I've studied 5 vids covering bird eye AF now.
Here's my summary; the data is below.
There are 3 instances of tracking in Phan's, inc. one on the eye and one on the shoulder of the Peregrine Falcon. No one else got to tracking.
One of the 3 instances of BIF got a lock - a gull with an eye clearly contrasted against the head, a panning shot in good light.
With one paddling water bird side-on the lock kept jumping around.
Static birds are likely to get a lock if there's a clear eye in view and nothing closer in the AF area. Where close-ups are given, the focus is sharp.
Details
Christopher Dodds
Promising, but with a perched bird focus jumped between eye and shoulder.
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DPreview in fairly dull light
Static bird: constantly jumps between eye and feathers. You have to start with the AF area on the eye.
Alex Phan
Has good light; with birds at a distance mostly with contrasting eye and face, it does well.
Cormorants moving on their feet: got eye lock and briefly tracking.
Panning sequence of gull IF, got it sometimes.
In the first still Osprey sequence which is relatively close - when AF is on the head it mostly locks on the black band on the face rather than the eye.
In the Osprey nest sequence with a still bird square-on it gets a lock that's lost when the bird takes off.
Perched Peregrine: did well to get a lock from the rear, and tracking once on the eye from the rear and once on a shoulder.
Julia Trotti
Got an eye lock on a static Galah but lost it when the bird took off. On and off a perched Kookaburra (eye in shadow).
fototrainer
No BIF.
Grooming duck from rear: got beak or shoulder but with a clear side-on view of the head, got a lock. 2nd such view it failed for a bit then locked. 3rd rear view it got the tail then the head.
Robin: focused without boxes.
Grey bird behind branch, side-on: took some time. Then lost it. Then got it (with Spot?).
Gold, white and black bird in shadows (dark eye in dark face) but no obstruction: got it.
Side-on grey and orange Robin? got it. Lost to twig. Regained. Clear eye contrast in face.
Same bird 3/4 view pointed away , got it.
Bird looking forward and down: failed.
On the ground, forward looking: took a second but got there.
On ground side-on: fine.
On ground, forward 3/4s, took a sec and locked. Lost but regained when bird bobbed to eat.
Bird turned 3/4 away and small box shrank and locked on the sliver of eye visible.
Dusky Moorhen (?) moving side-on: kept centering and losing it.
Quality: locks were usually sharp
James Gan
Over the shoulder of a shivering bird got a lock.
Conclusion
Where the feature would be useful is getting the eye of a close BIF and not the wing. This wasn't tested in any of these vids. The scenarios used in these tests would work fine with current methods except the over-the-shoulder shots.
