I use the-digital-picture.com to check Image Quality of EF 70-200mm f/4 L IS USM and i'm surprised. The-digital-picture.com shows that Image Quality of this lens is very sharp even at 70mm F/4 and 200mm F/4
http://www.the-digital-picture.com …ample-Crops.aspx?Lens=404
http://www.the-digital-picture.com …omp=0&FLIComp=0&APIComp=0