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Optical Fundamentals
Published in Anees Ahmad, Handbook of Optomechanical Engineering, 2018
Ronald R. Willey, Robert E. Parks
The amount of light which can get through a lens system at a given angle from the optical axis is determined by the pupils, apertures, and vignetting. We will neglect the effects of the transmittance of the lenses and reflectance of the mirrors in the system and only address the relative difference of some angle off-axis from the on-axis light. The entrance pupil of a lens is the aperture viewed from object space which can pass light to the image space. The exit pupil is the aperture viewed in image space which passes light from object space. Both of these pupils are the images of the same aperture stop as viewed from object and image space. In a photographic lens, the aperture stop is typically an iris diaphragm which is of adjustable aperture for light brightness control. The F-number of a lens is the effective focal length divided by the entrance pupil diameter. The numerical aperture is another statement of the same quantity where it is 1/(2*F-number) when objects are at infinity and in air or vacuum. The greater the numerical aperture, the more light will pass through the lens.
Optics Components and Electronic Equipment
Published in Vadim Backman, Adam Wax, Hao F. Zhang, A Laboratory Manual in Biophotonics, 2018
Vadim Backman, Adam Wax, Hao F. Zhang
There are several ways to characterize objectives and optical arrays. Each optical system features an entrance pupil, or the aperture where light can enter the system, and an exit pupil or back aperture, where light leaves. Magnification of an objective or optical system is a dimensionless number and reflects the ratio between the apparent size of an object seen through the system and its true size. The optical system's numerical aperture is another dimensionless number that describes the range of angles over which the system can accept or emit light. In most areas of optics, the numerical aperture is denoted NA and is defined byNA=nsinθ where n represents the index of refraction of the medium in which the lens is functioning, and θ denotes the half angle of the maximum cone of light that can enter or exit the lens (Figure 2.5).
Optomechanical Engineering Basics
Published in Anees Ahmad, Handbook of Optomechanical Engineering, 2017
Robert Parks, Ron Willey, Frédéric Lamontagne
The amount of light which can get through a lens system at a given angle from the optical axis is determined by the pupils, apertures, and vignetting. We will neglect the effects of the transmittance of the lenses and reflectance of the mirrors in the system and address only the relative difference of some angle off axis from the on-axis light. The entrance pupil of a lens is the aperture viewed from object space which can pass light to the image space. The exit pupil is the aperture viewed in image space which passes light from object space. Both of these pupils are the images of the same aperture stop as viewed from object and image space. In a photographic lens, the aperture stop is typically an iris diaphragm, which is of adjustable aperture for light brightness control. The F-number of a lens is the effective focal length divided by the entrance pupil diameter. The numerical aperture is another statement of the same quantity where it is 1/(2 × F-number) when objects are at infinity and in air or vacuum. The greater the numerical aperture, the more light will pass through the lens.
Geometric calibration method based on Euler transformation for a large field of view polarimetric imager
Published in Journal of Modern Optics, 2020
Chan Huang, Yuyang Chang, Lin Han, Su Wu, Shuang Li, Donggen Luo, Liang Sun, Jin Hong
The optical structure, composed of the front group, focusing group and back group, is made up of 12 lenses with the ‘negative-positive’ inverse telephoto structure which can achieve wide field of view and long working distance. The front group is an afocal system whose main function is to reduce the angle between the beam and the optical axis and to decrease astigmatism and distortion of the system. To avoid radiation from space environment, the first lens is made of fused silica. The second lens is designed as parabolic, in combination with a meniscus lens back to stop in the third position aiming to correct astigmatism and distortion. The focusing group consists of three cemented lenses. The back group is applied to balance residual astigmatism, distortion and spherical aberration from the front group, in which the thick lens in the first doublet is mainly used to correct the curvature of the field. Low dispersion material is exploited to decrease chromatic aberration. An aperture stop is placed between the telescope and the focusing group, in such a way that the lens is telecentric in image space. For optical systems of small field of view, the aperture of the entrance pupil is unique regardless of field of view. However, it is not applicable to optical systems of large field of view. To improve uniformity of illumination on the image surface, the off-axis beam vignetting is adopted, i.e. the aperture of the entrance pupil changes with field of view. Thus it can be seen from Figure 1 that in the front group, the sizes of beam apertures corresponding to different field of view are inconsistent and distributed in different positions of the lens.