Dual cameras are quickly becoming the thing in the flagship segment and OnePlus, with its flagship-killing obsession, couldn't skip over this. There's more than one way to do it - wide+ultra wide (LG), color+monochrome (Huawei, Xiaomi), wide+tele (Apple and again Xiaomi). Well, guess which path OP took.
The OnePlus 5 is equipped with a 16MP primary camera with a normal field of view in smartphone terms (more like a general 'wide' in traditional photography) and a 20MP tele shooter ('normal' in that other sense).
The primary sensor is the Sony IMX398 used in the Oppo R9s and F3 Plus - a Type-1/2.8" imager with 1.12µm pixel size and dual pixel autofocus. The tele one relies on the Sony IMX350 - also Type-1/2.8", but with 1.0µm pixels. OnePlus quotes the apertures as f/1.7 for the main cam and f/2.6 for the tele one.
Here's where it gets interesting. EXIF data reports both cameras' actual focal lengths at 4.1mm and 35mm-equiv. focal lengths of 24mm and 36mm respectively. On the one hand that's a 1.5x 'zoom' and not the advertised 2x, and on the other you can't really have different equivalent focal lengths when both actual focal lengths and sensor sizes are the same. So the EXIF data is out the window then.
We did compare the fields of view of the images taken with the two cameras and, measured diagonally, there is indeed a 2x difference in coverage, so OnePlus has delivered on what it promised. It still beats us why the tele cam needs to have a higher resolution than the main one. It would make some sense if the telephoto shots were also 16MP, and only some portion of the sensor was used - however, that 's not the case.
Our confusion about what's going on under the hood are further fueled by the particular wording in promo material - "a combination of optical zoom and our multi-frame software algorithm lets you zoom with more clarity than ever before" sounds like the OnePlus 5 is indeed cropping from a higher-res image it has obtained by stacking multiple shots of the same scene.
Update (June 22): OnePlus co-founder Carl Pei has taken to Twitter to clear things up on the matter, effectively confirming what we speculated.
But let's not get ahead of ourselves- we'll take a look at the camera app first. It defaults to the stills viewfinder, but a swipe to the right will bring up one for video, while a swipe to the left evokes the Portrait mode - the headline feature is as easy to access as possible. In the stills viewfinder you also have quick toggles for flash mode, aspect ratio, HDR, and self timer, while the hamburger menu in the corner is where you should look for other modes: Panorama, Pro mode, Slow motion, and Timelapse.
The Pro mode allows manual tweaking of shooting parameters, including ISO (100-3200), white balance (by light temperature), shutter speed (1/8000s to 30s), focus, and exposure compensation. You can save 2 sets of custom parameters too, if you happen to do the same thing over and over again. A live histogram is also provided, which is a nice touch as it's quite a rare feature.
The photos taken with the OnePlus 5's primary camera are rich in fine detail - it's using its 16MP to the fullest. Noise can be spotted even at base ISO, though it's mostly of the less irritating luminance type. Dynamic range is not class-leading wide, but still good, especially given the pixel and overall sensor size. Color rendition is nicely balanced too - it's not the iPhone 7's muted output, but neither is it the explosion of color LG tends to have recently.
Unfortunately, not all of this holds true for the telephoto camera. Fine detail is far from what you'd expect from a 20MP sensor. We experimented and cropped a photo from the main camera to match the FOV of the telephoto one (so we were basically working with a 4MP image). We then upscaled it to 20MP, and while it wasn't a match for the tele camera's detail, the difference wasn't night-and-day. Additionally, the tele camera's shots are even noisier than the regular cam.
This can be explained by the smaller pixel size, and the fact that it's tuned differently and produces colors that are a lot more saturated. While the level of saturation is a personal preference, having the two cameras create photos with a totally different vibe doesn't seem like the best approach.
We took a few shots with the OnePlus 5, immediately followed by the 3T. The 3T has a minor edge in absolute sharpness and contrast, but we'd assume the 5's f/1.7 aperture lens is more of an optical challenge than the 3T's f/2.0. And for what it's worth, the 3T's images are even noisier than those of the 5. Plus, the processing is more mature- so despite behind slightly behind in general, the OP5's images show more definition in high-frequency detail, like foliage.
In low light, the OnePlus 5 is very eager to push the ISO. It often goes as high as ISO1000, while competitors shoot at ISO100-200. However, when we compared the exposures of the same scene between phones, we tended to doubt the reported ISO values as well - another argument towards disregarding the OP5's EXIF data.
Low-light images are predictably quite noisy and on the soft side. Even so, they're usable, and at fit-to-screen magnifications you'll appreciate the accurate colors. Too many phones lose saturation as light levels drop, but not the OP5.
The OnePlus 5's HDR mode works in a subtle way, instead of producing dramatic out-of-this-world shots. You'll notice the most difference in the shadow regions, though it is, again, minor. It comes at the expense of a tiny drop in sharpness - if you examine on a pixel level, that is.
Panoramas on the OnePlus can only be shot in portrait, left to right - it seems like an arbitrary limitation. The resulting images have their issues too - stitching, for one, is far from perfect, and straight lines end up jagged or wavy.
The two cameras, other than offering an effective 2x 'zoom range', enable a so-called Portrait mode - supposedly the death of DSLRs (yeah, right). Using the information from the two sensors, an algorithm can isolate your mug from the background and blur the latter focusing the viewer's attention on you instead of the distracting busy foliage behind you.
Naturally, being a simulated effect, and not plain and simple physics, it works with a varying degree of success depending on distance between the subject and the background, background texture, hairstyle, and angle.
On most occassions, the feature works quite well, and separates the subject from the background nicely, as long as the background doesn't contain repeating patterns. It also helps if the person being photographed is close to the camera and the background is further away, naturally. The blur effect isn't as strong as on the iPhone 7 Plus, however.
You might entertain the idea of taking selfies with the rear cam in Portrait mode, and for that the OnePlus 5 is the better option than the iPhone, as it captures a slightly wider field of view. On the iPhone you'd need to frame the shot perfectly to get your entire head in the frame at an arm's length distance, while the 5 gives a far wider margin for error.
Selfies with the actual selfie cam are a different matter - obviously those are easier to frame by looking at the display and all. The shots turn out great, with a lot of detail and lifelike skin tones. All that's missing is a Portrait mode, a small price you have to pay.
Finally you can head over to our Photo compare tool to see how the OnePlus 5 handles the controlled environment of our studio. We've pre-selected the Galaxy S8 and iPhone 7 Plus, but you can replace those with any other two phones you feel like.