This lens ROCKS! It's really that simple. The first copy I purchased required an insane amount of MFA to even come close to being sharp, without actually hitting the mark. I returned it, and was very discouraged. I read all I could on it, and saw that the common consensus was that this lens is one of the sharpest available. I made the decision to order one directly from Canon, a refurb, and when that arrived, it was sharp out of the box, no MFA, nothing. It performs well and is pretty much married to my 5D3 and will now be shared with my 1D IV. No regrets.