I was perhaps a bit too fast in buying this lens and I have found out that the blades in the diaphram makes an odd shape at f/4.0 to f/5.6+½.The opening is symetric but the edges is kind of "starlike" well not quite but I don't know how to descripe it more precise. Can the aperture blades be adjusted? will it cost a fortune? The lens was cheap and I may be happy to use it either wide open or stopped down to f/8. There is a waranty on it so maybe.