Manuel pratique d'orthochromatisme
A French practical manual on orthochromatic photography by Léon Vidal, published in Paris by Gauthier-Villars in 1891, written for photographers and technicians working with colour-sensitive plates. Its pictures are precise line diagrams of optical apparatus, including a spectroscope-style light path, a prism setup, and sensitivity curves plotted against spectral letters, offering a designer clean technical schematics with lettered labels and fine hatched shading.
