AF Setting for Windsurf Photography with difficult background

[jcmorin]

Hi,
I'm having trouble to get a decent amount of sharp images of Windsurfer when shooting in front of a stone background.
Setup: EOS 40D, with 100-400mm, Manual setting on 1/1000 and max opening (4.5-5.6).
Pics are taken in stormy condition with wind and water blowing around.

First day I used AI Focus, with singe point: All pics taken at 100mm where sharp all pics at 400mm where not realy sharp, but not to bad.

Second day I used AI Servo, with multiple points: 50% of the pics where realy sharp (better than the ones on day one) , 50% of the pics where really unsharp. And as you can see on the posted pics, in one sequence the pic could go from sharp to unsharp alltough the surfer was in the middle of the frame.

What should I do:
1. Use AI Servo with single point: (Not easy to target the surfer)
2. Use AI Servo with multiple points and try to targen the surfer earlyer with the center point.
3. Get a 400mm 5.6 prime and a 70-200mm 2.8 instaed of the 100-400mm
4. Get a 1D MkIII

Sequence below are taken at 400mm 1/1000 5.6 with AI SERVO, multiple points (the pics a following each other in the same sequence).

[DDCSD]

Welcome to POTN!!!

The problem that you are having is keeping the AF point pinned on the target. One way to help remedy this would be to try and get closer to your target so that you can fill your frame more with your target. I understand that this likely isn't possible.

I would forget about AI Focus completely. It isn't all that good at choosing when to use the correct focus mode. AI Servo is what you want to use.

Use only the center point and practice keeping it pinned on your subject. Technique is important. I would also set the camera to Single Shot. Shooting bursts makes it tougher to keep that AF point on top of your subject, especially when the subject is moving erratically.

I think you'll be just fine. 50% sharp shots is actually a pretty decent keeper rate in a situation like this and with a little bit of practice with your timing and technique you'll be getting a lot better percentage than that.