[E. von Hoegh]

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.

I'll second the Micro Nikkor, it's one of those really fine lenses that seems to be undervalued.

The quality will be vastly better than your 1.4.

edit - I'm pretty sure Nikon made a slide duplicator to go with that lens, the 55/3.5 Micro Nikkor.