Doubts on 1Ds AF.

[aldvan]

Last week I've received my second hand 1Ds MkIII. I'm very happy about it since it is in very good condition. I started taking pictures in my usual way, focusing on the central sensor. Perfect focus and exposure.
Now, considered the sofisticated AF system of this camera, I started testing with AF but I found very difficult to get a sharp focus in that mode. I contacted the CPS and they told me to send them the camera for a tune up of the AF sensors. Is it any chance that I'm doing any mistake configuring the AF mode? Is it possible that I get a sharp focus with the central sensor and na out of focus with the other ones?
TIA

[TW]

What lens were you using?

[Viggo]

You should always calibrate your gear. I could be that you are using an AF-sensor that is not a crosstype, which makes it harder for it to get focus. It also depneds on the max aperture of your lens how good AF will be. Also the contrast of the subject. So if you are trying for it to fail, you will succeed, but as I said; calibrate it first, it has helped me from "no good" to "never misses an image"...

[aldvan]

It is lens insensitive. (100mm L Macro IS, 100-400 L, 16-35 L II, 24-105 L). I always microadjust my camera+lens, but the point is that focusing on the central spot the focus is just perfect, no matter the lens. Bad focus happens just with the AF (full sensors)...

[-zero-]

You mention it's a second hand camera, could it be that the previous user has set a particular micro focus adjusment (if it has the option, I have never touched this camera)
try a factory reset of all the settings

[Mt Spokane Photography]

Sending it to CPS was the right thing to do.  Its likely that the issue was always there, and the original user never tested it.  In any event, a inspection and cleaning while you just received it is a good idea.  Then, if they find a major issue, you can go back to the seller.

[Viggo]

You can adjust the front-and backfocusing in camera until your face turns blue (I have done it more then twice to say the least) But what you can't do is the adjustments to the body itself. I have had my lenses hitting spot on when it comes to back and forth, but the stability was way of. The focus was "nervous" in Ai Servo mode, trying to refocus and cause all kinds of issues. But after Canon calibrated the body, 95% of my lenses had to be microadjusted to "0" again, and the tracking with Ai Servo was such an improvement you wouldn't believe it!

Tell me how you have set up your Ai Servo C.Fn

[aldvan]

Thank you all for your advices. I tried to reset to the default values without any result. Now I tested individually each sensor and I found consistent differences. I think that a Canon service tune up should be the right thing to do...