Era: Introduced in the late 1950s (circa 1959), the IROOA was designed during the transition period when Leica was moving from the screw-mount (LTM/L39) era to the modern Leica M bayonet system.
Design Philosophy: Unlike circular hoods prone to blocking corners or larger segments of the viewfinder on rangefinder cameras, the rectangular geometry of the IROOA precisely matches the 3:2 frame aspect ratio. This maximized flare reduction while minimizing viewfinder blockage.
Predecessor & Successor: It evolved from earlier shade designs like the FOOKH (for 50mm lenses) and preceded later slip-on or screw-in locking hoods of the 1960s and 70s.
The IROOA is famously versatile, engineered to fit several vintage 35mm and 50mm lenses with a E39 (39mm) filter thread or standard clamp-style mounting rim from that era:
Leica Summicron 50mm f/2 (Rigid and Collapsible versions)
Leica Summicron 35mm f/2 ("8-Element" version)
Leica Summaron 35mm f/2.8
Leica Summaron 35mm f/3.5
Spring-Loaded Locking Mechanism: Features a clever clip/clamp mechanism on the base that locks securely onto the outer barrel of compatible lenses without damaging the finish.
Build Quality: Milled from solid brass with a durable, textured black enamel or matte crinkle finish ("hammered" paint), built to withstand decades of professional field use.
Engravings: Typically bears the classic script engraving "Ernst Leitz Wetzlar Germany" along with the code name IROOA.