Hi allThis is my first post, I am not totally new to photography but I do know that I have much to learn, and I suppose this is one of the ways to achieve that.One of my cameras is a Canon Powershot S3 IS. Great camera, nice functions. I practise aviation photography as a hobby, and when I used the S3 to take approach shots of aircraft landing at the airport, I get a lot of vignetting on my photos (dark corners). This only happens when I take photos of aircraft against a blue sky. If I take static shots, i.e. of aircraft parked at a gate, there is no vignetting at all. To combat the vignetting, I shoot in manual mode and use the lowest f-stop possible, then it is better, but still not completely gone. One of my friends has bought the Canon IXUS 70 and has the same problem.Both of us have Canon 350D (Rebel XT) SLR cameras as well, and now use them exclusively for our aviation photography, since they obviously do not produce any vignetting at all. My question is, why does my S3 produce vignetting on "blue sky" shots, but not with shots with anything else in the background? Or could it be related to speed/movement, since aircraft approach shots are fast movement photos.I know every photo is different/unique, and each one depends on the lightning and many more aspects, but this effect has always left me wondering.