AI Servo -- how to use?

Started Mar 5, 2010 | Discussions
MPekala
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AI Servo -- how to use?
Mar 5, 2010

Hi all,

I'm not sure I understand AI Servo focusing. I try to use it when I'm photographing my kids on the move, but I'm not getting good results on my T1i.

I use only one auto-focus point (in the center) and, if I'm not mistaken, I have to keep the subject centered on that point and fully depress the shutter release. Or do you do a half-press to engage the AI Servo? Is there a way to focus-recompose-shoot with AI Servo?

Any instructions or links would be most welcome.

Thank you!

balloonchasers
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Re: AI Servo -- how to use?
In reply to MPekala, Mar 5, 2010

Yes you have to half press and keep half pressing before you take the shot. You don't have to keep firing but you do have to keep half pressing while keeping the focus point on your subject. So focus lock/recompose is not an option.

Rather than trying to learn how to use AI Servo with kids running around the room (which could make you dizzy!) I would suggest you try something outside. Maybe someone walking from one side of your view point to another. Then have them running or maybe riding a bike. It's all about gaining experience and learning.

I was trying my hand at panning last year while sitting on my front porch and taking pictures of the cars that drove through the neighborhood and found that AI Servo works better when you take mutiple shots in a row. So I am not sure how helpful it would be inside of a house with your kids running around in circles.

John
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balloonchasers
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Re: AI Servo -- how to use?
In reply to balloonchasers, Mar 5, 2010

Forgot to mention that some people use back button focus * especially when shooting in AI Servo:

http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=2286&productID=290&articleTypeID=5

It's there as an option and many people swear by it... but I have tried to use it and find it too cumbersome. To each their own.

John

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jrkliny
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Re: AI Servo -- how to use?
In reply to MPekala, Mar 5, 2010

I recommend the videos from a Canon representative on the B&H webpage. Open the BH webpage, click on Event Space, click More Videos and then naviagate to the 3 videos that deal with the Canon focusing systems.

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John McCormack
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jrkliny: Can't Find B&H Videos
In reply to jrkliny, Mar 5, 2010

Is the Ai Servo info. listed in a specific camera video title? I found the Event Space page but there is no "More Videos" link that I could find, nor is there anything specific to Canon focusing systems in the B&H videos list. Can you provide a specific link or more info. Thanks.

jrkliny wrote:

I recommend the videos from a Canon representative on the B&H webpage. Open the BH webpage, click on Event Space, click More Videos and then naviagate to the 3 videos that deal with the Canon focusing systems.

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007peter
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AI Servo works better with all 9 Points AF instead of Center Only
In reply to MPekala, Mar 5, 2010

MPekala wrote:

I use only one auto-focus point (in the center) and, if I'm not mistaken, I have to keep the subject centered on that point and fully depress the shutter release. Or do you do a half-press to engage the AI Servo? Is there a way to focus-recompose-shoot with AI Servo?

Shooting sports is very difficult, it take practice and experience. I'm still learning myself. So far, here are what I learned from my experience

  • AI Servo is most effective when you activated all 9 AF points. The reason is that your subject moves about too much. If you leave it in the center point, the camera will focus on the Bench, Wall, or Trees behind the players

  • AI Servo + Center = is more appropriate for portrait shooting with portrait prime like (50mm f/1.8, 85mm f/1.8 etc....). 90% of my portraits shots are in the center. I used AI Servo because my portrait lens have a very limited DOF, if my subject moves forward or behind, AI Servo ensure sharp focusing on my subject.

  • You have to Half-Press (in anticipation) of the shot. When the player moves into the composition you want. Hit the shutter and snap away.

I haven't master the button focusing yet. That is my next frontier. Good luck on practicing.

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jrkliny
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Re: jrkliny: Can't Find B&H Videos
In reply to John McCormack, Mar 5, 2010

After you click on Event Space from the home page, you will see a blank video view screen. The bottom right of the screen will show the button for More Video.

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MPekala
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Re: AI Servo works better with all 9 Points AF instead of Center Only
In reply to 007peter, Mar 5, 2010

Thanks, everyone. These are excellent tips. Can't wait to try them all out.

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John McCormack
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Re: jrkliny: Found Them. Thanks!
In reply to jrkliny, Mar 5, 2010

Very informative - and I've been shooting Canon for 25 years. Always something new to learn....

jrkliny wrote:

After you click on Event Space from the home page, you will see a blank video view screen. The bottom right of the screen will show the button for More Video.

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dslrdave
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Re: AI Servo works better with all 9 Points AF instead of Center Only
In reply to MPekala, Mar 5, 2010

i am confused with holding the shutter button half way down to focus. isn't that how one would normally take pictures?

i thought ai-servo allowed you to "lock" focus on a moving subject, so once you have half pressed the shutter button and "lock" on to the target, just keep pushing down on the shutter button and follow the target, allowing ai-servo to keep refocusing as necessary?

no?

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WilbaW
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Re: jrkliny: Can't Find B&H Videos
In reply to John McCormack, Mar 6, 2010

John McCormack wrote:

jrkliny wrote:

I recommend the videos from a Canon representative on the B&H webpage. Open the BH webpage, click on Event Space, click More Videos and then naviagate to the 3 videos that deal with the Canon focusing systems.

Is the Ai Servo info. listed in a specific camera video title? I found the Event Space page but there is no "More Videos" link that I could find, nor is there anything specific to Canon focusing systems in the B&H videos list. Can you provide a specific link or more info. Thanks.

Go to http://www.video.bhphotovideo.com/index.jsp?fr_chl=d252ff8377eeca37691a416d3926942ad6b34b00 and search for "A Look at The Canon Autofocus System".

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WilbaW
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Re: jrkliny: Can't Find B&H Videos
In reply to WilbaW, Mar 6, 2010

Actually just http://www.video.bhphotovideo.com/ works, then search for "A Look at The Canon Autofocus System".

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007peter
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B&H Video are Fantastic, more people should WATCH them
In reply to WilbaW, Mar 6, 2010

Wow, I'm watching the video as were speaking and I am blown away by its usefulness. Today with affordable DVD media, I'm surprise canon didn't include a Video Tutorial. I find these video far more educational than the stupid dead manual.

The speaker does a wonderful job of explaining AI Servo and why we don't leave it on all the time. Outstanding. Worth watching 100%

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jrkliny
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Re: B&H Video are Fantastic, more people should WATCH them
In reply to 007peter, Mar 6, 2010

I also recommend looking at some of the other videos. I especially recommend the video called "Illuminating Creativity."

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henryp
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Re: B&H Video are Fantastic, more people should WATCH them
In reply to 007peter, Mar 8, 2010

Thank you. We're very glad you find them so useful and we're very gratified you took the time to say so.

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Henry Posner
B&H Photo-Video

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007peter
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Keep up the Good Work B&H - suggestion making VIDEO more prominent
In reply to henryp, Mar 8, 2010

henryp wrote:

Thank you. We're very glad you find them so useful and we're very gratified you took the time to say so.
Henry Posner
B&H Photo-Video

Henry I think you and B&H photo for providing these video. They're are wonderfully educational. I would like to suggest you revamp your WEB SITE in order to make these VIDEO more prominent. While they are very educational, they are very difficult to find. For example, I cannot create a short web link to the Canon AF system Part1/3 video. I must do the video search.

Another suggestion is: making Canon AF System VIDEO a Mandatory watch before a customer is allow to RMA their camera back. The more I watch the video, the more I realized all these focusing error complains on 7d/50d forum are usually user error.

I learned one thing that I didn't know about AI SERVO is that you must Start Tracking with the Center AF 1st, before the camera will follow the subject . I didn't know this. I just assume the AI Servo will track whatever subject that is moving in my screen. Manual didn't say anything about the subject has to be in the center 1st for the tracking to be effective. I bet, most people didn't know this either.

I had always thought my 30d has poor AI servo performance, now I know its me who made the mistake.

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John_A_G
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what is happening
In reply to dslrdave, Mar 8, 2010

dslrdave wrote:

i am confused with holding the shutter button half way down to focus. isn't that how one would normally take pictures?

i thought ai-servo allowed you to "lock" focus on a moving subject, so once you have half pressed the shutter button and "lock" on to the target, just keep pushing down on the shutter button and follow the target, allowing ai-servo to keep refocusing as necessary?

no?

If you are in one-shot and half-press and KEEP it half pressed, the camera does not change focus - the lens will only focus one time at the initial half press. Keep it half pressed for 5 seconds and the focus will never change.

With AI-Servo, the camera/lens does indeed try to lock on to a subject. If you have just a single point enabled it will focus on what is behind that point and not only continuously re-focus but PREDICTIVELY refocus - this is where the speed of the system comes into play. The camera calculates where it thinks the subject WILL BE based upon the subject's motion so it can "cheat" the focus a bit.

If you enable all points it does the same EXCEPT it will allow for the subject moving from point to point. But this is still an educated 'guess' by the camera. Sometimes it thinks your subject moved from one point to the next but it didn't, the camera simply picked up a different subject. It's not smart enough to know the difference between your kid and the tree so when you use multiple points some times the camera switches to the wrong subject.

As for whether to use all points or just center there are a couple things to consider:

First, the situation I described above - the camera can get confused. Have two kids playing together - it can be tough for the camera to know where one subject ends and the other begins so it can track the 'wrong' subject - or switch to the background.

The second aspect is: not all focus points are created equal in the Canon system. You have cross-type sensors and high precision sensors. You can do searches to find out about these topics. But, in all canon dslrs the center point is most accurate (both cross type and high precision). In the 1 series, you have many points that are cross type and high precision. But below that, to my knowledge NONE of the non-center points are high precision. Depending on camera model, some of the non center points may be cross type.

Third - shallow dof - if you are shooting with a shallow depth-of-field - for instance using an 85mm 1.8 lens - it's entirely possible the entire subject cannot be in focus. You don't want the camera focusing on a swinging arm. Using a single center point will help ensure the RIGHT part of your subject is in focus.

One of the reasons many people struggle shooting action though with people is they frame WAY too loosely. That makes it very difficult to keep a focus point on your subject. Framing tighter really helps keep your focus point on your subject and helps ensure good results.

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MPekala
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Re: what is happening
In reply to John_A_G, Mar 9, 2010

I agree with everyone that these videos are terrific. What a find! I also note that the video on Autofocus adds a lot of fuel to the fire on the debate about focus-recompose-shoot and the resulting soft images!

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WarCow
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Re: AI Servo -- how to use?
In reply to jrkliny, Mar 9, 2010

Brilliant videos! I had no idea there was so much to learn about the AF system

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007peter
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User Error vs Faulty Camera Debate!
In reply to MPekala, Mar 9, 2010

MPekala wrote:

I agree with everyone that these videos are terrific. What a find! I also note that the video on Autofocus adds a lot of fuel to the fire on the debate about focus-recompose-shoot and the resulting soft images!

Yup, I learned the hard way that Focus-recompose doesn't work as well anymore. For me, the these video settle the User Error-vs-Faulty Camera debate. I would estimate as high as 80% of camera return are the result of users not knowing how to use AI SERVO.

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