At its most basic, an aperture is simply a hole through which light travels–although the use of aperture to refer to any old portal through which light passes has certainly fallen out of a fashion. The term is most widely used in terms of optical systems such as cameras and telescopes.
When someone says they’ve adjusted the aperture of their camera, they’re saying they’ve used the controls on the camera to change the size of the opening of the mechanical iris inside the camera’s lens. Camera apertures are referenced using the f/X notation where the X number is the ratio of the focal length to the aperture diameter. Because it’s a ratio and not an absolute value, the larger the X value is, counterintuitively to new photography students, the smaller the physical opening of the aperture. A lens set to f/1.4 has an aperture opening so wide you can look right into the body of the camera lens where as a lens set to f/22 has a nearly pin-hole sized aperture opening.
For more information on camera apertures and how you can use aperture adjustments to improve and stylize your photography, check out the following How-To Geek articles: Improve Your Photography by Learning the Elements of Exposure, HTG Explains: Cameras, Lenses, and How Photography Works, and The How-To Geek Guide to Custom Photo Bokeh.
- By Jason Fitzpatrick on 04/12/13