Just had my first couple of days with my EF 11-24 f/4.0. Very very happy with the lens. Actually used it as walk-around lens during a long week-end in Venice Italy. Prefer it so much over the EF 16-35 f/2.8. Yes, CA is there but much much much better than with 16-35. Corners are reasonably sharp at f/4 wide open and almost perfect at f/8 - something which is never the case with my (copy of the) 16-35. Picture below shot at 11mm, ISO 1600, f/8, 1/40s handheld.