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Thread: what cause lenses to "hunt" during AF ?

  1. #21

    Default Re: what cause lenses to "hunt" during AF ?

    I had the same problem during a recent portrait shoot with my 70-200L f/2.8 IS. The model was back facing the sun (around sunset) and I'm more than 2 meter away. Probably the AF assist light on my flash (430EX) is too far to reach the model face.
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  2. #22

    Default Re: what cause lenses to "hunt" during AF ?

    cant remember where i saw this explanation but here goes.
    the af sensor will cause the focusing motor to move until it achieves maximum contrast between the light and dark side of the image.


    if the cam is pointed between [+][+] and the af area covers both [+], it will focus until [+] is very red and [+] is very bright.

    i substituted white with red and grey with black.

    so if the 2 areas have low contrast difference, then it's hard for it to af hence it hunts
    [QUOTE=dan_1337;2947523]if it was painted white, it would cost twice as much as Sigma =P[QUOTE]

  3. #23

    Default Re: what cause lenses to "hunt" during AF ?

    I believe AF is not a constant "on" thingy even if it's in C-AF (that's why it's predictive). What I don't really understand is that moving the lens to infinity focus and back to MFD does it help in getting the AF?

    Lens does help in 2 area, faster lens sould let AF focus better, also the "movement" and time required for it to cycle from infinity focus to MFD.

    There's also cases where AF is "over corrected" in my case it happens when I stick a 1.4x on my f5.6 sigma lens. In this case I experience the lens doing corrections shifting in and out of focus.
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