About 20 years ago I found this lens in a storage unit, I know nothing about it and am photography illiterate. I've been using it as a magnifying glass to look at coins over the years, which it does a great job. Can someone tell me anything about it? What is it specifically, what application is it used for, magnification level, value, ect...It does have threads on the outside and inside of the bigger end, lending me to think it's for a camera. Somebody once told me maybe a microscope or some chemistry setting or hospital tech. I have no idea. Any info is more than I have now so it's greatly appreciated.!