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Thread: Focusing on moving objects...advise...

  1. #1

    Default Focusing on moving objects...advise...

    Need some advise on the following:

    With AI focus, how do I ensure that my object which is running towards me will be in focus as it approaches....a fast lens? At what shutter speed.

    I keep getting out-of-focus shots...please advise...thanks!

  2. #2
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    The standard trick (of which I have not mastered)

    1. Prefocus on a point where the subject will pass.
    2. Fire when subject reaches that point.

    Preselect a aperture which will give you adequate DoF to cover any focus errors, and a shutter speed sufficient to freeze the action.

    Regards
    CK

  3. #3

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    I a situation where I am facing the person and he is running towards me, I will not be able to prefocus, presuming this is an open space....

  4. #4
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    I normally use CKiang's method for shooting oncoming subjects..

    Prefocus at the area where you want your subject to be.

    Eg: Taking a MRT approaching the station.... Focus lock your camera ( AF ) or
    Focus manually where you want to compose the first carriage. i normally focus anything near the area that is distinct. If you are familliar with your lense DOF.. you trigger the shutter at about 2/3(DOF)behind your focus point.
    Take a few if you want to play safe. The trick is timing to get your subject sharp. I use an AF camera ( not fast enuff for some fast moving subject), so i prefocus and lock it and snap when subject is in the frame. Or u can play safe by switching to manual after your prefocus.. so your AF wont hunt and wont miss the shot.

    My explanation is bad.. i know.. hheee.. but i hope you can understand.

  5. #5

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    apart from the traditional method outlined above, you need a cam with a quick enuf servo af mode, plus try setting you shutter speed at 1/125 to 1/500, should freeze most humans....

  6. #6

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    Originally posted by Paladin
    I a situation where I am facing the person and he is running towards me, I will not be able to prefocus, presuming this is an open space....
    Prefocus on a spot on the ground in his path and fire the shutter just before he reaches that spot.

  7. #7

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    This was taken using AI Focus / AI Servo with a D30:



    The tracking is pretty good, and you can shoot at will (as opposed to waiting for focus lock).

    The difference between the D30 and 10D is as follows:

    For D30, in Av mode (my most common shooting mode), there is only a choice between One Shot mode (where you have to wait for focus lock before firing the shutter) and AI Servo (where the AF continuously changes to track the subject, and you can fire without achieving focus lock).

    In 10D, you have a new choice, which is AI Focus. For stationary subjects, it will beep to indicate focus lock achieved (ie like One Shot mode). If the subject starts to move, it will switch automatically to AI Servo and start tracking the subject. Pretty smart and useful.

    However, if your subject is continuously moving (ie never stationary), you should still switch to AI Servo mode rather than use AI Focus.

  8. #8

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    old-school prefocus method works but it will make u crazy

    better to use continuous AF to track.(ie make full use of USM)

  9. #9

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    Originally posted by StreetShooter
    This was taken using AI Focus / AI Servo with a D30:



    The tracking is pretty good, and you can shoot at will (as opposed to waiting for focus lock).

    The difference between the D30 and 10D is as follows:

    For D30, in Av mode (my most common shooting mode), there is only a choice between One Shot mode (where you have to wait for focus lock before firing the shutter) and AI Servo (where the AF continuously changes to track the subject, and you can fire without achieving focus lock).

    In 10D, you have a new choice, which is AI Focus. For stationary subjects, it will beep to indicate focus lock achieved (ie like One Shot mode). If the subject starts to move, it will switch automatically to AI Servo and start tracking the subject. Pretty smart and useful.

    However, if your subject is continuously moving (ie never stationary), you should still switch to AI Servo mode rather than use AI Focus.
    This was the shot I had in mind....and I would like to know how effective is the AI in tracking the focus...the 10D manual did mentioned that it will auto predict and focus in AI focus mode....

  10. #10

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    better to use servo all the way, on the eos 30, when exactly the AF switches from 1 shot mode to servo in AI AF is unpredictable.....sometimes it doesnot switch if you subject is moving too slowly or starts and stops

  11. #11
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    I think even entry-level SLRs have good focus tracking ability, IF your subject is moving towards/away (in a single plane, at consistent speed) from your camera. If it moves across the frame, then it's more troublesome...

  12. #12
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    all the better if u have top of the line system.. but as for me i would learn to do it the old skool way first to train my eye and finger coordination to capture the right moment... since manual cameras doesnt have AF.. dont blame it on AF when u cant get the shot u want as it all depends on the speed of the subject and the light available.

    My dua sen

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