1. In a digital imaging system for assays, the system being of the type including a lens subassembly and an imaging subassembly disposed behind the lens subassembly for forming an image of a specimen disposed in front of the lens subassembly, the lens subassembly comprising: a lens, including a front lens element and having an optical axis; and a source of light disposed within said lens behind said front lens element and constructed so as to direct light towards said front lens element and out of said lens.