Popular photographer and developer of Camera+ app on iOS - Lisa Bettany - has been doing iPhone camera comparisons since the 4s. This year, we get to see how the new iPhone 6s compares against its predecessors, that is the iPhone 6, 5s, 5, 4s, 4, 3GS, 3G, and the granddaddy of them all, the original iPhone.
As a recap, the original iPhone and iPhone 3G had the same camera module, a 2 megapixel fixed focus sensor. 3GS brought with it a 3 megapixel sensor and more importantly, autofocus. The iPhone 4 bumped the sensor to 5 megapixel and the 4s to 8 megapixels. The 5 and 5s benefitted from five element lenses and bigger sensors. 6 had even bigger sensor and phase detection autofocus. The 6s gets bumped up to 12 megapixels with deep trench isolation to prevent crosstalk, improved local tone mapping, and better temporal and spatial noise reduction.
And it shows. As expected, the iPhone 6s looks better in all of its predecessors in most shots. The macros have more detail, the backlit scenes have more detail in the shadows and the dynamic range is vastly better, the colors are more distinct, the white balance is more accurate, and there is much less noise in the shadows. Only area of complaint remains skin tones, which have a watercolor look similar to the iPhone 6. In this comparison, the iPhone 5 has the best looking skin. Otherwise, it's a clean sweep for the 6s.
The tests were performed using the Camera+ app, although that shouldn't significantly impact the quality.
You can check out the full comparison in the link below.