F-Number

F-Number, also known as a focal ratio, is the ratio of the diameter of the lens aperture to the length of the lens. On a camera, a photographer can alter the f-number by changing the f-stop setting on the camera’s lens. Each increment of an f-stop (and, thus, and f-number) represents a decrease of light entering the lens by half the previous intensity.
The more light the lens allows into the camera, the faster theshutter speed should be set, so as not to overexpose the film. Therefore the smaller the f-number, the more light the camera lets in through the lens. So, moving to a higher f-number will halve the amount of light.
Most lenses have f-stops that are represented numerically by integral powers of the square root of two. Common f-numbers on a lens are f/1, f/2, f/4, f/8, etc.

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"World photography" is a photo community wich the initiative taken by Ismail El Moutaki with his two Friends Ayoub Filali and Driss El Amrani for a site, a facebook group and page on facebook, In the in order to help young beginner photographers to share their work and shoots with other photographers and exchanging their idea between them to improve their experiance in other side "worldcphotography " also gathers the professional photographers From differing countries of the world in order to give advices and share their experiences with the beginners in " world photography " , photographers can post their request to buy or sell cameras and accessories and photographs too