Wide angle lens for DX cameras?

I just have some things confused in my mind. I was thinking of buying wide angle lens. The thing is i have a nikon d3100 which is a crop sensor camera. So the standart mm for wide angle is at 35mm. This means that anything until 35 mm is considered wide angle right? So if i buy lets say a 12-24 mm lens shooting at 12 mm on my camera that would really be 18 mm(cause of 12 mm x 1.5 crop factor =18 mm).Unless i'm using DX Lens? If i buy a DX lens then i don't have to multiplie the mm x the crop sensor? So which wide angle lens is best for crop sensor cameras?
hope that makes sense
thanks

Added (1). What i'm trying to say is that if its stated on the lens DX does this means that when shooting for example at 12 mm, it will actually be 12 mm and not 18 mm( 12 x 1, 5 crop sensor=18 mm)? DX means the lens is especially for dx cameras?

35mm is normal/standard for crop sensor.

http://keerok-photography.blogspot.com/2011/05/lenses-so-many-of-them-there-is-no-best.html

http://www.bhphotovideo.com/...4109119986

Actually, the 18-55mm kit lens has wide angle at the 18mm end to around 24mm.

The 12-24 would be a good choice.

The focal length of a lens is the same whether it us a DX or an FX lens, so a 12mm FX lens would perform exactly the same on your camera as a 12mm DX lens. The difference is, the FX lens is a larger diameter so that it makes an image circle big enough to use on an FX sensor. It also covers the DX sensor totally. A DX lens would not work well on an FX sensor, because the image would be cut off at the edges.

Yes, a 12mm lens would "act like" an 18mm lens, but that's only because the smaller sensor sees less of the projected image - crops it - so that it appears to be bigger. Wikipedia has some great pictures to explain how "crop factor" works.

Add'l: Yes, a 12mm lens would "act like" an 18mm lens on your camera, but that's only because the smaller sensor sees less of the projected image - crops it - so that it appears to be bigger. Wikipedia has some great pictures to explain how "crop factor" works. A DX lens would not work well on an FX sensor, because the image would be cut off at the edges. DX lenses are made specifically for DX cameras.

First, the focal length of a lens never changes even on a crop sensor DSLR like your D3100. What does change, however, is the "equivalent angle of view". At 18mm your 18-55mm zoom will have the equivalent angle of view of a 27mm lens on a 35mm film camera or full-frame DSLR. The focal length is still 18mm. A 12mm lens on your D3100 will have the equivalent angle of view of an 18mm lens on a 35mm film camera or full-frame DSLR. The focal length is still 12mm.

Whether the lens is DX or FX the 1.5x crop factor applies.

On a 35mm film camera or full-frame DSLR a focal length of 50mm is considered a "normal" lens because its angle of view approximates that of your eyes. On your D3100 the 50mm has the equivalent angle of view of a 75mm lens so it is a good choice for portraits. A 35mm lens on your D3100 will have the equivalent angle of view of a 52.5mm lens so on your D3100 it would be considered a "normal" lens - just like a 50mm lens on a 35mm film camera or full-frame DSLR.