AI Servo problems with 40D

[Jimlevitt]

I'm having trouble achieving reliable AI Servo autofocus results with my 40D cameras. Here's an example, typical of many frustrating moments from tonight's gig alone. These were made in Seattle's premier jazz club. Lighting was decent (unlike most of the lower-rent dives...), enabling iso 800. These two frames were made with the 70-200/2.8IS, 1/40th sec @2.8, part of a three-frame burst. I had an illuminated focus point located on the trombone player's right eye. The first frame is right on. The second frame, with the focus point in exactly the same place, is not: the focus has moved to the bell of the instrument! These are quickie conversions done in Breezebrowser Pro, nothing fancy, just wanted to show the focus problems.

This sort of thing happened to me all night long. Sometimes, as when attempting to focus on a singer's face, I figure the spotlit skin is the cause, though often enough there's plenty of contrast present with eyes, mouth, shadows from the nose, etc. Most of the time, the focus seemed to drift for no reason. This happens with both my 40D bodies, with all my lenses.

Would AI-Focus be better in situations where the subjects are moving, but not rapidly? I used to use AI-Focus all the time; seems to me I get more of this focus-drift in AI Servo than I did in AI-Focus. All the forum advice says to use Servo.

I use * button focus, though that shouldn't make any difference in this case.

Short of buying a 1DMkIII, what can I do to ensure a better keeper ratio?

[FlyingPhotog]

There may be a technical issue I'm not aware of but for a seated musician, why not just use One Shot?

As for the focus shift, keep in mind that the actual focus point is larger than the little box that lights up. It's possible that your aim drifted just enough to let the camera grab a piece of the bell.

[Jimlevitt]

There may be a technical issue I'm not aware of but for a seated musician, why not just use One Shot?

As for the focus shift, keep in mind that the actual focus point is larger than the little box that lights up. It's possible that your aim drifted just enough to let the camera grab a piece of the bell.

This particular musician was seated. I was dealing with a standing singer, soloists who would stand up, and seated musicians who moved as they leaned in and out of a note or a phrase. So One Shot wouldn't be the best choice. AI-Focus, which is supposed to automatically shift between one-shot and servo, might be the way to go. I'd like to hear from others who photograph these sorts of subjects.

Here's a couple of screen captures - sorry about not getting just the photo portion of my monitor screen - from Breezebrowser, showing the focus point in use. As you can see, the focus point stayed right on the eye. This were shot in continuous drive, taken a fraction of a second apart. The focus point didn't move, but the camera shifted focus by several feet.

[EOS_JD]

Why not use one shot in a situarion like this? AI Servo is best used when you have moving subjects. Although the players may move a few inches, I think one shot would be a better option as they won't be moving quickly.

i take it you are only using one focus point?

[René Damkot]

The actual AF field is (quite a bit) larger then the "red dot". The bell offers way more contrast then the eye, so is an easier "target" to AF on. Probably bell was close enough to the AF field to be picked up. That made the life of the AF a bit easier, and yours a bit harder ;)

[Jimlevitt]

The actual AF field is (quite a bit) larger then the "red dot". The bell offers way more contrast then the eye, so is an easier "target" to AF on. Probably bell was close enough to the AF field to be picked up. That made the life of the AF a bit easier, and yours a bit harder ;)

Why then does the camera get it right in the first frame, but not in the second? Sometimes it's the other way around. In any case, the viewfinder isn't revealing enough of focus to be able to rely on strictly visual confirmation. Otherwise I'd focus on the eye, release the * button (thus making the AF function as if it were it one-shot AF) and fire away for several frames.

Will the camera do better in AI-Focus, rather than AI-Servo? Do the 1-series cameras have better servo control than the 40D (or is this the sort of static subject that results in AF errors with the 1DMKIII)? Is the 50D any better than the 40D?

[Coppatop85]

I had similar problems in the thread i just posted in this section as well.

[René Damkot]

Will the camera do better in AI-Focus, rather than AI-Servo? Do the 1-series cameras have better servo control than the 40D (or is this the sort of static subject that results in AF errors with the 1DMKIII)? Is the 50D any better than the 40D?

I never used AiFocus when I had a 10D. I prefer to make decisions myself, rather then have the camera make them.

My 1D2 sometimes also focus inconsistent in a case like this (say: singer behind a microphone). I try to keep alert for a risk like that, and make sure I "miss" the mic.

Then again, my camera needs to be sent in for cleaning / calibration, since it's acting up...

[mantra]

This particular musician was seated. I was dealing with a standing singer, soloists who would stand up, and seated musicians who moved as they leaned in and out of a note or a phrase. So One Shot wouldn't be the best choice. AI-Focus, which is supposed to automatically shift between one-shot and servo, might be the way to go. I'd like to hear from others who photograph these sorts of subjects.

Here's a couple of screen captures - sorry about not getting just the photo portion of my monitor screen - from Breezebrowser, showing the focus point in use. As you can see, the focus point stayed right on the eye. This were shot in continuous drive, taken a fraction of a second apart. The focus point didn't move, but the camera shifted focus by several feet.
sorry may i ask a question?

which software did you use to visualize the photo?

[Jimlevitt]

I used BreezeBrowser Pro to show those two images. It's a nice bit of software for doing a first edit of photos, as you can see a screen-sharpened version of the file. It'll also show the focus points in use, helpful for figuring out what went right or wrong. It has many other capabilities as well.

More info here:
http://www.breezesys.com/BreezeBrowser/index.htm

Jim

[DDCSD]

If you are using the * button for focus, let off of the focus when doing a burst of a stationary subject. I do this for concerts to avoid catching the mic stand or hands.