Vignetting at 18mm - Nikon D3100. 18-55mm lens?

I'm new to photography and I have no idea there's always some vignetting at 18mm. I don't seem to be able to shoot at 18mm. The vignetting only disappears at 24mm. Is there something wrong with my camera/lens?

Check the auto focus feature. Try a different manufacturer. If all these fail might be a problem with the cam itself.

Your lens shade might not be wide enough and that's what you're picking up.

If it disappears at a longer focal length closer to 55mm then that's probably it.
Try removing your lens shade or even a UV filter if you have one and see what happens.

18mm is VERY wide angle, approaching fish-eye lens capability.
An example is this Nikon 10.5mm f/2.8 Fisheye Nikkor Lens
http://www.amazon.com/...B000144I30

Your camera and lens are fine.

The problem is either with using a UV filter that is causing vignetting or worse you have purchased a generic lens hood which is designed for a different lens.

The lens hood you need for your lens is the HB-45 Lens Hood.

You will not get vignetting using this lens hood

*All* lenses have vignetting, some more apparent than others. Zoom lenses like the 18-55mm might have stronger vignetting at one or both ends, and sometimes only with certain apertures.

If it really bothers you, you'll have to use lenses with better design, most of which are much more expensive than your kit lens.

Filters and hoods can also block out light at the edges, as fhotoace says.

You can edit away vignetting with a good image editor. Adobe Lightroom is quite good at this, and even has profiles for many lenses to do this automatically.

Virtually all consumer-grade lenses will vignette a bit when used wide open. However, it is not usually noticeable unless you are shooting grey cards. And even then, stopping down one or two stops normally corrects this.

But it sounds as if you have severe vignetting. I agree with the other suppositions that you may not have the correct filter or lens hood. If you are using a filter, special wide-angle filters are available that are thinner than normal, which helps in this regard, and never stack filters on a wide angle lens.

Take off your lens hood. If that's not the supplied lens hood for your lens, then get the right one.