RU2556295C1 - Double-channel catadioptric lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens comprises a first mirror in the form of an off-axis fragment of a concave hyperbolic mirror, a lens aberration compensator of a visible channel comprising plane-convex and a biconvex lenses and a negative meniscus, a second mirror in the form of an off-axis fragment of a spherical convex mirror and a third mirror in the form of an off-axis fragment of a concave spherical mirror. The first surface of the first lens of the lens aberration compensator of the visible channel is coated with a spectrum-dividing coating which transmits radiation in the 450-1000 nm range and reflects in the 1500-1700 nm range. On the path of the reflected beams there is a lens aberration compensator of an infrared channel comprising three lenses in the form of off-axis fragments of biconvex, biconcave and biconvex lenses in the meridian section lying higher than the optical axis. The centres of curvature of all optical surfaces lie on a common axis. In the meridian section, the first mirror is lies lower than the optical axis and the second and third mirrors lie higher than the optical axis. Relationships given in the claim are satisfied.

EFFECT: high image quality in a wide spectral range of 450-1700 nm of the lens without central screening and improved manufacturability.

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Description

The invention relates to optical instrumentation and can be used in space telescopes.

Known mirror and mirror-lens optical systems with three reflections, differing in circuit design, dimensions and degree of correction of aberrations. For example, the lens described in RF patent No. 23237194, IPC G02B 17/06, published January 27, 2008, which is an anastigmatic optical system, off-axis and decentered both in the aperture and in the field angle, in which the first component is an off-axis fragment of the mirror hyperboloid , facing concavity to the object, with a positive optical power close to the strength of the entire system, the second component is a convex mirror spheroid, symmetrical about the optical axis of the system, with negative optical power, the third component is off-axis th fragment mirroring oblate ellipsoid facing concavity to the image, with a positive refractive power. Moreover, all three of these mirrors are formed by surfaces of revolution with a common axis. The distance between the first and second mirrors is less than the focal length of the first mirror, and the centers of the reflecting surfaces of all the mirrors are located at the vertices of the triangle, the plane of which includes the common axis of these mirrors, and from different sides relative to this axis; the vertices of the first and third mirrors are combined. The aperture diaphragm is located on the second mirror. The presence of two off-axis aspherical surfaces in the lens greatly complicates its assembly, alignment, and control. Moreover, the lens has a small angular field 2ω = 2.3 ° and low image quality.

Also known is the lens described in RF patent No. 2461030, IPC G02B 17/08, published on 09/10/2012, which is a three-mirror system with the centers of curvature of all optical surfaces located on one common axis, consisting of three consecutively installed first - off-axis concave, second — off-axis convex, third — off-axis concave fragments of spherical mirrors, a two-lens aberration corrector, the first lens of which is placed between the first and second mirrors and is made as a single fragment of the positive meniscus, the second lens is a Mangin lens and is the third mirror, the aperture diaphragm of the lens is located on the second mirror. This lens has a small angular field of 2ω = 3.1 °.

Closest to the proposed invention is a mirror lens in accordance with the publication of A.A. Tokarev “Long-focus lenses with an eccentrically located image field” // University News, Series "Instrument-Making", Volume XXXI, 1988, No. 7, pp. 74-79. It is a three-mirror system with the centers of curvature of all optical surfaces located on one common axis, consisting of three consecutively installed first — off-axis concave, second — off-axis convex, third — off-axis concave fragments of spherical mirrors, two-lens aberration corrector from the same brand optical glass placed between the first and second mirrors, and an aperture diaphragm coinciding with the frame of one of the corrector lenses. The first and third mirrors have positive optical power and are turned concave to the plane of objects, the second has negative optical power, and the lens corrector consists of two negative menisci facing a concave surface to the plane of objects. In this lens, the aperture ratio in the visible and infrared channels is the same. However, due to the fact that the signal-to-noise ratio for optoelectronic converters is proportional to the square of the aperture angle, and the sensitivity of receivers in the infrared range is much lower than the sensitivity of receivers in the visible range, the infrared channel must have a 4-6-fold signal to noise ratio more aperture of the visible channel.

The objective of the invention is the creation of a two-channel mirror lens with enhanced performance.

EFFECT: creation of a two-channel mirror-lens lens without central shielding with improved image quality within an angular field of 10 ° in a wide spectral range of 450-1700 nm and increased manufacturability.

This is achieved by the fact that the mirror-lens lens, consisting of a first mirror installed sequentially along the beam, made in the form of an off-axis fragment of a concave hyperbolic positive mirror facing concavity to the plane of objects, a lens aberration compensator, one of the lenses of which is a negative meniscus convex to the first mirror, the second mirror, made in the form of an off-axis fragment of a spherical convex negative mirror, convex to the lens component aberration, the third mirror, made in the form of an off-axis fragment of a concave spherical positive mirror, facing concavity to the plane of objects, and the centers of curvature of all optical surfaces are located on one common axis, while in the meridional section of the lens the first mirror is located below the optical axis, and the second and the third mirror is above the optical axis, in contrast to the known one, the lens aberration compensator consists of three lenses, the first of which is plano-convex, facing the first to the first a mirror, the second is biconvex, and the third is a negative meniscus, and on the first surface of the first lens of the lens aberration compensator is coated with a spectrodividing coating that transmits radiation in the spectral range of 450-1000 nm of the visible channel and reflects in the spectral range of 1500-1700 nm of the infrared channel, in addition , the lens is supplemented with a lens compensator for infrared channel aberrations, installed during the rays reflected from the first surface of the lens compensator for aberrations of the visible channel, the lens compensator aberrations of the infrared channel consists of three lenses made in the form of off-axis fragments of axisymmetric lenses, in the meridional section of the lens located above the optical axis, the first lens being biconvex, the second lens being biconcave, the third lens being biconvex, the aperture of the visible channel is located on the first pass of the surface of the biconvex lens of the lens compensator for aberrations of the visible channel, and the aperture diaphragm of the infrared channel is located on the flat surface of the plano-convex lens nzy visible channel compensator lens aberrations, the following relations hold in the lens:

0.06 ≤ | φ _1VD / φ _VD | ≤0.15; 1.75≤ | φ _1IR / φ _IR | ≤1.85; 0.9≤ | φ _2VD / φ _VD | ≤1,2; 2.5≤ | φ _2IK / φ _IR | ≤2.6; 0.7≤ | φ _3VD / φ _VD | ≤0.8; 1.55≤ | φ _3IK / φ _IR | ≤1.7; 0.65≤n _2VD / n _1VD ≤0.9; 0.87≤n _2IK / n _1IK ≤0.9; 1.05≤n _3VD / n _1VD ≤1.1; 0,8≤n _3IK / n _1IK ≤0,82; 1.68≤ν _2VD / ν _1VD ≤1.8; 0,93≤ν _2IK / ν _1IK ≤0,98; 0.95≤ν _3VD / ν _1VD ≤0.9; 1,8≤ν _3IK / ν _1IK ≤1,85;

Where

- φ _1VD, φ _2VD, φ _3VD - optical powers of the first, second and third lenses of the lens aberration compensator visible channel;

- φ _VD - the optical power of the lens of the visible channel;

- φ _IR - optical power of the lens of the infrared channel;

- n _1VD, n _2VD, n _3VD - the refractive indices of the first, second and third lenses of the lens aberration compensator visible channel;

- ν _1VD, ν _2VD, ν _3VD - dispersion coefficients of the first, second and third lenses of the lens aberration compensator visible channel;

- φ _1IK , φ _2IK , φ _3IK - the optical powers of the first, second and third lenses of the lens compensator for aberrations of the infrared channel;

- n _1IK , n _2IK , n _3IK - refractive indices of the first, second and third lens of the infrared channel;

- ν _1IK , ν _2IK , ν _3IK - dispersion coefficients of the first, second and third lenses of the lens compensator for aberrations of the infrared channel.

In addition, a plane-parallel plate can be installed in front of the image plane of the visible channel, the thickness of the _VD and the refractive index n of the _VD which satisfy the inequality

,

,

- фокусное расстояние объектива видимого канала.Where $$f_{0\mathrm{AT}D}^{\text{'}\text{'}}$$

- the focal length of the lens of the visible channel.

And in front of the image plane of the infrared channel, a plane-parallel plate can be installed, the thickness d _IR and the refractive index n _IR which satisfy the inequality

,

,

- фокусное расстояние объектива инфракрасного канала.Where $$f_{0\mathrm{AND}\mathrm{TO}}^{\text{'}\text{'}}$$

- the focal length of the infrared lens.

Figure 1 presents a schematic diagram of a two-channel mirror-lens lens, figure 2 - polychromatic modulation transfer function of the MPF of the visible channel, figure 3 - polychromatic MPF of the infrared channel.

Two-channel mirror lens (Fig.1) consists of two channels. The visible channel consists of a successively installed first mirror 1, a lens aberration compensator of the visible channel made of three single axisymmetric lenses, the first of which is lens 2, the second is lens 3 and the third is lens 4, the second mirror 5, and the third mirror 6 and aperture diaphragm 7. The first mirror 1 is made in the form of an off-axis fragment of a concave hyperbolic positive mirror facing with a concavity to the plane of objects and located in the meridional section of the lens below the optical axis. Lens 2 of the lens compensator of the aberrations of the visible channel is made in the form of a single axisymmetric plano-convex lens having an optical power of 0.06-0.15 of the optical power of the lens of the visible channel, the flat surface facing the first mirror 1. A spectro-splitting coating is applied to the flat surface of the lens 2, transmitting radiation in the spectral range of 450-1000 nm and reflective radiation in the spectral range of 1500-1700 nm. Lens 3 of the lens compensator for aberrations of the visible channel is made in the form of a single axisymmetric biconvex lens having an optical power of 0.9-1.2 of the optical power of the lens of the visible channel. Lens 4 is made in the form of a single axisymmetric negative meniscus having an optical power of 0.7-0.8 of the optical power of the lens of the visible channel and facing a convex surface to the first mirror 1. The refractive index of the lens 3 of the lens compensator for aberrations of the visible channel is 0.65 ... 0 , 9 times more, and the dispersion coefficient is 1.68 ... 1.8 times more than that of lens 2 of the lens compensator for aberrations of the visible channel, the refractive index of lens 4 of the lens compensator for aberrations of the visible channel is 1.05 ... 1.1 times more, and dispersion coefficient and 0.95 ... 1.0 times greater than that of the lens 2 of the lens aberration compensator visible channel. The second mirror 5 is made in the form of an off-axis fragment of a convex spherical negative mirror, convex to the first mirror 1 and is located in the meridional section of the lens above the optical axis. The third mirror 6 is made in the form of an off-axis fragment of a concave spherical positive mirror, faces with a concave surface to the plane of objects and is located in the meridional section of the lens above the optical axis. The infrared channel consists of sequentially along the beam of the installed first mirror 1, a flat mirror made in the form of the first surface of the first lens 2 of the lens aberration compensator of the VD channel with a spectro-splitting coating applied to it, reflecting radiation in the spectral range of 1500-1700 nm, and a lens compensator for aberrations of the infrared channel made of three single axisymmetric lenses. The first lens of the infrared channel aberration compensator is made in the form of a biconvex lens 9, the second lens is made in the form of a biconcave lens 10, the third lens is made in the form of a biconvex lens 11, and the parts of the lens of the infrared channel aberration compensator, located in the meridional section of the infrared channel lens below and just above the optical axis, removed, and thus off-axis segment lenses are formed. The first mirror 1 is common to two channels. The first lens of the lens compensator for the aberrations of the infrared channel is made in the form of a biconvex lens 9 having an optical power of 1.75-1.85 of the optical power of the lens of the infrared channel. The second lens of the lens compensator for the aberrations of the infrared channel is made in the form of a biconcave lens 10 having an optical power of 2.5-2.6 of the optical power of the entire lens. The third lens of the lens compensator for the aberrations of the infrared channel is made in the form of a biconvex lens 11 having an optical power of 1.55-1.7 of the optical power of the lens of the infrared channel. The refractive index of lens 10 of the lens compensator for infrared channel aberrations is 0.87 ... 0.9 times greater, and the dispersion coefficient is 0.93 ... 0.98 times more than lens 9 of the lens compensator for aberration of the infrared channel, the refractive index of lens 11 of the lens compensator the infrared channel aberrations are 0.8 ... 0.82 times greater, and the dispersion coefficient is 1.8 ... 1.85 times more than the lens 9 of the lens compensator for the infrared channel lens aberrations. The centers of curvature of all optical surfaces lie on one common axis. The aperture diaphragm 7 of the visible channel is located on the first along the beam surface of the lens 3 of the lens compensator for aberrations of the visible channel. The aperture diaphragm 12 of the infrared channel is located on the first along the beam surface of the lens 2 of the lens compensator for aberrations of the visible channel. Also, in the lens, in front of the image planes, a plane-parallel plate 8 in the visible channel and a plane-parallel plate 13 in the infrared channel, the thicknesses _VD and d _IR and the refractive indices n _VD and n _{IR of} which satisfy the inequalities

,

,

- фокусное расстояние объектива видимого канала.Where $$f_{0\mathrm{AT}D}^{\text{'}\text{'}}$$

- the focal length of the lens of the visible channel.

,

,

- фокусное расстояние объектива инфракрасного канала.Where $$f_{0\mathrm{AND}\mathrm{TO}}^{\text{'}\text{'}}$$

- the focal length of the infrared lens.

The inclusion of plane-parallel plates 8 and 13 in the optical circuit of the lens is due to the need to take into account the protective glass of the radiation receiver when calculating the lens.

The lens works as follows. The light from the radiation source enters the first mirror 1, then, reflected from it, enters the first surface of the lens 2, on which a spectro-splitting coating is applied. On this surface, radiation is separated by spectral ranges. Radiation with a spectral range of 450-1000 nm passes sequentially through lens 2, lens 3 and lens 4, is reflected on the second mirror 5 and third mirror 6, passes through a plane-parallel plate 8 and is focused in the image plane of the visible channel. Radiation with a spectral range of 1500-1700 nm is reflected from the first surface of the lens 2, passes sequentially through the lens 9, lens 10, lens 11, through a plane-parallel plate 13 and focuses in the image plane of the infrared channel.

In accordance with the proposed technical solution, a lens is calculated whose design parameters are given in table 1.

Table 1 Visible channel Infrared channel Radius mm Thickness mm Refractive index Radius mm Thickness mm Refractive index r ₁ = -3004.3 1,0 r ₁ = -3004.3 1,0 d ₁ = -525.5 -1.0 d ₁ = -525.5 -1.0 r ₂ = ∞ r ₂ = ∞ d ₂ = -16.0 N-SK2 d ₂ = 325.71 1,0 r ₃ = 10014.0 r ₃ = 1091.47 d ₃ = 60.0 S-LAH59 d ₃ = -3.2 -1.0 r ₄ = -566.08 r ₄ = -563.3 d ₄ = 2.08 1,0 d ₄ = -12.0 S-FPL53 r ₅ = -442,468 r ₅ = 4794.33 d ₅ = 21.0 N-KZFS4 d ₅ = -13.0 -1.0 r ₆ = 382,736 r ₆ = -2357,528 d ₆ = 18.12 1,0 d ₆ = -13.0 N-LAK14 r ₇ = 371.514 r ₇ = -781.49 d ₇ = 76.0 N-FK51A d ₇ = -183.07 -1.0 r ₈ = -758.33 r ₈ = -929.6 d ₈ = 258.22 1,0 d ₈ = 401.1 1,0 r ₉ = ∞ r ₉ = -1100.8 d ₉ = 5.0 K8 r ₁₀ = ∞ d ₉ = -581.1 -1.0 d ₁₀ = 10.0 1,0 r ₁₀ = ∞ d ₁₀ = -5.0 K8 r ₁₁ = ∞ d ₁₁ = -10.0 -1.0

The lens has the characteristics shown in table 2.

table 2 Visible channel Infrared channel Focal length mm 1260 878 Relative hole 1: 9.5 1: 4 Angular field in the meridional direction ω _y0 = 9.0 °, ω _ymax = 11.2 ° ω _y0 = 9.0 °, ω _ymax = 10.9 ° Angular field in the sagittal direction 2ω _x = 10 ° 2ω _x = 10 °

The lens has aberrations shown in table 3.

Table 3 Visible channel Infrared channel Wavelength nm 656.3 1620 Transverse spherical aberration of wide inclined beams within the entire angular field, not more than, mm 0.02 0.08 Meridional astigmatic segment no more than, mm 0.165 0,087 Sagittal astigmatic segment no more than, mm 0.1 0.3 Distortion no more,% 0.2 0.1 The chromaticity of the position in the spectral range (0.45 ÷ 1.0) μm 0.04 - The chromaticity of the position in the spectral range (1.5 ÷ 1.7) μm - 0.02

Thus, a two-channel mirror-lens without central shielding was created, having a relative aperture of 1: 9.5 in the visible channel and 1: 4 in the infrared channel, which has good image quality within an angular field of 10 ° in a wide spectral range of 450-1000 nm and 1500-1700 nm, in which central shielding can be avoided by using an eccentric image field, off-axis fragments of axisymmetric mirrors and a special arrangement of aperture diaphragms.

Claims (3)

1. A two-channel mirror-lens lens, consisting of a first mirror sequentially installed along the beam, made in the form of an off-axis fragment of a concave hyperbolic positive mirror facing concavity to the plane of objects, a lens aberration compensator, one of whose lenses is a negative meniscus convex to the first mirror, the second mirror, made in the form of an off-axis fragment of a spherical convex negative mirror, convex to the lens compensator a Here, the third mirror, made in the form of an off-axis fragment of a concave spherical positive mirror, facing concavity to the plane of objects, the centers of curvature of all optical surfaces being located on one common axis, while in the meridional section of the lens the first mirror is located below the optical axis, and the second and third mirrors - above the optical axis, characterized in that the lens aberration compensator consists of three lenses, the first of which is plano-convex, facing the first mirror, w paradise is biconvex, and the third is a negative meniscus, and on the first surface of the first lens of the lens aberration compensator a spectro-fission coating is applied that transmits radiation in the spectral range of the visible channel 450-1000 nm and reflects in the spectral range of the infrared channel 1500-1700 nm, in addition, the lens supplemented with a lens compensator for infrared channel aberrations, installed during the rays reflected from the first surface of the lens compensator for aberrations of the visible channel, a lens compensator for aberrations the infrared channel consists of three lenses made in the form of off-axis fragments of axisymmetric lenses, in the meridional section of the lens located above the optical axis, the first lens being biconvex, the second lens biconcave, the third lens biconvex, the aperture diaphragm of the visible channel is located on the first along the beam the surface of the biconvex lens of the lens compensator for aberrations of the visible channel, and the aperture diaphragm of the infrared channel is located on the flat surface of the plane-convex lens of the lens th compensator of aberrations of the visible channel, while the following relations are satisfied in the lens:
0.06 ≤ | φ _1VD / φ _VD | ≤0.15; 1.75≤ | φ _1IR / φ _IR | ≤1.85; 0.9≤ | φ _2VD / φ _VD | ≤1,2; 2.5≤ | φ _2IK / φ _IR | ≤2.6; 0.7≤ | φ _3VD / φ _VD | ≤0.8; 1.55≤ | φ _3IK / φ _IR | ≤1.7; 0.65≤n _2VD / n _1VD ≤0.9; 0.87≤n _2IK / n _1IK ≤0.9; 1.05≤n _3VD / n _1VD ≤1.1; 0,8≤n _3IK / n _1IK ≤0,82; 1.68≤ν _2VD / ν _1VD ≤1.8; 0,93≤ν _2IK / ν _1IK ≤0,98; 0.95≤ν _3VD / ν _1VD ≤1.0; 1,8≤ν _3IK / ν _1IK ≤1,85;
Where
- φ _1VD, φ _2VD, φ _3VD - optical powers of the first, second and third lenses of the lens aberration compensator visible channel;
- φ _VD - the optical power of the lens of the visible channel;
- φ _IR - optical power of the lens of the infrared channel;
- n _1VD, n _2VD, n _3VD - the refractive indices of the first, second and third lenses of the lens aberration compensator visible channel;
- ν _1VD, ν _2VD, ν _3VD - dispersion coefficients of the first, second and third lenses of the lens aberration compensator visible channel;
- φ _1IK , φ _2IK , φ _3IK - the optical powers of the first, second and third lenses of the lens compensator for aberrations of the infrared channel;
- n _1IK , n _2IK , n _3IK - refractive indices of the first, second and third lens of the infrared channel;
- ν _1IK , ν _2IK , ν _3IK - dispersion coefficients of the first, second and third lenses of the lens compensator for aberrations of the infrared channel. 2. Dual catadioptric lens according to claim 1, characterized in that before visible channel image plane mounted plane-parallel plate, the thickness d and the refractive index _{VD VD} n which satisfy the inequality

,
Where $$f_{0\mathrm{AT}D}^{\text{'}\text{'}}$$

- the focal length of the lens of the visible channel. 3. The two-channel mirror-lens lens according to claim 1, characterized in that a plane-parallel plate is installed in front of the image plane of the infrared channel, the thickness d _IR and the refractive index n _{IR of} which satisfy the inequality

,
Where $$f_{0\mathrm{AND}\mathrm{TO}}^{\text{'}\text{'}}$$

- the focal length of the infrared lens.

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