7d Question

Forgive me if this has been covered already (probably has) but I wasn't able to find it.

I frequently shoot birds in flight with a 50d. I always have the center point selected, and one of the problems I have is keeping it on the moving bird. As I understand it, the 7d has focus point expansion, which allows you to have the surrounding points "pick up the slack" when the selected point loses the subject. This sounds like it would be a big help to me, but I'm wondering if it really would be in actual use. I'd be interested in comments from those of you who've used this feature.

It's certainly what I use for birds. I've tried zone AF and AF point expansion, and while zone has its uses expansion is great for birds as long as you can keep the points on your target.

Have my 7D set up like that, also change the AF sensitivity down a notch else if you go off target it will go off looking for something else. This was a quick grab shot with those settings.

I use Centre point expanded all the time on my 7D for birds in flight. Works great. Seldom do I resort to zone settings.

i also use expanded centre point also helps more than hinders

I use Center zone and default AF speed and they have worked great. Still havent tried single Point expansion and dont really need to or want to as you have to keep the bird on that single point(or 5 ) I'd rather use nine...But thats just me. Here is a shot with using center zone AF.

IMAGE LINK: http://www.flickr.com …/83098356@N02/7​627272504/

I use expanded center point, or center zone. They both seem to produce pretty well the same results...
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They are different in principle. With a single point expansion, you always start tracking with the selected point. Then the camera can hand over to another point, if the starting point suddenly is way out of focus, which implies it's seeing the background at infinity or wherever it is.

With Zone AF, the point that's closest to you and has suitable contrast will be the point that starts tracking. You can't control where focus is initially accomplished.

A good thing with expansion is that you can use any of the 19 points as a starting point, so you can often compose properly on the fly, already in the viewfinder. You don't have to start with the center point.

single point expansion is great for shooting small BIF's

Joe52 wrote in post #14808281
single point expansion is great for shooting small BIF's

Great shots!

Still trying to shoot swallows here as well with my 100-400 and 1DMk2, with very little success. Nice shots Joe52
Just wondering what I could adjust to get more shots infocus, can or should I adjust AF sensitivity as well ?

Bsmooth wrote in post #14808830
Still trying to shoot swallows here as well with my 100-400 and 1DMk2, with very little success. Nice shots Joe52
Just wondering what I could adjust to get more shots infocus, can or should I adjust AF sensitivity as well ?

I have the AI Servo Tracking Sensitivity set to the slowest, on my 7D, I also use back button focus.

I don't shoot a lot of birds, but I used it AF Expansion to get these in Bermuda after failing several times with the regular center point.

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seems a common trend to slow the tracking down on the 7D, why is this?

When you are tracking focus, using Servo AF, the camera will keep on adjusting focus at the active AF point as long as focusing is active. This implies that if the camera finds that focus is a tad off, it will change over to the new setting, to bring the subject in focus again. There is a limit, though, for how much off the focus can be, before the camera thinks the AF point is no longer on the target. The camera accumulates statistics about the focus tracking while it's running, so it knows if it's likely that the subject is coming towards you at an easy speed, or if it has been approacing hastily while you were tracking. If now suddenly the active AF point says the subject isn't at all approaching any longer, but instead is very far away, perhaps at what the lens defines as "infinity", then it's very likely that the focus point is no longer covering the subject.

Now enters a time-out period, during which the camera is waiting for you to perhaps bring the AF point to bear on the subject again. It's this time-out you can change with the Custom function called Tracking sensitivity. Canon no longer officially tell us how long the time-out is, but they once did, for the 1D Mark II. The five different settings were then listed as 1, 0.75, 0.5, 0.25 and 0.125 s, with 0.5 seconds being the default setting.

If you are using expansion points, this time will not apply until all of your AF points, both the primary and the auxiliary points, have lost tracking of the subject. But the principle is the same.

Thus, when trying to take photos of birds that are flapping around in the sky in irregular patterns, it's likely that you now and then will loose them out of your sights. To let the camera wait a bit longer, before it sends the lens out on a large adjustment of focus, may improve the chance to get that bird back in focus again.

This also combines with some more settings for the AF, but it's pretty lengthy to go through them all, so I'll stop here.