Aperture

Aperture denotes the hole - or iris shaped opening of a lens, which opens and closes variably. The Aperture, in itself constructed in a lammella type fashion, is primarily responsible for the amount of exposure and also adjusts the focal depth of a shot. The maximum amount of focal depth can be archieved with the maximum amount of aperture.

Luminosity

The ratio of the maximum possible aperture (expressed through a f-number) to the focal length is called the luminosity. A lens has a higher luminosity, the higher its maximum aperture is and therefore light, acting upon the film or sensor, is transmitted.