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Guys, question. When shooting in AI Servo, should I set my AF points to be ALL? Usually in One Shot I'm using the center AF sensor

With AI servo, im using this for fast moving objects..

I use centre point only (or another point if i want to offset the item im tracking in the frame)

I wouldnt go with all points, unless the opbect youre tracking will fill the whole frame.

or unless you own the Mark III

I need to start panning and so on, never used this shooting style as all my shots are static.

For rally and drags, i use centre point only, and haven't had any real problems. I am led to believe that it is the best point to use, unless you have 2.8 or wider lenses.

Tristan

All my lens are f2.8 or faster (F2 & F1. so I can use all the AF points?

Ive never heard that before????

2.8 or faster glass allows the extra 6 sensors around the center point to activate for more accurate AI tracking. on a 5d.

1d's are able to do it up to F4

Sweet. So its glass dependant, not aperture dependant?

So if I set my 70-200 F2.8 @ F4, it would activate right on a 1D? or would activate on F2.8 on a 5D

Kris wrote:Sweet. So its glass dependant, not aperture dependant?

So if I set my 70-200 F2.8 @ F4, it would activate right on a 1D? or would activate on F2.8 on a 5D

Its glass dependent, any glass you have mounted will always be completely wide open when you look through the viewfinder and when using auto-focus.

So even if you select F4 on your 70-200 2.8, the lens is kept open @ 2.8 until the very moment of exposure, lens stops down, shutter blind lifts.

If you hit the DOF preview button at F8, you'll see how dark the viewfinder gets

centre point AF, AI servo or AI Focus, continuous drive and blaze away

Thanks guys!

DanINqld wrote:2.8 or faster glass allows the extra 6 sensors around the center point to activate for more accurate AI tracking. on a 5d.

1d's are able to do it up to F4

What about on a poorman's 400D? Is this feature only available on the 5D and above? And is it applicable to Canon 2.8 lenses only? What about third party "fast" lens such as Sigma and Tamron?

ssschen wrote:What about on a poorman's 400D? Is this feature only available on the 5D and above? And is it applicable to Canon 2.8 lenses only? What about third party "fast" lens such as Sigma and Tamron?

No, the f/4 is strictly a 1-series feature - the 5D won't do it, neither will the 400D. Cheaper cameras will work better with f/2.8 glass, but that's relative to their performance with slower glass, you don't get 1-series performance from a 400D by using fast glass.

Yes, it's purely aperture, not brand. But Sigma etc are often slower to focus than Canon L lenses, so while the camera might be asking for focus, the question becomes whether the lens can get there fast enough.

What you do get with fast glass on the 20D/30D/5D is 1/3 DoF focus accuracy, I'm not sure if the 3-digit bodies do that at all.

The other thing is that if you only have 9 focus points servo focus is limited just by not having as much information about what's going on. The 1-series cameras with their 45 focus points can track stuff moving in the frame a lot better, so that predictive focus becomes a much more reliable thing. Again, I don't know if the cheap bodies even have predictive focus, let alone how well it works.

Excellent read this one!

Thanks for posting this Kris.