The Digital Picture has recently posted their review on Canon EF 70-300mm f/4-5.6 IS USM and wrote:
” The Canon EF 70-300mm f/4-5.6 IS USM Lens has decent sharpness wide open and good sharpness when stopped down a stop or so. Corner sharpness is good even at full frame. The long end of the focal length continues to be the weakest performing over the range. Overall, sharpness is definitely improved from the 75-300 IS.
The Canon EF 70-300mm f/4-5.6 IS USM Lens exhibits barrel distortion (on a full frame body from 70mm to 120mm or so. Slight pincushion distortion is visible at 300mm. CA is very well controlled.
Light fall-off is quite noticeable wide open (f/5) at 200mm and improves slowly as the focal length is increased or decreased – or the lens is stopped down one stop. Light fall-off is still noticeable at 100mm f/4.5 and 300mm f/5.6. 1.3x and 1.6x FOVCF body users will avoid most of this issue. “