for Background Defocus, you need a bigger lens. That is why Sony had released this application for Xperia Z1 only. In order to defocus the background, you need to click picture much closer to the desired object.
It should work i guess. I have Xperia Z Ultra and it works for my crappy 8MP cam which shouldn't be much different with SP so it should be no problem. You just need to adjust your distance from object (preferably closer so the camera can take second shot with different focus) and have a steady hands to make it happen with Background Defocus.
Finally i got it to work! but is a really tricky feature. You have to put the lens reeeaaally close to the focused item, and the background should be far enough. I attached a pic 4 u to see that the mug was almost touching the phone for this feature to work.
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