One last 7D focus issue to tackle ...

OK, you are in AI servo, BUT are you panning to follow the action or ae you holding the camera stationary? AI Servo attempts to calculate a rate that the focus point is moving towards or away from the camera and then extrapolate ahead to the time that the shutter is open. If the camera is being moved around while AI Servo is actively tracking a moving subject, the result can be unpredictable. If you do pan the camera, try to keep the camera motion smooth and steady. Also, erratic movement by the players can be much harder to track. You might need to adjust the tracking sensitivity. Whatever you pick as the focus point needs to be kept nailed in the focus box when using single point. Maybe try area or single point expansion if it is not reasonable to maintain the focus box nailed to a single point. Finally, make sure that the focus point presents a very sharp high contrast edge that is easy to focus on.

Auto Focus needs lots of light for accurate focusing. A night football game does not come close to the amount of light during the middle of the day.

What drive priorities are you using?

in C.Fn III.2 are you using setting 0? If not, and you have it set to any of the others, you may be losing focus as a result. Also, in 3.3, are you using just the main focus point priority, or the continuous track setting? I doubt that the latter has anything to do with it, but your settings in III.2 could be a factor

mikemo618 wrote in post #11201293
... in C.Fn III.2 are you using setting 0? If not, and you have it set to any of the others, you may be losing focus as a result. ....

True only for high speed shooting.

You are not alone. I have lost a lot of pictures of relatively simple things because my single point focus decides to focus on something else. I can get most all of my action shots fine, but simple walking shots are the most difficult for me.

Are you using only one focus box to insure that focus is not being handed off (like expanded or zone might)?Maybe if you tried spot focus (if you are only using one focus point) it won't drift as easily just a thought, as you are shooting large targets.

Based on your shutter 1/500, aperture f2.8 , and ISO 2500, you are trying to focus at too low of an EV for Ai-Servo. You are focusing in light with 7 to 8 EV which is kind of dim for Ai-servo and is causing AF problems. I bet if you use Ai-Servo in daylight it will be fine.

Snyderman,

When you say "Spot AF", do you mean "Spot AF"? Not the metering mode, which your EXIF shows to be "Spot". The two aren't related, right?! Not doubting you or trying to insult your intellect, just making sure we're all on the same page. Personally I use the "AF point expansion" mode for sports.

Garycoleman,

You're not giving the 7D enough credit here.. The shot below was taken with an f/4 lens. Here's the relevant EXIF information:

Camera: Canon
Model: Canon EOS 7D
ISO: 5000
Exposure: 1/400 sec
Aperture: 4.0
Focal Length: 300mm
Flash Used: No

snyderman wrote in post #11200987
Other than setting it to the slowest (to release a target) setting, what others should I be looking at?

Thanks!

dave

I don't have a 7D, but plan to get one soon. In preparation for that, I've been reading David Busch's book on the 7D, where he devotes an entire chapter to the 7D autofocus and the myriad of functions associated with it. From my reading, it is a very sophisticated AF system with a lot of controls. You have to know how all the functions work in order to get the most out of the system, or, in your case, to avoid unexpected results.

I think Bill Boheme and mikemo618 are on the right track. You should be looking at your custom function that are associated with autofocus, particularly in the AI Servo mode.

Custom Function C.FnIII-01 controls how the 7D's autofocus system in AI Servo AF operates when new subjects appear in the frame temporarily, perhaps passing in front of the subject you are shooting. As others have mentioned, you can set a Slow, Normal, or Fast reaction time for these situations.

Custom Function C.FnIII-02 allows you to specify whether the 7D should take a picture immediately when the shutter is release is pressed down all the way when using AI Servo AF (called Release Priority) or whether the camera should wait until sharpest focus is achieved before taking the picture (called Focus Priority). Here, the choice is essentially whether you want a picture at any cost, even if it might be slightly out of focus, or whether you're willing to miss the decision moment in order to achieve a sharper image.

Custom Function C.FnIII-03 can be used to tell the 7D to switch to a closer subject that appears in the frame, or whether to ignore close subjects and continue to track the original subject when using AI Servo AF mode. This function is used to control the camera's behavior when unexpected subject move into the frame. This control should be used in conjunction with C.FnIII-01 above.

To complicate things even further, the AI Servo AF in the 7D uses a technology called "predictive AF" which allows the 7D to calculate the correct focus if the subject is moving towards or away from the camera at a constant rate.

You may want to read the manual to understand these 3 custom functions, and perhaps play around with them to see how they behave for your shooting style.