Vivitar MD 2X teleconverter destructively modified.
MD mount was removed and replaced with a turned down Maxxum T mount adapter.
Focuses from infinity down to 1:1 by action of built-in focusing helicoid.
Coarse adjustment across the full range is possible with the teleconverters
focus ring. When set at compressed position, the lens focus ring operates normally.
Also a highly corrected (for macro) 2X teleconverter. so working distance is twice that of a 50mm lens.

Dual scale shows reproduction ratios for a 50mmm lens when minimally and fully extended.