jittery focus

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Has anyone come across this problem before.

I use AI servo on the back button to focus with my 10d. A while ago, I noticed that when using my Sigma 15-30, it it seemed to jitter in and out of fcus on static subjects. ie, if I held the button down it would jump back and fore (up to about 5mm on the focus scale).
Sigma agreed it sounded faulty, and I arranged to send it back to them and used it on manual focus in the meantime, It worked on manual focus quite well, so i never actually sent it, but I decided to recently and bought a Sigma 10-20 to replace it while it was away.
Well, as soon as i put the 10-20, that did the same thing. I was aware that focus on the sigma 100-300 was a bit jittery and I always put that down to it being a long telephoto. I was convinced that it never happened on my Canon 28-135, but have realised that it does, although it takes longer for it to manifest with the button held down.
So what I first thought was an isolated lens problem, then a sigma problem, I have now realised is a canon body problem.

So I am just wondereing, before i send the body back to canon, if anyone alse has come across this or how it was overcome?

Thanks.

PS, it also happens in One Shot Focus, gets focus, beeps, stays, buit if i press again, focus moves and re-confirms.

PPS, I've tried it on flat subjetcs, so i know it's not re-focussing.

Cheers
 
Ive done exactly the same thing with my 350 and Sigma 70-300, so I'd be very interested to hear any replies.

With the focus ring moving slightly, I thought it wasn't actually focusing, just the ring moving eeever so slightly.
 
I've had the same problems. For obvious reasons I use servo a lot at speedway, but always have problems when using it if I want to focus on static riders (ie lined up at the start). I had always assumed it was just that I wasn't holding the camera absolutely steady and that the AF was a little over-sensitive in servo. One solution with a 30D is to use AI focus, but I'm pretty sure there isn't that option on the 10D.
 
Witch said:
One solution with a 30D is to use AI focus, but I'm pretty sure there isn't that option on the 10D.
Click to expand...
The 10D has the same 3 focus modes as the 20 & 30D i.e. One Shot, AI Focus and AI Servo :)
 
I've never been 100% happy with AI Servo on either the 10D or 30D. Instead of changing focus smoothly, it seems to do it in steps. Maybe it has something to do with the predicitive focus getting confused if the subject isn't actually moving towards or away from you. I get better results with One Shot or manual focus, although sometimes One Shot can't really make its mind up, as you say.

Bring back the Canon A-1. :clap:
 
its because its trying to predict movement, i find it best to stick to "one shot" for static subjects, but ive never had a problem with AI servo not being acurate.


remember the way canons (im told anyway) work- the first shot of a burst is taken with the cameras criteria of MUST FIRE SHUTTER (shutter being the most important thing so as not to miss the shot) the next shots in the burst will be taken with the cameras criteria of MUST ENSURE CORRECT FOCUS BEFORE FIRING SHUTTER, so the 2nd, 3rd, 4th etc shots in a burst will more than likely be sharper focused etc.
 
I use A1 servo most of the time and can't say I've experienced this problem. Does this happen with the camera on a tripod?
 
CT said:
I use A1 servo most of the time and can't say I've experienced this problem. Does this happen with the camera on a tripod?
Click to expand...

Yes, it happens on a tripod too. and on static subjects in a test environment. One shot will move if i refocus on a static, flat subjet, on a tripod :(
 
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