Horizontal vs verticle focus issues

I have used my 85 1.8 on my 30d and this evening shot with my 200mm 2.8 on my canon 5D mkii. From what I can see focusing on both bodies always appears to me more accurate when I'm shooting my son's hockey games in a verticle orientation. Many more keepers as opposed to shooting horizontal. I am using the center point only and shooting in ai servo mode to track. I think the focusing technology is the same in both bodies. Does anyone have a clue as to why this Is happening. If there is nothing else in the frame except one kid, why should it matter which way the camera is held? Should I just use all focus points and hope for the best? It's not that cameras are way off but the verticle shots always razor sharp.

If you are using cross type focus points, in theory it should be similar. For non cross type points, it will definitely make a difference. I shoot 99% of sports in portrait (vertical) orientation because that is usually the best composition, if shooting tight crops.

When using lenses with max aperture of f/2.8 or better, the center point allows for higher precision in focusing. However, this is only for contrasts in one direction. The normal precision at the center point is supported by a cross-type point, but the added high precision by a linear one only.

The 40D is the first Canon EOS camera to support cross-type high precison at the center point. Only this year (2012) did that come to camera series like the 5D Mark III and 1DX.

Thanks for the tips. After doings bit of reading I figured out that my bodies both have invisible assist points. These points seem to be more effective in achieving focus simply cause of where they are. If the object is verticle and filling he frame, they fall directly over the subject when shooting verticle. In horizontal positing and verticle subject they don't cover vertically very well at all. At least is I know what to expect.

No, the 30D does not have any invisible assist points. But the 5D and 5D Mark II do have that. They have essentially the same AF specification as the 20D/30D, but add the six invisible assist points around the center point. Just remember that the assist points are active when using Servo AF only.

Thanks for that info, there sure is a lot more to this auto focusing technology then I thought. So am I better off to use all the points or keep Center one active only in ai servo mode?

That can't be said without knowing about the circumstances. With a 5D/5D Mark II, you have basically two options (now we are talking Servo AF only): Either you use one point, or you use all. If you use one point, then the center one is better equipped than the other points. If you use all points, you always have to start with the center point. Then, if that point looses track of the subject, the camera will check if any of the other eight points have something in focus at about the same distance as the subject was just a moment ago. If it has, tracking will shift to that other point. If not, the camera will or will not perform a focus search, depending upon the conditions and the camera settings.

Now on the 5D/5D Mark II, you can also enable the invisible assist points. Since they are clustered around the center point, you effectively get an AF point coverage that's approaching what the 19 point AF system in the 7D can give you, except the 5D/5D Mark II only offers linear AF points outside the center one. At least it's similar to using center point with expansion on the 7D. Since the assist points are grouped closer together than the other eight points, the probability that you can still track the subject with one of the assist points, when the subject is lost from the center point, is higher than it is if you can only rely on the normal eight non-centered points.

But which is best for a particular case is something you'll have to experiment to find out, or ask someone who has already done that, if you have such a person nearby.

Thanks, I'm gonna experiment and see what works best.