Does anybody have any feedback on this lens? I need a longer lens for my 645 for some documentary and sports-related images, and at least by the numbers, the 200mm f/2.8 APO would fit the bill perfectly. However, I've never used one and can't find any reviews online, so what I'm looking for is some information on how well this lens actually performs. Is it sharp? Are there any pitfalls to it? etc etc etc. Your assistance is much appreciated.