Role of Luminance in Digital Photography

The second fundamental data of a lens is it's luminance : meaning, the maximum intensity of light that can be transmitted; it's represented by the maximum aperture of it's scale. Therefore, for example, a lens who's maximum aperture is f1.4 is twice a bright as an f2, and four times brighter than a f2.8

The luminance expresses the relation between the focal length of a lens and the diameter (in millimeters) of

the maximum diaphragm aperture. Therefore, a lens of greater luminance and equal focal length than another will have to have a greater diameter. Precisely this greater diameter is what allows capturing and letting a greater intensity of light reach the film, in a similar way to what happens with the eyes of certain animals capable of excellent nocturnal