Méthode pratique pour déterminer exactement le temps de pose en photographie : applicable à tous les procédés et à tous les objectifs, indispensable pour l'usage des nouveaux procédés rapides gélatino-bromure et autres
A French photography manual by R. Clément, published in Paris by Gauthier-Villars in 1880, written for practical photographers working with the new fast gelatin-bromide plates to calculate exposure times. Its single picture is a geometric line diagram, a simple optical sketch of a lens with converging lines from two points, labelled B, C, O, and b, c, f, showing how the image of an object is formed. A designer might take from it the clean, schematic look of nineteenth-century technical diagrams: thin black rules, lettered points, and a spare, precise layout.
