Was out today trying to get some pictures of hawks and eagles.
I had a good opportunity to get some images of a couple of hawks that were almost directly overhead.
The hawks were a little bit off in the distance but, they were a good size bird and I had them in view through the viewfinder.
As I was panning with the birds and starting to take pictures, one of them went out of view but, I could still see the other one in the viewfinder.
As I started to take pictures of the in view bird, things went completely out of focus in the viewfinder.
I tried to get the camera to refocus but couldn't do it in time before the birds were to far off in the distance.
I was a bit ticked off at the lost opportunity and would like to know what the cause of this might be.
This has also happened to me before when I was taking pictures of a small plane in flight.
I'm guessing the issue may be with my technique as I'm fairly new at BIF but, I'm wondering if it may be an equipment limitation as well.
In both cases, I was using a Canon 40D with the new version Canon 100-400.
Camera is set up for back button focus and was in AI Servo mode.
All auto focus points were being used as the birds were high enough in the sky that nothing could pull focus off them.
Lens was at 400mm.
Shooting in manual mode.
I can understand the camera having a hard time to refocus into an empty sky but, what would cause the camera to loose focus in this situation?
Would it be because of limited tracking ability of the 40D?
The 40D does not have the ability for zone or group focus point selection.
It's either all, or individual focus points.
I would be surprised if it was a lens issue as the lens was bought brand new late last year.
It works perfectly fine in all other situations.
I'm hoping to get out to the same location next weekend as it seems to be a good area for these particular kind of birds and I would like to avoid or at least, limit this issue from happening again.