Aperture

Aperture or opening size of a lens or an antenna refers to the free opening or the diameter, through which the light rays or radio waves are transmitted or received. The defining component is called aperture and is in photography often adjustable, see photographic aperture / f-number.

Because of the shaft deflection, the angular resolution of the diameter depends in proportion to the wavelength of the radiation used. Has such a radar antenna of 1000 times the diameter of the pupil of one-tenth of the resolution, since the wavelength of the radar 10,000 times as large as that of the visible light ( for the quantitative relationship see Rayleigh criterion). By coherent superposition of several apertures can be combined resolution -enhancing, for examples in the optical range, see the category interferometric telescope. Due to the given radio frequency possibility of coherent signal processing, even the most distant apertures can be combined, see Langbasisinterferometrie, and calculated from the signal of a rigid object moving against a synthetic aperture antenna a.

The area of ​​the aperture (e.g., a patch antenna or a telescope ) determines the received power from a plane wave. This is distributed in an imaging optical system on the surface of the image whose size increases with the focal length, so that the ratio aperture diameter: focal length is called the aperture of the lens. The fact that formally the same light intensity, a mobile phone camera is inferior in low light conditions a larger camera, is mainly because that they can capture by the smaller area of ​​the aperture less light.

This relationship, more precisely, the numerical aperture also determines the spatial resolution of the focussing optics, such as a microscope, with respect to the wavelength.