Lensbaby has all sorts of trick lenses for your DSLR camera and one that stands out to us is their Double Glass Optic. This optical glass is multi coated to allow an incredibly sharp sweet spot for your subject while giving a minimum of diffusion at all aperture settings. You would use this optic to give you some of those artsy shots where the subject of the photo is very crisp and the edges seem to blur out slowly. Here are some examples shot with this optic: Here, Here, and Here.