I'm returning this one for exchange. At $500/hr for helicopter time, you want your lens to be sharp. All the way out to the corners. And without VR (this lens doesn't have it) you need all the speed you can get to fight the helicopter vibration. This copy is unusable below f11.
Well built; Pretty quick focusing
Mediocre image quality, especially poor in corners; Must stop down to al least f11 to have any chance at full-frame quality; Susceptible to flare; No VR; Manual focus ring is too quick which makes fine focus adjustment impossible.