Historical Context

When Mamiya dropped the Mamiya M645 in 1975, they completely disrupted the medium format world. Until then, shooting 120 roll film usually meant handling massive, heavy square-format systems ($6 \times 6\text{ cm}$) or giant studio cameras ($6 \times 7\text{ cm}$).

By opting for the smaller, rectangular 6×4.5cm frame format, Mamiya created a modular SLR system that brought 35mm-style speed, handling, and ergonomics to medium format photography. You got 15 shots on a single roll of 120 film (instead of the standard 12 or 10), making it a massive hit for wedding, portrait, and editorial photographers who needed to work fast.