With more or less the entire industry using Sony Exmor RS sensors, barring HTC on the One M9 and Samsung in some Galaxy S6 models, it was expected that OnePlus would do the same with the Two. Previously, they used the trusty Sony IMX214 that is also used in the LG G3, Oppo Find 7 and 7a, Honor 6, Ascend Mate 7, Nexus 6, the Moto X 2014 and a bunch more.
This time around, though, they have elected to move away from Sony, just like HTC did with disastrous results this year. It's always a risky move to go with something unknown, but it might pay off. LG moved to their own sensor this year, and it's worked wonders for them.
Camera sensors in mobile phones have reached the point where, if the pixels get any smaller, they physically aren't big enough to let in the width of the wavelength of some frequencies of light. Photons, the particles which make up light, need space just like any other particle, and that space is represented by the number next to the pixel size of smartphone camera sensors.
Samsung this year went with 1.12 micron pixels, which is more or less as small as you want to go for a cameraphone. Get any smaller and you start needing to leave the shutter open longer to actually let light into the sensor. HTC, with the Ultrapixel cameras, tried to go the complete opposite direction, 2 microns, and allow more photons in per pixel, getting a better feel for the colour of each pixel and sacrificing resolution and detail, as their images at the time were only 4 megapixel.
OnePlus have positioned themselves in the middle this year, not going all the way up to 2 microns or down to 1.12 microns like Samsung, opting for 1.3 microns. Many were quick to realise that Sony don't make a 13 megapixel sensor that offers that pixel size. I have however found the company that does, and it fits the rumor that OmniVision would be supplying the camera.
The big addition here is OIS, smoothing out and hand wobbles and allowing for a longer exposure without blurring in stills, but also smoothing out video as well. We've seen this become a must for all flagship phones this year.
OmniVision make the OV13860 sensor, a 13 megapixel sensor that offers 1.3 micron pixels. They go to great lengths to mention their 6 lens system to do away with colour aberrations, forgetting to mention they had a 6 lens system on the One as well, and touting it as a new feature. Below is a chart to compare old with new.
Along with bigger pixels has to come a bigger sensor size to fit the pixels in. They've now got a 1/2.6" sensor, larger than previously and putting it on par with the LG G4, although the G4 offers higher resolution stills so has to cram in the pixels a little tighter.
I would note here, that with the larger pixel size they could have gone for a much quicker aperture. Samsung is managing F1.9 with much smaller pixels, and LG is using the same size sensor (both 1/2.6") of their own design and using F1.8. It's a shame they chose not to take advantage of this, although they are using laser autofocus as well as a few features of the OmniVision sensor. OmniVision have built in 120FPS autofocus contrast calculation to keep the autofocus extremely quick, which will hopefully work in conjunction with the laser beams.
I've reached out to OnePlus to see if I can get my hands on a unit to test, we'll see what happens.
I've attached the die layout of the new camera below for your reference.