multi-area autofocus

Discussion in 'Digital Photography' started by hellman@stanford.edu, May 2, 2005.

  1. Guest

    Can anyone help me on how multi-area autofocus works? My Panasonic FZ20
    has four AF modes. What they call 1-area seems to be the old AF, that
    works on an area near the center of the picture. Spot AF seems to be a
    smaller area version of the same. But how do 3-area and 9-area AF (the
    FZ20's other options) work? Clearly, the camera lens can only be
    focused at one distance. Do multi-area AF average the distance of the
    areas? pick the easiest one to discern? increase the f-stop if it finds
    different distances? or ??

    Also, how do these affect shutter lag? The manual says that 3-area is
    the fastest, yet 1-area was the default. Are there tradeoffs?

    Many thanks for any help.

    Martin
     
    , May 2, 2005
    #1
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  2. Mark² Guest

    <> wrote in message
    news:...
    > Can anyone help me on how multi-area autofocus works? My Panasonic FZ20
    > has four AF modes. What they call 1-area seems to be the old AF, that
    > works on an area near the center of the picture. Spot AF seems to be a
    > smaller area version of the same. But how do 3-area and 9-area AF (the
    > FZ20's other options) work? Clearly, the camera lens can only be
    > focused at one distance. Do multi-area AF average the distance of the
    > areas? pick the easiest one to discern? increase the f-stop if it finds
    > different distances? or ??
    >
    > Also, how do these affect shutter lag? The manual says that 3-area is
    > the fastest, yet 1-area was the default. Are there tradeoffs?
    >
    > Many thanks for any help.
    >
    > Martin


    It simply means that it uses whatever focus point you have selected as the
    point in the scene upon which focus is based. This means that you don't
    have to focus...and then re-frame the shot. If you want to shoot an image of
    something in the right, left, or other portion of your frame WITHOUT having
    to focus first...then reframe...you use the alternate focus points.

    If you were (for example) wanting to photograph a runner as he runs by you
    from your right...you could use the right side focus point. This way, as
    you track him (panning with him as he runs by) you could keep him in the
    right portion of the frame as he runs, keeping open space in front of him in
    the picture. By selecting the right focus point, you can keep him in focus
    without having to have him right in the center of your picture (a poor
    framing choice in many circumstances).

    So no... It doesn't average the points. Those are simply the points at
    which the camera will look for contrasting lines/textures upon which to
    focus for a given shot.

    -Mark
     
    Mark², May 2, 2005
    #2
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  3. Paul Rubin Guest

    writes:
    > Can anyone help me on how multi-area autofocus works? My Panasonic FZ20
    > has four AF modes. What they call 1-area seems to be the old AF, that
    > works on an area near the center of the picture. Spot AF seems to be a
    > smaller area version of the same. But how do 3-area and 9-area AF (the
    > FZ20's other options) work? Clearly, the camera lens can only be
    > focused at one distance. Do multi-area AF average the distance of the
    > areas? pick the easiest one to discern? increase the f-stop if it finds
    > different distances? or ??


    Typically they focus on whatever is closest. The classic AF error
    with a single central AF sensor is a shot of two people side by side.
    The camera focuses on the background between them. Using multiple
    sensors and focusing on the nearest subject fixes that error.

    Fancier cameras use all kinds of fancy algorithms to track moving
    subjects with multiple sensors and predict where the subject will be
    at the instant the shutter fires.
     
    Paul Rubin, May 2, 2005
    #3
  4. wrote:
    > Can anyone help me on how multi-area autofocus works? My Panasonic
    > FZ20 has four AF modes. What they call 1-area seems to be the old AF,
    > that works on an area near the center of the picture. Spot AF seems
    > to be a smaller area version of the same. But how do 3-area and
    > 9-area AF (the FZ20's other options) work? Clearly, the camera lens
    > can only be focused at one distance. Do multi-area AF average the
    > distance of the areas? pick the easiest one to discern? increase the
    > f-stop if it finds different distances? or ??
    >
    > Also, how do these affect shutter lag? The manual says that 3-area is
    > the fastest, yet 1-area was the default. Are there tradeoffs?
    >
    > Many thanks for any help.
    >
    > Martin


    Different cameras have different features. Here are a few used with
    multi focus spots:

    * SELECTIVE POINT The user selects which point will be active via a on
    camera control or eye sensing technology.

    * DOF CONTROL The camera selects an aperture based on the distance to
    the closest and furthest point to keep all in focus.

    * CLOSE POINT The camera focuses on the closest point sensed.

    * AVERAGE

    * ANTICIPATIVE Predicts where the subject will be when exposed and
    focusing there.

    I am sure there are others and I doubt if any one cameras has them all.


    --
    Joseph Meehan

    Dia duit
     
    Joseph Meehan, May 2, 2005
    #4
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