Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



My cameras are 1D and 40D. Neither show that phenomena.

Happy shooting,
Yakim.

Jeff wrote:
OK, so I finished the first round edit on 1795 cycling images from Sunday, and 30% were unusable due to AF issues, only a small amount of those user error.



Happy shooting,
Yakim.

apdieb wrote:
Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



EXACTLY. That is EXACTLY what I see often.

Me too! I have since given up on AI Servo. I keep it at One Shot and it works just fine (fast moving subjects or not)

Oddly enough I have started to use AI Servo more now than ever before. I used to use One Shot whenever it was possible just because I liked to control the focus. Now though I am finding I can save a lot of time by just keeping it in AI. Sometimes while moving and shooting at the same time I get some OOF shots but I am not sure if that is a flaw.

momv630 wrote:
apdieb wrote:
Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



EXACTLY. That is EXACTLY what I see often.

Me too! I have since given up on AI Servo. I keep it at One Shot and it works just fine (fast moving subjects or not)



EXACTLY what I see in AI Servo mode as well (post sub-mirror fix). Interestingly, One-Shot accuracy has improved dramatically since the fix, but AI Servo not at all.

marchantron wrote:
momv630 wrote:
apdieb wrote:
Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



EXACTLY. That is EXACTLY what I see often.

Me too! I have since given up on AI Servo. I keep it at One Shot and it works just fine (fast moving subjects or not)



EXACTLY what I see in AI Servo mode as well (post sub-mirror fix). Interestingly, One-Shot accuracy has improved dramatically since the fix, but AI Servo not at all.


Correct! I haven't used AI Servo at all since I've had 2 fixes. I seem to be in a happier place now

Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



It's probably totally wrong, but could it be because when the camera starts off from an unfocussed state each AF sensor receives information from all over the frame and not only from where the sensor is pointed at? Some sort of "phase mixing" occurs when strong patterns outside of the sensor area prevail and affect the camera's decision where to focus.

Jeff wrote:
AI Servo at medium tracking sensitivity, center-point with left-right assist enabled. Looking forward to some cycling shooting today, we'll see how it does with faster subjects.
Regardless, this is more like it.
-Jeff


Jeff, since following this thread closely from time to time and trying various things, two weeks ago I decided to take all pics for awhile on AI SERVO as I had almost always used 1shot. I was pleasantly surprised. My percentage OOF didn't change much BUT second and following shots in a sequence InFocus went way up. Still not impressive but better. After two weeks of this I read your above note and the LR Expand is the way I set all my previous 1V and 1d's - I tried it again. I changed the sensitivity down to, C.Fn III 2,center; and left, right assist, C.Fn III 8,1. My last 600 shots testing these settings show a noticeable inprovement. Thanks for all your related experiences.
Good Shooting !!

Hello,

I recently bought a 1D MkIII (s/n out of the affected range) and have shot a few thousand frames since then (primarily wildlife, birds; with a 500mm and 1.4 TC). Everything seems to work perfectly, except… Ai Servo. What I’ve observed so far (especially regarding the first point I’m very interested to hear from other MkIII owners if this behaviour is normal, thanks):

- Center AF point only, pointing on a stationary subject, stable support (tripod or bean bag) --> the AF is continuously adjusting back and forth by a significant amount even if camera and subject aren’t moving at all. This results in a lot of out of focus images (even at f8), as with wildlife you haven’t always the time to switch to One Shot mode. (The MkIII white paper states: " Even if AI Servo AF is used to focus on a still subject, stable control is enabled so that the lens drive isn’t constantly fine-tuning. If the subject starts to move, the focusing responds immediately to detect the subject constantly.”).

- The slower a subject moves the less reliable is the AF tracking. I had rather good results at 10fps testing on cars driving towards me on a motorway at 120km/h, but with 4fps and birds slowly flying, walking or swimming towards me, more than half of the images are out of focus. Again, this is in contrast to what the white paper says (“During low-speed continuous shooting, the subject distance can change significantly between shots. The slower the continuous shooting speed, the more the lens is driven between shots to detect the subject. Thus, subject tracking is more precise.”). And, if the there are only slightest changes in the subjects speed and/or the light/contrast is not optimal (overcast sky, no direct sunlight), AF tracking performance is even worse.

- In (very) low light, after sunset, Ai Servo on a stationary subject doesn’t work at all, One shot does work though. A 40D used at the same time did work in Ai Servo.

Currently I feel that the MkIII isn’t worth the money; of course I will continue testing Ai Servo performance before sending it in, weather forecast fortunately is good for the coming weekend…

I have the same exact problem and mine was repaired in mid december. When I get back to the states in a month I will ship it back out Also, on a side note I have this one pixel that is intermittently hot regardless of exposure.

lermite wrote:the AF is continuously adjusting back and forth by a significant amount even if camera and subject aren’t moving at all. This results in a lot of out of focus images (even at f8),

Lermite, I noticed this as well, but I have found that changing CF III-4 (AI Servo AF Tracking Method) to 1 (Continuous AF track priority) results in significantly more stable performance with static subjects. It also seems to help to disable AF point expansion (CF III-8). This is with firmware 1.1.3.

My experience at this stage is still pretty limited (I only recently received a body on loan from CPS--serial number 512xxx). So I don't have a handle on how this setting affects performance with moving subjects, but you may want to give this a try.

I expect that a reasonable argument could be made (by Canon) that AI Servo is for moving subjects only, and is not intended for general AF use. I personally use One Shot a lot, but I know lots of shooters who never take their bodies out of AI Servo.

Some of the prosumer bodies have an intermediate AF setting that begins in One Shot but switches to Servo if subject movement is detected. It seems this would be desiable behavior in many instances.

Edited by garyvot on Apr 22, 2008 at 11:36 AM GMT

garyvot wrote:

It also seems to help to disable AF point expansion (CF III-8). This is with firmware 1.1.3.




I do not understand this statement at all.

Colin

Colin Key wrote:
garyvot wrote:

It also seems to help to disable AF point expansion (CF III-8). This is with firmware 1.1.3.




I do not understand this statement at all.

Colin

CF III-8 turns on AF point expansion which enables "helper" AF points that surround the selected AF point. In my (admittedly limted) experience, leaving this at the default setting--disabled--seems to improve stability for static subjects. YMMV.

With my 20D I pretty much left it in servo all the time - no problems.

Doing that with my 1DMkIIIs resulted in lots of hunting when tripod mounted and shooting a stationary subject. Also resulted in lots of OOF shots as did One Shot.

With my 1DsMkIII I use servo most of the time and the hunting problem is gone. So are the OOF problems in both Servo and One Shot.

Canon told me that that the hunting was my fault for leaving it in Servo. Therefore I can deduce that my 20D and 1DsMkIII are broken.

garyvot wrote: Lermite, I noticed this as well, but I have found that changing CF III-4 (AI Servo AF Tracking Method) to 1 (Continuous AF track priority) results in significantly more stable performance with static subjects. It also seems to help to disable AF point expansion (CF III-8). This is with firmware 1.1.3.

I have set the CFs as you suggest. AF point expansion seems only useable for flight shots (birds against the sky or another background with less contrast than the subject), for larger birds/closer range when the central circle in the viewfinder is more or less covered by the subject or for very fast tracking action when the background blurs completely. But I haven't had the opportunity yet to test this properly.

garyvot wrote: I expect that a reasonable argument could be made (by Canon) that AI Servo is for moving subjects only, and is not intended for general AF use.

This is of course a reasonable argument (One Shot is certainly more precise for static subjects). But when my 20D most of the time can correctly focus on a still subject in Ai Servo and Canon is stressing the ability of the 1D to stabilize Ai Servo when pointing on a static subject in there own white paper, I expect it to work...

Hrow wrote: With my 20D I pretty much left it in servo all the time - no problems.

Same here. That's one reason I'm so surprised about the behavior of the 1D.

Hrow wrote: Canon told me that that the hunting was my fault for leaving it in Servo. Therefore I can deduce that my 20D and 1DsMkIII are broken.

Canon states in the 1Ds MkIII white paper that the AF system is almost identical to the 1D. As you own both cameras, it should be easy to prove them wrong and get the 1D repaired, no?
("The state-of-the-art AF sensor in the EOS-1Ds Mark III is shared with the EOS-1D Mark III. The AI SERVO AF algorithm has been optimized to match the continuous shooting speed of the EOS-1Ds Mark III, approximately 5 fps. Also, due to the full-frame CMOS sensor, the Area AF coverage with respect to the viewfinder is slightly smaller than with the EOS-1D Mark III. The AF speed and predictive AF performance are the same as with the EOS-1D Mark III. All other AF-related specifications not mentioned here are also the same as the best-inclass EOS-1D Mark III."

lermite,

I gave up on the camera a while ago and trade it in for a 1DsMkIII. After months of fighting, Canon agreed to take it back and hopefully it went into a deep pit somewhere.

Lermite, I could not tell from your response if you specifically tried changing CFIII-4 to 1 (disregarding AF point expansion). On my body, this causes the constant focus hunting with static subjects to almost completely cease (at least with the lenses I have tried). I can still get it to hunt from time to time, but it is quite a significant improvement.

I only have experienced with one sample of this camera, so I don't know if mine is "typical" or not...

garyvot, I had set CFIII-4 all the time to 1, tracking priority (seemed more logical for my type of shooting). I didn't specifically test if setting it to 0 changes something.

Interestede to see what the new firmware has done for some of the main posters here, if any have tried it, esp those shooting sports or with focus plane issues.

New firmware did nothing for my camera, although I suppose it is possible (based upon recent flaky results with the 24-70) that it made it worse. I hadn't thought of that...

So, situation is still that you have better AF than the first body but still not 100% satisfactory?

Happy shooting,
Yakim.

gfiksel wrote:
Alan321 wrote:
apdieb wrote:
I am becoming more and more convinced that the AF sensors are locking on objects with more texture/contrast in the frame regardless of the point chosen.

Now that is an impression that my 40D gave me. It focused on edges that were nowhere near the chosen AF sensor. However, it's hard to imagine how it can happen. BTW there was no cure for my 40D - Canon reckoned it was within spec.

- Alan



It's probably totally wrong, but could it be because when the camera starts off from an unfocussed state each AF sensor receives information from all over the frame and not only from where the sensor is pointed at? Some sort of "phase mixing" occurs when strong patterns outside of the sensor area prevail and affect the camera's decision where to focus.

A seemingly plausible explanation except that the subject was already in focus in some cases and the camera AI Servo decided to look elsewhere. I was tracking accurately and so there was no justification for that camera behaviour.

The new cameras have a larger sensor for extreme defocus situations but as it homes in on the subject the designated standard sensor is supposed to take over and finish the job. Therefore even a massively defocused subject should either be found eventually by the designated sensor or else not found at all.

If the problem is not with the AF or sensor hardware then I am beginning to suspect there is a flaw in the Digic III computer. I recall that Intel Pentiums had a flaw at one stage that produced incorrect results in some calculations, and I guess the Digic III could be doing the same sort of thing no matter how well Canon double-check the AF program code. The Digic III is common to all of the recent camera models but not every camera uses every feature.

- Alan

Well, in case Intel processors, all of them had it (was it a round-off error?). In case of 40D, most of them lock on just fine. I know mine does. And when it doesn't - it's my own error.
100% crop, 40D, 135/2.0 +1.4x

Yakim Peled wrote:
So, situation is still that you have better AF than the first body but still not 100% satisfactory?

Happy shooting,
Yakim.


Correct; definitely better in AI Servo than the first one, but still has erratic One-Shot focusing (mostly at f/2.8).

geeze isn't this thread like dead a long time ago?