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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 ...
Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.. An f-number is a measure of the light-gathering ability of an optical system such as a camera lens.
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).
In a medium with an index of refraction close to 1, such as air, the angular aperture is approximately equal to twice the numerical aperture of the lens. [1] Formally, the numerical aperture in air is: = / = ()
Here NA is the numerical aperture, is half the included angle of the lens, which depends on the diameter of the lens and its focal length, is the refractive index of the medium between the lens and the specimen, and is the wavelength of light illuminating or emanating from (in the case of fluorescence microscopy) the sample.
The ability of a lens to resolve detail is usually determined by the quality of the lens, but is ultimately limited by diffraction.Light coming from a point source in the object diffracts through the lens aperture such that it forms a diffraction pattern in the image, which has a central spot and surrounding bright rings, separated by dark nulls; this pattern is known as an Airy pattern, and ...
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 ...
This method, called immersion lithography, is the current cutting edge of practical production technology. It works because numerical aperture is a function of the maximum angle of light that can enter the lens and the refractive index of the medium through which the light passes. When water is employed as the medium, it greatly increases ...