Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Soft With Horrible Vignetting

I just purchased this lens and I noticed horrible vignetting through the viewfinder the second I mounted it to my camera. I ran some tests at all focal lengths and apertures which confirmed my initial observation.The vignetting is unbelievable at 17mm. I've been a photographer for 35 years and I've NEVER seen a lens this bad.This is unacceptable for any lens, much less a Canon branded lens.The vignetting is not the only problem. There is nothing sharp about this lens except when stopped down.Pardon me, but if I buy a 17mm f4.0 lens is it too much to ask that I actually be able to use it at this focal length and aperture?I'm returning this lens immediately.