7D and AL servo ?

Quick question,

Once you get a focus lock on a moving subject and continue holding the shutter button halfway down do you have to keep the focus point on the moving subject or will the auto focus track on its own. Example you have one bird flying by and the camera is fixed on a tripod and flies right over your focus point to at which time you hit and hold focus, will the bird stay in focus as it flies across the screen or do you have to follow it with the focus point held on the bird and move the camera. Does this make sense?

When I currently use al servo I have always tried to keep my focus point on the moving subject at all times. However while trying to compose a fast moving shot some times my focus point is set to the wrong spot which forces me to get a focus lock on the subject then recompose. This is the reason for the question.

AL servo has been a slight gray area for me. Now with kids in sports I want to be sure I am understanding the true Bennie's of al servo. I have been experimenting in the custom menu's and am really liking the control this camera offers

Depends on the AF area selection mode you have chosen (in custom functions). For what you want to do, you'll probably set it to 19-point auto-selection. In AI Servo mode, you can pick which of the 19-points to start tracking from.

Also, probably want to decouple AF from your shutter button and use the dedicated AF on the back. Look up back-button focusing.

-alex

I am using back button auto focus and AF point expansion however, I read when using the al servo mode the camera does not switch to the expanded points. The camera only switches to the expanded mode when using One- Shot AF

jlstan wrote in post #16271805
I read when using the al servo mode the camera does not switch to the expanded points. The camera only switches to the expanded mode when using One- Shot AF

I don't know where you read that, but it is 100% wrong. Only in AI Servo will the camera switch to different focus points if the subject moves.

hollis_f wrote in post #16272448
I don't know where you read that, but it is 100% wrong. Only in AI Servo will the camera switch to different focus points if the subject moves.

I read it in David Busch's Canon EOS 7D Guide to digital SLR Photography book, I questioned that too when I read it...thought it was a backwards definition

jlstan wrote in post #16272450
I read it in David Busch's Canon EOS 7D Guide to digital SLR Photography book, I questioned that too when I read it...thought it was a backwards definition

It must have been a typo/misprint that got through editing because it is completely backwards.

To track a moving object (which could be moving towards you or away) must, by definition, require the AF system to keep focusing to adjust for any changes in distance to subject. That would be AI servo, not One shot.

hollis_f wrote in post #16272448
I don't know where you read that, but it is 100% wrong. Only in AI Servo will the camera switch to different focus points if the subject moves.

I think there may be two different things going on here. The OP said he read that in AI servo you cannot switch to to expanded points. I interpret that as switching from say single point focus to expanded before you even start to shoot. Which by the way you canin AI Servo.

Also like you said, depending on focus mode you select in AI Servo the focus points will switch as it tracks. If you set it to single point it will not change focus points automatically. The user can do that manually.

Of course I can be wrong with my interpretation of what the OP was saying.

My real question is, there must be a active focus point on the moving subject at all times while using AL Servo to render crisp focus correct?

If using a single AF point, I would have to keep that point on the subject myself as the subject moves across the screen seeing there are no other available points for the camera to choose. So if I were then to switch to say 19 point auto focus, shift my focus point to the extreme left and lock focus on my subject as it entered my screen on the left and did "NOT" follow the subject with the camera the focus point would shift across the screen as the subject passed across each point. Am I correct in that thinking?

Does that make sense?

jlstan wrote in post #16274205
...So if I were then to switch to say 19 point auto focus, shift my focus point to the extreme left and lock focus on my subject as it entered my screen on the left and did "NOT" follow the subject with the camera the focus point would shift across the screen as the subject passed across each point. Am I correct in that thinking?

Does that make sense?

Yes. What you said above is exactly how AI Servo with the 19-point auto-selection mode works.

-alex

jlstan wrote in post #16274205
My real question is, there must be a active focus point on the moving subject at all times while using AL Servo to render crisp focus correct?

Yes. As long as AI servo is active (you are half pressing shutter button or pressing the AF-ON button) it is constantly focusing, so if the focus point isn't over the subject then it will be focusing on whatever the AF point is pointing at - which may be a distant tree or someone several feet behind your intended target.

Yes.