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04/17/2005 11:24:26 PM · #1 |
A 20D has three options of focus mode:
1) one shot AF - the camera focuses just once on a still subject
2) Al Servo - the camera focuses continuously on moving subjects
3) Al Focus - the camera uses one shot AF on a still subject, but if it senses movement, it switches to Al Servo.
It sounds like such a no-brainer - Al Focus does it all. But since I firmly believe that there is no such thing as a free lunch, I must be missing a drawback somewhere.
Could somebody please explain why I would NOT want to leave the camera on Al Focus all the time.
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04/17/2005 11:26:41 PM · #2 |
10D is the same. AI servo is faster than AI focus. good for air shows and shots like this that I took today.
Dave
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04/17/2005 11:29:21 PM · #3 |
wow David, they are great, I especially like the first two.
Such fabulous detail - so that was done on "al servo" ?? |
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04/17/2005 11:33:44 PM · #4 |
yup. you'll notice that AI Servo is also what gets set when you go to "Sports" mode.
I haven't used AI focus since experimenting with AI servo and finding it reacted faster. Here are some more examples, from an air show last summer, using the Canon 70-200/f4 L.
If anyone has advice for when AI focus should be used, I'd be interested in hearing about it.
Dave
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04/17/2005 11:51:04 PM · #5 |
On the rebel, it's automatically AI focus. But when you switch to sports mode, it's AI servo -- which is basically, as long as you hold the shutter down half-way, the camera will continually re-focus as the subject moves toward or away from you. The only part about that that is bad is in Sports mode, you are also stuck with ISO 400 (on the 300d).
Really, the only time you want to use servo is when you're trying to focus on a moving subject. Any other time, you're probably just wasting battery life and the focus could possibly jump off-subject if something were to move.
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04/18/2005 12:49:19 AM · #6 |
RC Plane from today... 4L AI Servo mode
The key is choose your mode accordingly
Don't try to shot a hummingbird in AI Servo AF, move a bit and the cam will start hunting.
Don't try to follow a Hawk with Single Shot AF or the background may end up in focus and the hawk OOF.
The biggest thing I learned with AI Servo mode (with the 70-200mm 4L) is don't panic...I mean is was tracking a hawk in the sky the other day and got off the bird...wham instant OOF...keep your finger half squeezed and the lens will find the bird.
My buddie who was shooting with me had his Minolta 7D in single shot AF (he forgot to go to AI) and all his shots were blurry...he would get a focus lock and track the bird, the distance (to the bird) would change and boom...OOF
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04/18/2005 12:53:29 AM · #7 |
Originally posted by awpollard:
The biggest thing I learned with AI Servo mode (with the 70-200mm 4L) is don't panic......keep your finger half squeezed and the lens will find the bird.
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That sounds like something useful to keep in mind.
Thank you very much, gents, you have helped me understand this.
edited to say:
AWESOME shot of that plane!!
Message edited by author 2005-04-18 00:54:14. |
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