CANON - Canon FD lens mechanism

A comprehensive technical guide to the locking mechanism of Canon FD lenses, offering hands-on instruction for anyone seeking to understand how these vintage optics function internally. Whether you're performing maintenance, troubleshooting an issue, or simply curious about the engineering, this service manual walks you through the complete disassembly and inspection process. You'll start with removal of the three external fixing screws and the metal securing ring, then systematically access the rear cap assembly and examine each component's role in the overall mechanism. The guide explains how the movable ring, U-shaped slot, and lock button work together to control aperture engagement—critical knowledge for diagnosing why a lens might not stop down correctly or feel stiff during operation. Detailed reassembly notes highlight the importance of keeping the stop-down lever open during reinstallation, preventing damage during the final stages. Throughout the document, color photography illustrates every disassembly stage and key internal parts, making even complex mechanical relationships easy to follow. This is essential reading for technicians, enthusiasts, and anyone undertaking Canon FD lens repair work.