We've already taken a look at how the primary 16MP camera of the OnePlus 5 compares to some of the best shooters currently on the market, but what about the larger, 20MP camera next to it, that's actually responsible for all the cool photo tricks the phone's capable of?
Similarly to the iPhone 7 Plus, the OnePlus 5 features a telephoto lens that has a longer focal length than the main camera, which allows you to zoom in on a scene without compromising quality. However, unlike the iPhone 7 Plus, which can do true 2x optical zoom, the OnePlus cannot. Its optical zoom is instead limited to 1.6x, but the phone simulates the full 2x zoom digitally.
That's not that big of a margin that the OP5 has to cover for digitally, and besides, its telelens is powered by a 20MP Sony IMX 350 sensor that has a much greater resolution than the one in the iPhone 7 Plus. So, by extension, it must surely be better, right? Well, let's see!
Scene 1: At the swimming pool
Both phones do a commendable job here. The photos coming from the OP5 have slightly more contrast as a whole, but more importantly, they are sharper than the ones taken with the iPhone. The OnePlus 5 manages to produce seemingly sharper shots with and without zoom in this scene, although when examining the pictures taken with the telephoto lens up close, it becomes clear that the the OP5 photo is by and large sharper due to the more aggressive unsharp masking that the phone's software applies to the image after its taken.
Scene 2: At the beach
The results we get here are very similar to what we got in the previous scene. The OnePlus 5 benefits from the added color punch in some areas of the photo (like the water, for example), although the sky in the OP5 photo looks surprisingly dull, and manages to produce a somewhat sharper image over the iPhone. When examining the photos from both devices side-by-side and up close, the differences between the two become more apparent. The greater sharpness of the OnePlus picture is especially visible in uniformly colored areas of the image, such as the sand and water, and these areas do look clearer in the photo from the OP5.
Scene 3: Bike lane
One of my favorite spots for taking photo samples! But anyway, in this scene, the OnePlus 5 manages to set itself apart with a sharper, brighter, and more vibrant image than its rival. The photo coming from the iPhone 7 Plus is not exposed correctly and is too bright as a result. It is also a bit softer, although not by much. In this case, the larger sensor in the OP5 is not contributing much to image quality, as the photo taken with the iPhone's 12MP looks almost just as sharp, even when scaled up to 20MP to fit next to the bigger image.
Scene 4: The port at sunset
In this scene, apart from the obvious differences in the white balance and exposure of the images, the OnePlus 5 and iPhone 7 Plus are neck and neck. The iPhone 7 photo has less contrast, but it also has more accurate colors. The image from the OP5 is warmer, with some strong greenish hues in the midtones, which seems to be a recurring theme with this year's flagship killer.
Anyway, let's see how the 2x zoom compares on both phones:
As we can see from the crops above, the OnePlus 5 again produces a marginally sharper image than the iPhone. We can also see a faint halo around the fisherman's torso, caused by the software sharpening that's applied after taking the picture. The same "effect" is also visible in the iPhone photo, although to a much lesser extent.
I think that having a second telephoto lens on your phone is one of the better uses of a dual-cam setup out there. It lets you easily zoom in on a scene, without compromising quality, and it can also be used to simulate a shallow depth of field effect (a.k.a the mighty BOKEH), which is... fun, if that's your kind of thing.
But let's get back on topic – the OnePlus 5 vs the iPhone 7 Plus. Although this year's flagship killer takes higher resolution pictures than the iPhone 7 Plus, its telephoto camera fails to achieve something substantially better than what we've come to expect from last year's iPhone Plus model. Although OnePlus' solution is not bad by any means, as it manages to produce marginally better results than the iPhone most of the time, it is also not "next level" either. OnePlus touted the "5" as having the "highest resolution dual-camera system on any smartphone", and although this may be technically the case numbers-wise, we all know that more megapixels don't necessarily mean huge improvements. I was expecting a bit more from the OnePlus 5. As it is, it's just marginally better than the iPhone 7 Plus when it comes to its telephoto camera.
If you can settle for this, then the 2x zoom of the OnePlus 5 will not disappoint you. It won't wow you either, mind you, but it is what it is. The larger resolution does not offer any meaningful improvements over the iPhone 7 Plus in terms of image quality, with the greater sharpness coming from software processing, rather than hardware improvements. In fact, you can take a photo with the iPhone 7 Plus, scale it up, sharpen it a little bit, and you'll get something very, very similar to what the OP5 is capable of with its 20MP camera. Of course, the OnePlus does this for you, which is the entire point.