How wide is 12mm?

Wide-Angle View (12mm)
Originally uploaded by Cajie.

Short answer: Very wide!

I recently acquired the Sigma 12-24 wide angle lens. I was in two minds whether to pick up the newer 10-20 (which is wider) but is designed only for DX sensors. On the other hand the 12-24 will work fine with a full-frame sensor or even a film camera.
But my main reason for choosing the 12-24 over the wider counterpart was that the 12-24 feels solid and professional, while the 10-20 looks like a flimsy affair.

On my Nikon D70 (with it's 1.5 crop factor), the 12-24 translates into 18-36mm. So my question should really be "How wide is 18mm?".

Even at 18mm, the lens is very wide. It is like a whole new world opening up. Till now, I have been constrained by the lack of wide angle lens in my arsenal.

Now I am looking forward to creating some dramatic looking panaromic shots.