I had good luck using Canon's 28 to 200 zoom on my 10D. It covered most shots but could have used a little more reach when he played outfield. I also used a monopod. I shot the images in Raw format so I could enhance and crop the distant shots of the outfield. The 200mm is equl to a 320MM with the 10D as you probably already know. Just thought about buying a 1.4 or 2X extender. I wonder, has anyone tried these with the digitals, is there any problems with reflections off the extenders?? I did have good results with the 28 to 200 lens. I do have a Tamron 28 to 200 for minolta that I like a little better because it does not do the creep when at a angle. I have not tried the APS lenses as of yet.

calaculations are easy enough, just remember that in the vertical format the 35mm frame requires a distance of 20 feet to fill the frame with a 100mm lens, adjust for the Canon 1.6 factor.