ice as large in lineal dimensions, that is four times as large in area. If an object be focussed with two such lenses, and the stop marked //8 inserted in each — that is, the stop whose diameter is ^ the focal length — we get in the one case an image four times larger than in the other, and also… … image of a certain size and brightness ; through the smaller lens only twenty-five can pass, but as these form an image only I the size of the other they will make it of equal brightness. Hence, stops which bear the same ratio to the focal length require the same exposure, whatever the focal length…
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
![An illustration from Photographic optics and colour photography [electronic resource] : including the camera, kinematograph, optical lantern, and the theory and practice of image formation (1909)](https://img.insideoutlibrary.com/img/200/ia-b21287223-228-0.webp)
