SLR Camera, Aperture

The aperture is the size of the opening through which light enters, controlled by the leaves of the diaphragm.

You can resize the diaphragm by turning the aperture ring, and changing to different f-numbers and f-stops. The difference between these two goes thus:

"In the language of photography, when you set a lense to a particular f-number on the aperture ring, you have chosen an f-stop. If you then change to another f-number setting on the lens, you have selected a different f-stop." (Shipman)

The f-number series practically doubles every other stop. The stop series goes thus:

1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22

The series on my camera is:

3.5 - 5.6 - 8 - 11 - 16 - 22

It is important to remember that these numbers are always inverse: 1.4 is actually 1/1.4, 2 is actually 1/2, and so on. Accordingly, as the numbers increase, the aperture size decreases.

Although the numbers double every other stop, the light allowed in the aperture halves between each stop.

"If you have a lens set at f-8 and change it to f-11, the amount of light passing through the aperture will be reduced to half. If you change the aperture from f-2 to f-1.4, the amount of light reaching the film will be doubled."

Another terminology note: changing from a smaller f-stop to a larger f-stop is called stopping down, while the reverse is stopping up. Again, one must keep in mind that the f-numbers are actually inverse to themselves.

Shipman, Carl. How to Select & Use Nikon SLR Cameras. Los Angeles, CA: HPBooks, 1989.