RU2635830C1 - Photographic telephoto lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens contains two lens groups. The first group consists of a positive meniscus with convexity toward the object, a negative meniscus with convexity to the object, a biconvex lens, a negative meniscus with convexity to the image, a negative meniscus with convexity to the object and having the ability to move along the optical axis. There is an aperture diaphragm between the first and the second lenses of the first group. The second group consists of a positive and a negative menisci with convexity to the object. In the first group, the fifth lens can move along the optical axis.

EFFECT: increasing the aperture while maintaining acceptable image quality in the visible and near IR ranges in the extended temperature range.

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Description

The present invention relates to the field of optoelectronic technology and can be used as a receiving lens in optoelectronic devices that form images of earth's objects through the real atmosphere and work with photodetectors of visible and near-IR ranges in various equipment, for example, in aerial photography equipment or in space equipment.

A well-known apochromat lens for observation and photographing, consisting of six lenses (S. A. Veselkov, E. G. Lapukhin. New fast apochromatic lenses for astronomical research. Vestnik SibGAU. No 3 (49), 2013, p. 17 -21, Fig. 1) with a focal length f '= 615 mm, a relative aperture of 1: 3, a linear field of view of 52 mm, with a good correction of all aberrations. The lens consists of 6 lenses arranged in two components — a three-lens lens and a three-lens field corrector, which contain lenses 1 and 4 — biconvex, lenses 2 and 6 — biconcave, lens 3 — positive meniscus facing concavity to the image, lens 5 — negative meniscus convex to the image.

The disadvantage of this lens is an insufficient linear field of view (52 mm) and the provision of correction only in the visible wavelength range (0.486-0.656 μm).

The closest in technical essence is the lens (patent RU 2079863 C1, publ. 05.20.1997) with a focal length f '= 2700 mm, a relative aperture of 1: 6, a linear field of view of 230 mm (with an angular field of view of 4 ° 50'), with a good correction of all aberrations, consisting of two groups of lenses, the first of which contains five consecutive lenses, the first of which is biconvex, the second is biconcave, the third is biconvex, the fourth is biconcave, and the fifth is a positive meniscus with a concavity towards the image and the second r The lens group consists of single biconvex and biconcave lenses. The aperture diaphragm is located between the components. When scaling the focal length of this lens to ~ 440 mm, a sufficiently large field of view is provided with good correction of all aberrations.

The disadvantage of this lens is the small value of the relative aperture (aperture ratio 1: 6), as well as the small size of the operating temperature range, which reduces resistance to external temperatures.

The objective of the present invention is to increase the luminosity while maintaining acceptable image quality in the visible and near infrared ranges in an extended temperature range.

The technical result due to the task is achieved by the fact that in a lens containing two groups of lenses separated by an air gap, the first of which contains a positive lens, a negative lens, a biconvex positive lens, a negative lens, the second group of lenses contains a positive and negative lens, characterized the fact that in the first group of lenses between the first and second lenses there is an aperture diaphragm, the first lens is made in the form of a positive meniscus, convex to the etu, the second in the form of a negative meniscus convex to the object, the fourth in the form of a negative meniscus convex to the image, the fifth in the form of a negative meniscus convex to the object, in the second group of lenses the first lens is made in the form of a positive meniscus, convex to the object, the second in the form of a negative meniscus, convex to the object, and in the first group of lenses the fifth lens has the ability to move along the optical axis, and in the lens there is a corresponding shenie:

where Δl _1g5l ^{_ the} amount of movement along the optical axis of the fifth lens in the first group of lenses;

ƒ 'r - the focal length of the lens.

A diagram of the lens is shown in the drawing.

The lens consists of rays from the I and II groups of lenses, the I-th group of lenses consists of a convex concave lens 1, convex to the object, convex lens 2, convex to the object, biconvex lens 3, convex lens 4, convex to the image, convex concave lens 5, convex to the object, the 2nd group of lenses consists of a convex concave lens 6, convex to the subject, convex lens 7, convex to the subject and plane parallel plate 8. In this case, the lens 5 has the ability to move along the optical axis.

The aperture diaphragm is located in the 1st group of lenses between the first 1 and second 2 lenses.

The design data of the lens are shown in table 1.

When the lens 5 is moved along the optical axis by a value of ± 0.9 mm, the position of the plane of the best installation is thermally compensated in the temperature range from +5 to + 35 ° С.

Thus, the parameters of the lens options:

estimated wavelength 0.6 μm working spectral range 0.4 ... 0.9 μm focal length 440.2 mm linear field of view 64.0 mm relative hole 1: 3.3 distortion 0.23% back focal length 46.44 mm optical axis length 491.3 mm mass of optical parts 2.98 kg

The principle of the lens is as follows.

The lens works as follows.

The luminous flux emanating from the plane of objects at infinity passes through a photographic telephoto lens and is displayed in the plane of the best setting, in which there is a photodetector (not shown), the digital signal from which forms the image.

The fifth lens 5 in the first group of lenses I is mounted with the possibility of movement along the optical axis, which allows you to compensate for the temperature shift of the plane of the best installation.

The amount of displacement of the fifth lens 5 in the first group of lenses I, sufficient to thermally compensate for the PND displacement in the temperature range from +5 to + 35 ° С, is ± 0.9 mm, which does not exceed the value:

In the optical calculation, the thickness of the protective glass 8 of the photodetector is taken into account.

Asked by the quality criterion - the value of the polychromatic contrast transfer coefficient (CPC) and given

- thickness of the protective glass of the photodetector, equal to 2.0 mm;

- spectral efficiency at wavelengths, taking into account the sensitivity of the photodetector and the light transmission of the lens, equal;

0.4 microns - 0.4;

0.5 microns - 0.6;

0.6 microns - 1.0;

0.7 microns - 1.0;

0.8 microns - 0.6;

0.9 microns - 0.3;

- spatial frequency of 100 lines / mm (Nyquist frequency for a photodetector with a sensor element size equal to 5 μm), we obtain the following calculated values of the qualitative characteristics of the lens:

for a point on the axis (diffraction quality) PDA = 72.8% for a point on the axis (aberration quality) PDA = 48.4% for field point 24 mm CPC _m = 51.6% CPCs = 40.5% for field point 32 mm CPC _m = 49.2% CPCs = 56.1%

As can be seen from the calculations, the lens, with its simplicity of design, provides high aperture ratio (1: 3,3) and acceptable image quality for optoelectronic devices using arrays or arrays with pixel sizes up to 5 microns as photodetectors.

Claims (4)

A photographic telephoto lens containing two lens groups separated by an air gap, the first of which contains a positive lens, a negative lens, a biconvex positive lens, a negative lens, the second group of lenses contains a positive and negative lens, characterized in that in the first group of lenses between the first and second the aperture diaphragm is located with the lenses, the first lens is made in the form of a positive meniscus convex to the object, the second - in the form of a negative meniscus inverted bone to the object, the fourth in the form of a negative meniscus convex to the image, the fifth in the form of a negative meniscus convex to the object, in the second group of lenses the first lens is made in the form of a positive meniscus, convex to the object, the second in the form of negative the meniscus, convex to the object, and in the first group of lenses the fifth lens has the ability to move along the optical axis, and in the lens there is a ratio:

, where Δl _1g5l - the amount of movement along the optical axis of the fifth lens in the first group of lenses;

- the focal length of the lens.

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