i realize that you were talking about sharpness in the beginning, but that is only one part of the image quality difference and quite frequently one of the smallest areas of difference. One of the easiest areas to see differences between versions of lenses in ANY size or resolution of image is flare followed by CA. Given the number of lenses that show substantial improvements in these areas with each successive version I can see the initial challenge could get rather costly at a $100 a pop. Covering a lot of outdoor sports events myself I can really appreciate the improvements in the coatings when at the start/finish line in the early mornings and late in the day.