AI Servo mode - How does it work?

[Ken Nielsen]

I've seen the knowledgeable say here that AI Servo mode works for moving objects.

My user's guide for the Rebel XTi says that AI Servo mode can set the focus by targeting the center dot on the object you want sharp, hold the shutter button half-way down to set the focus and then shoot continuous frames. What it doesn't elaborate on is if that object moves, say toward you, does the focus follow the object while you are continuously firing off frames? The way the manual is written, it still seems to hint that you need to hold down the button half-way, for each new change of subject location.

It would be great if it knew to follow the subject you selected in the first place.

How does it actually work?

[400dabuser]

I think there is a point where the focus will stop focusing or be unable to focus, albeit, it will be at least a metre or slightly more near the lens

[Ken Nielsen]

I think there is a point where the focus will stop focusing or be unable to focus, albeit, it will be at least a metre or slightly more near the lens

Does that mean that it will focus, as long as it is able, on the moving object without my having to do any more than to continue shooting?

[400dabuser]

Does that mean that it will focus, as long as it is able, on the moving object without my having to do any more than to continue shooting?


Up to a point, if you leave it on AF, and the object is too close, it won't be able to focus therefore you won't be able to shoot anymore

[Ken Nielsen]

Up to a point, if you leave it on AF, and the object is too close, it won't be able to focus therefore you won't be able to shoot anymore

I understand that. My question was actually: "will it follow the subject and focus during continuous frame shooting without further intervention on the part of the user." I meant to imply that the subject is always within the normal focusing distances to the lens.

[400dabuser]

Should do, so long as you point it in the direction of the bird(s)

[Ken Nielsen]

Should do, so long as you point it in the direction of the bird(s)

Okay, I see you are having fun.

I will post this question elsewhere.

Thank You,

Ken

[Stormin_24]

Okay, I see you are having fun.

I will post this question elsewhere.

Thank You,

Ken


He's not having with you fun here, he's telling you like it is..

[davebreal]

my 40D never comes off of AI Servo Mode.

[Ken Nielsen]

He's not having with you fun here, he's telling you like it is..

Okay, It seems like bringing up that you need to be within the focusing capabilities of the lens would be a given. I'll leave it at that.

My question is about how the process works.

Back to my original question: The manual leaves off by saying you press the shutter button once to get the focus. This leads me to believe that if the bird flies toward you after you start continuous frame shooting that the focus follows the subject. Does the reading take place at the onset of each shot? Is the center point (used to get the first reading) used to determine the focal point for each subsequent shot? If so, then that point must remain on the subject as it is moving?

Thank You,

Ken

[davebreal]

this should answer all questions

http://www.shutterfreaks.com/Tips/CanonAIServo.html

[BradM]

Okay, It seems like bringing up that you need to be within the focusing capabilities of the lens would be a given. I'll leave it at that.

My question is about how the process works.

Back to my original question: The manual leaves off by saying you press the shutter button once to get the focus. This leads me to believe that if the bird flies toward you after you start continuous frame shooting that the focus follows the subject. Does the reading take place at the onset of each shot? Is the center point (used to get the first reading) used to determine the focal point for each subsequent shot? If so, then that point must remain on the subject as it is moving?

Thank You,

Ken

Ken, if you keep the shutter button pressed then AI Servo will continue to focus on the subject regardless if the shutter button is fully or half pressed.

The metering will be locked in at the initial half or full press of the shutter and won't change if you don't release and re-press the shutter. However this means you have lost the focus on the subject and the camera must re-acquire it. The metering is set based on what metering mode you have chosen and again does not change as long as the shutter is depressed.

That is why many of us will use the * or AF button with cn. F 4-3 set. With this technique you can continue to keep the subect under focus and as lighting changes a slight release of the shutter button and then re-press will result in having updated metering for the change in lighting. This pause can be as fast as you can release and re-press the shutter and new metering is set.

Even if you aren't shooting a burst of images you can pcik up focus on a subject coming into to where you would like to capture an image without being concerned that the metering is set for the point where you first picked it up.

Hope this helps answer your questions.

[sparker1]

What's the difference between AI Focus and AI Servo?

[Ken Nielsen]

this should answer all questions

http://www.shutterfreaks.com/Tips/CanonAIServo.html

"the predictive AF control works effectively from the first shot even with subjects moving erratically."

Thanks for that link. I'm guessing then, that the AF point is based on 'predictable' behavior of a moving subject, but also, somehow, can track erratic movement. I had one bird I was tracking that flew behind a few tall posts. Those posts were in line and in front of, for brief moments, with the subject flying behind. Would those foreground objects confuse the AF going on tracking the moving subject?

I'm sure I will learn with experience, but for now, wanted to gather info on the 'heart' of the system so I could shoot with it intelligently.

Thanks for all post here.

Ken

[Menelaus]

Maybe you should take your camera outside and take some test shots instead of theory crafting all day long :lol:

[Ken Nielsen]

Ken, if you keep the shutter button pressed then AI Servo will continue to focus on the subject regardless if the shutter button is fully or half pressed.

This answers my basic question.

Because of the narrow depth of field of longer lenses, understanding of AI Servo seems central to successful bird photography.

Thanks,


Ken

[Ken Nielsen]

Maybe you should take your camera outside and take some test shots instead of theory crafting all day long :lol:

You are right JohnnyNapalm. I've been doing that also, but results in continuous burst after focusing on the subject have gone wild with everything from the background trees to the bird itself coming into focus over several shots in the burst.

This made me come here to see if I could get a better understanding of how AI Servo works so I could use it successfully, the way it was designed to work.

[Menelaus]

I'm just busting your chops, man. I'd comment on the OP, but I've never played with Servo.

[dustyporch]

With my XTi, my experience says that anything coming between the camera and the subject will mess up the focus.

I also read something by Chuck Westfall from Canon the other day, which said that AI-Servo is not as accurate as one-shot....

[Marius B]

I recommend you to use back button focus, I love it. Use it on both my camera, and they are in AI servo, When you use back button focus, you start the focus by pressing the AF on or *, and you can stop focusing when you want it to, by letting go off the button.

[Ken Nielsen]

This is great input. Thanks again to each of you.

Marius B, I'll do it. You make it sound perfectly natural. A way to overcome what dustyporch says above.

[Ken Nielsen]

That is why many of us will use the * or AF button with cn. F 4-3 set.

I want to set my camera as Marius B indicates above.

I'm not sure which custom function I need to set, or if I need to set anything.

While I'm shooting, I want to hold the * button down at any time to engage Auto Focus (AF Servo) and by letting that button up, to turn AF off and hold the focus.

In looking at my C. Fn Custom Function settings, 03 is Flash sync. speed in Av mode and 04 is Shutter/AE lock button - I don't think either of these things is what I want.

Marius B, how do I set the * button to do what you say above?

[Marius B]

Ok, on my 40D its in C.fn. IV (Operation/Others) + 1 (shutter button/AF-ON button)

Set to 2 (Metering start/Meter + AF Start)

Then I have switched the C.fn. IV + 2

Set to 1
AF-ON/AE Lock button switch so I can use the * as AF (then it works on my grip aswell)

Sorry for my bad english, but do you understand?

[Marius B]

http://photography-on-the.net/forum/showthread.php?t=682381

[400dabuser]

He's not having with you fun here, he's telling you like it is..


:DAt least I tried my best

[Ken Nielsen]

You are a good fellow 400dabuser. I apologize for any misunderstanding. Here we are from all over the earth, but with a common interest. I hope you will accept my apology and that we can go on learning and enjoying by sharing our experiences in this wonderful craft.

Thanks,

Ken

[Ken Nielsen]

Ok, on my 40D its in C.fn. IV (Operation/Others) + 1 (shutter button/AF-ON button)

Set to 2 (Metering start/Meter + AF Start)

Then I have switched the C.fn. IV + 2

Set to 1
AF-ON/AE Lock button switch so I can use the * as AF (then it works on my grip aswell)

Sorry for my bad english, but do you understand?

Your English is very good. I see that you use Roman Numerals in one place for the number 4.

I will sit down in the quiet time this evening and ponder all of this. There are options to suit most everyone's particular working style.

I'm still thinking that I need to keep the center focusing point (the one that is used for the initial focus) on the subject as it is moving. This is hard to do when the subject is starting out small, heading toward you getting larger and larger. Plus the advent of a disruptive foreground object or two, makes it all quite challenging.

Quiet time with the camera tonight, then out shooting with this new found information tomorrow. Should be fun.

Thanks to all,

Ken

[Marius B]

Your English is very good. I see that you use Roman Numerals in one place for the number 4.

Ken

That's just because they've used roman numbers in the menu on the Camera :)

Good luck shooting.

Post nr 100!! Yoohoo!

[Ken Nielsen]

Post nr 100!! Yoohoo!

Party!

[canonloader]

Ken, first of all, that XTi is not even a prosumer model camera and the AF it has is not really first rate. I'm just telling you this because the next Canon model line up is a whole other experience when using AI Servo, and the 1D models, the next line above the XXD's is even better. Almost universally, one model is not even in the same league with the next. That's why people end up spending all their money on camera equipment.

In AI Servo, using any camera capable of it, and any USM lens capable of fast and silent focus, the lens should follow any object and keep it in focus if the object is coming closer or getting further away, and if the center focus point is kept on the subject. All the models need to follow that basic rule. But that's where the different models part ways. Your XXXD camera's AF is not the same as a XXD camera and will not do as good in all situations, like low light, low contrast situations, while the XXD model will. By the same token, the XXD will lose tracking if say a bird flies into a bush. Tracking will get confused by the branches and leaves and can no longer follow the bird, where a 1D will follow that bird right into the bush and keep focus on him "most" of the time.

I guess it's a matter of money and sensitivity of the built in AF mechanism. The more money you spend, the better the AF they put in the camera. It's like the old story of the breadcrumbs. In the end, if your a die hard hobbyist or professional, Canon will get all your bread. ;)

[Ken Nielsen]

Canon will get all your bread. ;)

Oh, Lordy.

I'm feeling the tug of the 5D MKII.

If I can scrape together the bread, this will be my next gobble on the road of endless breadcrumbs.

BTW, I'd rather spend all my money on camera equipment than on destructive addictions.

We are better off being photography slaves.

If you find me under the bridge, it will be because I'm waiting for the birds to fly by, not pink elephants.


Thanks for that input.

Ken