The Mamiya MSX 500 and MSX 1000 cameras were introduced in May 1974. They were cameras with through-the-lens (TTL) spot metering only. Like the Mamiya/Sekor TL/DTL series models, they used M42 screw mount. SX lenses, a part of the system, featured a mechanical pin which transmitted the F-stop information to the camera, eliminating the need to stop-down for metering.
The Mamiya DSX 500 and DSX 1000 cameras were introduced in October 1974. The main difference between the DSX and MSX series was the addition of the average metering system to the DSX cameras.