I went out to play with my Tokina 12-24 that is made for cropped sensors on my full frame 5D. Ordinarily, it would make an incomplete circular image in the sensor, but I found quite by accident that the petal shaped hood really does it's job by shading in a rough rectangle. It turned out to be a neat effect in my mind for at least some of the compositions that I came upon. Again, a great little stroll through Izuminomori Park not ten minutes walk from our house.