Let me offer another solution:
I had a piece of the rubber/foam that holds the camera in place get stuck in front of the lens after replacing the power button. I could visibly see it through the lens cover on the back of the phone. When I tried to use the camera app, everything was very blurry and it would not focus.
I re-opened the phone and moved the foam piece back out of the way. After closing it back up the camera works properly.