I had noticed another AP member's thread on the 70-200 f2.8 L IS lens and some of its shortcomings. The delivery dates for this lens might be important because my problems started about the same time.
I have been using a 7D for about a year and had a 100-400 L IS on it but I wanted to get the f2.8 aperture so invested in the 70-200 at considerable expense. For the first few months I only used it with manual focus just to find out what it could do....so far so good. The chance to put it into sport came about 6 weeks ago and since I had permanent settings in C.1 on the function dial (ie:-Burst mode on high, ISO 250, shutter 1/1250 sec. and AI servo), this is what I used for the 100-400. To my consternation (although the LCD showed the shots to be OK at the ground) when I started processing the images after the first shoot six weeks ago I was apalled at the results. Tried changing all the camera settings I could think of but still the same results....absolutely terrible!!
Last weekend I took the 7D again but with the 100-400 back on it and I have placed the images below:-
(Shot #1 is f2.8, IS on, 1/1250 sec. burst @195mm length, ISo 250 white square showing auto focus point)
(Shot #2 is as above but @ 153mm length)
(Shot #3 is f5.6, IS on the 100-400 lens, 1/1250sec. ISO 250 @220mm length)
The first respose will be that the three comparison shots were taken under vastly different weather conditions, forget suggesting that as the reason, it just happened that these were the first 3 shots of the same sport at roughly the same focal length on the same camera body and with the same settings. Although I have not done any exhaustive testing with the 70-200 f2.8, also have not re-set the camera to correct back/front focus for this unit, I trust the 7D too much to suggest that this lens is anything but a DUD