PENTAX - pentax spotmatic f meter

This service manual provides the technical foundation for understanding and servicing the light metering system in the PENTAX Spotmatic F camera (Product No. 23110). The documentation covers the three core elements of the metering circuit: the differential ammeter (J100), CdS photocell calibration and adjustment procedures, and the photo switch (Photo-SW) that manages exposure measurement across the full range of lighting conditions. The differential ammeter section explains how the dual-circuit design responds to light intensity changes—the galvanometer needle centers when currents balance, deflects upward when the CdS photocell current exceeds the variable resistor current, and downward when the relationship reverses. This forms the basis for all exposure readings. Detailed procedures walk through linear adjustment (full aperture metering) and level calibration of the CdS photocells, with specific checkpoint values at EV16, EV12, and EV8 that help technicians verify the meter is responding correctly across the exposure range. When calibration drifts beyond tolerance, the manual lists ten fixed resistor values (J504) ranging from 110 kΩ to 1.1 MΩ—each one selected to correct specific needle deflection errors without replacing the entire meter assembly. The photo switch section explains how the circuit cuts at extremely low light levels (EV2) and includes straightforward circuit testing methods to verify proper operation. Wiring diagrams, component schematics, and an exploded view of the metering assembly round out the technical content, making this an indispensable workshop manual for camera technicians performing meter repair, adjustment, and troubleshooting on Spotmatic F equipment.