It is a rather odd combination I think. No money to buy a 21/4 RF version to complete the collection and it is properly the only method.
1. A very rare Nippon Kogaku 21 viewfinder for S
2. Voigtlander F-S/C adapter, properly as rare as item 1.
3. A Nikon 21/4 mirror lock-up version for F with hood
4. My belovded Nikon M.
5. A rare chorme ring Nikon yellow filter