I just gotten a new toy, sigma 18-50mm at f/2.8. Been serving me very well indoor and outdoor with pretty colours.
I then begun to notice what is called "Vignetting" on pictures taken at 18mm, f/2.8 right up to f/4. A friend of mine cheekily passed a comment that it might be a bad copy. Being a noob, I hope to learn from you guys.
So how bad is considered as 'bad'? I mean, it can an artistic effect but bad on landscape pictures...
Here are 2 recent pictures with obvious vignetting effect.