1DX - Ai Servo Issue - Low light focus failure! Final Update 05/09/12

[robin]

Sorry to hear about these problems, but this does not seem to be usual. I have got 3 1DX yesterday and checked all three, and none has these issues. We did a lot of tests, because we are leaving for Olympia tomorrow, and you can guess we did not need any problems with new cameras there (bad enough that we got them "in the last minute"..

[howhigh]

Although I understand there are some differences between the 1DX and the 5D3 AF, I think it might be worth noting, that the 5D3 has the same issue (at least mine has. low light servo tracking = not possible (one shot works)).

[Sycotek]

Although I understand there are some differences between the 1DX and the 5D3 AF, I think it might be worth noting, that the 5D3 has the same issue (at least mine has. low light servo tracking = not possible (one shot works)).

Thank You for this input - I returned my 5D3's so I couldn't test myself - I was curious if it would effect them too.

Maybe it's just a *feature* I'll need to learn to live with.

Will keep you guys posted when I meet with canon this afternoon.

[bbasiaga]

Obviously not an expert here, but I wonder if there is some pre-act/PID type algorithm in the AI servo software where by its reading info from the AF sensor and trying to 'predict' the motion of the target before it moves the lens to the focus point.  With no movement, it get no info, it makes no change....If there is just not enough light for it to accurrately calculate movement, the same outcome would occur as in these test cases where the target is not actually moving.

I have seen some behavior like this out of control loops in production facilities I have worked in.  Most of the time the software can be tuned to stop the issue.

-Brian

[Sycotek]

Obviously not an expert here, but I wonder if there is some pre-act/PID type algorithm in the AI servo software where by its reading info from the AF sensor and trying to 'predict' the motion of the target before it moves the lens to the focus point.  With no movement, it get no info, it makes no change....If there is just not enough light for it to accurately calculate movement, the same outcome would occur as in these test cases where the target is not actually moving.

I have seen some behavior like this out of control loops in production facilities I have worked in.  Most of the time the software can be tuned to stop the issue.

-Brian

possible - however you need to assign a target for the cameras first af point priority. You need that to lock regardless or it doesn't know what you are pointing at what colour or face to register and track.

The camera failed to lock on for me on a runway/catwalk which has plenty of movement.

Furthermore the second set of test i put up were single shot vs moving target ai servo - in these instances the camera failed to lock on the target correctly and ended up with everything out of focus.

Agree'd it could be software/firmware fixed and hopefully thats all it is!

[Sycotek]

Updated main post

[justaphotographer]

Hi Sycotek,

I am having exactly the same problem.  I mean EXACTLY the same problem.  In low(ish) (not even really that low light actually) when in AF-SERVO mode the camera just goes to infinity and back and does not lock focus at all.  In ONE-SHOT it locks on very very quickly.  Back to AF-SERVO...AF craps out again.  It is 100% repeatable.  Below you wrote that if you leave the AF setting at stock default it works properly.  Well not for me.  After I made a backup of all my current settings I reset everything back to default (including the custom function setting).  The camera was in "out of the box" state.  Yet, the AF-SERVO in low(ish) light problem is still there.  This tells me that it isn't a settings issue, but something else that is going on with the camera.

I tested this with every single one of my lenses and they all have exactly the same problem.  ONE-SHOT nails focus, but AF-SERVO (go to infinity and back and never locks focus).

The troubling thing about this is that this is not even that low of a light setting.  Clearly ONE-SHOT has no problem.  Even my older 5D2 with center focus on AF-SERVO can lock on just fine.  There is definitely something strange going on here.  Please keep this thread updated as to what Canon says.

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Update 27/07:

OK so speaking with Canon We have isolated it down to an AF function/modification. It doesn't seem to be a custom function change.

I tend to use case 1 and case 4 and modify case 4 (all sliders moved to the very left) - now I can't seem to figure out what combination of changes make the AF balls up. I had everything set as I like it last night but the second i changed over rotation to computer only (as i tend to shoot portrait mode) the af started to play up. Undoing the rotation change did not fix the issue. Had to reset to a working backup.

If I leave the af setting as stock default everything works properly.

And as it has always been this only shows up in low light Servo.

If anyone is interested I can load a broken config they can play around with and see if they can work it out.

It's a little frustrating as I don't know what I am changing that's causing the AF to bug out. As proved to me when I was shooting with canon in and underground car park the 1DX could lock onto a black car moving at 20+ km/hr in next to no light and get a ridiculously sharp image.

Canon is working on it, as am I - keep keep this updated.

[justaphotographer]

I just now tested a 5D classic in AF-SERVO mode (center point) on the same object in the same light and was ABLE to track focus perfectly.

Again the 5D2 and 5D Classic on the same object in AF-SERVO mode can lock on no problem.

[justaphotographer]

One more update.  I actually think this isn't a low light AF-SERVO problem, but rather a low contrast AF-SERVO problem.  I just tested in bright light trying to focus using AF-SERVO on a low contrast object and this is what happened...

1Dx...fail
5D2...perfect tracking
5D Classic...perfect tracking

Remember this is in bright light.  So my current conclusion is that the new 61 AF system in AF-SERVO mode cannot lock on to or track low contrast objects.  This make sense, because the other day (in daylight no less) I was trying to track someone in AF-SERVO, but the 1Dx kept failing.  I just tossed it up to the fact that it was a fluke, but now I think about it he had a solid black shirt with hardly any contrast.

If all cameras failed under these conditions we can just say well Phase Detection AF can't track low contrast objects and just live with it, but as I have tested on the 5D2 and 5D classic in AF-SERVO, it shows that those older cameras can track without a problem, the exact same objects that the 1Dx and 5D3 fails to track.

[justaphotographer]

Okay I've made a very helpful discovery on the 1Dx that could be a slight workaround until Canon fixes this problem.  In an attempt to solve this problem I discovered something pretty interesting.

If you go to C.Fn3:Drive and then the Continuous Shooting Speed setting and change High Speed from 12 (default) to anything 10 or less you will get a boost in AI-SERVO tracking in low light.  As soon as I bump that back up to 12fps the camera cannot track in low light very.  Change back down to 10 or slower and tracking is definitely better.  This is 100% repeatable.

Even at 10fps setting the tracking isn't nearly as good in low light as an older 5D2, but still better (without question) than when the camera is set to 12fps.

I am wondering if Canon traded off low light tracking to get that high rate of 12fps and that is why at 14fps the autofocus stops all together.  Interesting.

In the meantime what I have done as a workaround is to set the Low Speed setting to 10fps and left the High Speed setting to 12fps.  This way when I'm in good contrast/good light I can get the benefit of the full 12fps and when I am in low light I can just quickly switch the AF Drive mode to Low and get greatly increased tracking ability under that lighting condition.

Could you guys report this to Canon (I will when I get back from my 2 week assignment---I leave tomorrow so I don't have time) so that they can be aware of this in case they can adjust this in the next firmware?

[justaphotographer]

Okay last update for now.  The settings change totally improves AI-SERVO tracking in low light, but it is still definitely not even close to as good as the 5D2 (center point) for low light/low contrast tracking.

Still though, there is definite improvement for low light AI-SERVO tracking by simply changing the max FPS from 12 to 10.  I just hope Canon can tweak things so that it is as good as the 5D2 center point focus tracking in low light/contrast (yeah I know strange that I have to even write that sentence).

I hope this is fixable in firmware rather than it being a tradeoff for having 12fps shooting.

[Sycotek]

Hi justaphotographer,

I haven't had any issues using the reset config I got from canon - I have now reconfigured my own without touching the af settings and it worked fine last-night at another runway tracking black subjects at 1/250 f4 iso 10K <- this was not fun...)

I believe like you its a contrast issue. But the default configuration doesn't exhibit the same issues that I had with my tweaked config.

eg. single 60w equivalent cfl room light trying to track my gf face - the broken config wont lock on anything. The reset config locks on Her eye brows and eyes, under her nose and lips as if it was nothing.

The test with canon was well below -2ev (i could not see the other reps eyes yet the camera locked on as if it was nothing and focussed accurately) broken config just hunted - canon rep couldn't believe it.

---

As annoying as it is if you haven't tried it - i would recommend making a backup of your current config and send it to me, then testing out the config i got from canon - i'll pass your broken one to canon so they have a second point of reference.

I will also test out your finding tomorrow and get back you if i can replicate it

[justaphotographer]

Thank you so much for you reply Sycotek.  I just sent you a private message.

Hi justaphotographer,

I haven't had any issues using the reset config I got from canon - I have now reconfigured my own without touching the af settings and it worked fine last-night at another runway tracking black subjects at 1/250 f4 iso 10K <- this was not fun...)

I believe like you its a contrast issue. But the default configuration doesn't exhibit the same issues that I had with my tweaked config.

eg. single 60w equivalent cfl room light trying to track my gf face - the broken config wont lock on anything. The reset config locks on Her eye brows and eyes, under her nose and lips as if it was nothing.

The test with canon was well below -2ev (i could not see the other reps eyes yet the camera locked on as if it was nothing and focussed accurately) broken config just hunted - canon rep couldn't believe it.

---

As annoying as it is if you haven't tried it - i would recommend making a backup of your current config and send it to me, then testing out the config i got from canon - i'll pass your broken one to canon so they have a second point of reference.

I will also test out your finding tomorrow and get back you if i can replicate it

[justaphotographer]

Okay Sycotek,

I had a chance to load and play around with your "canon fixed" config version.  It totally confirmed my finding actually.  As soon as I loaded your fixed config I noticed that it put the camera into multi-shot L drive mode.  It tracked wonderfully in low(ish) light.  Do you know why?  Because in the C.Fn3:Drive setting section, the multi-shot L drive mode puts the camera into 3 frames per second (fps).  As soon as I changed to multi-shot H drive mode (which is set for 12 fps) you're fixed camera craps out again in AI-SERVO in low light/contrast.  As soon as I go back to 3 fps (in multi-shot L drive mode) the camera performs much better in low light/contrast.

That is the only setting I changed on your fixed version and it totally affected the tracking ability (or a lack there of) of the camera in low light/contrast.  This confirms my finding.  All that the fix version is doing is putting your camera into 3 frames per second mode.

Can you test it yourself and confirm?  Thank again for all the great work you are doing to help try and solve this.  I am now convinced mostly that Canon needs to tweak this camera for better tracking in low light/contrast when it is in 12 fps mode.

Hi justaphotographer,

I haven't had any issues using the reset config I got from canon - I have now reconfigured my own without touching the af settings and it worked fine last-night at another runway tracking black subjects at 1/250 f4 iso 10K <- this was not fun...)

I believe like you its a contrast issue. But the default configuration doesn't exhibit the same issues that I had with my tweaked config.

eg. single 60w equivalent cfl room light trying to track my gf face - the broken config wont lock on anything. The reset config locks on Her eye brows and eyes, under her nose and lips as if it was nothing.

The test with canon was well below -2ev (i could not see the other reps eyes yet the camera locked on as if it was nothing and focussed accurately) broken config just hunted - canon rep couldn't believe it.

---

As annoying as it is if you haven't tried it - i would recommend making a backup of your current config and send it to me, then testing out the config i got from canon - i'll pass your broken one to canon so they have a second point of reference.

I will also test out your finding tomorrow and get back you if i can replicate it

[Sycotek]

Hi Mate,

Just tested your theory out - in my configuration where i know the camera will fail if i used the bugged out config - my fixed version works regardless of being on L or H.

Scratch that - I can confirm similar findings!!!

Is it possible to upload an image regarding the scene/target that you are testing on? And please add what lenses you are using (as canon will ask)

-Alex