RU2313812C2 - Wide-angle objective with extended entrance pupil - Google Patents

Abstract

FIELD: electro-optics.

SUBSTANCE: objective can be used for operation with CCD receivers. Objective with extended entrance pupil has four components. First component is negative menisci turned with its concavity to area of objects; second and third components are positive menisci and the fourth component is biconcave lens. Second component is glued of positive and negative menisci, which menisci are turned with their concavities to area of objects. Thickness of first component relates to light diameter as 0,2 and shorter. There is flat-parallel plate between third and fourth components. Quality of images is close to diffraction limit of resolution.

EFFECT: wider linear field in area of images; higher quality of images.

2 dwg

Description

The invention relates to optical instrumentation, and more specifically to lenses that work with CCD receivers, and can be used to obtain information from external objects.

Known fast lens with a remote entrance pupil according to the patent of Russia N 2024038, IPC G02B 9/12, B.I.P.M. N22, 1994, which contains three components, the first of which is a negative meniscus facing concavity to the object and glued from the negative and positive menisci, the second component is positive glued from a biconvex lens and the negative meniscus facing concavity to the object, and the third is positive meniscus facing concavity to the image.

A disadvantage of the known lens is a small projection of the entrance pupil and poor image quality.

The closest in technical solution is a wide-angle lens with a remote entrance pupil according to the patent of Russia N 2133488, IPC G02B 9/12, B.I.P.M. No. 20, 1999, which is selected by the authors for the prototype.

The prototype lens contains four components: the first component is the negative meniscus facing concavity to the space of objects, the second component is positive, the third component is the positive meniscus facing concavity to the image space, and the second component is made in the form of a meniscus facing concavity to the space of objects, and between the second and third components a positive glued component is installed, which can be glued from a negative meniscus and a biconvex lens or glued from a biconvex lens and a negative meniscus.

The disadvantages of the prototype include a small projection of the entrance pupil, a small linear field in the space of images, and poor image quality.

The objective of the invention is to create a lens with increased information content by increasing the extension of the entrance pupil and the linear field in the image space while improving image quality due to the constructive implementation of its optical design.

The solution to this problem is achieved by the fact that in a wide-angle lens with a remote entrance pupil containing four components, the first of which is the negative meniscus facing the concavity of the space of objects, the second and third are positive, the third component is glued from two lenses, and the fourth is a single lens while the first component is made with the ratio of its thickness to the light diameter not exceeding 0.2, the second component is made of glued from the positive and negative menisci facing concavity to the space count objects, and a fourth component - a biconcave lens, and between the third and fourth components mounted plane-parallel plate.

The implementation of the first component - the negative meniscus, facing concavity to the object, with a ratio of its thickness to the light diameter not exceeding 0.2, allows to increase the extension of the entrance pupil of the lens, as well as to increase the linear field of the image and minimize the effect of higher-order aberrations that occur when increasing image fields. The ratio of the thickness of the first component to its light diameter was obtained by calculation and is optimal for solving the problem of the invention, with a larger value, the design requirements for the lens are not met and the required image quality is not achieved.

The implementation of the second component (in conjunction with the previously mentioned feature) glued from the positive and negative menisci facing concavity to the space of objects also leads to an increase in the removal of the entrance pupil of the lens, the linear field of the image and the minimization of higher order aberrations that occur when the image field increases, in In this case, astigmochromatic aberrations and coma of a higher order in a wide inclined beam are minimized.

The embodiment of the fourth component in the form of a biconcave lens is in this invention optimal for the correction of higher order aberrations that occur while increasing the extension of the entrance pupil and the linear field in the image space.

The installation between the third and fourth components of the plane-parallel plate is made in order to ensure the functioning of the lens of the present invention as part of a CCD camera. The plate in this case plays the role of a filter, its thickness is usually 0.1 of its diameter. In known lenses, the filter is located in the focal plane and in any case should be taken into account when calculating the image quality of the system as a whole. The location of the plane-parallel plate directly between the components of the lens contributes to the correction of aberrations, in particular astigmatism and coma, arising from an increase in the extension of the entrance pupil of the lens with a simultaneous increase in its field of view in the image space.

The specified combination allows you to get the necessary and sufficient number of parameters of the optical system, allowing you to create a lens with high information content by increasing the extension of the entrance pupil and the linear field in the image space while improving image quality due to the constructive implementation of its optical design.

The combination of all the features allows us to solve the problem, the exclusion of any of them leads to the inability to implement a wide-angle lens with a remote entrance pupil, a large linear field in the image space, while also having improved image quality.

The invention is illustrated by drawings:

- figure 1 presents the optical scheme of a wide-angle lens with a remote entrance pupil;

- figure 2 presents graphs of the frequency-contrast characteristics of the lens according to the invention.

A wide-angle lens with a remote entrance pupil, combined with aperture diaphragm 1, contains four components sequentially located along the beam, the first of which is the negative meniscus 2, facing the concavity to the space of objects, the second 3 and third 4 are positive, and the third component is glued from two lenses 5 and 6, and the fourth is a single lens 8, characterized in that the first component 2 is made with a ratio of its thickness to the light diameter not exceeding 0.2, the second component is glued from a positive 3 and negative 4 menisci facing concavity to the space of objects, and the fourth component 8 is a biconcave lens, and between the third (lenses 5, 6) and the fourth 8 components there is a plane-parallel plate 7.

The lens works as follows. The luminous flux from an infinitely distant object sequentially passes through all the elements of the lens 1-8, after which an image is formed in the focal plane of the lens. The image is then aligned with the photosensitive layer of the CCD (not shown).

An example of a specific implementation of the invention is a wide-angle lens with a remote entrance pupil having a focal length of 6 mm, a relative aperture of 1: 5.9 and an angular field of 2w = 90 angular degrees, the thickness of the plate made of BK4 glass is 1 mm.

The design parameters of the lens are presented in table 1, and its characteristics are shown in table 2.

Table 1 Lens design N surface Radii, mm Thickness mm Glass brands Light diameters, mm An object infinity Air 1 - aperture plane 1.8 Air 1.0 2 -6.223 0.7 TF10 3.9 3 -38.28 0.1 Air 5.0 four -37.95 1.55 TF10 5.2 5 -3.32 0.7 STK19 5.5 6 -4.365 0 Air 6.46 7 7.38 3.2 STK19 9.0 8 -7.38 0.6 TF2 9.0 9 -55.85 0.21 air 8.42 10 Plane 1.0 BK4 8.02 eleven Plane 1.0 air 7.7 12 -8.75 0.75 TF10 7.5 13 22.84 air 7.6 Picture Plane air 8.5 table 2 Lens specifications. N Feature Name Value one Focal length mm 6.0 2 Corner field hail 90 3 Relative hole 1: 5.9 four Rear focal length, mm 1.87 5 Total length mm 11.33 6 Linear field mm 8.5

The technical advantages of the invention in comparison with the prototype are:

- an increase in the relative magnitude of the removal of the entrance pupil by 2 times,

- an increase in the linear field in the space of images by 1.4 times,

- improvement of image quality according to the frequency response criterion at a frequency of 50 lines / mm by 2 times, which practically corresponds to the value of the diffraction limit for a lens with the specified characteristics.

The implementation of the technical advantages of the lens according to the invention improves its information content, which allows it to be used as a wide-angle lens with a remote entrance pupil and with a large linear field in the image space, having an image quality close to the diffraction limit of resolution.

Claims (1)

A wide-angle lens with a remote entrance pupil containing four components, the first of which is the negative meniscus facing the concavity of the space of objects, the second and third are positive, the third component is glued from two lenses, and the fourth is a single lens, characterized in that the first component made with the ratio of its thickness to the light diameter not exceeding 0.2, the second component is made of glued from the positive and negative menisci facing concavity to the space of objects, and the fourth to exponentials - biconcave lens, and between the third and fourth components mounted plane-parallel plate.

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