Aperture on Camera

Written by Bruce Saturday, 10 April 2010 05:39

In some contexts, especially in photography, the aperture is the hole inside the lens that allows light through. Aperture is measured in "f" numbers - a ratio of the diameter of the hole and the focal length of the lens.

 

 

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time).

58mm__lens.jpgAn optical system typically has many openings, or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.

In some contexts, especially in photography,the aperture is the hole inside the lens that allows light through. Aperture is measured in “f” numbers - a ratio of the diameter of the hole and the focal length of the lens. The size of this hole can be adjusted – a larger hole allows more light in, a smaller hole less. An important effect of this is the depth of field. A smaller hole (higher “f” number) produces a lot of depth of field. The reverse happens with a larger hole (smaller “f” number). In digital photography, DSLRs  can produce a range of depth of field effects. Compact digital cameras can’t. This is due to the smaller sensors and shorter focal lengths used.

APERTURE PREVIEW - Controlled by a button or switch on some cameras, this feature permits you to look at the scene in the viewfinder with the aperture stopped down to the opening you intend to use when taking the picture. It is a handy aid in checking the effect of depth of field - i.e. what will be in focus.

APERTURE PRIORITY - A function or shooting mode of a semi-automatic camera that permits the photographer to preset the aperture and leaves the camera to automatically determine the correct shutter speed. What does that mean? You select the aperture setting you want and the camera then automatically calculates the appropriate corresponding shutter speed for proper exposure. It's like a fully-automatic camera except you totally control the aperture.

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Last Updated on Tuesday, 16 November 2010 11:49