A telecentric lens is a complex lens , in which the main rays of all non - axial light beams are parallel to the optical axis in object space or in image space [1] . Such a course of light is possible in the case when the entrance or exit pupils, respectively, are in βinfinityβ [2] . Designs of bitelecentric lenses are known, in which the main rays of non-axial beams are parallel to the optical axis both in the space of objects and in the space of images. The parallelism of the optical axis of the non-axial beams in optics entering or emerging from the lens is called telecentricity .
Content
Types of telecentricity
Telecentric objectives with a parallel course of beams in the space of objects are used in measuring microscopes and computer vision systems, since their increase does not depend on the distance to objects. The image given by such a lens has an unnatural telecentric perspective , displaying objects at any distances on a constant scale [3] . The type of image of objects obtained at the same time coincides with their orthogonal projection in geometry. The angular field of such a lens is zero, and the displayed space is inside an infinite cylinder with one base coinciding with the front lens [4] . Entirely can be displayed items that are not larger than the diameter of the front lens. Larger objects are displayed only partially at any distance from the lens.
With the telecentricity of the beams in the image space, the usual enthocentric perspective is obtained, and the image is no different from that obtained with the help of ordinary lenses [2] . But in this case, the light falls perpendicular to the light detector within the entire image field , and not just in the center. Due to this beam path, the image size does not change when the lens is focused, which is important in photogrammetry . Telecentricity of the output beams is preferable in lenses for digital photography and television, because it provides a sheer drop of light over the entire area of ββthe sensor, excluding darkening of the corners and color separation distortion [5] . This is especially true for modern photomatrix with microlenses , the angle of incidence of light on which strongly affects the sharpness and illumination .
Telecentricity in image space is especially effective for wide-angle optics , the lateral beams of which, with the usual design of the lens, fall on the matrix at acute angles. The telecentricity of the outgoing beams ensures that the light falls steeply on all the photodiodes of the matrix, regardless of the focal length of the lens. A similar device of the lens, common in modern digital photography, has begun to be used even for color multi-layer photographic films with internal color separation [5] . In the prism color separation systems of three-matrix television cameras, the telecentricity of the lens makes it possible to avoid raster alignment errors. An important advantage of telecentric lenses is the almost complete absence of distortion and vignetting [6] .
For these reasons, modern lenses for digital cameras are designed to achieve the telecentricity of the output beams [7] . It is not always advisable to achieve their complete parallelism of the optical axis, but the designers try to minimize the divergence of the edge rays and their deviation from the normal to the matrix surface. This is achieved by increasing the complexity of the optical system and increasing its dimensions, but the gain in resolution of the entire optical path justifies its cumbersomeness. Another factor that allows to increase the telecentricity is the large diameter of the rear lens of the lens. For full telecentricity, it should not be less than the diagonal of the frame, which is taken into account, including when designing the latest wide-bore bayonet .
See also
- Orthogonal projection
Notes
- β Theory of Optical Systems, 1992 , p. 93.
- β 1 2 Photographic Optics, 1978 , p. 60
- β Handbook of the designer of optical-mechanical devices, 1980 , p. 85.
- β The Advantages of Telecentricity (English) . Edmund Optics Worldwide. The appeal date is December 12, 2018.
- β 1 2 Theory of Optical Systems, 1992 , p. 94.
- β Telecentric lenses tutorial (English) . Opto Engineering. The appeal date is December 13, 2018.
- β Detailed description of telecentricity (inaccessible link) . Circulation date July 18, 2010. Archived March 1, 2009.
Literature
- D.S. Volosov . Chapter I. Properties of an ideal lens // Photographic optics. - 2nd ed. - M .: "Art", 1978. - p. 123-131. - 543 s.
- N.P. Zakaznov, S.I. Kiryushin, V.I. Kuzichev. Chapter VI. Restriction of beams of beams in optical systems // Theory of Optical Systems / T. V. Abivova. - M .: "Mechanical Engineering", 1992. - pp. 92-102. - 448 s. - 2300 copies - ISBN 5-217-01995-6 .
- V. A. Panov. Chapter 2. Geometrical optics // Reference book of the designer of optical-mechanical devices / V.V. Khvalovsky. - L .: "Mechanical Engineering", 1980. - p. 63-147. - 742 s. - 25 000 copies