lens callibaration

i have read the phrase over and over on here but never really understood whats involved from canons perspective and how the user (me, you) know your lens requires it, so can anyone who has had a lens callibrated please explain?

Cheers

btw its damn HOT today in sydaney

nobody? :P so can i take it that none of you actually know but say your lens needs it withouth knowing? :P

If your body/lens combination doesn't take sharp images at the point focused on then it could be the fault of either one of them.
If your camera body takes sharp images with one lens and not with another then the lens which doesn't take sharp images 'may' need calibrating; which is another way of saying that it needs setting back to factory settings. (Of course it could just be a lens which will never take sharp images - in which case ............).
If just one lens in your outfit isn't sharp then Canon won't need your camera as well as each item is reset to a factory standard setting - not each of your lenses to the camera body, which would mean that if your camera body was wrong your lenses wouldn't work properly on another body - and the whole point of camera body/lens systems is that they are all interchangable one with another.

Well I got a Sigma 70-200 2.8 that needed "calibration" I assume - I don't care , I just new it was too soft wide open. After the first try of the lens , noticed no wide open shot looked acceptably sharp. Tried many techniques over the next few days - could not get a wide open shot I was happy with. I could see it was not a front / back focus problem , I tried manual focus , near and far subjects , various focal lenghths ,so I was confident it was too soft wide open. Compared images taken with an earlier Pentax mount Sigma 70-200 - they were obviously much better. A bit soft wide open as you would expect , but much better than my new lens.

So that is it - I could describe precisely the symptons - I'm curious to know what needs to be adjusted by the techs , but I probably would not understand anyway

Its bloody hot in SA (adelaide) too.... it was 35 Deg C :O (for you americans and alike 95 Deg F)

Cam

when you guys say sharp are you pixel peeking? ie deciding if its sharp at 100% crop? or not?