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Thread: Selecting the AF Point: Automatic or Center Point

  1. #1
    Senior Member Mark Elberson's Avatar
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    Selecting the AF Point: Automatic or Center Point



    Is there an advantage in letting the camera automatically select the AF point vs. manually selecting the center point? I find that manually selecting the center point often works better for me because it allows me to have more control and many times what the camerathinks is the best focusing point is outside of where I would like it to be.


    Am I losing any speed or accuracy in doing this though?


    Also, what if I was in AI Servo as apposed toOne Shot? Would it matter then?

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    Re: Selecting the AF Point: Automatic or Center Point



    I use center point, half-press the shutter, then recompose. I supposea holdover from my cheapo Pentax camera years ago.

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    Re: Selecting the AF Point: Automatic or Center Point



    None of the above. Using my 5D and 40D's I manually select the AF point via the small wheel behind the shutter button. With my MKIII I use both the small wheel and large rear wheel to select points (half press the shutter button for AF lock). For shooting fast action Center AF point is most accurate on most, if not all, non-1-series bodies but it depends on what exactly your focusing on and where its located in the frame. AI servo, for the most part, should be used when focusing on a quicker moving subject and One shot on slow moving or still subjects. Focus and recompose works, but only when in 'one shot' and shooting at more narrow apertures while shooting very slow moving or still subject matter. Read up in your manual for a better understanding.


    -Matt

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    Re: Selecting the AF Point: Automatic or Center Point



    I normally shoot AI Servo, center point only, with AF-ON mapped to be an AF-STOP button instead. Allowing the camera to choose focus points can really slow down the AF system in my experience, and you REALLY have to know how the camera wants to behave. The joystick allows me to choose an alternate point on the fly for off-center compositions, but I gravitate back to center point quickly.
    We're a Canon/Profoto family: five cameras, sixteen lenses, fifteen Profoto lights, too many modifiers.

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    Re: Selecting the AF Point: Automatic or Center Point



    I never use auto. I rarely even use the center point. I find recomposing often compromises tight focus especially on close subjects.


    I am constantly switching between points manually.

  6. #6
    Senior Member Mark Elberson's Avatar
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    Re: Selecting the AF Point: Automatic or Center Point



    Thanks everyone for your input!

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    Re: Selecting the AF Point: Automatic or Center Point



    Center point for me.

  8. #8

    Re: Selecting the AF Point: Automatic or Center Point



    focus and recomposing is in general a bad idea ...it lets the camera focus however when you recompose you are actually changing the focus distance from where you held the shutter at half way ..and what you now are actually wanting to focus on ...there for you do not get optimium focus... its ok if you want the focus to be on the obejctive to the right or left dependimng which way you went when you recomposed ...but if you want the focus for example to be on a persons right eye in a shot then use the coresponding focus point for that ye for best results ...or use MF
























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    Re: Selecting the AF Point: Automatic or Center Point



    Of course most of the time, I'm in MF anyway, so I guess my bad AF practices are somewhat moot, heh.

  10. #10
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    Re: Selecting the AF Point: Automatic or Center Point



    The problem with the recomposing after focusing is that the focal plane is not a hemisphere. I.e., even if you can manage to keep the camera equidistant from the point of focus, the focal plane is not equidistant from the camera, even if it's curved. Recomposing may, though, be the best you cann do in a quick situation, and if your depth of field is deep enough, more than just fine.


    Still, I figured out that hard way that while it can be convenient (and was suggested in my XT manual, as I remember), it didn't seem to work consistently. With wide apertures, it became really frustrating. Before reading up on Bryan's website and realizing that'the focus distance'was, if not perfectly, close to a plane and not really a fixed focusing distance, I thought I was just misfocusing.


    If I have the time, I prefer to dial the closest autofocus point into something it can grab some lines on, eyes or eyelashes being the obvious human targets,and take the picture like that, or maybe recompose slightly if it's a really minor shift.


    Sometimes, though, when I'm lazy, I like to use all points, and try to line up the point I want to use with a detail, and see if I can duck the others into areas that either lack quick transitions in contrast, or are simply farther away, in which case the closer points seem to get priority. I may halfway press the shutter button a few times, and when I see the point I want blink, squeeze.


    In AI servo, I usually use the center point if it's something I can keep a good aim on. However, if it's something that is moving enough laterally or vertically, I may use all points just to give me a better chance of not accidentally losing the lock and getting a nice blurry subject with a really clear background.

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