Pentax's first auto Spotmatic — the Electro Spotmatic, aperture-priority auto, M42, 1971.
The Pentax Electro Spotmatic of 1971 was the first automatic-exposure camera in the Spotmatic family, introducing aperture-priority auto exposure to Asahi's screw-mount line. It was sold in most markets as the ES, with the Electro Spotmatic name used chiefly in Japan. It pointed the way from the manual Spotmatics towards electronically controlled bodies.
This is a 35mm film SLR using the M42 screw lens mount, taking universal M42 lenses, with open-aperture metering on the correct SMC Takumar lenses. It has an electronically-timed focal-plane shutter offering stepless automatic speeds in aperture-priority mode plus manual speeds, and a fixed eye-level pentaprism with an instant-return mirror. Because the timing is electronic, the automatic and slow speeds depend on a battery; without power the camera is limited to its few mechanical speeds. Metering is TTL.
The Electro Spotmatic suits photographers who want automatic exposure within the M42 system, easing travel, documentary and portrait work where quick response matters. It handles like a Spotmatic but adds set-and-shoot convenience through aperture priority. It works best with the matching SMC Takumar lenses and remains compatible with the wider M42 pool.
As an early-1970s electronic body, checks are important. Inspect and expect to replace perished foam light seals and mirror-damper foam. Test the electronically-timed shutter across auto and manual, listening for even, accurate speeds, since ageing electronics can drift. The meter and auto system need a working battery, and the design assumed a 1.35V mercury cell, so a modern replacement may affect accuracy. Check the pentaprism for desilvering or foam haze, and test the advance and rewind. With a dead battery only the mechanical speeds remain.