Vivitar 2X Macro Focusing Tele-Converter for Nikon Ai 50mm lens.

This somewhat hard to find and unique accessory will convert your Nikon Nikkor 50mm Ai lens into a 100mm macro lens with  maximum aperture reduction of 2 f-stops.  

So, if you attach it to your Ai Nikkor 50mm f/1.4 lens, you will have a 100mm f/2.8 macro lens with up to 1:1 reproduction ratio.

It is primarily intended for the Nikkor fast 50mm lens (as evidenced by the reproduction ratio scale labelled 50mm), but can be uised with other focal lengths.

This solid, metal and glass tele-converter has excellent build quality and surprisingly good optical performance.  Glass elements are clean clear; focusing action is smooth and precise.

Comes with caps.