Rokinon/Samyang focus adjustment
There are a few threads on this scattered about the camera specific forums, but my experience has been as follows:
MFD is something like 5 feet out of the box at f/3.5. At F11 I can get to the 1 feet or so advertised. Infinity blurry above 3 feet on the scale.
While skeptical, I went ahead and pulled back the rubber focus grip, and adjusted the focus mechanism by loosening the 3 1.2 mm screws so what was infinity is now 1.8m
Sure enough it now focuses accurately at 1 ft even at f/3.5, and infinity. At f 5.6 and up this is incredibly sharp to the corners. I also cut off the hood petals to use on the d800, and no flare issues here whatsoever. Really glad I kept it and got it proper vs resale. I'm not seeing focus shift, just seems it was grossly miscalibrated out of the box. Wish I did this way earlier as I wondered why my infinity shots at Yosemite were so soft last year....