So how does Auto-Focus work?

Discussion in 'Photographic Discussions' started by Chairman7w, May 14, 2009.

  1. Chairman7w

    Chairman7w TPF Noob!

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    I mean, I know the meaning of it (focuses automatically), but how does it work from a physics standpoint? Is there a little radar? Sonar? Infra-red?

    How in the WORLD does it do that?
     
  2. Dao

    Dao No longer a newbie, moving up!

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    I believe there is a contrast based autofocus. So maybe that's why it doesn't work too well in low light situation.
     
  3. Dao

    Dao No longer a newbie, moving up!

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    bhop No longer a newbie, moving up!

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  5. KmH

    KmH Helping photographers learn to fish Supporting Member

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  6. Garbz

    Garbz No longer a newbie, moving up!

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    Neither of those apply to DSLRs.

    Contrast based autofocus is slow, clugy and relies on image processing (see the slow complaint). This is the autofocus mode that cameras revert to when you enable live view, and also the AF mode used by all point and shoots.

    Edit: Found it include an animation on Nikon's site. http://www.nikon.com/about/technology/core/software/caf/index.htm This is how the predictive focus works on Nikon cameras, but the principles of phase detection are the same for all DSLRs.
     
    Last edited: May 14, 2009

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