The 50mm lens that you are thinking about is a C lens. C lenses use B-50 filters and are less ergonomic than the newer lenses. The CF and newer lenses use B-60 filters. If you buy C lenses and CF lenses you will need two sets of pricey filters, B-50 and B-60. I strongly recommend that you only buy CF or newer lenses and avoid the C lenses. The CF lenses are the most cost efficient lenses since later models add mostly electronics and some add a front end focus adjustment [FLE]. I have not found FLE worth the additional costs.