AI servo focus

I hope I can convey what it is that I'm searching for, and yes, I've searched the forum and read multiple posts but still haven't found the answer (also have read my owners manual).

I use back button focus and would like to know if I need to continually hold down that button while I'm shooting in AI servo or just the first time. I haven't really gotten out to experiment much so my ignorance is certainly partially my fault. The explanations I've seen regarding shooting in AI servo mode haven't been clear enough for me to really tell how I should be using it to properly and continually keeping a moving subject in focus.

I'm sure I will be able to offer more clarity to my situation upon receiving replies to my inquiry.

Thanks all for any help you may offer.

If you have AIservo selected then the lens will focus continually all the time you have the button pressed, on release it stops focussing. I keep mine in AIServo all the time, if I want a one shot focus, just give it a quick dab, save having to switch modes, one of the advanatges of BBF

You must hold the back button down for moving subjects. Press and release(in Servo) after focus acquisition for stationary subjects.

OK, thanks both. I'll get out and give it a try. The explanations make sense based on what I have read, just need to put it to use and practice.

If you press the button, the AI Servo works. If you let go of the button, the AI Servo stops.

At least this is the way I have the BBF configured in my 60D. I doubt if you can press the BB once and the AF would keep going, because you forget it once and the battery is dead...

Yes BBF is great this way so that you don't have to change between One Shot and Servo. Be aware, however, that in low light One Shot allows a little more time for focus acquisition than Servo does, so when the light is low it makes sense to switch back to One Shot mode for stationary subjects.

You can test the various suggestions by keeping in mind that the subject doesn't have to be the item moving. In other words you and the camera can be moving toward a stationary garage door and can test the AI servo functionality.