The f-stop on a camera is the opening that lets light in. The numbers on the f-stop setting set the size of the opening that lets the light into the camera.
The f-stops on a camera are measured by what is called the f-stop scale. The numbers on the scale measure the diameter of the aperture. To understand the f-stop setting, a little math is necessary.
When setting the aperture of F8 with a lens set on a zoom of 40 millimeters, the diameter of the aperture is 5 millimeters. So, photographers can find the diameter of the aperture by dividing the zoom set by the aperture. In this case, 40 divided by 8 equals 5 millimeters.