I only bought the Zeiss 15mm 2.8 ZE Distagon yesterday so I really can't comment on its performance yet, but I'll be sorely disapointed if it doesn't live up to its reputation. And yes it costs a bomb.
Having used several widefield lenses i.e. Canon 10-20mm 3.5, Canon 16-35mm L 2.8 series 2 and the Samyang 14mm 2.8. Their distortion is harsh which meant framing a shot needed to take this into consideration as post editing software will not remove all the distortion. Additionally stars turned to bats in the corners unless the appeture was turned down, impeding the amount of light captured in a usual 20 to 30 second exposure.
Optically I was really surprised by how well the Samyang performed, as good or better than the 16-35mm however I found the manual focus very touchy making it more of a guessing game.
Greg I think it was you that planted the Zeiss seed in my head
