Aperture

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The articles aperture , iris diaphragm , critical diaphragm , entrance pupil , exit pupil and light intensity (photography) overlap thematically. Help me to better differentiate or merge the articles (→  instructions ) . To do this, take part in the relevant redundancy discussion . Please remove this module only after the redundancy has been completely processed and do not forget to include the relevant entry on the redundancy discussion page{{ Done | 1 = ~~~~}}to mark. - Alturand … D 20:14, 11 Jun. 2018 (CEST)
Effect of different apertures

In optics, aperture or opening width denotes the free opening or its diameter through which the light rays are transmitted or received. The determining component is called the aperture diaphragm and is often adjustable in photography, see f-number . The object-side image of the aperture is called the entrance pupil , the image-side exit pupil .

Because of wave diffraction , the angular resolution depends on the diameter in relation to the wavelength of the radiation used. For example, a radar antenna 1000 times the diameter of the pupil has only a tenth of the resolution because the wavelength of the radar is 10,000 times that of visible light (for the quantitative relationship see Rayleigh criterion ). By means of coherent superimposition , several apertures can be combined to increase the resolution, for examples in the optical area see the category Interferometric telescope . The possibility of coherent signal processing available in the radio frequency range means that apertures that are far away can also be combined, see long-base interferometry , and a synthetic aperture can be calculated from the signal from an antenna that is moving in relation to a rigid object .

The area of ​​the aperture (e.g. a planar antenna or a telescope ) determines the power absorbed from a plane wave . In the case of imaging optics, this is distributed over the surface of the image, the size of which increases with the focal length , so that the ratio of aperture diameter: focal length is referred to as the luminous intensity of the objective . The fact that a cell phone camera is inferior to a larger camera in weak light conditions with the same light intensity is mainly due to the fact that it can capture less light due to the smaller area of ​​the aperture.

This relationship, or more precisely: the numerical aperture , also determines the spatial resolution of a focusing lens, such as a microscope , in relation to the wavelength.

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