Méthode pratique pour déterminer exactement le temps de pose en photographie : applicable a tous le procédés et a 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 1884, explaining how to calculate exposure time for any process and lens, aimed at photographers adopting the new fast gelatino-bromide plates. Its single picture is a geometric diagram of two triangles meeting at a common point, with labelled vertices B, C, O, and a, b, c, showing how lens aperture and distance relate to exposure. A designer could take from it the clean, schematic line-drawing style of nineteenth-century technical figures, with minimal labelling and strong diagonal construction lines.
