AI Servo and nailing focus.

toadstool

toadstool

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Toni
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Is there a knack to it? I've used it a fair amount of times but getting focus nailed is coming more down to luck than anything else.

I've set up my camera so the focus points can be changed at the touch of the one button on the back but I'm still struggling - by the time I've got the right focus point selected and pressed back button focus, the moment is gone and my subject is also no longer where they were :lol:

I aim to keep my shutter speed at about 1/150 at a minimum with an aperture of about 3.2 when photographing kids.

Just wondering if there were any do's or don'ts I might not have stumbled on already - anything I'm missing (other than the shot I wanted! :lol:)?
 
Try leaving the camera on centre point focussing and then track the subject with the back button focus, then just press the shutter when you want to take the shot. I use AI Servo and BBF practically all the time and have a keeper rate in the high 80's percent on both my 5D3 and 70D. Try a faster shutter speed as well, you haven't said what lens you're using but AI Servo is mainly for action and 1/150 doesn't seem fast enough. I usually have mine set to a minimum of 1/250 for any action shots and much higher if possible.
 
That's what I was doing Stuart, keeping it centered. I then read an article where it suggests changing the setting of the focal points so they could be changed at the touch of a button and tried that out but it was the same - a really small keeper rate with luck playing a big part in nailing focus. I was using my 50mm 1.8 and tamron 28-75 2.8.

Anything faster than 1/150 wouldn't have been possible on my last try. My nephews 2nd birthday and my sisters house has the most awful light I've seen - she often has her lights on in the middle of the afternoon in the summer! And I'd left my flash back home (different country so couldn't just pop back and get it haha). I had to over expose by a good amount to get anything workable.

It was also my first play with the tamron - I'd just received it the morning I flew out. I've only ever taken photos of fast moving kids outside before where there was plenty of light so high shutter speeds was never a problem.
 
For sure AI focus is an acquired skill, depending onyour subject. My keeper rate with my 7D on birds in flight is nowt to write home about, but it is very rewarding when all comes together. I use AI focus for cycle racing too, but my keeper rate is much higher. Modchild is right in that you should use the very highest shutter speed you can (unless you want to blur wheels etc.) and don't be afraid to up the ISO as necessary and set your camera for high speed multiple shots too.

Focus systems work on a basis of predicting where your subject will be in the next frame or three, so you need to track with centre point for a second or two before pressing the button.

Practice is the key here.
 
My ISO was set as high as it would go - H (which I believe is 3200) and I do track whilst using the burst shooting mode. I guess, like you say, it will take lots of practice. I don't get much of a chance for that - the only time I use it is when photographing kids and the only kids I photograph are in a different country :P I think I might go out and shoot other things where AI Servo would be used just with practicing for what I want to shoot in mind.

I guess it's something I knew but needed confirmation. Thanks guys :)
 
You're using a camera that doesn't have the best AF in a situation so dark you need 3200ISO. I think we've found the problem.

Only your centre point has any chance, from there it's trial and error, don't expect a great return.
 
Thanks for the replies :) Still building my kit back up after selling to fund necessities when my mum was diagnosed with cancer so faster lenses are in the future :)
 
I'm not quite sure how people are making a connection between exposure time and AI servo functionality. It may be relevant to motion blur, but not really autofocus failure.

Toni - you mention that you are using 1/150th, but unless you let us know the focal length of your lens, this does not help much. For the record this should be good for up to 150mm with no SR.

AI servo function is very much down to your camera. You can help it by choosing to take the picture when the subject is moving or changing direction slowest. It is also usually helped by fast lenses.
 
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I always wonder what I should do when shooting kids in portrait mode on my 7D in servo mode, I tend to use the centre autofocus point but obviously then the kids face is central and not in the top 3rd of the image as I want it. Is it better to use the centre autofocus point focussing on the face/eyes, and recompose (will it still focus track?) or to use the right most point and track from there?

I guess to answe my own question the latter would be most obvious - I've found thr quick selection hard to get used to after not having it on my 20d for nie on 10 years!
 
Oggy said:
I'm not quite sure how people are making a connection between exposure time and AI servo functionality. It may be relevant to motion blur, but not really autofocus failure.
Click to expand...
I mentioned it because it's obvious from the OP's settings that he's taking pictures in seriously low light, which will definitely affect the AF performance. ;)
 
A_S said:
I always wonder what I should do when shooting kids in portrait mode on my 7D in servo mode, I tend to use the centre autofocus point but obviously then the kids face is central and not in the top 3rd of the image as I want it. Is it better to use the centre autofocus point focussing on the face/eyes, and recompose (will it still focus track?) or to use the right most point and track from there?

I guess to answe my own question the latter would be most obvious - I've found thr quick selection hard to get used to after not having it on my 20d for nie on 10 years!
Click to expand...
The outer AF points on your 7d are easily capable of tracking a child. Don't worry too much about changing AF points whilst shooting, the calmest method is to 2nd guess your AF point for the composition, then use BBF keeping that focus point over the kids face.
 
Oggy said:
I'm not quite sure how people are making a connection between exposure time and AI servo functionality. It may be relevant to motion blur, but not really autofocus failure.

Toni - you mention that you are using 1/150th, but unless you let us know the focal length of your lens, this does not help much. For the record this should be good for up to 150mm with no SR.

AI servo function is very much down to your camera. You can help it by choosing to take the picture when the subject is moving or changing direction slowest. It is also usually helped by fast lenses.
Click to expand...

Mentioned further up, I was was using 50mm 1.8 and tamron 28-75 2.8. As Phil mentioned, they're not the fastest lenses and I needed an ISO of 3200 plus over-exposure in camera to even get the speed of 1/150th - 1/160th. Not the most ideal conditions, bearing in mind my preferred style is what most would probably consider over exposed.

Like Andrew mentioned, by keeping the center focal point activated you're quite limited to a central composition but I guess that's a compromise with my camera - I understand the 5D doesn't function as well with the other focal points? From experience, the central focal point is much faster than the outer ones.

Here's an example. Focal length was 71mm, 2.8, ISO 3200, 1/160, +1 EV
10571149556_257eccc51f_z.jpg


And another with the same settings
10571110045_0360f13a7a_z.jpg
 
Apologies for the pedantry, but it's a focus point. A focal point is something else entirely. Again I'm sorry but it winds me up. :)

It's getting common misuse round these parts and will add to confusion for some people.
 
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