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In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. By incorporating index of refraction in its definition, NA has the property that it is constant for a beam as it goes from one material to another, provided there is no ...
Memorial in Jena, Germany to Ernst Karl Abbe, who approximated the diffraction limit of a microscope as = , where d is the resolvable feature size, λ is the wavelength of light, n is the index of refraction of the medium being imaged in, and θ (depicted as α in the inscription) is the half-angle subtended by the optical objective lens (representing the numerical aperture).
A perfect optical system produces an image with the same etendue as the source. The etendue is related to the Lagrange invariant and the optical invariant, which also share the property of being constant in an ideal optical system. The radiance of an optical system is equal to the derivative of the radiant flux with respect to the etendue.
The digital analysis of a set of holograms recorded from different directions or with different direction of the reference wave allows the numerical emulation of an objective with large numerical aperture, leading to corresponding enhancement of the resolution. [22] [23] [24] This technique is called interferometric microscopy.
The pupil function or aperture function describes how a light wave is affected upon transmission through an optical imaging system such as a camera, microscope, or the human eye. More specifically, it is a complex function of the position in the pupil [ 1 ] or aperture (often an iris ) that indicates the relative change in amplitude and phase ...
The photography term "one f-stop" refers to a factor of √ 2 (approx. 1.41) change in f-number which corresponds to a √ 2 change in aperture diameter, which in turn corresponds to a factor of 2 change in light intensity (by a factor 2 change in the aperture area). Aperture priority is a semi-automatic shooting mode used in cameras.
Optical units are dimensionless units of length used in optical microscopy. They are used to express distances in terms of the numerical aperture of the system and the wavelength of the light used for observation. Using these units allows comparison of the properties of different microscopes. [1]
In an optical fiber, the normalized frequency, V (also called the V number), is given by = =, where a is the core radius, λ is the wavelength in vacuum, n 1 is the maximum refractive index of the core, n 2 is the refractive index of the homogeneous cladding, and applying the usual definition of the numerical aperture NA.