AF Issue in AI SERVO.

I was recently on my local Rallying track, and there was a Race held, where I wanted to take some photos.

I used a 5D mk II, and the 70-200 2.8 IS II.

Car enters the picture, I start tracking it with the Center AF point, I can clearly see in the viewfinder, that the focus is spot-on,
from the moment I start tracking until the moment I press the shutter, and then it "jumps off".
(Mostly I find sharp piece of the road in front of the car.)

Before anyone says, that is an old AF system, I have been using this 9-point system for 4 years now! (40D, 400D)
Never had problems with it.

But that day it happend to me multiple times, and could not explain why.
Sadly I had no other lens by me, so I could not test if it is caused by the lens, or the Camera, or by myself.

Anyone had similar problems?!

Here is a picture, that has this issue:
In the top richt corner you can see, the car being OOF, and with green I marked the part of the picture, that is in focus.

AI Servo on the 5DII isn't the best, I rarely got satisfactory results using it.

I also use a 5Dii and have found out the hard way that its absolutely vital to keep the AF point totally nailed to the same part of the vehicle. Allow it to wander even a fraction while following the action and focus can be literally anywhere.

Other than that, mine is very successful for rallies, track events etc.

Lowner wrote in post #16145579
I also use a 5Dii and have found out the hard way that its absolutely vital to keep the AF point totally nailed to the same part of the vehicle. Allow it to wander even a fraction while following the action and focus can be literally anywhere.

Other than that, mine is very successful for rallies, track events etc.

Thanks for the tip Lowner, might be the case

What about, AF point expansion, and/or when all points are active?! - How does it work then?
Asking you, since you have more experience with it.

I tend to choose a single AF point, generally the centre point. To be honest I've not tried the alternatives.

The fact that the focus "jumps" when you hit the shutter suggests the AF is losing the plot while the mirror is up. The predictive AF is playing a guessing game between samples and losing.

Mike Deep wrote in post #16145940
The fact that the focus "jumps" when you hit the shutter suggests the AF is losing the plot while the mirror is up. The predictive AF is playing a guessing game between samples and losing.

I was also thinking on this, but what can be done about it?!
Also interesting is, that this is not constantly the case.

NemethR wrote in post #16145968
I was also thinking on this, but what can be done about it?!
Also interesting is, that this is not constantly the case.

Could it be that the car's changing its angle of approach and confusing the camera? In the 2nd pic the car's further around the corner and therefore further away from a predicted path...it's moving paralell (ish) rather than continuing perpendicular (ish).

NemethR wrote in post #16145851
Thanks for the tip Lowner, might be the case

What about, AF point expansion, and/or when all points are active?! - How does it work then?
Asking you, since you have more experience with it.

Unfortunately the 5D Mark II has the old style AF System which does not include AF Expansion and others found on 7D and and after. Also the Distance between AF points is greater as there are less. This was one of the reasons I opted out of the Mark II when I needed an additional body for 7D.

Nick5 wrote in post #16146032
Unfortunately the 5D Mark II has the old style AF System which does not include AF Expansion and others found on 7D and and after. Also the Distance between AF points is greater as there are less. This was one of the reasons I opted out of the Mark II when I needed an additional body for 7D.

Actually it does:

http://cpn.canon-europe.com …tions_explained​.do?page=6

However, it's probably not the best choice in a demanding AF environment.

Nick5 wrote in post #16146032
Unfortunately the 5D Mark II has the old style AF System which does not include AF Expansion and others found on 7D and and after. Also the Distance between AF points is greater as there are less. This was one of the reasons I opted out of the Mark II when I needed an additional body for 7D.

Actually this is why I've been shying away from the 6D as well (it lacks AF performance in a similar way) -- my experiments with AI Servo when I rented it -- in the condition where my dogs moving towards me -- had worse AI Servo performance than my 40D. I wanted something superior to move up. Sounds like the same issue as documented here.

I generally use AI-Servo (60D & 5D) with the center point only, and that requires me to keep that point on target. So far so good. Most of the misses are my fault, like AF point falling of the player and catching the background. Oh, I use BBAF exclusively. I think it is more natural to focus and expose separately.

Guys, before you say, 5D AF system is bad, etc...

I used, a 40D for 3 years, and before that a 400D.
Did not have this kind of issue with those cameras. Both have the 9 point AF system.

5D II has the same 9 point system + 6 hidden AF ponts (AF Point expansion).

The Actual AF system:

I photograph a lot of running dogs - I'll definitely say that the 5D AF (center w/or w/o expansion, BBF) leaves me disappointed 50% of the time. I've been experimenting with different techniques and I'm getting better, but I knew this would be an issue coming from my 7D prior.

I have wondered if the 5D2 shutter lag causes the AF (in Al SERVO) to mis-focus on objects moving toward the camera (example - running dog). According to: http://www.the-digital-picture.com …igital-Camera-Review.aspx the 5D has a 73ms lag, while the 40D (as you mentioned above) has a 59ms shutter lag.

Not much of a difference but when shooting at a wider aperture with a non telephoto lens, it could be enough for that 1-2 FT shift in your focus point on the subject. Now, I believe that the AF Al Servo probably has a "predictive" measurement, but this doesn't seem to cut it. Best part of the 7D was being able to adjust the sensitivity of the al servo - (crosses fingers for firmware upgrade).

Not much of a help of a reply - but just some of the things I've noticed.

I feel that my 60D's AF system runs circles around my 5D, in AI-Servo, anyway.