Purest Unobtainium!! UV Lens and Filter, Exacta Mount!!!
Found and bought on Internet, a 50mm f/3.5 macro uncoated pure quartz lens, a U340 filter (passes 300-380nm, blocks visible light) T-mount, with Exacta, SA, and C-mounts, screw lens covers, all mint. Unobtainium, finest kind! Costs too much, but if I can make this work, there will be photos in ultraviolet light. Will fit my Topcon and Sigma SLR's.