I've read reviews saying the image quality of the Sigma 70-300mm f/4-5.6 APO DG Macro Autofocus Lens (a $200 us lens) between 70 and 200 with mid-f-stop rivals the Canon 70-200 f/4 L. I've only found a few reviews and find this very hard to believe. But, anything is possible. Anyone with experience (no Sigma dealer any where near me) please let me know. Just my curious nature requesting. And, yes Colin, I know "Curiosity killed the Cat".