The Leica Production of the M4 was wound down in 1972, in favour of the Leica M5, which had been introduced in 1971. However, the relatively bulky and expensive M5 met with a cool reception, and sales did not live up to Leica's expectations. Production of the M4 was therefore restarted in 1975, for Leica's 50th Anniversary, and in 1977 the company launched the updated M4-2, which was based on the M4's body, but with a streamlined production process that reduced manufacturing cost. The M4-2 added a hot shoe and motor drive compatibility as standard, but removed the self-timer.(Wikipedia)