I recently purchased a Canon EF 300 f/4 L IS for my 20D and must say I am impressed by the image quality of this lens. I have noticed however that there is some diagonal banding in the background on some of the images. They occur in the out-of-focus/ bokeh area of my images and do not continue into the sharp/ in-focus areas. Has anyone else experienced this problem? Have not noticed this problem with my EF 70-200 f/4 or EF 180 f/3.5 Macro. The banding all seem to move from the top-right corner to the bottom-left corner. I am wondering if this is a lens problem or just the image sensor limitation.