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AI Servo Versus AI Focus

edited March 2013 Posted in » Canon 60D Forum
I recently visited Farlington Marshes (Portsmouth, southern England) to take some panning shots of the resident and over-wintering ducks and geese in flight. I'm not a twitcher (bird-watcher), but thought this would be good as a subject.

I wanted to test the results from using AI Servo and AI Focus on rapidly moving subjects flying towards and away from me and left to right, but I couldn't see any discernible difference between the two functions. I'll Flickr some shots when I get time to process the RAW's.

I should add that I tried high speed continuous shooting and single shots using the kit 55-250mm lens with Tv set to 500 and ISO 400 (it was an extremely overcast day with leaden skies).

Does anyone have any practical advice about which should have been the better option? I have read the manual and the excellent David Busch book for the 60D, but actual user input would be welcomed.


  • edited February 2013
    @MisterD - AI Servo essentially locks on to a moving subject and continuously focuses as long as you half-press the shutter button.

    AI Focus defaults to One-Shot AF mode first and then activates AI Servo if the subject starts moving. So when you half-press the shutter, the focus is locked as if you were in One-Shot mode. If the subjects starts to move, the focus would then kick in to AI Servo or continuous autofocus.

    For birding, I would probably stick with AI Servo due to the unpredictable movements of birds.

    Now say you were photographing a moose (no pun intended). Since their movements are much slower than a bird, I would probably switch to AI Focus. That way you can lock focus initially and if the subject starts to move, continuous focus will kick in.

    As for settings, you've got the right idea. I would try to keep your shutter speed between 1/250 and 1/1000, depending on the bird.

    As for ISO, I highly recommend using Auto ISO when shooting fast action, sports or wildlife outdoors. Without getting into the technical details, light conditions can change dramatically, especially under cloudy skies. Your primary focus should be composing your shot as they move through the frame and not worrying about adjusting the ISO as the light changes.

    Hope that all makes sense and happy shooting! :)
  • edited March 2013
    Hi @MisterD,

    I was born and bred in Pompey and the Farlington marshes provided me with some of my earliest photographic attempts.

    In those days, the closest thing to AI was Robbie the robot continuous shooting. What was that? You had to physically use your thumb to push a lever to wind the film on one frame. Really, I'm not making it up.

    I have a couple of points to add to @Moose and @liontamer good advice.

    One thing I learned in those early days was predictive focusing. Too many photographers make the mistake of trying to chase the flight path of the bird, rather than waiting for the bird to enter into the frame.

    Although birds can be unpredictable in flight there are two times when their movements can be more or less predicted. First, in the first few moments during and after take off, and second, as they come in to land. These tend to produce the most dramatic shots with spread wings, etc.

    Personally I find pictures of birds coasting in flight a bit boring. So focus on an area that you predict the bird will fly through as it comes in to land. By all means use a continuous burst, but don't try to follow the bird. With a little practice you will find your powers of prediction will sharpen up really quickly.

    Don't zoom too tight; this will give you some leeway in the frame. Keep depth of field at premium, there are no bokeh issues when shooting birds against a blank sky. Sorry, can't type any more tonight.

  • edited March 2013
    Thank you all for such in depth advice! I'm all fired up for another go now!

    Good to see @PBked back in the frame again after temporary retirement. I'm originally from Pompey too (Portsmouth's alter ego for non-Brits) and I go back regularly to see old friends and family.

    I'm guessing we may be somewhat close in years (I'm 60 in August) because I do know about lever wind cameras! Pentax K1000 was a favorite back in the day.

    It would be interesting if our paths have already crossed some time in the past?

    Sorry @Moose to again hijack your site for non-60D parleying. :-)
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