# AI Servo Question



## nehemiah (Mar 3, 2012)

Hello. It's my first post and am asking for your help on what may be a fairly basic question.

I have a 7D. I have the custom functions set so that the "AF-ON" button in the back is my focusing button (not the halfway pressed shutter button -- that has been disabled). 

I have some questions re: AI Servo. 

1) Do I need to keep the "AF-ON" button pressed the whole time I am shooting?
2) If I start the subject (with the subject in motion) focused (using expanded focusing -- the five squares) -- if I want to place the subject (for compositiional reasons) outside the 19 focusing areas, say at the extreme side, is the AI Servo still able to follow the subject? If it can be done, how would I do it? Do I still keep the "AF-ON" button pressed the whole time even if my subject is not near the focusing squares?

Sorry if this is very basic. Would appreciate your help.


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## Timothy_Bruce (Mar 3, 2012)

1. You have too keep it pressed. The Camera will stop focusing the moment you release it.
2. You just can track a subject when it is in an area with AF-points. Not outside the 19 point frame. 

I would recommend you to get the shutter for AF back again and take the "AF-ON" Button as AF-OFF and just lay your thumb on to it when you want the 7D to not focus. 

hope this is helpful


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## Crapking (Mar 3, 2012)

http://learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml?categoryId=121

Try reading this simple explanation of how to best use the back button AF - very helpful.


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## Mt Spokane Photography (Mar 3, 2012)

Different people set the buttons differently, thats why they have the options, there is no "Right Way", just what works for you.

Try the different settings to see if you prefer one over the other. You must keep the button depressed while in AI Servo, but its easier than holding the shutter halfway, particularly if you are moving around.

The camera will focus on the closest point if all points are active, otherwise it focuses on the active point. If your subject is not under the active point, something else may be in focus.


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## nehemiah (Mar 4, 2012)

Thank you for the replies. I found all three responses helpful, and did read the helpful article at the link.


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## papa-razzi (Mar 4, 2012)

With AI Servo using the full 19 focus points, you can select a single focus point that the camera will begin tracking focus with. As the subject moves through the frame the other focus points will pick up the subject as it moves behind them. For example, if you are tracking an actor on a stage who moves from one side to the other and you always want to keep the whole stage framed - then this would be a good approach.

If you can pan the camera to keep the subject in the same area of the frame, then it is better to use a single point only, or an expanded single point. For example if you were tracking a bird in flight.

If you use Zone AF with AI servo, then you can't select a starting focus point, so the camera will pick the closest subject in the zone, just as it would with single shot. However, if the chosen subject moves within the zone, then the other focus points will engage when the subject moves behind them.

If a subject moves outside of the focus point(s) you have activated (i.e. outside the zone you have selected) then the camera cannot focus on it further.


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## nehemiah (Mar 4, 2012)

papa-razzi said:


> With AI Servo using the full 19 focus points, you can select a single focus point that the camera will begin tracking focus with. As the subject moves through the frame the other focus points will pick up the subject as it moves behind them. For example, if you are tracking an actor on a stage who moves from one side to the other and you always want to keep the whole stage framed - then this would be a good approach.
> 
> If you can pan the camera to keep the subject in the same area of the frame, then it is better to use a single point only, or an expanded single point. For example if you were tracking a bird in flight.
> 
> ...



Thanks Papa. This was very helpful as well and addressed an issue I had thought about (re: panning vs still) that I had been thinking about. So thanks again.


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