This post is mainly to meet my obligations to AusPhoto. Something that might be of interest to some people is the microadjustment feature of some Canon Cameras. I have a Canon 400mm f5.6 L USM lens for my bird shots. I was very dissappointed with the performance of this lens until someone put me on to the ability of my Canon 50D to adjust its AF to match lenses. Normally this feature is not required but if a lens is giving consistently soft results it is worth a try. The adjustment is menu driven and involves taking shots at the same target using different adjustment settings which range from -20 to +20. Compare the results until you determine which is the sharpest image, use the image properties information to see what adjustment was used and then set the camera to that adjustment. Plenty of internet sites available to give more precise instructions than I have given here.
After making the adjustment for my lens the results are unbelievably better than I was getting.