OK, I've been having a problem with dark areas on images taken with apertures of about f11 and smaller for a while. There are at least 2 very noticable areas of dirt on the sensor, but despite my best efforts to clean it on several occasions using a wet cleaning kit (swabs, sensor fluid etc. - you probably all know the drill) but unfortunately the dirt seems to be encrusted on the sensor and will not budge. Does anyone have any thoughts on other techniques that I couls use to remove the dirt that may be more effective? Thanks in advance.