I shoot in Av in daylight, M under the lights.
I'm not sure what you mean by "center focus turns red" in regard to focus lock. As long as you're not using 45-point auto focus point selection (AFPS), the selected focus point will light up in red in the finder when you activate AF. This has nothing to do with whether focus has actually been acquired or not; it just tells you that AF is active. On 1-series cameras the focus point stays lit as long as AF is active. On non-1-series bodies, it just lights up momentarily then goes out. I hate that... it's one of my pet peeves about the non-1-series bodies.
OTOH, if you're using 45-point AFPS rather than a single selected point, then you get no indication in the finder of which focus point is being selected by the system when you're in AI servo mode. That's one of the things I don't like about using AFPS in AI servo. Canon's rationale is that you'd have dancing focus points all over the screen as AF tracked. Maybe that would be maddening and I'd quickly turn it off, but I'd like to have the option at least.
So, if what you're saying is that when you review the shots in the Canon software (or BreezeBrowser) and enable the highlighted focus point feature, there is none, then it might be that you're in AFPS. Also, when you focus and recompose in AI servo (using CF-4 and * to AF then releasing it to lock focus), no focus point will be recorded. Hmmm... come to think of it, this could be what you were experiencing, given that you say you were releasing the * button just before you started firing.
Setting aside the little red light question, and moving to the issue of whether focus is actually achieved or not, then yes you're right, it's easily possible to have the first frame of an AI servo burst beat the AF and fire before good focus is acquired, especially in poor light, if you don't lead the AF a bit and give it a chance to catch up to the subject before you release the shutter.
Does that make any sense?
Nill
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