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Thread: What determines AF speed?

  1. #1
    Senior Member zoossh's Avatar
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    Nov 2005

    Default What determines AF speed?

    Does the body determines AF speed or is it the lens? WHat are the main factors that affect the ability to control AF? is it the software program inside the camera body's ability to decipher contrast of the object and calculate how to set the focus that is the main factor? or is it the ability of the lens to turn that is the main factor?

    if i have a lens with motor, e.g. Nikkor AF-S & Sigma HSM, and a body with motor, such as any nikon DSLR except for D40, which motor would be in function?

  2. #2

    Default Re: What determines AF speed?

    the comments below are from what i observe and i might be wrong

    i think the body's AF algorithm, AF motor, and the lens all contribute to the AF speed.
    if lens have motor, lens motor will be in function

    the algorithm in the body would determine how fast the lens AF will react (e.g. when u use continuous AF). AF motor, whether in body or lens, determine the speed the lens get from out of focus to focused.

    hope im right
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  3. #3

    Default Re: What determines AF speed?

    There is 2 things in play here.

    The first is the AF module in the camera. This is the "brian" of the camera that determines whether the image is in focus and commands the AF motor to adjust the lens accordingly. Higher end camera usually have more powerful AF module and can evaluate the focusing faster.

    The second is the AF motor that drives the focusing of the lens. This can be the built-in motor of the camera or the SWM/HSM/USM/SDM motor of the lens. Generally, the motor built into the lens is faster. For lenses without motor, it will depends on the motor in the camera. Higher end models may have faster motors built-in.

    There is one more thing that may affect the AF speed.... the lens construction. Some lenses requires more turns than others... e.g. some macro lenses. Some lens have internal focusing which may speed up focusing. Some lens have very big elements to move while focusing, which slows down focusing.

    Last edited by Scaglietti; 6th March 2007 at 11:41 AM.

  4. #4

    Default Re: What determines AF speed?

    Scaglietti said it best
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  5. #5

    Default Re: What determines AF speed?


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