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Archive 2012 · Canon 1D MK3 Auto-Focus Technique
  
 
Gonemad
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p.1 #1 · p.1 #1 · Canon 1D MK3 Auto-Focus Technique


I was wondering if anyone could shed some light on techniques to track a subject, say a soccer player. I noticed that, even though the AF point was dead on the subject, many shots were out-of-focus because the player had turned around. I don't know if it's just a coincidence or just how the AF algorithm works. For example, while tracking a player facing in one direction, when suddenly the same player turns to shield the ball away from a defending player, the camera seems to easily lose focus because to the sensor the subject "no longer looks the same" and loses focus (when setting CFn III-2 default tracking sensitivity and CFn III-4 to '1' continuous expansion). Can anyone confirm/deny my observation? In those scenarios, I've learned to re-acquire focus as the player turns. While that's not so bad, I also lose a lot of good shots since the AI servo needs about a second to lock.

I always shoot @ full 10fps burst mode at least 1/2000th to "freeze" action. Still, the out-of-focus situation seems to occur more frequently when the subject turns away from the original tracking path. Re-focusing (releasing and pressing the back focus button) periodically seems to fair well...


Edited on Aug 10, 2012 at 08:28 PM · View previous versions



Aug 10, 2012 at 06:22 PM
martines34
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p.1 #2 · p.1 #2 · Canon 1D MK3 Auto-Focus Technique


Are you shooting single shots or burst mode??

You may find burst mode giving you more acceptable images.



Aug 10, 2012 at 06:45 PM
Gonemad
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p.1 #3 · p.1 #3 · Canon 1D MK3 Auto-Focus Technique


I always shoot @ full 10fps burst mode at least 1/2000th to "freeze" action. Still, the out-of-focus situation seems to occur more frequently when the subject turns away from the original tracking path. Re-focusing (releasing and pressing the back focus button) periodically seems to fair well...


Aug 10, 2012 at 06:55 PM
 

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jstephens62
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p.1 #4 · p.1 #4 · Canon 1D MK3 Auto-Focus Technique


Hve you tried Servo with back-button focus?


Aug 10, 2012 at 07:08 PM
jcolwell
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p.1 #5 · p.1 #5 · Canon 1D MK3 Auto-Focus Technique


Have a look at these references.

Getting the Most from your EOS 1-Series Camera www.jcolwell.ca/ftp/EOS_Digital-Getting-the-most.pdf [was http://www.usa.canon.com/content/Handling/EOS_Digital.pdf ]

Sports Illustrated Photo http://www.siphoto.com/?canon1DM2.inc

The Canon doc is from the 1DII era, but most is completely relevant to the 1DIII.

The 'refocusing' technique you mention is often called 'pumping' the AF. It's a good way to re-establish focus. The 1DII and 1DIII AF algorithm predicts where the subject will be when the shutter fires, based on current/past motion. This requires you to hold down the shutter for at least a few images - i.e. machine gun.

Also, the AF on any camera, including the 1D-series, works better with a faster lens. Your f/4 and f/4.5-5.6 zooms won't perform as well as their f/2.8 companions. Not that this will help you a lot...



Aug 11, 2012 at 12:39 AM
dwweiche
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p.1 #6 · p.1 #6 · Canon 1D MK3 Auto-Focus Technique


Mad,

It seems a lot of the posts are going down the "make sure you know what you're doing" path.

However, your description is interesting. I could see how the AF algorithm could get confused if the object it is tracking suddenly disappeared because a player turns around. Let's say it is tracking the number on the front of the jersey, and when the player turns around it loses the number and doesn't know what to do... Seems like a plausible explanation.

Not that this really helps you



Aug 11, 2012 at 02:51 AM





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