Rack and pinion focusing is a mechanical focusing system commonly used on copying cameras, large-format cameras, and monorail cameras. It works by engaging a pinion gear with a toothed rack mounted on a sliding component, such as the lens board or film panel. Turning a knob or wheel moves the slide precisely, allowing the photographer to achieve accurate focus.
This system provides fine, controlled adjustments, making it ideal for macro, architectural, and studio photography, where exact focus is critical. Its reliability and precision make rack and pinion focusing a staple in professional photographic equipment.