From Leica Wiki (English)
- Code name - SBOOI - 12015
- Production era - 1951-1970s
- Type - Enclosed, cylindrical viewfinder for 5 cm lenses
- Evolution - First version inscribed "5 cm" and later version inscribed "50 mm" and with grooves for gripping
- Reference - Page 16 of Dennis Laney's Leica 1984 Accessory Guide courtesy of Mike Butkus.
- Forum discussion