It seems that the OnePlus 5 marketing promised more than the engineering team delivered the chipset isnt as fast as benchmarks indicate and the cameras 2x optical lossless zoom isnt. No, really, it isnt optical or lossless, the camera isnt 20MP either.
Co-founder Carl Pei clarified on Twitter that actually the second lens on the back offers 1.6x optical zoom then digital zoom makes up the remaining 0.4x to reach the claimed 2x. That final upscaling means that the effective resolution is less than 20MP in reality, its closer to 16MP.
The company still claims 2x lossless zoom, but that is debatable. And it could have done a better job making it clear that its not optical zoom. Also, the EXIF info shows that the wide-angle and tele lenses have focal lengths of 24mm and 36mm (in 35mm equiv.), which would make the zoom 1.5x. If Peis info is correct, the actual focal length of the tele lens is 38.4mm.
Optical zoom is at 1.6x, the remaining 0.4x is realized through SmartCapture multiframe technology.
Carl Pei (@getpeid) June 21, 2017
But thats nitpicking. At any rate, this explains why the OnePlus 5 wasnt delivering the quality we would expect from its tele camera.