The Mamiya/Sekor 500 TL and 1000 TL cameras were introduced in October 1966. They were fully mechanical cameras with through-the-lens (TTL) metering. Auto Mamiya/Sekor lenses with M42 screw mount were part of the system.
The Mamiya/Sekor 500 DTL and 1000 DTL cameras were introduced in July 1968. The major difference was the addition of two separate metering systems - the spot metering system for limited area light measuring and the average metering system for full area light measuring.
Mamiya also introduced a black-bodied 2000 DTL in 1969.