How Do Digital Cameras auto-focus?

Discussion in 'Digital Photography' started by Ralph O'Rourke, Sep 26, 2003.

  1. Most every auto-focus 35mm camera, I've ever used, auto-focuses by
    using a sonar signal

    How does the typical digital camera auto-focus? Sonar also?
    RR
     
    Ralph O'Rourke, Sep 26, 2003
    #1
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  2. Ralph O'Rourke

    mcgyverjones Guest

    Sonar? You're thinking of Polaroids.
    Digicams use contrast measurment from the CCD.

    MJ
     
    mcgyverjones, Sep 26, 2003
    #2
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  3. In fact, just about the only cameras that use sonar are some Polaroid
    ones. You can tell by the big gold-coloured ultrasonic transducer.
    Just where did you get this information?

    Most point&shoot cameras actually measure distance to the subject using
    triangulation, with an infrared light projector located one place on the
    camera front and a receiver located some distance away. Most SLR
    cameras take two samples of the light coming out of the back of the lens
    and image it on a pair of CCDs, then compare the data from the CCDs.
    For digital SLRs: same as film SLRs. Most other digital cameras just
    run the lens through a range of positions and detect the point of
    maximum contrast in the resulting image.

    Dave
     
    Dave Martindale, Sep 26, 2003
    #3
  4. Ralph O'Rourke

    Stewy Guest

    Invisible elves fly out of that little door on the front of the camera,
    (naturally this door is concealed when it's closed) fly to the subject,
    measure the distance then fly back and pass the info to other elves in the
    camera. Sometimes gremlins get the message first and put the picture out of
    focus. Naturally we don't know about any of this as we have our eye glued to
    the viewfinder. There! A scientific explanation!!!
     
    Stewy, Sep 27, 2003
    #4
  5. Ralph O'Rourke

    Paul Bartram Guest

    Hence the expression "elves have left the building..."
    So what happens when you focus on say, the moon? Must be a lot of elves in
    orbit up there...

    Paul
     
    Paul Bartram, Sep 27, 2003
    #5
  6. Ralph O'Rourke

    MarkH Guest

    You don’t know much about photography do you, the elves never fly further
    than the hyperfocal distance. They just report that it is further away
    then the hyperfocal and the camera gets set to infinity.
     
    MarkH, Sep 27, 2003
    #6
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