20D w/ Canon EF 400mm 2.8 L USM Mk I

I borrowed a Mk I (series I) 400 f2.8 yesterday to shoot some U14 baseball on my 20D, substituting it for my Sigma EX 120-300 f2.8 that I normally use.

This 400 is used all the time by another shooter with his 1D Mk II and he gets top notch results shooting baseball, soccer, etc. However, on my 20D, the lens frequently lost AF on runners coming straight at me (using AI servo), showed a ton of CA, yielded soft images, and overall, was a HUGE disappointment compared to my lowly Sigma 120-300.

Anyone have any idea why this might have happened? Should I have changed my settings on the 20D when I changed lenses? The fellow who let me borrow the lens was willing to make me a real good deal on it, but now I'm not so interested.

Dennis
http://www.pbase.com/d​mwierz45/sports_shots

I'm not saying this was the culprit, but the 45-point AF with predictive AI servo and the dedicated processor for autofocus could be a darn good reason why the 1DMkII kept focus better. As for CA, that could just be conditions you're shooting in. As to softness, again, it could be either lacking AF (although myself and others have done great with sports on a 20D) or just slower than adequate shutter speeds.

Ronald,

OK, but why would this explain why I've done great with the Sigma 120-300 and the 20D and not with the Canon 400? THIS is the puzzle. Same camera AF settings - same conditions - same camera - different lens - different results.

Virtually all the shots taken at the link below were with the 20D and the 120-300 in conditions much more challenging than those under which I shot with the 400 Mk I and the 20D yesterday.

My question comes down to: what, if anything, about the older Canon 400 lens might cause it to behave this way, and should I have changed my camera settings from those chosen for the 120-300?

Dennis
http://www.pbase.com/d​mwierz45/sports_shots

Shutter speed, mainly. A couple hundredths of a second could make a world of difference. I don't have experience with either lens, but maybe the AF is faster on the 120-300. That 400 is older, obviously. I imagine the AF on the new 400 is improved to match newer bodies as well.

Ronald - they're both f2.8 lenses, so, unless I changed the ISO, which I didn't, the shutter speed is the same, no? Unless you're saying 1/4000 on the Canon is really 1/3700, or something like that Vs an accurate 1/4000 on the Sigma?

Maybe the AF is faster, since the lenses are 13 years apart in technology. While the Canon is a pro lens from 1993, and the Sigma is an "almost pro" lens from today, the Sigma is 13 years newer technology, and that just might make enough difference.

Dennis
http://www.pbase.com/d​mwierz45/sports_shots

Not every 2.8 lens will get the same shutter speed. You'll need a faster shutter on the 400 to negate camera shake. Plus, there's little chance that the light was exactly the same.

Agreed about the technology. You should rent a MkII sometime when you need a long lens, and see how the performance is.