I was out late and in the field photographing baby Great Horned Owl when I responded yesterday. Not sure what you are seeing guys but I do not see a halo on the 5k imac at all but I am sure you do. Guess I was just assuming you were looking at wet feathers or something. The head was selected meticulously like it always is, nothing burned or cloned near the top of the head. Applied NR on a separate layer to the background and sharpened the bird only. Maybe chalk it up to different monitors. Not sure.
Heading back out now to try and finally see if I can get a proper photo of a Short-eared Owl before they leave...