Surprised and puzzled at RG's AI servo settings

Started Sep 5, 2009 | Discussions thread
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liquidstone
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Surprised and puzzled at RG's AI servo settings
Sep 5, 2009

Looking at RG's continuous focus settings, I'm very surprised and puzzled why he chose Spot AF and Zone AF in his AI servo tests.

A reading of the 7D manual (posted in the link below and relevant pages reproduced here) says in Spot AF, "focusing might be difficult..... for a moving subject."

Likewise, Zone AF (9 points in the center) shouldn't be the setting of choice for his other AI servo tests. Single Point AF (expanded or not) should've been a faster focusing choice.

Hence, I'm not very suprised at all at the less than stellar results he posted.

For my hands-on next week at BIFs, I'll try the following settings:

1. Single-point AF (play around with expansion/no expansion).
2. AI servo priority = "0" (AF priority/tracking priority)
3. Tracking method = "1" (contniuous AF track priority)
4. Play around with tracking sensitivity

I hope I get better results than what RG reported.

7D Manual:

http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=DownloadDetailTabAct&fcategoryid=314&modelid=19356

Relevant pages on AF settings from the manual:

RG's comments from this page:
http://www.robgalbraith.com/bins/multi_page.asp?cid=7-10042-10239-10240

During light-duty shooting over a couple of days with a beta 7D, mostly of static subjects and a good portion of it in foggy outdoor conditions, we noticed the following:

Static autofocus was excellent, using Spot AF, various AF points, AI Servo (we almost never use One Shot) and a small batch of different lenses. With the EF 16-35mm f/2.8L II, EF-S 15-85mm f/3.5-5.6 IS (also introduced today), EF 70-200mm f/4L IS, EF 200mm f/2L IS and EF 800mm f/5.6L IS, photos were simply in focus. We also used the EF 85mm f/1.2L II, and focus was all over the place. The same lens exhibited the same unstable AF on an EOS 5D Mark II, suggesting the problem was more a function of the lens than the camera.

Continuous focus using Spot AF, centre AF point, AI Servo and the EF 200mm f/2L IS, tracking a soccer player for a few minutes in fading light, the results showed promise but were ultimately inconclusive: through about 200 frames, the camera was able to hang onto focus properly for portions of several sequences, better than we've ever seen from the 50D, as well as deal with the AF point moving off the subject briefly. But it would also lose focus for several frames for no apparent reason, even when the AF point was right on the mark and the subject was moving at an easy pace.

Continuous focus using Zone AF, nine points in the centre, AI Servo and the EF 800mm f/5.6L IS, tracking distant seagulls in semi-overcast light, the results were pretty good. The camera-to-subject distance wasn't changing too rapidly, but the position of the bird within the AF point group was changing constantly, and the camera handled this just fine.

Continuous focus using Zone AF, nine points in the centre, AI Servo and the EF 200mm f/2L IS, tracking a running dog in fading light, the results were terrible. Over about 80 frames the camera got almost nothing usably in focus. If this result is representative of Zone AF, then Zone AF will be the way wrong choice for fast-moving subjects. We had better luck tracking the same dog with Spot AF.

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Romy

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