The amount of light passing through the lens is controlled by the aperture hole. The aperture value indicates how much light can pass through. Since it is expressed as f/2.8, f/16, etc., it is also called the "f-number." The f/1 aperture value represent the maximum diameter of the aperture. When the aperture is half the size, it is called f/2, and when a quarter of the full size, it is f/4. The f-number is therefore the denominator of the fractional size. The larger the denominator or f-number, the smaller the aperture size and the less light can pass through. Note that although f/2 is half the diameter of f/1, the total area of the hole is only one-fourth of the full-size hole (1/2 x 1/2 = 1/4). And so the amount of light passing through is only 1/4 that of the full-size hole. When the f-number is doubled, the amount of light shrinks to 1/4 of amount.