Made by Luminac, this is a three element air spaced fully coated Anastigmat lens assembly with a 4 inch focal length (102mm) f/3.5. Anastigmat lenses are photographic lenses completely corrected for spherical aberration, coma, and astigmatism. Barrel is 48mm diameter by 52mm long. Three element air spaced lens assembly consists of the following elements: DCX 30mm dia x 53mm fl (almost PCX-slight curve on one side), DCV 25mm dia x -33mm fl, and DCX 28mm dia x 48mm fl. Could make a nice compact finder as the images with an eyepiece are sharp, flat and color corrected. Also makes a nice color corrected magnifier. Other ideas: Put two together for shorter focal length, line up several and/or take some apart to experiment with optics, or use your creative juices for other ideas. Unused in mint condition.