Hello, I have purchased a used 40mm CF lens (in the mail). So far, I've discovered that the outer ring marked 93/40 (40693) is called a lens "shade" and that it can be split in two sections (I wouldn't have guessed). Apparently it is used only with "drop in" filters. (Good luck with finding 93mm unthreaded filters!) I'd like to use a dark red filter - and possibly a UV for protection. A suggestion I found (referenced by carlo_d) would be to use a 93mm to 95mm step up adapter ring, allowing to use (relatively) more common 95mm threaded filters. I'm having a hard time finding one... and 95mm filters are pricey. I'd love to read your recommendations. Thanks in advance. Chris (Republic of Panama).