ASUS' ZenFone Zoom is ultimately held back by a mediocre sensor

Its 3x optical zoom alone doesn't guarantee stellar image quality.

ASUS has been trying to make a mark in the US phone market for years, first with its hit-or-miss Padfone line and more recently with the budget-friendly ZenFone 2. Then, for reasons nearly beyond comprehension, the company decided to shoehorn a zoom lens system from Hoya into one of its phones. And lo, the ZenFone Zoom was born.

As a smartphone, the Zoom doesn't stray far from the formula ASUS introduced with the ZenFone 2: It squeezes enough power out of its quad-core Intel Atom Z3580 chipset, and the 4GB of memory helps keep this bloatware-ridden build of Android Marshmallow running smoothly. The battery will get you through a long workday but not much more than that. Of course, the camera is the real star of the show -- that's why the Zoom costs an extra $100 over the $299 ZenFone 2. Spoiler alert: For the vast majority of you, the premium just ain't worth it.

The name says it all, really. The Zoom's claim to fame isn't its 13-megapixel rear camera; it's the built-in 3x optical zoom lens. You can't miss it, either; the camera assembly looks like an enormous plastic disk on the phone's faux-leather back. Lumia 1020 fans might feel a pang of nostalgia, but the hump of the ZenFone's camera has nothing on that Windows Phone's notable 42-megapixel hunchback. While it's not subtle, exactly, the bump does a good enough job physically fitting into the body that you won't mind it much in day-to-day use.

It's pretty rare to see a hardware maker squeeze a proper moving zoom lens into a handset, but I can't argue with the results. Typically when you zoom in with your smartphone's shooter, the device is just expanding what's already in the frame and cropping off whatever doesn't fit. This, friends, is digital zoom, and it generally sucks. Here, though, you can zoom in up to 3x without losing any crispness, because the lens array is physically moving to magnify your field of view. You know, like on a camera.

To ASUS' credit, zooming works just as well as you'd expect. In addition to pinching-to-zoom, the volume buttons double as zoom controls (complete with the proper iconography). I wish we could have gotten more than 3x zoom out of this lens setup, but that probably would've required a far more insane configuration. Need I remind you of Samsung's bonkers Galaxy K Zoom? Still, if you're going to build -- and name! -- a smartphone with one specific feature in mind, why not go all out?

So yes, all that zooming works as advertised. It's too bad, then, that the sensor setup behind the lens isn't worth writing home about. What we have here is a 13-megapixel, Panasonic-made sensor that mostly yields decent color saturation and an adequate level of detail. Considering how good smartphone cameras have gotten, though, those are table stakes. Pictures shot with the ZenFone Zoom routinely seemed lifeless and indistinct compared with shots obtained with an iPhone 6s or Galaxy S6 (yes, last year's model).

Don't get me wrong. None of the photos were bad; just unremarkable. What's more, low-light performance isn't great. That pesky grain is kept under control fairly well, but the amount of detail drops off pretty dramatically. There's at least a low-light-specific mode that helps somewhat. And it's hard to forget, as the phone frequently nags you to use it.

Zoom lens aside, the phone's biggest photographic asset is its autofocusing system, which uses a laser to lock onto subjects in a fraction of a second. The feature has popped up in a handful of great phones so far -- LG's most recent flagships and both new Nexuses spring to mind -- and it's a fantastic tool for quick, off-the-cuff shots. It's certainly fast at locking onto subjects, which makes the occasional sluggishness when snapping shots all the more frustrating.

Of course, you can take even more control over photos with the Zoom's surprisingly extensive manual settings. Beyond the usual ISO, exposure, autofocus and white-balance controls, you can also fiddle with sharpness and contrast values, as well as bring up a histogram to make sure your photos are well exposed. ASUS' camera interface is also nuanced enough to make you feel like you're using a proper camera, though the lackluster sensor means those controls will only ever take you so far.

Ditto for shooting video. Maybe it's just me, but a modern smartphone with a clear focus on photography -- even one that costs only $399 -- should be able to record in 4K. Instead, the Zoom tops out at 1080p, and you'll be able to use the handy stabilization feature only if you drop that resolution down further to 720p. The Zoom's video prowess is about on par with its photo chops, meaning you'll get perfectly passable (but forgettable) clips.

Before I started using the ZenFone Zoom, I was hesitant: Isn't its single standout feature just a big gimmick? The answer is a pretty resounding no. ASUS has put together a pretty impressive bit of zooming machinery here; it was the sensor itself I should have been more concerned about. Couple that poorly balanced photographic equation with a thick chassis and lackluster performance, and we're left with one serious question mark of a phone. I can see buying it as a curio -- an example of how smartphones are evolving -- but its practical value is limited at best. If you're serious about getting a first-rate smartphone camera, save up a little more and splurge on a Galaxy S7 instead.