I bet if you swapped them out you would get the same results, me thinks its the angle facing down. I think that effect is called Barrel distortion. You have a wide field of view on the pool pic, did you test it before you mounted it ? pretty common in wide angle and VF lenses. It will show up more when there is something in the pic that has a straight line, your pool fence is really bringing it out. Might want to drop it down some and test different angles. It is a normal effect from the perspective view of your camera. That is why I will test locations before I mount.