5D Mark II fault: shifted CMOS sensor???

[limmes]

1 year old 5D Mark II began little by little to do front focusing with all the lenses. I took it local authorized Canon service center.

At first I thought that maybe only AF calibration may be needed. But after couple of days I got message, that "CMOS sensor moved/shifted from it's place", so service center first will have to "put back in place CMOS sensor" and then to do the AF calibration.

How's that possible?? I looked to camera drawings and I don't see ways that sensors can be moved from place. Especially when camera was never dropped and was used very carefully. Talked with service center and they state that it is possible and they told that "have info directly from Canon" that under certain angles even  by soft punch/bump CMOS sensor can be shifted from it place.

Anyone got similar situation or knowledge is that really possible

For me it sounds unbelievable ...

[TCampbell]

I've never heard of this before, BUT... the sensor is mounted on shims which are "factory" adjustable (the shims are not accessible to end-users -- significant disassembly is required and definitiely lands squarely in the "attempting to do this on your own may destroy your camera" category.)  

The shims allow manufacturing to make sure the sensor is mounted parallel to a focus calibration target.  Otherwise you'd have issues where the top of the image is in focus but the bottom is out of focus or the right side is in focus but the left side is not, etc.  (BTW... this exact scenario happened to the Nikon D800 which, for a time, had a number of models being mis-calibrated.  The error turned out to be a focus calibration target at the plant which was not mounted parallel to the camera's focus plane.)  Anyway... these shims would not normally move all on their own.  I would think the camera would have needed to take a hard smack at some point.

The AF sensors are on the "floor" of the camera body.  They are supposed to be mounted and calibrated such that the distance to the AF points (when the mirror is down) and the distance to the sensor (when the mirror is up) are the same -- thus insuring that when the AF points "think" the image should be focused... it really is focused.  

I do not know to what extent the AF points can be adjusted mechanically but it wouldn't surprise me to learn that they might also be mounted on shims.

It is likely that you would only need to have the camera sensor shimmed in correctly -- but this is something Canon service can do.