Does anyone know exactly how this item is used? It's about 5 inches long with opitical glass on both ends. It looks a little like a loop. Turned backwards (small end pressed to the ground glass) it can make ground glass focusing a little easier but I have no idea how this thing was designed to work. It came with a Crown Graphic set. There were a few Ednalight Filters in the box as well. Thanks for any info- Google revealed nothing!