Principle photography is focusing light with the help of refraction so as to set fire to medium light catcher. Medium that had been burned with the proper size light lumination will produce shadow identical to refraction of light entering the medium (hereinafter referred to as the lens).
To produce the proper light intensity to produce an image, use the form lightmeter help gauge. After obtaining the size of proper lighting, a photographer can adjust the light intensity by changing the combination of ISO / ASA (ISO Speed), diaphragm (Aperture), and shutter speed (speed). The combination of ISO, aperture & Speed referred to as the exposure (exposure).