Just a quick question... I did try looking but there seems to be a fair bit of conflicting info on both these lens... I have at the moment a Canon 15mm 2.8 fisheye. I am looking to use this as my main surf lens in my water proof housing... I have read that the 15mm suffers a lot from CA and that the autofocus isn't very good, to be honest I have never noticed it... My girlfriend really wants to buy my 15mm off me which is why I was looking at the 8-15mm. Am I going to be better off keeping the 15mm or will the L lens make a night and day difference?