Focusing issues: 30D vs 5D

why does my 70-200 f2.8L IS focus better with the 5D? when i mount it on the 30D, it has sometimes front or back focus issues (not bad, maybe 1/4 to 1/2 inch off target when at 70mm. not as bad at 200mm), on the 5D its focus is perfect.

30D has no problem focusing with my other lenses. have you guys encountered anything like this before?

I own a 30D and use 70-200 f2.8 IS and I haven't noticed any focusing issue at general use but for fast moving subject such as bird at flight and running dogs, I have to say I have extremely hard time getting focus on the subject.
I'd say only about 30% of the result comes back with spot on focus...
Anyways I thought 5D has better AF system over 30D right?

yeah, the 5D does have a better AF system. but the problem im describing happens when i do a staggered battery test on the 30D. sometimes its front, sometimes its back focussing. sometimes its spot-on (very rarely). and its not that bad, its off by a few millimeters -- but damnit, its still off!!

Could be a calibration issue, with the camera, and the lens. One combo might be calibrated correctly(5D and lens), the other not (30D and lens). I wouldn't send it to Canon, cause that may cause some other issues, such as now being out of calibration with the 5D, etc.

Sucks...feel bad for ya. That would drive me nuts.

The 5D has better AI servo focus when using the center focus point as it has those extended 'hidden' AF points. It makes a HUGE difference when shooting action. Not like the kind of difference you'd see with a 1D series AF, but it's still a noticeable difference (I use a 5D and 20D).

inthedeck wrote in post #2832551
Could be a calibration issue, with the camera, and the lens. One combo might be calibrated correctly(5D and lens), the other not (30D and lens). I wouldn't send it to Canon, cause that may cause some other issues, such as now being out of calibration with the 5D, etc.

Lenses are calibrated independently of bodies. There's no such thing as calibrating a lens to a body.

cataclysmcow wrote in post #2832714
Lenses are calibrated independently of bodies. There's no such thing as calibrating a lens to a body.

That is true. Never denied that.

Just the inference in the OP's post is that it could be the camera + lens combo...how does one explain that? Makes no sense that the lens works fine on one camera, and not on the other. Would you say that crop factor cameras have issues with lenses that were made for FF cameras? Or that there is either something wrong with one or the other...which is it? Dunno...but that's why I said it's not worth correcting, unless it's going to be used more frequently on the 30D, with which there is an issue.

I understand the better tracking of the 5D, I used to own a 20D, so I can relatively compare focus speed. The 5D will also do better with lenses that are faster than, or equal to, f2.8 as compared to f4.0 lenses and slower lenses. I'd say lenses also have a say, in the focusing speed...as they are the ones with the motors.

Nonetheless, I do feel for the OP...and wish him luck with his decision. Cheers.