In 1874, John Henry Dallmeyer called the ratio 1 / N {\displaystyle 1/N} the "intensity ratio" of a lens: The rapidity of a lens depends upon the relation or ratio of the aperture to the equivalent focus.
Pada 1874, John Henry Dallmeyer menyebut rasio 1 / N {\displaystyle 1/N} sebagai intensity ratio sebuah lensa: The rapidity of a lens depends upon the relation or ratio of the aperture to the equivalent focus.