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Archive 2012 · Backfocusing in AI Servo (Canon 30D)
Caleb Williams
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p.1 #1 · Backfocusing in AI Servo (Canon 30D)

Hey guys,

First a little of my background: I shoot sports (90% of the time). I use AI Servo with the center point 90% of the time (the rest I'm using a different point or one shot focus). I'm generally shooting at ISO 1600 at shutter speeds of 1/400 at the low end and 1/800 on the high end. I use back-button (*) focus all the time, no matter what focus mode I'm using.

The camera I use, the Canon 30D was sent in for the Error 99 fix in late August/September 2009 and seemed to work great for me until about September 2010, when I noticed that a few shots were back focused (not enough to miss critical shots with no replacement). I didn't shoot a ton of sports last school year, but I this school year and noticed that more and more of my shots seem to be back-focused.

I primary have used the Canon 70-200mm 2.8 (non IS) since September 2010. I have used at least four versions of this lens at various times and with each, I seemed to be getting back-focused action photos. The lens I'm using right now is a friends and when it's on, it's the sharpest lens I've ever used for a 70-200 2.8.

The following set of images are from a hockey game last night. This is shot through the glass at ISO 1600, f2.8 and 1/640th. Through the glass, which only exacerbates the problem.






It took five shots to get a sharp face (not shown in the last photo).

I could post countless samples of recent games where it seem the next person back is in focus, not the person I'm focusing on.

Any ideas? Would this fix be covered by Canon? I can't afford to have it sent in if costs $200.


- Caleb

PS: I have noticed any back focus issue when shooting in One Shot focus with stationary targets.
PPS: I test this same lens with a Canon 7D and saw no issue that's couldn't be explained by user error.
PPPS: I have noticed this issue with the 16-35mm f/2.8 II as well.

Jan 21, 2012 at 09:49 PM
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p.1 #2 · Backfocusing in AI Servo (Canon 30D)

I doubt that Canon will work on a 30D for free. The warranty is long gone and 3 other xxD models have since been released. My 30D had a similar problem about a year ago. Canon wanted $350 to just look at the camera, so I ended up using the loyality program to upgrade to a refurbished 50D. Much better camera in the end though I hadn't planned to upgrade at the time.

Good luck with your 30D.


Jan 22, 2012 at 03:37 PM
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p.1 #3 · Backfocusing in AI Servo (Canon 30D)

It seems that you have established that the problem is with your camera rather than the lens(es). You've also established that one shot AF works ok, and yet it uses the same mirror and AF lens systems as AI Servo. The only variable that I can think of is the timing of physical movements. The sub-mirror that is behind the main mirror may not be resetting itself into correct alignment between shots in continuous shooting. The mirror probably is getting there eventually but not fast enough to suit the AF system.

Are you getting the problems in AI Servo while shooting continuously ?

Is the first shot affected or just the subsequent shots ?

If the problem is with the mirror then it could be a minor fix such as a seal somewhere needing replacement because it has deteriorated and gone a bit sticky. Or it could be that a mirror vibration dampening component is not working correctly. Maybe a whole new mirror box assembly is required.

If the first shot is affected in AI Servo mode then you'd expect any shot in One Shot mode to be affected too, as in both cases the mirror has plenty of time to settle between shots.

If the problem is something else then I'd very much like to know what it could be.

- Alan

Jan 22, 2012 at 03:50 PM
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p.1 #4 · Backfocusing in AI Servo (Canon 30D)

These shots really don't prove anything unfortunately. Shooting through the glass will mess up any camera's focus especially if it is dirty glass or if you shoot at an angle. We have no idea where the focus point is when looking at these shots too. They all seem to be quite underexposed as well.
My suggestion is to put the camera to a test in conditions which should allow for a reliable AF performance. Hockey through the glass is simply introducing too many variables into it.
Just my thoughts. FWIW I shoot with a 1D Mark IV in Div. 1 lighting and I do not shoot through the glass because it is so unreliable and results in crappy images (merely my opinion of course)
good luck,

Jan 22, 2012 at 03:59 PM
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p.1 #5 · Backfocusing in AI Servo (Canon 30D)

I ran into similar issues shooting hockey, also with a 70-200 non-IS, a 30D and also a 40D. I shot over low glass near the bench, so the glass wasn't a variable. I even sent the lens and the 40D to Canon because of the problem, and they both came back as OK within spec.

Frankly the problem continued until I upgraded to a 7D, when things improved, and then I finally tried a microadjustment, and things got even better.

In your case you may have an easier situation for Canon to fix, since it seems like your issues started after the Err99 service. I decided I was dealing with the low-light AI Servo limitations of the xxD cameras, and maybe some indifference from Canon but admittedly with a problem that might not have been easy for them to reproduce.

Does your camera also back focus in good light, maybe shooting soccer? Mine didn't, which was another reason I decided the low light played a major role.


Jan 22, 2012 at 05:27 PM

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