Aperture is “An opening usually variable in size, located in or near a lens, that is used to control the amount of light that reaches the photosensitive material.” by Bruce Warren.

The Aperture controls the Depth-of-Field (or the area in focus). Apertures are measured in units called Focal Stops, Focal Numbers or commonly known as F-stops.

Most digital cameras allow for 1/3 F-stop increments, which can be confusing.  It is best to try and memorize the full f-stops below, as opposed to the 1/3 increments (F2.8, F3.2, F3.5, F4 etc.).

F2,  F2.8,  F4,  F5.6,  F8,  F11,  F16,  F22,  F32,  F64

Adjacent numbers in the above series of full stops allow light to spill into the camera in a proportion of 2 to 1.   For example, changing an aperture from F4 to F5.6 will decrease the amount of light spilling into the camera by half.  This is known as Stopping Down. Changing the aperture from F16 to F11 is called Opening Up and doubles the amount of light entering the camera.

Aperture Diagram courtesy of www.camaraphotography.com

When the lens is Wide Open, the smallest aperture is used, letting in the most amount of light.  Each individual lens will have a set Wide Open aperture.  The smaller the aperture, the more expensive the lens.  Standard lenses use a wide open aperture of F4-F5.6.  More expensive lenses use F2.8 or smaller.

More aperture discussions to come.  Please feel free to comment if you have any questions or if you would like to request a PhotoTips topic.

Warren, Bruce . Photography: Second Edition, 2002 (Albany, NY, USA: Delmar with Thomson Learning INC, 2002), A24.