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Please explain AF modes for 300D

Discussion in 'Photography Forums' started by dood, Jul 1, 2005.

  1. dood

    dood
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    Could some-one please explain the difference between AF, AI focus AF, and AI servo AF as pertains to the 300D. Also in which modes (eg aperture or shutter priority, manual, basic functions) can I select these settings and how do I do so?


    Another question: When selecting exposure lock (asterisk button), I've read that you need to hold this button down until the exposure is made to lock the exposure. However on my camera it seems to keep the exposure locked even after releasing the exp lock button, until the picture is taken. Am I right in assuming that this is how it should be and that the only time you need to keep the exp lock button pressed is if you wish to maintain the same exposure for subsequent pictures?
     
  2. Peakoverload

    Peakoverload
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    Its actually very simple to understand just harder to remember.

    AF = Auto Focus. This is the default mode, you half press the shutter release and the camera focuses, job done.

    AI Focus = This is the same as AF focus BUT if the camera detects that the subject then starts to move it will adjust focus for you by switching to AI Servo mode, incidentally you need to keep the shutter release half depressed the whole time for this to work.

    AI Servo = This mode continually focuses on subjects and is the one to use when shooting any moving object. There are two things to be aware of:
    1. If you have just selected one AF point you must make sure that this is placed over the subject you want to be in focus the whole time as otherwise you will loose focus.
    2. You wont get a beep when focus is achieved as the camera is continually focusing.


    You can set any of these in aperture and shutter priority and if you use the creative sports setting AI Servo is selected for you by default where as in Landscape, portrait, close-up and night modes the camera sets the standard AF mode for you.

    As for exposure lock, you do NOT need to keep the asterix button depressed, your camera is working as it should.

    HTH
     

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