When I was starting out in the '8o's I was (OK, still am) a bit of a camera nerd. Couldn't wait for that next issue of Shutterbug. Starting out meant a tight budget for me, but I perused used gear not just for bargains but for knowledge and for fun. I remember "rare earth" lenses, so called because rare earth elements were used in in their lens coatings. They were very scarce, highly sought after, and unbelievably expensive even decades after they were made. The discussion of fluorite sparked this memory.
I always wanted one, and always wanted to know more about them. Wondering if anyone else had a similar curiosity, or any amount of erudition they could share.
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