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Old Mar 1, 2008, 11:09 AM   #1
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Just learing about this function on my Rebel XT. As I understand, after I set up the camera in this mode, all that I have to do is hold down the * to focus, keep it pressed, and hit the main "shoot" button to take continuous shots. I'm in AI servo mode, and AV. I also changed the focus point to be the center.

Any other comments, or suggestions on if that is right to use for "action" shots?

thx.
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Old Mar 1, 2008, 2:43 PM   #2
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It's certainly popular to use this function for action shots. But, you should understand what it does to better understand WHEN it will help you and when it will NOT.

What the function does is divorce focusing from the shutter button. The * button controls focusing and the shutter controls metering and shutter release.

So, you focus with your thumb and meter/take the shot with your index finger.

Now - if you're taking shots of athletes in coninuous motion, there really is no benefit over leaving the focus on the shutter button. You still hold down a button to keep tracking your subject - only now you are using your thumb vs. a half-press of the shutter. So for sports like basketball, soccer etc you get no real benefit.

So, when does it provide a benefit? Basically any time you can pre-focus. Think of shooting a play at 2nd base (attempted steal or double play) - you can focus on the bag and then take your thumb off. Unlike single shot you don't have to keep the half-press on the shutter. And unlike using ai-servo on the shutter button you won't re-focus constantly. You can then re-compose the image and wait for the action to come into the frame. You don't have to worry about tracking a player because you know where they'll be. You don't have to worry about a focus point slipping off your subject at the critical moment. THEN, if the runner slides into second and there's a bad throw and they start to run you can press the * button and start tracking them again.

So, it allows you to get the best of all the focus modes - one shot, ai-servo and manual. But there are only a few instances where that is really helpful. But it's very useful to always keep the same workflow. So most of us leave it on back button focusing all the time so camera workflow is always the same.
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Old Mar 1, 2008, 10:20 PM   #3
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JohnG,

Great explanation on the use to that function button. I had not quite grasped the idea of it until now.

Thanks,

Craig

P.S.

Thanks to the OP, saved me having to ask the same question.:G
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Old Mar 3, 2008, 2:17 AM   #4
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Have to disagree with Johns point abouttaking shots of athletes in continuous motion, there really is no benefit over leaving the focus on the shutter button. There is a benefit when using C.Fn-4-3 as there is no exposure lock and you get a separate exposure reading for every shot (even in a continuous burst). Veryuseful for panning when your background changes or the light changes (brighter light or shadows etc) so you get the correct exposure.
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Old Mar 4, 2008, 12:50 AM   #5
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TG wrote:
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Have to disagree with Johns point abouttaking shots of athletes in continuous motion, there really is no benefit over leaving the focus on the shutter button. There is a benefit when using C.Fn-4-3 as there is no exposure lock and you get a separate exposure reading for every shot (even in a continuous burst). Veryuseful for panning when your background changes or the light changes (brighter light or shadows etc) so you get the correct exposure.
Do you agree with John's explanation of how that function buttonwork butjust disagree on when to use that functionwhen shooting?
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Old Mar 4, 2008, 3:25 AM   #6
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Calicajun wrote:
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Do you agree with John's explanation of how that function buttonwork butjust disagree on when to use that functionwhen shooting?
IUse the * button all the time for focus and C.Fn 4-3 with Ai Servo when shootingaction.I use a different technique to John,mainly shoot motorsport use C.Fn 4-3, AI Servo,single focus point (I like to pick what I want to focus on and not let the camera decide, AF also works faster with a single point). Focus on the car early so the AI Servo AF can settle and lock on the subject take the shot. Do use continuous shooting mode but prefer to take a single shot than the spray and pray method. Also just dab the * button when in AI Servo if I want to focus like one shot mode.
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Old Mar 4, 2008, 6:51 AM   #7
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TG wrote:
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I use a different technique to John,
Actually the technique you describe is pretty much the same. There aren't too many sports shooters that use all focus points - most (including me) use just one (although with the mkIII I do enable the helper points). And I dont believe in the spray and pray approach either. Typically for humans though a 2-3 shot burst is a good apprach - strides can look akward, hands and arms can enter and leave the frame and, you cant predict facial expressions. It all depends though. Some events (hurdles, high jump, play at a bag) have a single timed moment you want to capture - but for sports like soccer, football, basketball, track - the stride of the player, facial expressios and lack of extraneous body parts in the frame are better gotten by picking the best out of a 2-3 shot burst. Big difference between that and 'spray and pray'.
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Old Mar 4, 2008, 8:00 AM   #8
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JohnG wrote:
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Actually the technique you describe is pretty much the same.
OK, agree with you about using burst on your last point.

How do you find the expanded focus points on the MKIII tried them on the MKII N hard to tell if there is a benefit, my only issue with them is the chance offocusing on something with better contrast.
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Old Mar 4, 2008, 8:41 AM   #9
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on the mkIII the focus points actually light up even in Servo. I've really only seen the assist points light up maybe 1% of the shots. I would think they are more beneficial for wildlife shooters where there subject is filling up a smaller portion of the frame. With my shooting style, my subject fills at least 1/2 the frame.

All I can say is - so far I haven't noticed an occurance where the assist point has taken over when it shouldn't. But I honestly think part of it is technique - I'm used to the 9 point system of the xxD series. So not much margin for error using a single focus point. So you get good at keeping that point on the contrasty area of your subject (or you dont get results).


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Old Mar 5, 2008, 1:21 AM   #10
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This set up also works for reporters and paparazzi shooters. It allows you to get a pretty quick focus on unwilling subjects. I had trouble with coordination and had to go back to the "normal" setup (weddings).
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