[quote author=Elite link=topic=2736.msg28765#msg28765 date=1198629031]
Yeah but I just found out a problem with it >
..
When shot at 18mm, there is a black shadow right in the middle of the bottom and the four corners. >
I think there is something wrong with this len. I'm going to call the vendor when they reopen tomorrow.
[/quote]
did you use flash?
It's called vignetting, it happens to most zoom lenses when you shoot on the wide end.
http://en.wikipedia.org/wiki/Vignetting
The one in the middle is your lens casting a shadow on the wall... though not sure why yours is orange... and not sure why the lower right has red. To remedy this, you need an external flash to mount, a ringflash, or off camera flash... or no flash at all.
To remedy the vignetting... well you can't really with that lens, you'll probably need to photoshop (which is super easy to remove vignetting from RAW files) or a different lens.
Do you have a filter on it? Sometimes at 18mm the thicker filters also cause a bit of vignetting.
Sometimes vignetting looks ok in photos. This one of my car is most likely one of the few where I didn't correct the vignetting in photoshop: