The hood vignettes under 20mm. Under 30mm if you have a filter on the lens.
The build is good - hard plastic. It screws on and has a locking ring. Could use filter threads on the front for a circular polarizer, (you can wedge one in if you in a pinch).
Over all not for full frame camera use. Ok for APS sensor cameras with lenses 35mm and above
This thing is a pile. At wide angle it vignettes the corners of your photos. Save your money and buy the hood specific to the lens. I would not recommend this to anybody I liked.
This is a nice lens hood. However, it DOES cut the corners of the picture at 18mm. I have a 18-200 digital lens and can't use the hood from 18-25 without cutting the corners. I was a little disappointed given the description. It was slightly difficult to thread, but once it was on it worked great.