This square metal lens hood is specifically designed for Rolleiflex cameras equipped with Bayonet II (Bay II) mounts, such as the 3.5F. The square shape is more efficient than a circular hood for the 6x6 square film format, providing maximum protection against lens flare and ghosting without causing vignetting at the corners of the frame. It features a spring-loaded bayonet locking mechanism for a secure fit on the outer ring of the taking lens. This accessory is essential for maintaining the high contrast and color saturation the Zeiss Planar lens is known for, especially when shooting in backlit or side-lit conditions.