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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 05 Sep 2009 (Saturday) 16:29
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AI Focus VS. AI Servo

 
texshooter
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Sep 05, 2009 16:29 |  #1

AI Focus and AI Servo seem like the same thing to me.

AI Focus is suppose to continuously change focus if your subject is moving, but AI Servo only changes focus if "you anticipate the subject moving."

Uhh?

Either the subject is moving or it isn't. So why would I use one focus setting instead of the other?

To make things more confusing, the 5D Mark ii has a custom function "C.Fn III-7 AF Point area expansion" that is suppose to expand the focusing area when you are on the AI Servo focus mode. Isn't that the same thing as selecting all focus nodes with that button on the front top right of the camera with the square puzzle icon? Why use C.Fn II-7. I'm sure I'm missing something.




  
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Jezza8
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Sep 05, 2009 17:20 |  #2

AI Servo is effectively the mode you use if you know you want to track a moving subject, simple and straightforward.

AI Focus is supposed to be more intelligent, it works out if the subject is moving or not, if not it will fix the focus on the point it initially locks on and not move (One shot mode) otherwise it will switch to tracking mode like AI Servo. In theory this should give you the best of both worlds, in practice it is a bit of a dogs dinner and you are never quite sure which mode you are in, so my advice is to forget AI Focus and use either One Shot or AI Servo.




  
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artyman
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Sep 05, 2009 17:22 |  #3

I have my camera set to AI Servo allocated to the * button, one press and you have one shot , just hold for servo :)


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texshooter
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Sep 05, 2009 17:34 as a reply to  @ Jezza8's post |  #4

Fact 1: AI Focus mode locks the focus when the subject is still.
Fact 2: AI Focus mode unlocks the focus when the subject moves

Fact 3: AI Servo mode keeps the focus still when the subject is still.
Fact 4: AI Servo mode moves the focus when the subject moves

If I have my facts straight, the only difference between fact 1 and 2 is that AI servo mode technically does not "lock" the focus when the subject remains still. Instead, it only keeps the focus "still."

I may be splitting hairs, but I don't see any difference between "locking" the focus and "keeping it still." I still don't see any meaningful distinction between AI Focus and AI Servo modes, unless.....

There is a time delay when the focus control goes from the locked position to the unlocked position. If that's the case, then AI Servo mode will have a practical advantage for really quick shooting.




  
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buddy4344
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Sep 05, 2009 17:37 |  #5

i have always wondered the same, though I mostly use Servo if I expect movement. I also wonder about single point focus vs. matrix of points when shooting moving subjects.


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ed ­ rader
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Sep 05, 2009 17:40 |  #6

buddy4344 wrote in post #8590393 (external link)
i have always wondered the same, though I mostly use Servo if I expect movement. I also wonder about single point focus vs. matrix of points when shooting moving subjects.

i suppose it depends on style and what you are shooting. i always use a single point and never focus/recompose.

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texshooter
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Sep 05, 2009 17:43 as a reply to  @ ed rader's post |  #7

A still small voice in the back of my mind tells me there must have been a reason why Canon added the AI Focus mode. I just can't figure out when it is better to shoot AI Focus over AI Servo.




  
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Mark_Cohran
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Sep 05, 2009 17:43 |  #8

It's been my experience that AI Focus isn't as intelligent as Canon would like you to think. If I need AI Servo, then I use AI Servo, otherwise, I use One Shot.


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texshooter
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Sep 05, 2009 17:55 as a reply to  @ Mark_Cohran's post |  #9

I figured it out. You want to use the AI Focus mode when you plan to shoot in situations where you wan't to switch back and forth from On Shot mode to AI Servo mode without having to turn dials on the camera.




  
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artyman
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Sep 05, 2009 18:00 |  #10

texshooter wrote in post #8590460 (external link)
I figured it out. You want to use the AI Focus mode when you plan to shoot in situations where you wan't to switch back and forth from On Shot mode to AI Servo mode without having to turn dials on the camera.

That is effectively what I said I do with allocatiing focus to my * button.


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Owhat
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Jun 23, 2011 14:52 |  #11

Interesting.


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kf095
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Jun 23, 2011 15:47 |  #12

I like AI Focus for pictures like this.

IMAGE: https://lh4.googleusercontent.com/-KAeuqcS-HjM/TfV4ur-Am1I/AAAAAAAAUqI/ODyOb-Fd4L8/s800/_MG_7873.jpg

IMAGE: https://lh6.googleusercontent.com/-9I2rO42ZNbk/TfV4wabrRTI/AAAAAAAAUqQ/koyj2e4PRZ8/s800/_MG_7877.jpg


I'll have all AF points enabled and camera will lock to the object almost always.
Once focus is locked, it will red-light selected focus point(s).
It allows me to take quick snapshots, without selecting focusing point, camera does it for me and if objects moves, but not a lot, it is tracking it.

IMAGE: https://lh6.googleusercontent.com/-fNUtJI6jOuo/TfTIOzFWarI/AAAAAAAAUh4/aQULVniES_E/s800/_MG_7359.jpg

IMAGE: https://lh6.googleusercontent.com/-yhcy7qQFRDg/TfTIPnJPQzI/AAAAAAAAUh8/_xKucj1teDo/s800/_MG_7365.jpg


If I have all AF points enabled on AI Servo camera is focusing, but no red-lights on AF points once it is locked.
I use AI Servo for fast moving objects with single AF point. At this case it is showing red-light square for AF once it is locked.

IMAGE: https://lh3.googleusercontent.com/-CGQpB6MlUvg/TLMvjhDN6FI/AAAAAAAAOIM/_bZLboiOB_s/s720/2010_10_11_8824.JPG

And my focus button is on *, of course.

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Snydremark
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Jun 23, 2011 15:51 |  #13

texshooter wrote in post #8590414 (external link)
A still small voice in the back of my mind tells me there must have been a reason why Canon added the AI Focus mode. I just can't figure out when it is better to shoot AI Focus over AI Servo.

Pretty much never. AI Focus is a "smart" mode that is really poor at what it does. I suggest forgetting the setting is even there and use either One Shot if you know your subject is going to be still, or Servo if you know it may move.


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fotocrack
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Jun 23, 2011 16:38 |  #14

Snydremark wrote in post #12646361 (external link)
Pretty much never. AI Focus is a "smart" mode that is really poor at what it does. I suggest forgetting the setting is even there and use either One Shot if you know your subject is going to be still, or Servo if you know it may move.

Do you have any pictures in the different modes? I have a 7D too and I have been using it pretty much have it on One shot all the time. Would try out the other and see what the difference would be. What would be the best way to test this?


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EL_PIC
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Jun 23, 2011 16:51 |  #15
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Mark_Cohran wrote in post #8590416 (external link)
It's been my experience that AI Focus isn't as intelligent as Canon would like you to think. If I need AI Servo, then I use AI Servo, otherwise, I use One Shot.

AI = Artifical Intelligence.
I think a photographer needs Natural Intelligence more that AI.
Same for Military Intelligence !


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AI Focus VS. AI Servo
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