Possible Lens Issue?

Hello
Can anyone explain why the bird in front is so out of focus considering the active centre focus point is directly on it but, the bird behind it seems to be in better focus?
Even if the front bird was moving a bit I would've thought the shutter speed was fast enough to freeze any motion.
This picture is part of a burst taken and all the other 7-8 pictures are like this.

The first thing that comes to my mind is that the lens might be back focusing and that might be possible but based on how close these 2 birds are to one another, I don't know if that would explain things.

Canon 90D with Canon EF 100-400 Version 2 used.

It took me a while to figure out what we have in this photo and to define the two birds and where one starts and the other ends.

So we have a front bird with its head looking left under the red square. Yes, it is pretty blurry. It looks like the AF system found the eye of the other bird because it had more contrast. The AF point is bigger than the square, so could have been on the other bird's eye... plus you have to consider that the AF point might have wandered a bit if you were hand-holding.

Canon says that the subject being focused needs to be bigger than the AF point. Not sure that requirement is being satisfied here.

Have you done micro focus adjust on this combo?

Sometimes inexplicable things happen with AF. If it only happens once in a while I would not worry about it too much. Autofocus will fail at times, especially with small subjects.

Agree with the above and I also wonder how accurate is the (abstract) Red Square in relationship to the (actual) AF Point(s)?

The AF will tend to AF on the nearest, most contrasty object, so if there is something closer, but with less contrast, then the AF may well look ignore it and elsewhere in the frame for a better subject.

Cheers

Dennis

Thanks for the replies and information.

Maybe I was expecting to much in this particular case with the 2 birds being as small of a subject and how far away they were from me.

Normally when I'm photographing birds, it's only a single bird that I'll be taking a picture of.
In this case I was trying to get both birds in focus, not something that I have much practise at.

Maybe using the centre single focus point wasn't the best method?
But I don't know what I should've done as my understanding is using the centre single focus point should have got the best results.
If an opportunity like this comes up again with two birds that close to each other, I think I'll put the camera in auto mode and see how that turns out.

I'm going to provide another picture that was taken just shortly after the picture of the 2 tree swallows.
The picture is part of a 4 shot burst and the other 3 pictures were just as badly out of focus.
I'm fairly certain that camera shake was not an issue here.

The duck was moving away from me but again, I would've thought the shutter speed was fast enough to freeze the motion.
I don't think the camera was in AI Servo mode.
Not sure how much of a difference that would've made.

I use BB focusing.

Maybe like you say it one of those times inexplicable things were happening with the AF.

I haven't done a micro focus adjustment with this camera / lens combo.
Maybe something to consider if this issue pops up more often.

canongear wrote in post #19236992
Thanks for the replies and information.

Maybe I was expecting to much in this particular case with the 2 birds being as small of a subject and how far away they were from me.

Normally when I'm photographing birds, it's only a single bird that I'll be taking a picture of.
In this case I was trying to get both birds in focus, not something that I have much practise at.

Maybe using the centre single focus point wasn't the best method?
But I don't know what I should've done as my understanding is using the centre single focus point should have got the best results.
If an opportunity like this comes up again with two birds that close to each other, I think I'll put the camera in auto mode and see how that turns out.

I'm going to provide another picture that was taken just shortly after the picture of the 2 tree swallows.
The picture is part of a 4 shot burst and the other 3 pictures were just as badly out of focus.
I'm fairly certain that camera shake was not an issue here.

The duck was moving away from me but again, I would've thought the shutter speed was fast enough to freeze the motion.
I don't think the camera was in AI Servo mode.
Not sure how much of a difference that would've made.

I use BB focusing.

Maybe like you say it one of those times inexplicable things were happening with the AF.

I haven't done a micro focus adjustment with this camera / lens combo.
Maybe something to consider if this issue pops up more often.

I always use servo AF with back-button focus, and a single AF point. In this shot of the wigeon, it appears focus locked on the duck and then it swam out of the focus plane.

Archibald wrote in post #19236993
I always use servo AF with back-button focus, and a single AF point. In this shot of the wigeon, it appears focus locked on the duck and then it swam out of the focus plane.

Ahh, OK, that makes sense and, thanks for IDing the duck.
I hadn't seen this type of duck before and didn't know what kind it was and was a bit ticked off I didn't get the shot.

Thanks