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附录 D 术语表 Lateral Color： Chromatic aberration associated with the chief ray. Magnification： Ratio of image height to object height. Marginal Ray： Ray from the axial object point to the rim of the entrance pupil. Merit Function： A number that summarizes the state of optimization of an imaging system. The lower the number, the better the optimization. Modulation Transfer Function （MTF）： A measure of image contrast as a function of spatial frequency. Null Lens： A refractive or reflective optical system interposed between a test point and an aspheric mirror in a radius of curvature test configuration. Compensates for the spherical aberration associated with the normals to the mirror surface. Numerical Aperture： Defines the light collection capability of an optical system in object space for a finite object distance. Optical Path Length： The actual path length multiplied by the refractive index within that path. Optical Path Difference： The separation between an aberrated wavefront and a reference sphere at some point in the exit pupil. Optical Power： The reciprocal of focal length. Principal Plane（s）： An optical imaging system has a pair of principal planes （front and rear）. These planes, along with a knowledge of focal point locations, can represent the first order imaging properties of the system （no matter how complicated that system may be）. The image point location of any object point can be determined via simple graphical ray tracing techniques. Paraxial Plane： For an optical imaging system,trace rays which lie close to the optical axis through the system for a given axial object point. The convergence point of such rays in image space defines the location of the paraxial
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透镜设计导论
附录 D 术语表
Aberration： An ideal monochromatic point image is formed from a spherical converging wavefront. Wavefronts that are not spherical are considered aberrated as are the images they form. The common aberrations affecting the point image are spherical aberration,coma,and astigmatism. Aberrations that effect image point location axially and laterally also occur. These are field curvature and distortion. Abbe number： A number which quantifies the dispersive nature of glass. Achromat： A lens composed of two elements with different dispersive properties which correct primary axial color. Airy Disk： In geometric optics,an ideal lens forms a point image of a point object. When physical optics is taken into account,the point object is imaged by an ideal lens as a finite－sized circular disk （assuming a circular aperture）. Aplanat： An optical imaging system that has no spherical aberration or coma. Aspheric： An optical surface that is not spherical in shape. Axial Color： The refractive index of glass is wavelength dependent so glass lenses form images of different colors at different points along the optical axis. Back Image Distance： The separation between the last optical surface in an imaging system and the paraxial image plane. Chief Ray： The ray from the maximum field position that passes through the center of the stop. Conic Constant： A number that defines an optical surface's departure from a spherical surface. Corrector Plate： A refractive optical element that eliminates spherical aberration in an imaging system. Curvature： The reciprocal of the radius of curvature for an optical surface. Defocus： The axial separation between the paraxial image plane and a different plane of observation. Depth of Focus： Roughly the axial range over which the image appears unchanged to an observer. Dispersion： Variation of the refractive index with wavelength. Diffraction Limited： The performance of the imaging system is limited not by geometric aberrations, but by the physical optics phenomenon of diffraction. Effective Focal Length： The separation between the rear principal plane and the paraxial image plane. Entrance Pupil： Image of stop formed by optics to the left of stop. Exit Pupil： Image of stop formed by optics to the right of stop. Field Angle： The angle an object point makes with respect to the optical axis as determined from the vertex of the entrance pupil. Field Flattener： Usually a negative element close to the image plane that reduces or eliminates Petzval field curvature. Field of View： Object scene that fits within defined image plane format. Format： That which physically limits the image scene extent in the image plane, e.g., the size of a CCD chip. f－number： The ratio of the effective focal length to the entrance pupil diameter for an object at infinity.