5DII AI Servo and plain background

Hi,i asked this question on another forum and had little help there so hopefully someone here can help. I'm using a 5DII to track birds in flight and wondering if there is an answer to this problem I am experiencing. I always use centre point/af area expansion enabled/ focus search off. If I am tracking against a busy background the camera locks on perfectly and holds the subject perfectly. However if the subject moves a bit higher for instance so that the background is now a cloudy or plain blue sky the camera racks in to min focus distance and thats it, subject lost. The camera cannot acquire or track a subject against a nondescript background but works perfectly to track against a busy background even if the subject is very small in the frame. I have experienced this with a number of different teles of Canon and Sigma so it has to be the camera. I dont think its me either because there is no issue with busy backgrounds.

Has anyone else experienced this as I thought busy backgrounds were supposed to be more confusing for cameras?
Cheers,
Ciaran

what is your AF CF.n settings ? (when you say expansion, which expansion are you referring to?)

what range is the lens focus limiter switch set to?

Hi Arash, I am using the centre point with the six invisible assist points enabled and focus search off. I normally have my 70-200 f4 set to 3m for birds and other lenses I have experienced the problem with do not have distance limiter switches.
In one shot mode the camera can acquire focus on a BIF against a plain background. Is this normal?

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Originally Posted by Ciaran Walsh

Hi Arash, I am using the centre point with the six invisible assist points enabled and focus search off. I normally have my 70-200 f4 set to 3m for birds and other lenses I have experienced the problem with do not have distance limiter switches.
In one shot mode the camera can acquire focus on a BIF against a plain background. Is this normal?

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can you post a screen shot of the image where the focus hunts when bird goes against sky BG?

what is the firmware version of the camera?

Firmware is 2.0.3 I had a quick look but I dont have any good examples since I normally delete OOF shots in camera before importing. It may be the weekend before I can replicate the issue but I will post a sequence when I have it.
Thanks!

Quote:

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Originally Posted by Ciaran Walsh

Firmware is 2.0.3 I had a quick look but I dont have any good examples since I normally delete OOF shots in camera before importing. It may be the weekend before I can replicate the issue but I will post a sequence when I have it.
Thanks!

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The current firmware is 2.1.12 update the firmware and see if you can replicate the problem again. To eliminate chances of hunting take off any TCs and use the limiter switch to limit range.

focus search off -i think you should have it ON
Rob.

Hmm could be that. I've read that its best OFF for BIF's but I will try it ON and see what happens.

focus search will slow down AF and it shouldn't matter if focus distance is not changing significantly once BG changes from foliage to sky. I keep it off on my cameras but do give it a shot.

Ok, I got out for a couple of hours this morning to experiment with various settings. Basically the six invisible AF assist are causing the issue. With that feature switched off I can track a bird in flight against a sky background. Acquisition is slow but very accurate. However with a busy background at least 50% of shots were focussed on the background or not in focus. It seems that feature is only useful for busy backgrounds? I would be interested to hear if anyone else can replicate this.

Quote:

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Originally Posted by Ciaran Walsh

Ok, I got out for a couple of hours this morning to experiment with various settings. Basically the six invisible AF assist are causing the issue. With that feature switched off I can track a bird in flight against a sky background. Acquisition is slow but very accurate. However with a busy background at least 50% of shots were focussed on the background or not in focus. It seems that feature is only useful for busy backgrounds? I would be interested to hear if anyone else can replicate this.

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Ciaran,
The assit points in 5D2 work well for sky and busy BG, if anything they work even better for sky BG because there is nothing else to lock on. Can you provide an example of camera not being able to focus against a sky BG? If it is not a particular situation that fools the AF, my guess is your camera needs to be calibrated by Canon.

My thinking is that with focus search OFF your loseing the bird for a moment and the focuse then just stops as its just seeing sky ? With focus search on and the same conditions it would try to refocus once you get back on the bird .
Rob.

Hi Rob, I tried focus search on and off but I still could not acquire the bird against a sky background. I haven't update the firmware next see if that helps. Thanks!

Well im at a loss as to were to go from here , any camera should pick a bird up against a sky BG and should do this better or far easier than a busy BG .
I really carnt think of any reason ANY camera would behave this way ,

There is no setting/custom fuction that would allow this even if you wanted it.
My last thought is take the battries out for 15mins then put them back and reset the camera to defaut settings and try again.
Rob.

Well firmware made no difference. I have dropped a mail to Canon customer support. I will see what they come back with. Thanks for all your help!