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AI Servo - what is is for?

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peter008

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I'm still confused about AI Servo.

There is single shot AF and continous AF, simple enough. But why AI Servo?

If I select continous AF and object doesn't move, focus shouldn't move either. If the object starts moving, focus should follow. So what is the purpose of AI Servo? When I should use it instead of continuous AF?
 
With single shot, half pressing locks the focus on the subject, allowing you to focus and recompose if needed.

With continious AF, when you are half pressing, the focus updates as you move the camera, meaning you can't lock focus and recompose.

AI Servo technically gives the best of both worlds. When it works.

--
http://www.picturepunk.com
 
peter008 said:
I'm still confused about AI Servo.

There is single shot AF and continous AF, simple enough. But why AI
Servo?

If I select continous AF and object doesn't move, focus shouldn't
move either. If the object starts moving, focus should follow. So
what is the purpose of AI Servo? When I should use it instead of
continuous AF?
Click to expand...
One Shot stops when it confirms focus and will not refocus unless you let up then half-press the shutter button again (or * or AF-ON, depending on CF configuration). AI Servo is continuous focus. So long as you have the shutter button (or * or AF-ON) half-pressed, it will continuously analyze and adjust focus. It also incorporates predictive focus, anticipating where a moving subject will be when the shutter actually opens. AI Focus is a combination of the two and doesn't work as well as either. It starts in One-Shot and will switch to AI Servo if it senses the subject has moved out of focus. It should be avoided. AI Focus is not included on professional models.
 
If you are in continous AF mode and the subject moves (and you have a single AF point selected) then your focus will jump to the point behind where the subject was initially, once it has moved away from the AF point.

With multiple AF points, the focus may or may not stay with the moving subejct, depending on what mood your camera is in ;)
peter008 said:
how does the camera know it's camera that's moving and not the subject?
Click to expand...
--
http://www.picturepunk.com
 
AL Servo detects movement by the subject and switches to continuous focus. Useful when you anticipate that the subjecy may start moving at a moments notice.

Why AI Servo ? Because in cont AF the lens and the battery are always working to maintain focus with every tiny bit of motion.
--
Guillermo
 
... AI Servo (original poster really meant AI Focus) works well for focus-recompose, as it will compensate for the known problem of the subject drifting slightly out of focus as you recompose. All you need to remember that AI Servo locks on with the center point first, and to recompose slowly enough for the helper focus points to lock on as you shift. It works well enough that I leave my 5D in AI Servo (continuous AF) mode most of the time.

I don't know what AI Focus is good for. I've never used it, at least not intentionally.
--
Street: http://www.wonderworks.com/streetphotographydigest.html
Flickr: http://www.flickr.com/photos/kyle_jones/
 
I think you are confusing Ai Focus AF and Ai Servo AF. Ai Servo AF is continuous focus, 1/2 press the shutter and keep it pressed and the focus constantly updates itself against the focused subject. Ai Focus AF acts as One Shot on still subjects and switches to Ai Servo AF once the focus sensor detects movement in the subject. On the 30D, the Ai Focus AF did not work very consistently. I haven't tried Ai Focus AF on the new 40D yet, I just use Ai Servo AF, which can also work as One Shot if you transfer focusing to the AF-ON button, as soon as you press and then release the AF-ON button, focus locks on your subject.
--
Cheers,

Bryan P.

OneDMarkTwoN, FortyD, ThirtyD, ASixThirty, ASixForty, ASevenTenIS
http://www.flickr.com/photos/29386469@N00/
http://blplhp.smugmug.com/

The best thing that could poke you in the eye....is your viewfinder.
 
ok ok, there is a lot of misinformation in this thread.

ONE SHOT - focus setting for stationary subjects. You're telling the camera, this subject is NOT going to move. It locks the focus when it beeps.

AI FOCUS - idiot mode for those who have no idea how to work a camera. alternates between one shot and ai servo without your knowledge.

AI SERVO - continuous, perfectly fine for moving subjects. It also works fine on stationary subjects, fwiw, but it won't lock.
 
triple said:
ok ok, there is a lot of misinformation in this thread.

ONE SHOT - focus setting for stationary subjects. You're telling the
camera, this subject is NOT going to move. It locks the focus when it
beeps.
Click to expand...
Agree.
triple said:
AI FOCUS - idiot mode for those who have no idea how to work a
camera. alternates between one shot and ai servo without your
knowledge.
Click to expand...
Totally agree here.
triple said:
AI SERVO - continuous, perfectly fine for moving subjects. It also
works fine on stationary subjects, fwiw,
Click to expand...
Agree here, too.
triple said:
but it won't lock.
Click to expand...
On the surface, this is true. But you can force Ai Servo AF to lock focus on a stationary object by transferring focus to the * button or the AF-ON button. Press and hold the * or AF-ON button, and then as soon as you release the button, the focus will "lock". You not get any beeps or red outlined focus boxes, but the focus will lock. Press the shutter button to take the picture. In this way, Ai Servo AF works not only as continuous focusing, but it also works as One Shot. This is a much better alternative than using the quirky Ai Focus AF. :o)
--
Cheers,

Bryan P.

OneDMarkTwoN, FortyD, ThirtyD, ASixThirty, ASixForty, ASevenTenIS
http://www.flickr.com/photos/29386469@N00/
http://blplhp.smugmug.com/

The best thing that could poke you in the eye....is your viewfinder.
 
Hi Chris,

What do mean?

Ai Servo AF is for tracking moving subjects, which is something Image Stabilization is not used for, unless you are tracking a moving subject in low light and your shutter speed is dangerously close to your focal length and you are worried about camera shake as you pan the camera to follow your subject (and even in that case, you would have to use Mode #2 on the lens).

But I'm not sure what you mean when you say, "can I use Ai Servo AF like IS".
--
Cheers,

Bryan P.

OneDMarkTwoN, FortyD, ThirtyD, ASixThirty, ASixForty, ASevenTenIS
http://www.flickr.com/photos/29386469@N00/
http://blplhp.smugmug.com/

The best thing that could poke you in the eye....is your viewfinder.
 
The AF mode (3 modes) has been confusing me for a while. I used to rely on manual focus with Pre-Focus subject, especially when shooting moving subject such as kids, sports, or weddings [lots of movement]. Basically, i need to estimate the distance between the camera and subject, know the depth of field for the lens i use. All i need to do is get exposure, pre-focus and keep moving with the subjects until it falls within the range i want , then shoot. Those things are what i learned from school and friends. Pro always carries at least 2 cameras when shooting event with lots of movements.

being said that, i still prefer AI Servo AF with * button to lock focus when shooting moving subjects
 
hvu said:
being said that, i still prefer AI Servo AF with * button to lock
focus when shooting moving subjects
Click to expand...
IMO, that's the only way to go. With the 40D, you can use the * button or the AF-ON button. And just as a point of clarification, with Ai Servo AF, you really don't "lock" focus, you acquire focus, because the focus keeps changing (as long as you have the * button or AF-ON button continually pressed). It will only "lock" focus if you release the * button or AF-ON button. :o)
--
Cheers,

Bryan P.

OneDMarkTwoN, FortyD, ThirtyD, ASixThirty, ASixForty, ASevenTenIS
http://www.flickr.com/photos/29386469@N00/
http://blplhp.smugmug.com/

The best thing that could poke you in the eye....is your viewfinder.
 
Hi Bryan,

I was wonder since AI Servo tracks moving subjects when you're/camera's still wouldn't it also track a still subject with me moving, hand shaking? It's kind of like the opposite of what AI Servo is for.

Thanks!
Chris
 
Single shot AF can give sharper results for still objects because Servo AF's very nature is to minutely adjust focus all the time to see if the scene gets sharper (even on a still object).

You can often hear the AF motor buzzing and clicking a tiny bit when holding down the focus engage button while pointing at a stationary object in servo mode.

This can be fine when the AF point is over a detail of high contrast, but you could fire the shutter when the AF is in one of these little flicks of the focus and get a slightly softer shot than single shot AF would have provided. It doesn't matter if you have the AF set to the * button and use it to lock AF by letting go of it, because you could let go of the button also when the AF is searching for sharper contrast also.

I still leave my camera in AI Servo if theres any chance of moving subjects around me, especially on my 1D as the servo is more reliable. But when i know ill just be shooting completely stationary objects i change to single shot.
 
BryanP said:
I just use Ai Servo AF, which can also
work as One Shot if you transfer focusing to the AF-ON button, as
soon as you press and then release the AF-ON button, focus locks on
your subject.
Click to expand...
Interesting...I never though of using AF-ON that way. Most of my shooting is with AI Server but at times I want to quickly get to One Shot.

I am assuming you set C.Fn IV-1 to 1 to accomplish this?
 
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