I am aware that ultra-wide angle lenses do not work well with polarising filters in that there is a very unnatural variation in brightness of the sky between the centre and the corners when they are used. However, unlike the various 7-14mm lenses released and announced, the Olympus 9-18mm lenses (both Four Thirds and Micro Four Thirds - I have the former) have filter threads. Does anyone use a polarising filter with one of these lenses at 9mm? If so, does it exhibit the unnatural appearance in the sky, or is 9mm not wide enough for this to be an issue? I should be interested in any sample photographs of the use of a polariser at 9mm, too.