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Thread: Auto focus problem

  1. #1
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    Default Auto focus problem

    I face some autofocus problem. May i know why sometime i was unable to autofocus when i am shooting? the lens keep zoom in zoom out, but keep failing (cannot autofocus). Is this because of low light?

    I using 50D with Sigma 17-70.

  2. #2

    Default Re: Auto focus problem

    Quote Originally Posted by chujou87 View Post
    I face some autofocus problem. May i know why sometime i was unable to autofocus when i am shooting? the lens keep zoom in zoom out, but keep failing (cannot autofocus). Is this because of low light?

    I using 50D with Sigma 17-70.
    It might be low light or lack of contrast, this will cause the slower lenses to be unable to catch the plane of focus.

  3. #3
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    Default Re: Auto focus problem

    so with my EOS 50d, any lens (general use) that u can recommended to reduce these problem to minimum?

  4. #4

    Default Re: Auto focus problem

    Quote Originally Posted by chujou87 View Post
    so with my EOS 50d, any lens (general use) that u can recommended to reduce these problem to minimum?
    If you are shooting indoors in low light why not get a flash, the flash's IR will have AF assist and you probably need the flash anyway.

  5. #5

    Default Re: Auto focus problem

    Quote Originally Posted by chujou87 View Post
    I face some autofocus problem. May i know why sometime i was unable to autofocus when i am shooting? the lens keep zoom in zoom out, but keep failing (cannot autofocus). Is this because of low light?

    I using 50D with Sigma 17-70.
    Low light & focusing distance from object too near.

  6. #6
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    Default Re: Auto focus problem

    Quote Originally Posted by Jeremy1 View Post
    Low light & focusing distance from object too near.
    How far were you from the subject?

    Some lenses minimum focusing is a mere 20cm, others 50cm, some 1.5m, etc, etc.
    It depends on lens design. Were you too near?

  7. #7

    Default Re: Auto focus problem

    Quote Originally Posted by Oberon View Post
    How far were you from the subject?

    Some lenses minimum focusing is a mere 20cm, others 50cm, some 1.5m, etc, etc.
    It depends on lens design. Were you too near?
    No lah, I was wondering is the TS can't focus due because of this.
    Last edited by Jeremy1; 6th October 2010 at 08:51 AM.

  8. #8
    Member enzeru21's Avatar
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    Default Re: Auto focus problem

    Focusing works by detecting contrast within your selected focus point, i.e. if you are using the centre focus point, then whatever you are pointing at has to have contrast. If you're pointing at a white wall or clear sky, the camera will not be able to figure out what is the distance between you and the object you are focusing at, and thus will not be able to focus.

    Similarly, if it's dark, naturally the contrast between things is much lower. It then becomes difficult for the camera to pick out the contrast in order to focus.

    The best thing to do is to (a) look for something with a high contrast to focus on (e.g. something lit by a lamppost) or (b) open your on camera flash and let the focus assist flash fire, then when it's focused, close the flash and take your photo
    enzeru21 Canon 500D |Tamron17-50mm f/2.8| Sigma30mm f/1.4 | 580EX II
    mylightedreams

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