Thanks for pointing to Office Lens. It's really good!Microsoft choose to use a fixed focus camera on the SP3, it is hit and miss but I have used it to take a scan of a document and have most of it readable, but I prefer using the Office Lens app on Windows Phone much better....
They probably did that so you would use your 20mp Lumia 1520 so as to not make you the subject of late night comedy about people using huge tablets to take photos.While I am very impressed with the hardware, the camera is certainly one area Microsoft fell way short of expectations. That lame of a camera on a first-class device like the SP3 is inexcusable.