The Mamiya MSX 500 and MSX 1000, introduced in May 1974, were cameras with through-the-lens (TTL) spot metering only. The Mamiya DSX 500 and DSX 1000, introduced in October 1974, added the average metering system. Like the Mamiya/Sekor TL/DTL series models, all these cameras used the 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.