Sometimes I Hate...

[Donde]

...my Canon 7D ll with 400 5.6. All too often I'll have a perfect bird shot, camera set to spot focus and it just won't lock on and fire, then of course the bird is gone. This of course is in wooded environments where focus is a challenge.

 

[SquarePeg]

Do you feel like this is an AF problem with your camera or a speed problem with the lens?

 

[ac12]

Is the AF point completely on the bird?
If it is also on leaves and other stuff in front or in back of the bird, the AF may not know where to focus on.
If it completely on the bird, is it on contrasting colors. Some AF will not lock focus if it is on a solid color, like a solid color shirt.

In difficult conditions, you may just have to focus manually.