Apertur

Apertur is a term used across science and engineering to denote an opening through which waves or particles pass. In most contexts it refers to the opening in an optical system that determines how much light is transmitted, such as in cameras, telescopes, and microscopes.

The word derives from the Latin apertura, meaning opening. In several languages the form Apertur is used to signify the same concept as the English aperture, reflecting its role as the controllable opening in an instrument.

In optics and photography, the Apertur is the size of the lens or iris opening. It is typically adjusted with an iris mechanism and expressed as an f-number (f/N). A larger Apertur (smaller f-number) lets in more light and produces a shallower depth of field, while a smaller Apertur (larger f-number) reduces light and increases depth of field. Very small openings can introduce diffraction, which can soften image sharpness.

In astronomy, the Apertur of a telescope is the diameter of its objective lens or mirror. This parameter largely determines the light-gathering power and the theoretical angular resolution of the instrument. Larger apertures improve the ability to observe faint objects and resolve fine detail, though practical limits include weight, cost, and optical quality.

In microscopy and spectroscopy, the Apertur influences performance as well. In microscopy, numerical aperture and the entrance aperture affect resolving power and brightness. In spectroscopy, the entrance Apertur controls spatial sampling and can influence spectral resolution.

See also: aperture, f-number, depth of field, numerical aperture.