with a swanky new IV badge and some 4K markings.

It's constructed of a sturdy metal chassis, with a reassuring but not excessive 290g weight all-in. At just 41mm deep it's a dinky design too, and the lens stows away neatly inside the body to make it truly pocketable. While competitors' cameras seem to be growing - take a look at the Fujifilm X30 or Canon PowerShot G5 X - Sony has stuck to small, and really made it work.

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However, small can bring its downsides too: the small buttons on the rear; the d-pad being a little close to the LCD screen; and the on-board battery having limits to capacity given its physical size.

The fact a 180-degree tilt-angle screen has been squeezed into such a small body design is impressive however. A vari-angle, side-mounted bracket would be too large, we suspect, so we can see why Sony has stuck with this mechanism - and even if we've never used the front-facing selfie position, the option for 90-degree waist-level work is something we've been using aplenty. If only it offered touchscreen controls to simplify that shooting process, then we'd be even happier - and this deep into the iterations it seems bizarre for such a feature to be omitted.

The built-in EVF, while excellent, does also carry forward some of the relics of the last generation model. Not only is tugging that rear lens out a bit of a fiddle (we'd prefer it to spring out on its own, then be pressed to click back into place for stowage) but stowing it away switches the camera off. C'mon Sony, we fussed about that over a year ago in the RX100 III - that's got to be an easy fix? We'd like the option to control this from within the menus as we don't always want the finder exposed due to its eye-level sensor meaning the rear screen will switch off if anything is too close to that sensor. Useful when raising it to your eye to use it, of course, but not always desirable when not.

When it comes to lenses, most professionals will hanker for a 24-70mm with a fast aperture as a decent optic to cover the majority of situations. Which is exactly what the RX100 IV offers; a fast f/1.8-2.8 maximum aperture across that equivalent focal length, in fact.

It's not a new lens, though, being the very same as that found in the previous RX100 III. We had nothing but good things to say about that lens when tested, though, so that translates well in this latest model too. It's sharp, it's quick to operate and, despite not delivering the ultra-zoom that some compact competitors might, it's perfectly fitting for the scale of a camera such as this.

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There's also a lens control ring to the front that freely rotates to cycle through controls. It doesn't click, though, so when sifting through aperture values, for example, it's not as decisive as it could be: you'll be looking visually, rather than counting stops in your head, and as the rear rotational d-pad does click per f-stop position this is the preferable option to use. However, that control ring's motion is silky smooth, although the software seems to be more a step behind the physical rotation in displaying the current adjusted value on screen - it should be snappier.

In addition to the zoom toggle around the shutter button this lens control ring can also be used for zoom, with the principal focal lengths - 24mm, 35mm, 50mm and 70mm - presented in a clear-to-read format on the screen to assist. Or there's a step zoom option which jumps between those specific focal lengths at a faster pace.

As per the Mark III model the Mark IV maintains the built-in neutral density (ND) filter, which can be switched on or set to auto for those particularly bright scenarios when you'd still like to use a wide-open aperture.

In terms of performance the RX100 IV is just as good as the previous model - but in the ever-progressing world of cameras it would have benefitted from a few tweaks here and there.

For example, the three sizes of autofocus area - small, medium and large; all of which are rather small really - or auto area selection lack the advances of something like the Panasonic Lumix G-series in terms of pinpoint focus. And seeing as this Sony is as expensive as an interchangeable lens system camera it really ought to be as proficient in all areas. And without touchscreen controls, digging in to adjust the focus point is harder work than it ought to be.

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The same thing can be said about autofocus speed. Yes, it's quick, but again it's not always the quickest. It's also not perfect: in low-light we've had some slip-ups, while even bright light reflecting from metal rims of cars has scuppered the system to fail to focus on the subject. As compacts go it's a solid experience, but we want Sony's absolute best system on board given the price tag.

We found shooting close-up delivered good results, although the 5cm-from-lens focus at the 24mm wide-angle setting does quickly drop to 30cm-from-lens at the 50mm setting. Manual focus works well thanks to the smooth rotation of that lens, coupled with focus peaking and an 8.6x digital magnification that shows an enhanced focus area on the rear LCD screen or in the viewfinder.

In summary, the RX100 IV performs well, it's just hard to not be extra critical about it given the price bump and advance of surrounding competition. And with Canon launching cheaper touch-control-based cameras such as the PowerShot G9 X, Sony needs to ensure its crown doesn't slip due to complacency. The RX100 IV doesn't feel complacent, per se, but it's resting on its predecessor's success a little too much.

Despite our minor performance quibbles, it's near impossible to complain about the quality of images we've been getting from the RX100 IV. From low-light snaps in late night tapas bars, to ISO 4000 shots being able to focus with relative ease thanks to the fast f/1.8 aperture, this camera is kitted out the max to ensure you get the images you're after.

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In its fourth generation guise - and thanks to Exmor RS - this RX100 delivers the best quality yet from the series. That, ultimately, is what you're paying for: the new sensor. Thing is, there's only so much of an incremental bump that can be achieved these days, so to expect moon-landing-like steps forward would be to expect too much. The RX100 IV is better than the RX100 III, but it's a marginal difference.

Even so, it's hard to believe such a small camera can deliver images with such clarity. A lot of it isn't just down to the sensor, but the combination of features. Having a fast aperture keeps higher ISO sensitivities at bay, while beautiful bokeh backgrounds are easily achieved thanks to the larger-than-average 1-inch sensor size coupled with wide-open aperture options.

Even when high sensitivities do need to be used, the results are still impressive all things considered. Shots at ISO 1600 show little disruptive image or colour noise and there's still plenty of detail to play with, whether working from JPEG or raw files - the latter being altogether noisier but sharper. It's this kind of performance that puts the Sony leaps ahead of a standard compact. Although the top-end ISO 25,600 is a step too far really.

As before our main qualm is that Sony's Auto ISO isn't particularly intelligent. When snapping moving subjects we often found it wasn't quick enough to bump up the shutter speed, despite an apparently agreeable auto scene mode kicking in.

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Overall, though, the RX100 IV delivers where it matters. We even attended a product launch with only this camera in tow, leaving behind DSLR and CSC options. Now that's a statement in itself, as we're chuffed with the pictures.

Verdict

There's no escaping it - the Sony Cyber-shot RX100 IV is one pricey compact camera. Is that the price of perfection? Almost.

The main thing to weigh-up in the mind is whether this latest model is worth the extra £250 over its predecessor. The extra EVF resolution, faster processing and burst mode, 4K video capture and a boost in image quality (albeit slight) are certainly aspirational features, but it's this price point which, ironically, costs the RX100 IV from a perfect score.

Finding genuine gripes with this camera is tricky. Sure, Canon has come out with its touchscreen G9 X, but that feels like a plaything by comparison to this Sony (despite being excusable at half the price), while most competitors offer nothing nearly as capable, nor as pocketable. A more detailed and faster autofocus system wouldn't go amiss, but even so the Sony RX100 is still the high-end compact camera to beat.