The Kodak Retina series of cameras is one of the most iconic ranges of German-made cameras and introduced the first cameras using 135 film, a film still in existence today. The early models were folding cameras with viewfinders. Each new type brought small improvements, but apart from the top housing the styling changed little until the introduction of the IB, near the end of the line. By that time the rangefinders had become more attractive.
The number designations were simple, Retina Is are viewfinders, Retina IIs are rangefinders, Retina IIIs are rangefinders with lightmeters. The 'a' series introduced lever winders.