OUFRO

• Production era - 1959-1983
• Code number - OUFRO 16469
• Type - Extension ring used with OUBIO for all the longer (125mm+) Visoflex lenses and without OUBIO for 35/50mm. OUFRO can be stacked for greater magnification per Forum discussion [1] below.
• Optical thickness - 1 cm
• Source
  • Dennis Laney's Leica Accessory Guide (1st edition) pgs 49-50 courtesy of Mike Butkus
• Forum discussion
  • [1]
  • [2]
  • [3]