All of the 55 Micro Nikkors are dirt cheap and amazingly good. I had one laying around and adapted it to my non-Nikon, non-film camera for this same sort of use. I would assume performance should be considerably better than your 1.4, but if you are happy with the results, that is all that matters.
I am talking about manual focus lenses, but see you have an AF 50. I think manual focus would be an advantage in this situation, but you'd have to check what models are compatible with your Nikon.