Oskar Barnack's work on his small format camera was interrupted by the First World War. It wasn't until 1920 that a fourth prototype, the Handmuster, gave birth, after further developments throughout 1923/24, to the first small series – the so-called Null series – with numbers 100 to 130.
Probably only 26 cameras were built. As of serial number 123 they had become prototypes for the Leica I A, which was already equipped with a shutter, which no longer needed to be covered after winding to avoid a second exposure.
These prototypes also already possessed the Leica I A's Galilean telescope, while the earlier Null series models were equipped with a fold down finder with swing-up front sight.
Nowadays probably only 17 cameras of this series remain. On May 21, 2012, one of them was sold by auction at Westlicht in Vienna for 2,160,000 euros – the highest price ever paid for a camera.