Canon Function-04 Shutter Button / AE Lock Button

Discussion in 'Beyond the Basics' started by RacePhoto, May 14, 2007.

  1. RacePhoto

    RacePhoto TPF Noob!

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    I read this in the manual, and I get more confused. (by the way, this is a question about that * button we are always talking about) :lmao:

    Say I'm shooting sports, if I use the #3 setting AF "pulse" No AE lock, am I stopping the auto focus? Wouldn't I want the autofocus to be on, since the subjects are in motion?

    Why wouldn't I want to use mode 1 where the autofocus is started when I hit the button?

    Or did I read it wrong, and all the * button, Mode 3, does is manually focus the camera, and then the auto takes over when I'm panning? Because that's what I want to do. Force a starting focus point and then have the AI Servo take over and track the subject.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I'm not sure I understand what you are asking. :scratch:

    CF#4 does not affect the AF mode (single, servo, AI Servo etc.) it only affects how you activate AF. (That's how I understand it, anyway).

    I think what I use is option #2 for CF#4. This way, AF is activated with the * button and AE lock is with the half press of the shutter button. So is this scenario, you could set the AF to servo...then focus on any point (starting point) by pressing the * button...Then release the button. When you want to start having AF servo take over, just press the * button again. Actually, in this case, it might be easier to have the AF on the shutter button and you could just keep it half way presses to keep AF going.

    I find that the benefit of having the focus on the * button is that you don't have the AF system picking up stray objects while pressing the shutter button. So for sports, you could focus on a subject and then release the * button...then, the AF will not start up again while you are pressing the shutter button to snap the photos. If you want to start tracking the subject, then just hold the * button down while shooting.
     
  3. RacePhoto

    RacePhoto TPF Noob!

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    Clear as mud, now I'm more confused than ever. :mrgreen:

    Here's what I want to do. I know a car is going to come around the corner, I want to start shooting, but I don't want the lens to have to focus as I push the shutter button half way. I want to already be focused at point "A".

    Now as the car is passing (which could be a football player, succor player or hockey player... any moving action sports) I want the camera to follow and focus on the subject to point "B" and "C"

    If I activate and deactivate the focus by the * button, then doesn't it turn it off when I push it the first time, to set point "A" (Mode 3) Starts and stops AI servo. Or does it turn it on, when I first push it, and stays on. In which case, pushing it again, turns off the AI Servo.

    Mode 2 locks the focus, like you said, if some object comes between you and the subject.
     
  4. EOS_JD

    EOS_JD TPF Noob!

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    First set AF mode to AI Servo. this will allow you to focus on a moving subject. You then need to pre focus on the spot you want no matter which AF button you use (half press or * button). Pre focus and keep the AF button pressed down. Also use only the centre AF point.

    As the subject passes the point of focus you need to follow the subject with the camera with the centre AF point locked on the subject. The camera will track the movement (AI Servo does this).

    you need to keep the * button pressed all the time to keep focus and to try and keep the lock on your subject you need to follow the subject with the active AF point on the subject at all time.

    It's really pretty easy once you know what you're doing. My main reason to use the * button is that it separates AF lock from exposure lock. Exposure is only calculated when you take the shot. When using the same button for both and you track the subject using AI Servo (expoure is locked at the time the shutter button is half pressed), then when you take the shot the subject may be in completely different light.

    Does the above help?
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    That's right. The * button isn't like a toggle switch (press to turn it on, press again to turn it off)...when it's set to control the AF...you activate AF when you press and hold the * button.

    In your scenario...you would set the AF mode to AI Servo, prefocus and then hold the button down as you are panning with the subject, as JD said.
     
  6. darich

    darich TPF Noob!

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    i use the * button to focus aswell.
    It's also useful for landsapes on a tripod. I have a tree that i want to be in focus. So i focus on that in the centre of the frame using the * button. I can then recompose the shot with the tree to the left of the frame. when i use my remote shutter release the camera won't refocus. If i then want to recompose with the tree on the right side, i just simply recompose and the focus hasn't changed.

    If also means that if using f2.8, then f8 then f11 (or any other variable) for each shot, the focus isn't being adjusted for every frame - it's only adjusted by pressing the * button
     

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