7D AF in AI SERVO (photos included)

Started Feb 4, 2013 | Discussions thread
TTMartin
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Re: 7D AF in AI SERVO (photos included)
In reply to Ondrej Zeman, Feb 4, 2013

Ondrej Zeman wrote:

A lot has been written about the AF of 7D. Some say it is brilliant, some find it faulty. Unfortunately I have to lean towards the second group. Perhaps it is due to camera/lens/user error or maybe simply my expectations are just too high? Look at the sequence of following images:

http://don.vn.cz/lenstest/135mm_1/IMG_7046.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7047.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7048.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7049.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7050.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7051.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7052.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7053.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7054.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7055.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7056.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7057.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7058.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7059.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7060.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7061.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7062.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7063.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7064.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7065.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7066.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7067.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7068.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7069.jpg
http://don.vn.cz/lenstest/135mm_1/IMG_7070.jpg

(Shot in RAW and converted to JPG without any adjustments, used Canon 135/f2 L lens)
I set the camera to 1/1000, ISO 100, f2.0, AI SERVO, central AF point selected, sequence shooting. The car was travelling 50 km/h. Out of these 25 photos, I would consider 7 photos to be in focus, 18 out of focus.

It would seem like the camera/lens is slightly backfocusing, but why are some of the photos in focus? I tried experimenting with Spot AF and AF Expansion as well, but in both modes the results were even worse.

Could it be faulty lens? I get kinda the same results with Canon EF 200mm f/2.8 L II USM. Faulty camera? Maybe? User error? What am I doing wrong?

Some might say that the situation is extreme - well not really for me, as I shoot a lot of fast moving cars in lack of light and altough I don't shoot as low as f2 but very often at f2.8. If I knew I could trust the AF, I wouldn't mind shooting at f2.
Any tips welcomed.

From what I recall Spot AF is NOT recommended for AI servo.

AF expansion should have been fine. What focus mode was used in this series of photos?

The photos did appear to be fairly consistently back focused, which would lead me to believe you may have a calibration issue.

What drive mode were you in?

Have you made any changes to the AF system in the CnF s?

In the third video there is an in-depth discussion of the Canon 1D MkIII focus system, which the 7D inherited. All 3 videos are worth watching, but, as a minimum watch the 3rd one.

Part 1 of 3: A Look at The Canon Autofocus System

Part 2 of 3: A Look at The Canon Autofocus System

Part 3 of 3: A Look at The Canon Autofocus System

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