# What does AI-Focus do?



## keith204 (Sep 28, 2007)

I see three modes... normal, AI FOCUS, and AI SERVO.  I use AI servo a lot, and normal a lot.  What's AI FOCUS do?


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## Garbz (Sep 28, 2007)

Page 76 and 77 of your manual.


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## LaFoto (Sep 28, 2007)

Oh come on Garbz!
Please!
Tell *me* if you don't what to tell Keith.
I was so hoping that you, who you seem to know so much about the technical side of cameras and such, would GIVE the answer.
PLEASE DO!


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## TCimages (Sep 28, 2007)

AI Focus switches from one shot AF to AI Servo AF automatically if the still subjects start moving.


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## keith204 (Sep 28, 2007)

Garbz said:


> Page 76 and 77 of your manual.


 
you jerk...   no, not really...you've helped me on some other topics. 



LaFoto said:


> Oh come on Garbz!
> Please!
> Tell *me* if you don't what to tell Keith.
> I was so hoping that you, who you seem to know so much about the technical side of cameras and such, would GIVE the answer.
> PLEASE DO!


 
yeah! Thanks for backing me up, (what do I owe you?)



TCimages said:


> AI Focus switches from one shot AF to AI Servo AF automatically if the still subjects start moving.


 
great!  Whoa that's awesome!  I could really use this!  Thanks!


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## usayit (Sep 28, 2007)

LOL

"You Jerk", "Yeah!", "Great!" 

All rolled into one post.


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## Garbz (Sep 28, 2007)

LOL. Not my place to comment on a Canon , especially since I had to look at a pdf of the 40D manual to answer the question :er:

In reality though I didn't get it, which is one of the reasons why I posted like I did. AI Focus doesn't make sense to me. It's either one shot or continuous. Why bother having an extra mode if the subject starts moving. Surely a continuous servo could handle this like it does on the Nikons. The continuous would focus on the subject wherever it is if it's moving or not.


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## keith204 (Sep 28, 2007)

Garbz said:


> LOL. Not my place to comment on a Canon , especially since I had to look at a pdf of the 40D manual to answer the question :er:
> 
> In reality though I didn't get it, which is one of the reasons why I posted like I did. AI Focus doesn't make sense to me. It's either one shot or continuous. Why bother having an extra mode if the subject starts moving. Surely a continuous servo could handle this like it does on the Nikons. The continuous would focus on the subject wherever it is if it's moving or not.


 

I actually agree with you, now.  I tried it and it's not as cool as it sounds.

Ideally, when I'm shooting cars going around the track, it would kick into AI servo, then for victory lane, it would know... ok one-shot.   I am afraid it won't work as smart as it sounds.


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## WDodd (Sep 28, 2007)

Its page 70-72 in my manual 

I actually don't really understand that either. It says after you focus with the center focus point it will track your subject using the other AF points. But doesn't AF-Servo do that too?


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## neogfx (Jul 25, 2010)

AI servo is not ideal for a stationary subject as it constantly tries to refocus, this can lead to a slightly out of focus image if you hit the button at the wrong moment, this doesn't matter with a moving target as you have to constantly refocus anyway, that's the point. So for a stationary subject use One Shot Focus, you will get much better shots much more reliably. For a moving constantly moving subject use AI Servo as it allows you to track and constantly refocus on your subject.
AI Focus is for situations say like bird photography. A perched bird is best shot with One Shot Focus, however if that bird takes off it is best shot with AI Servo, AI Focus is supposed to handle this change where a subject can go from stationary to moving without warning.


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## LaFoto (Jul 25, 2010)

Wow, almost three years until we get a clear answer to this! I wonder if the OP is still around after all this time!?!?!


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## csgrafix (Jul 25, 2010)

LaFoto said:


> Wow, almost three years until we get a clear answer to this! I wonder if the OP is still around after all this time!?!?!


 
Didnt notice that at first 
lol that quote just put this thread @#1 for me.


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## neogfx (Jul 26, 2010)

lol Sorry, I don't come on here all that often anymore.


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## Taylor510ce (Jul 26, 2010)

neogfx said:


> AI servo is not ideal for a stationary subject as it constantly tries to refocus, this can lead to a slightly out of focus image if you hit the button at the wrong moment, this doesn't matter with a moving target as you have to constantly refocus anyway, that's the point. So for a stationary subject use One Shot Focus, you will get much better shots much more reliably. For a moving constantly moving subject use AI Servo as it allows you to track and constantly refocus on your subject.
> AI Focus is for situations say like bird photography. A perched bird is best shot with One Shot Focus, however if that bird takes off it is best shot with AI Servo, AI Focus is supposed to handle this change where a subject can go from stationary to moving without warning.


 The reason why you cant always use AI servo for stationary is if you commonly focus withthe release pressed half way and recompose ( which is typically how i shoot stationary subjects.) The focus will adjust when you dont want it to.


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## sovietdoc (Jul 26, 2010)

when you use AI focus, the little lights light up in the viewfinder, if you have it set to auto focus.  With AI servo, it will still pick the points of focus automatically, but the lights won't light up so you don't know where its currently focusing.  A slight downside I've found out.

Though unless you have a 7D or something higher, I'd stay away from auto focusing in most cases where it can be avoided.  It's simply terrible.


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## neogfx (Jul 26, 2010)

Taylor510ce said:


> neogfx said:
> 
> 
> > AI servo is not ideal for a stationary subject as it constantly tries to refocus, this can lead to a slightly out of focus image if you hit the button at the wrong moment, this doesn't matter with a moving target as you have to constantly refocus anyway, that's the point. So for a stationary subject use One Shot Focus, you will get much better shots much more reliably. For a moving constantly moving subject use AI Servo as it allows you to track and constantly refocus on your subject.
> ...


 
As I said in my original post, that you quoted, even if you don't recompose, AI Servo constantly refocuses anyway. With the amount of AF points on modern SLRs there should be little need to recompose. And of course, the main reason not to use AI Servo when shooting a stationary object is that it simply isn't designed for that purpose.



sovietdoc said:


> when you use AI focus, the little lights light up in the viewfinder, if you have it set to auto focus. With AI servo, it will still pick the points of focus automatically, but the lights won't light up so you don't know where its currently focusing. A slight downside I've found out.
> 
> Though unless you have a 7D or something higher, I'd stay away from auto focusing in most cases where it can be avoided. It's simply terrible.


 
I have a 7D and you can select the primary autofocus point for AI Servo. It will always focus on this primary point, but will also try to focus more points as well.


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