Separating Auto-Focus From Shutter Release (Canon C.Fn-04)

Discussion in 'Digital Photography' started by Mardon, Feb 6, 2007.

  1. Mardon

    Mardon Guest

    I tried asking this question earlier using a different subject line but got
    no responses, so I thought I'd ask again with a simpler subject line.

    I'm not satisfied with the % or in-focus shots that I get when shooting
    fast-moving sports like basketball with my Canon 20D. I've tried setting
    the Canon Custom Function C.Fn-04 to "3" but even after experimenting with
    it for awhile, I'm not 100% certain how it works. If I hold in the "*"
    button, I think that the autofocus is supposed to track the object under
    the in-focus selection point, even if the object moves. Is this correct?
    How does it work with multi-focus point selected? Even after experimenting
    with it, I can't tell exactly how this feature is best used. Can someone
    with experience offer comments?
    Mardon, Feb 6, 2007
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  2. Mardon

    Jim Townsend Guest

    Are you sure this is a focus issue?

    I ask because basketball is usually played indoors under artificial light.
    If your shutter speeds are too slow, you'll get motion blur which could be
    mistaken for out-of-focus blur.

    What lens are you using and what f numbers and shutter speeds are
    you seeing in the EXIF of your action shots?
    Jim Townsend, Feb 6, 2007
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  3. I've used this occasionally but nearly always revert to the default setting
    after a few shots.
    Are you confident that your camera and lenses are focusing correctly with
    well defined static objects? (i.e. no front or rear focus issues.)
    Malcolm Stewart, Feb 6, 2007
  4. Mardon

    Mardon Guest

    Thanks for your feedback.

    I agree that there are multiple issues when trying to shoot action sports
    in marginal lighting conditions. Motion blur is a problem for sure. I did
    a game this weekend and had to shoot at 1/320 or lower to get enough light
    at ISO1600. I've tried ISO3200 but my experience is that a slight under-
    exposure at ISO1600 is better than a correct exposure at ISO3200 with the
    20D. 1/320 is not really fast enough to get clean shots, that are
    consistently without motion blur, but it is as fast as I could go given the
    available light. They do not allow strobes in this arena. I did lose a lot
    of shots to motion blur but I know what that is. What I am hoping someone
    will know about is Canon's custom function C.Fn-04 and how to use it to
    maximum advantage to achieve focus on a moving subject.

    Incidentally, my shots from Sunday are on my website. If you look, you
    will see evidence of some images with motion blur, some with poor focus and
    some with poor detail from the noise reduction software that I had to use
    to get rid of the grain caused by ISO1600 being underexposed. Hopefully,
    some are OK too! :)

    Here's the URL:

    BTW, most shots were with a Canon 70-200mm F/2.8L and a few with a 16-35mm
    f/2.8L. Obviously, focus is not such a critical issue with the wide lens.
    Mardon, Feb 6, 2007
  5. Mardon

    Mardon Guest

    Thanks Malcolm. Yes, my lenses focus fine. I generally use a Canon 70-
    200mm f/2.8L for most basketball shots and supplement it with a Canon EF
    16-35mm f/2.8L for a few wide shots. You can see my reply to Jim for more
    details of what I'm doing.

    I have a feeling that putting the focus on the "*" button is a good idea
    but I'd really like to have some comments from someone who has a lot of
    experience with this. It sounds like perhaps you and I are both in the
    'experimental' stage with this setting.
    Mardon, Feb 6, 2007
  6. Mardon

    Mardon Guest

    With much embarrassment I have to admit that my problem was really MY
    problem. I had C.Fn-04 enabled alright but I'd left the AF on One-Shot
    instead of AI Servo. No wonder the "*" button wasn't tracking well! Sorry
    for causing a 'wild goose chase'.
    Mardon, Feb 6, 2007
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