Nikon 135mm f/2 DC

I just got myself the Nikon 135mm/f2 DC. DC is for "Defocus Control", which is Nikon's patented system for controlling the background or foreground blur.

I've only been able to try it out a bit, but the technique is that the "Defocus Image Control" ring correlates to the aperture you're using. Se it to 0 and it's a normal lens, but if you use it, you set it to 2 to the "R" (rear) side if you're shooting at f2, which enhances the background blur.