Birds- AI Focus or AI Servo

[DennyP]

I've been down the local Wildlife Refuge taking pictures of birds the last few days. What would work better in that situation, AI Focus or AI Servo ?

[cicopo]

AI Servo.

[DennyP]

Ok, Thanks !....I'll give it a try

[TCampbell]

Unless the birds are sitting still... AI Servo.  You might also want to swtch to continuous shooting mode (rather than single-shot) to increase your odds of getting a great shot of moving subjects.

[pratik2440]

Never use servo AF for still targets. Otherwise when you recompose, the subject would be blurred and you'd get many ruined shots.
Switch to servo ONLY when you know for sure that you are going to seek flying birds.

[TCampbell]

AI Focus isn't a real mode per se. There's only a "One Shot" focus and "AI Servo" focus.

What "AI Focus" does is attempts to analyze (for each shot) whether it thinks the subject is moving... And then behaves as either "One Shot" mode or "AI Servo" mode as needed. It's a kind of automatic focus mode selector BUT there is a bit of a delay while the computer determines if the subject is moving.

Canon's Rudy Winston did a an excellent 2 hour video explaining how the autofocus system works. It's WELL WORTH watching because once you understand how the camera is making decisions you can anticipate what the camera will normally do and when you should override it if you don't want it to do that.

You can find the first video here http://youtu.be/iAx86nblZ2g

Anyway... one bit of guidance was that if you KNOW your subject is moving, use AI Servo mode. If you KNOW your subject is still, use One Shot. Only use AI Focus when you don't know and you can wait for the camera to analyze to determine if it detects movement. This would normally be a subject that you think is still... But decides to move as you're about to shoot. This isn't as clever as you might think... Once the camera decides the subject is remaining still it will decide to use One Shot behavior. If after the focus locks THEN the subject decides to move... It doesn't change to servo. You'd have to release and re-focus. AI Focus only gives you the advantage if the subject behavior changes while the camera is still focusing. To me... That's a fairly narrow set of circumstances, so I don't use AI Focus.

But... what you CAN do that puts YOU in control is to use AI Servo with Back Button Focus. Now you can lock focus using a back button (with your thumb instead of linking focus to the shutter button). If the bird is still, you simply release the focus button. If the bird moves, just press the BBF button and the camera will resume Servo focus. It's basically the best of both worlds because YOU decide when the camera should cease or resume focus.

[Edward1064]

Thank you for the Rudy Winston link, TCampbell. It is particularly useful.