You really don't need to alter the dff. Also specify what sort of shades/sunglasses you'd want, there's a huge variety of them out there.
E/ 5 minutes work, that's what I'd consider the basic style of sunglasses
(http://img838.imageshack.us/img838/6356/roldan.png) (http://imageshack.us/photo/my-images/838/roldan.png/)