Aperture

Aperture denotes the whole - 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 adjust the focal depth of a shot. The maximum amount of focal depth can be achieved with the maximum amount of aperture.

Exposure Compensation

The light meter of a digital camera measures automatically exposure to light. The resulting values for shutter speed and aperture can be adjusted subsequently in cameras with exposure compensation (f.E. by turning of the adjustment knob).

Underexposure

In underexposure a frame is exposed under too little light which can be easily identified by its lack of brightness.

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.