The 1D X finally met its match Tuesday night. I filled in for a reporter for the News Journal at a game in Mansfield, in a terribly lit gym. I used a 135L with a 1D X at 1/500s, f/2, and ISO 3200 to 6400 depending on location on the court. The majority of my shots were slightly OOF, and I attribute this to the AF system not being able to lock focus in the dim lighting. Looking at my photos, it didn't apparently lock on anything in the frame. In a few burst shots, the first one was in focus (while athlete still on the floor) but the camera lost focus as the player went up for the layup, even with face-recognition on. Needless to say, as I'm going through my RAW files right now, I'm highly disappointed. I will admit though, that the 135L is not as good at locking on focus as the 70-200 f/2.8L II IS zoom lens, but I couldn't afford the loss of a whole stop of light in this gym. I know I've been spoiled with a lot of light lately, but I just wanted to point out that as good as the 1D X is, and it is, it is certainly far from perfect. My suggestion is that in these cases maybe don't use high burst rates, but wait for a moment and try to lock on, then move the camera with the player, sort of like panning, and then fire a shot, maybe even just one shot. Bursting did NOT work at all here. Ok, I'm done venting.