Friends, I have a bead on a 180mm but need to know if these are essentially the same lens with a different designation, all for price comparison reasons. The N MC is in an all black copal (no metal ring). What would a fair price be for the N MC in like new condition, and what does a "42 mount" mean? I am new to this format. Would this mount work with my Toyo 45A? Much obliged.