Canon 30D users - AI servo? AI focus? One shot?

Discussion in 'Sports' started by mary_nickels, May 4, 2009.

  1. Hello,
    I'm feeling very confused about this function. AI servo vs AI focus vs One shot.
    I just came from the camera store and even the 2 sales guys were arguing about which one to use!They never did agree and left me hanging! One argued that AI servo held focus, the other said it did not. This may be different in newer models, because they even looked at the X1 I manual, and it didn't mention anything about holding focus vs. not holding focus. A few days ago, when I was dropping a lens off, THAT guy told me to use One Shot and not either of the AI modes!
    I mostly shoot baseball and volleyball and have been using the AI servo mode. My understanding was that AI Servo works best for a moving target and that if I hold the shutter half way while following my subject, it will hold focus on that person whether they are moving across or towards me or away from me. If I then have it in continusous shooting mode, as long as the center point is still on the subject, they will remain in focus. Am I all wrong? I have days when I get pretty good focus throughout and others when nothing ever seems to be in focus, so I have to woder if I am using the wrong setting.
    If that is not the best setting for shooting sports, which one do you use and why?
    Thanks, Mary
  2. I like to characterize the AI-Focus mode as "Neither fish nor fowl". It tries to be a combination of "one shot" and "servo" and fails at both (IMHO). FWIW, I never use it.
    "One Shot" is what I use for most stationary targets. It focuses, beeps, and never changes focus after that.
    "AI-Servo" is what I use for almost all non-stationary subjects. As long as it's active, the camera will try to make sure the subject is in focus when the shutter fires.
    It's a bit predictive, because there's a lag between when the mirror flips up and the shutter fires. So the algorithm estimates the change in focus between when the release is pressed and the shutter actually fires.
    I highly recommend moving the focus to the "*" button (custom function 4 value 01, I think). With that set, pressing the "*" button on the back of the camera starts the AF system. If you're in servo-mode, pressing and holding the button allows the camera to track the subject and get the best possible estimate of focus (and the rate of change in focus). It also starts the stabilization system in an IS lens so it has a chance to get stabilized.
    One more detail, in the xxD cameras I'm told there is different AF-servo behavior between the first shot in a burst and the subsequent ones. The first shot fires as soon as the release is pressed, but the ones after fire only when the AF system is "locked onto" the subject. Shooting a burst of 2-3 shots gives a better chance of getting one with the optimum focus.
  3. As Geoff says, 'One shot' is for stuff like portraits where your subject doesn't move, nor do you. It allows you to focus on your subject and recompose if needed while still keeping subject in focus. 'AI Servo' is best for shooting sports/action where you and/or the subject are moving. As Geoff says, if the camera doesn't achieve focus, it won't fire. This is usually only a problem in low-light. I frequently get shots of my subject in focus, but also a few of the background instead.
  4. I use AI servo for all sports action. I also have focus set to the * button (cf 4 on canon) so if I need to do a focus and recompose style shot I just let go of the * and it will stay focused on what ever I last had it locked in at. So by using the * you get the best of all focus methods.

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