So how does Auto-Focus work?

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

  1. Chairman7w

    Chairman7w TPF Noob!

    Joined:
    Jan 21, 2009
    Messages:
    301
    Likes Received:
    0
    Location:
    Sacramento, CA
    Can others edit my Photos:
    Photos NOT OK to edit
    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!

    Joined:
    Mar 24, 2008
    Messages:
    6,252
    Likes Received:
    418
    Location:
    St. Louis
    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!

    Joined:
    Mar 24, 2008
    Messages:
    6,252
    Likes Received:
    418
    Location:
    St. Louis
  4. bhop

    bhop No longer a newbie, moving up!

    Joined:
    Dec 10, 2007
    Messages:
    2,224
    Likes Received:
    253
    Location:
    Los Angeles
    Can others edit my Photos:
    Photos OK to edit
  5. KmH

    KmH Helping photographers learn to fish Supporting Member

    Joined:
    Apr 9, 2009
    Messages:
    40,096
    Likes Received:
    5,461
    Location:
    Iowa
    Can others edit my Photos:
    Photos OK to edit
    Ya gotta just love the I N T E R N E T.
     
  6. Garbz

    Garbz No longer a newbie, moving up!

    Joined:
    Oct 26, 2003
    Messages:
    9,713
    Likes Received:
    203
    Location:
    Brisbane, Australia
    Can others edit my Photos:
    Photos NOT OK to edit


    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

Share This Page