Lensbaby's optic swap system consists of a bendable mount (in this case the Composer Pro II) and drop-in lenses. The Edge 50 Optic is the newest in the line, but the mount can work with most of its optics.
This is the mount without the optic in it. Although it's not substantially different from the first generation, the focus ring feels a lot smoother than before. The bend allows you to switch the plane of focus for a "slice" like the effect of a tilt-shift lens.