The Zorki 4K is identical but used an advance lever instead of the old-style wind knob. With over 2 million units produced, the Zorki 4 is the most successful Zorki and has a reputation as one of the best Russian cameras, although the self-timer and slow shutter speeds are unreliable. The Zorki Mir of 1959 is a lower-cost Zorki 4 with fewer shutter speeds.