63mm

I recently got a 63mm f/2.8 EL Nikkor. It's in very nice condition. While I may eventually use it for printing, I will probably use it for slide copying or other macro work first. I know that past a certain magnification, it is better to use the lens reversed. My first idea was to get a 40.5mm to 52mm step-up ring and attach it to a BR ring. The step-up ring is on its way. While looking around on the auction site I saw two Nikon reversing rings for tne 63/2.8 or 50/2.8 EL Nikkor. One had a price of $125. The other had a staring bid of $ 25. I wound up getting it for $27. Even judging from the macro work I have seen online with the 63, it is capable of good results past 1:1.

The lab I worked for used a 63mm EL-Nikkor for 1:1 35mm slide duping on a ChromaPro.
Excellent lens.

Yes, I have used one for years for standard 35mm enlarging. I think original f 3.5 version was intended for 127 4x4 cm niche.