REPAIR & TROUBLESHOOTING - Rebuilding CdS lightmeters3

Comprehensive technical guide dedicated to the design and reconstruction of CdS cell-based exposure meters. The work begins with fundamental physics principles governing photoresistive elements, progressing from idealized behavior to practical real-world considerations including dark resistance and performance limitations. A key section addresses linearity requirements and the critical need for logarithmic scale response to achieve accurate exposure measurement. The document examines galvanometer movements available during the mechanical camera era and explores the essential role of reference values in measurement systems. The second portion provides thorough analysis of mercury cell type meters, including general theory followed by a detailed handheld meter design example covering galvanometer selection, LDR photocell characteristics, resistor and trimming potentiometer dimensioning, scale design, and geometric techniques for scale expansion. Practical implementation challenges, particularly regarding light path delivery to the photosensitive element, are also addressed. This resource combines theoretical foundations with practical calculation methodologies essential for understanding and implementing CdS-based light metering technology.