My brother, pictured earlier, just bought this lens on Ebay. It's a Charles Beseler compound lens with a focal length of 18 inches (441 mm) and a diameter of 5 inches. The lens has three elements, the properties of which I haven't yet determined. It has a few scratches but mostly needs a good cleaning. We think it came out of a drive-in theater projector. Anyone got any creative ideas for it's use in photography? We're leaning toward a home-made telescope of sorts (I'm no stranger to telescope building).