20D backfocus problem gets worse the more shots I shoot.

Just Bob

I am pretty convinced I have a backfocus problem. Please tell me what you think.

Here are the details.

20D
135mm f 2.0 L
1600 iso
Good lighting at a hockey game. (it actually is pretty good lighting)(brand new lights)
1/800 @ f 3.5 or 1/640 @ f 4.0 (mostly the settings I shoot).
AI Servo with CF4 set to 3
Monopod mounted.


I am focusing with CF4 set to 3, so I am not "following" the subject and expecting the camera to track. I usually focus at a point about 5 feet in front of the crease (me looking into the goal), lock the focus there, and shoot a sequence when the action is right. I use AI Servo for when I need to track a player, which is not that often. I am usually focused at one point near the goal.

When I am about 125 feet away, it backfocuses about 8-10 feet behind that.

When I am about 50 feet away, the back focus is about 4-5 feet behind where I focused.

I also noticed that the problem seems to get worse as the game progresses. I will shoot about 400 frames during a game and the photos towards the end seem to be worse than at the beginning of the game.

Does this sound legit? Could I possibly be doing something wrong?

The camera is well past warranty. Do I need to send the lens with the body to Canon? Any ideas on cost and turn-around time?

Any advice is greatly appreciated.

Thanks in advance,
Bob

aktse

Can you post some example photos? It's difficult to answer without seeing the real problem.

Also, what AF points are you using?

ziggy53

Bob,

Is there a gallery we can look at with full sized images demonstrating the problem?

How many focus points are you using? (You mention "I am usually focused at one point near the goal.", but I am not clear if that means you only used one focus point or not.)

PS I have to learn how to type faster. Thanks Aktse!

Just Bob

Hello all,

Unfortunatly I am at work goofing-off, so I don't have images on hand to post.

To clarify:

I focus on a stationary player (AI Servo, One Shot, or Manual) it doesn't seem to matter (same backfocus issue), at a set point on the ice with the center autofocus point, and I am fairly consistently seeing the actual focus several feet behind where I focused.

I verified my focus points in EOS viewer and I am correct on where I know I am taking a focus point.

It definately seems worse the more shots I take.

I hope this answers some questions.

I will try to post some photos tomorrow.

Thanks again,
Bob

kdog

What happens if you simply focus at a completely stationary object like a tree and take the picture. Still backfocuses?

Regards,
-joel

aktse

Just Bob wrote:

...I focus on a stationary player (AI Servo, One Shot, or Manual) it doesn't seem to matter (same backfocus issue), at a set point on the ice with the center autofocus point, and I am fairly consistently seeing the actual focus several feet behind where I focused.

I verified my focus points in EOS viewer and I am correct on where I know I am taking a focus point...

EOS viewer? Is this the screen on the back of the camera or the viewer on top with the various settings? Set point on ice with the center autofocus point? In the viewfinder?

And sorry to ask one more time, but did you change the AF points from standard nine points to the center one point? You mention that you're focusing on the subject with the center point, but never stated that you actually changed it.

Sample photos would be really helpful.

Are you seeing something like this?

ziggy53 wrote:

PS I have to learn how to type faster. Thanks Aktse!

hheheh... blame my mom. I started typing when I was in 1st grade and thought it was piano scale exercises. And if you think I type fast, you don't want to hear how fast I speak...

Scott_Quier

Hey April!!

EOS viewer is one of the software programs that comes with Canon cameras (at least it did with my 300D, 20D, and 30D). I believe you can, among other things, use this to show which focus points were active when the photo was captured.

ian408

You are focusing with the "*" button but otherwise leave the lens AF on?
Are you choosing a point on the ice for focus? If so, there's a good chance
the camera hasn't actually locked focus on that spot. Otherwise, given the
settings you mention, everything about 15 feet in front of your subject
and to about the boards should be in focus. Love to see some examples.

How often do you check focus during the game? Is it possible that you're
brushing the lens barrel and accidently changing focus?

If you really think you have back focus problems, I would try one of the
yardstick tests.