A fifth mode is "stopped down AE", in which the aperture is closed and alterable by the photographer and the camera selects the shutter speed based on the actual light reading.

The 1970s and 1980s were an era of intense competition among the major SLR brands: Canon, Nikon, Minolta, Pentax and Olympus.

In addition, because of rapid advances in electronics, the brands continually leapfrogged each other with models having new or more automatic features, and less expensive components and assembly.

The industry was trying to expand out from the saturated high-end professional market and appeal to the large mass of low-end amateur photographers keen to move up from compact automatic leaf shutter rangefinder cameras to the more "glamorous" SLR but were intimidated by the need to learn all the details of operating a traditional SLR.

They all use the same compact aluminum alloy chassis, but with differing feature levels and outer cosmetic acrylonitrile-butadiene-styrene (ABS) plastic panels.

By sharing most major components, and an inexpensive horizontal cloth-curtain shutter, costs could be spread out over a larger production volumes.

Some professional photographers worried about the long term reliability of its consumer-level mechanical and electronic components under heavy daily use, the relatively slow flash sync and top shutter speeds.

Canon's abandonment of the FD lens mount for the EOS design also had a significant effect on demand for the A-1 on the used market.