JWellman, I am curious why you say that "you are not getting it" with your 100-400 images. You are shooting with a 50D (a very good camera in my opinion) which will give you a field of view equivalent to shooting with a 160-640 on a FF...so, a couple of questions, are you shooting raw or jpg? and which part of the 100 to 400 are you not happy with? I have a 100-400 that I use for wildlife on my 5D and I never cease to be amazed at the sharpeness of the images it produces, even after some cropping - although I do get the odd OOF image - my fault! As well, it does not seem to matter at what part of the lens I shoot - the 100 end, the 400 end or somewhere in between, I always seem to be able to get sharp images, although I do get a small amount of vignetting at the 400 end from time to time. I do shoot raw and after initial processing in Lightroom, I always sharpen my images for display or printing, depending on the final "output". More questions...do you use the IS on the lens? Do you shoot mostly hand-held or from a tripod? What type of post-processing do you do? Often, it is not necessarily the lens that is the "ultimate" problem, but some other part of the whole "image-capturing/processing" process that contributes to the problem. Maybe some answers to these will help us to help you, because, quite honestly, I don't see the that the problem is as serious as you make it out to be. :mrgreen:
Regards,
WesternGuy