A wide-band, large-field-of-view, low-distortion optical system

Abstract

The present invention discloses a wide-band, large-field-of-view, low-distortion optical system, comprising: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, an aperture stop, a seventh cemented lens, an eighth cemented lens, and a ninth lens, arranged sequentially from the object side to the image side. The first, second, third, fourth, fifth, and sixth lenses constitute a front lens group, the seventh cemented lens, the eighth cemented lens, and the ninth lens constitute a rear lens group. The aperture stop is located at the front focal plane of the rear lens group, and both the second and sixth lenses are aspherical. The optical system disclosed by the present invention simultaneously achieves the characteristics of a wide field of view, low distortion, a wide band, a long back focus, excellent imaging quality, and image-side telecentricity, and is particularly suitable for the field of space remote sensing imaging.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to a wide-band, large-field-of-view, low-distortion optical system that can be applied to aerospace remote sensing imaging. Background Art

[0002] In recent years, with the rapid development of remote sensing technology, wide-band, large-field-of-view, and wide-wavelength remote sensing detection has become an important development trend in optical remote sensing instruments, with broad application prospects in environmental monitoring, meteorological observation, resource surveys, marine remote sensing, and other fields. Therefore, the research on wide-band, large-field-of-view optical systems is of great significance.

[0003] For large field of view optical systems, in order to meet the needs of practical applications, they are usually required to have characteristics such as large field of view, long back focus, low distortion, and compact structure. Due to the sharp increase in aberrations caused by the increase in field of view, the correction of distortion is particularly difficult, and aspheric surface balance distortion and astigmatism are usually introduced at a position far away from the field of view stop. For example, a Chinese patent application number CN112817119A discloses an optical lens for aerospace use, which includes a first lens to a tenth lens arranged in sequence from the object side to the image side. All lenses adopt a separate structure, wherein the first lens and the tenth lens adopt glass aspheric surfaces, and have the characteristics of large field of view, image side telecentricity, and good imaging quality. However, the edge field of view distortion is about 40%, and the distortion value is relatively large, which makes it difficult to apply to remote sensing instruments with high distortion requirements. The Xi'an Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences has proposed a large-field-of-view, low-distortion lens. It includes a reverse telephoto group, a double Gaussian group, and an output group coaxially arranged along the direction of light incidence. It uses a total of three aspherical surfaces and two cemented groups. The maximum distortion is less than 4.7%, and the dimensions are ≤Φ28×56mm. It is small and can achieve good imaging quality under temperature conditions of -40°C to 60°C. However, the lens does not have the characteristics of image-space telecentricity, and the edge illumination drops significantly. The maximum field of view is only 115°, and there is still room for improvement. Summary of the Invention

[0004] In order to solve the technical problems of large distortion and low edge illumination in existing large-field-of-view optical systems, the present invention provides a wide-band, large-field-of-view, low-distortion optical system, so as to achieve an imaging effect with a large field of view angle, low distortion, a wide band, a long back intercept, image telecentricity, and good imaging quality, thereby being more suitable for space remote sensing imaging.

[0005] In order to solve the above problems, the technical solutions provided by the present invention are as follows:

[0006] The present invention provides a wide-band, large-field-of-view, low-distortion optical system characterized by comprising: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, an aperture stop, a seventh cemented lens, an eighth cemented lens, and a ninth lens, which are coaxially arranged in sequence along an incident direction; wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens constitute a front lens group; the seventh cemented lens, the eighth cemented lens, and the ninth lens constitute a rear lens group; and the aperture stop is located near a front focal plane of the rear lens group.

[0007] The first lens is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the first lens is in the range of [0.0025, 0.005];

[0008] The second lens is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the second lens is in the range of [0.01, 0.03];

[0009] The third lens is a biconvex lens, and the absolute value of the focal length of the third lens is in the range of [0.006, 0.01];

[0010] The fourth lens is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the fourth lens is in the range of [0.03, 0.05];

[0011] The fifth lens is a biconcave lens, and the absolute value of the focal length of the fifth lens is in the range of [0.02, 0.04];

[0012] The sixth lens is a biconvex lens, and the absolute value of the focal length of the sixth lens is in the range of [0.03, 0.05];

[0013] The seventh cemented lens is composed of a seventh cemented positive lens and a seventh cemented meniscus negative lens coaxially arranged in sequence along the incident direction of light, and the absolute value of the optical focus of the seventh cemented lens is in the range of [0.01, 0.04];

[0014] The eighth cemented lens is composed of an eighth cemented meniscus negative lens convex to the object side, an eighth cemented positive lens, and an eighth cemented meniscus negative lens convex to the image side, which are coaxially arranged in sequence along the incident direction of light, and the absolute value of the optical focal length of the eighth cemented lens is in the range of [0.01, 0.04];

[0015] The ninth lens is a biconvex lens, and the absolute value of the focal length of the ninth lens is in the range of [0.02, 0.05].

[0016] The wide-band, large-field-of-view, low-distortion optical system described in the present invention is also characterized in that: the first lens is made of fused quartz material; and the second lens is made of radiation-resistant heavy crown glass material.

[0017] Furthermore, the refractive index of the second lens is in the range of [1.60, 1.70], and the dispersion is in the range of [50, 65];

[0018] The refractive index of the third lens is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60];

[0019] The refractive index of the fourth lens is in the range of [1.70, 1.80], and the dispersion is in the range of [40, 55];

[0020] The refractive index of the fifth lens is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28];

[0021] The refractive index of the sixth lens is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28];

[0022] The refractive index of the seventh cemented positive lens is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90];

[0023] The refractive index of the seventh cemented meniscus negative lens is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60];

[0024] The refractive index of the eighth cemented meniscus negative lens is in the range of [1.70, 1.75], and the dispersion is in the range of [30, 40];

[0025] The refractive index of the eighth cemented positive lens is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90];

[0026] The refractive index of the eighth cemented meniscus negative lens is in the range of [1.80, 1.85], and the dispersion is in the range of [40, 50];

[0027] The refractive index of the ninth lens element is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90].

[0028] Furthermore, the second lens and the sixth lens are both aspherical.

[0029] Furthermore, the equation of the aspheric surface is constructed using formula (1):

[0030] (1)

[0031] In formula (1), z is the aspheric height, c is the vertex curvature of the aspheric surface, y is the aperture of the aspheric surface, k is the cone coefficient, A4 is the fourth-order aspheric coefficient, A6 is the sixth-order aspheric coefficient, A8 is the eighth-order aspheric coefficient, and A 10 is the 10th-order aspheric coefficient.

[0032] Furthermore, the operating band is from visible light to near infrared.

[0033] Furthermore, the clear aperture of the first lens (1) is less than 200 mm.

[0034] Furthermore, the incident angle of the chief ray of all fields of view on the focal plane is less than 3°.

[0035] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0036] 1. The second and sixth lenses of the present invention both adopt single-sided aspheric surfaces, which reduces the pressure of correcting distortion and astigmatism on a single aspheric surface, solves the problem of difficulty in aspheric surface processing caused by excessive sag depth when using a single aspheric surface, meets the current aspheric surface processing technology, and has strong engineering feasibility.

[0037] 2. By employing low-refractive-index, low-dispersion materials, this invention addresses the chromatic aberration problem associated with broadband optical systems, achieving a maximum lateral chromatic aberration of less than 20 μm. Furthermore, by constraining the incident angle of the principal ray at the edge of the field of view, quasi-image telecentricity is achieved, improving illumination uniformity at the edge of the field of view. The optical system's back intercept is greater than 25 mm, leaving ample space for detector installation.

[0038] 3. The first lens and second lens in the present invention are made of quartz and radiation-resistant heavy crown glass, respectively. Both are radiation-resistant materials. Compared with the traditional optical system in which only the first lens is made of quartz, the radiation resistance of the space environment is further improved. It is particularly suitable for optical remote sensing instruments in orbital environments with high total space radiation doses, such as medium orbit and medium-high orbit. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the structure of the wide-band, large-field-of-view, low-distortion optical system of the present invention;

[0040] Figure 2 The modulation transfer function (MTF) curve of the wide-band, large-field-of-view, low-distortion optical system of the present invention is shown in FIG.

[0041] Figure 3 The field curvature and distortion curves of the wide-band, large-field-of-view, low-distortion optical system of the present invention;

[0042] Figure 4is the lateral chromatic aberration curve of the wide-band, large-field-of-view, low-distortion optical system of the present invention;

[0043] Numbers in the figure: L1-first lens; L2-second lens; L3-third lens; L4-fourth lens; L5-fifth lens; L6-sixth lens; S-aperture stop; L7-seventh cemented lens; L700-seventh cemented positive lens; L701-seventh cemented negative lens; L8-eighth cemented lens; L800-eighth cemented negative lens convex to the object side; L801-eighth cemented positive lens; L802-eighth cemented negative lens convex to the image side; L9-ninth cemented lens. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings.

[0045] like Figure 1 Figure 2 is a schematic diagram of the structure of the wide-band, large-field-of-view, low-distortion optical system of the present invention. The optical system comprises 12 lenses, two of which are aspherical, and the rest are spherical. It adopts a reverse telephoto structure with a negative-positive focal power distribution. Specifically, it includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop S, a seventh cemented lens L7, an eighth cemented lens L8, and a ninth lens L9, arranged coaxially along the incident direction. The first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 constitute a front lens group, while the seventh cemented lens L7, the eighth cemented lens L8, and the ninth lens L9 constitute a rear lens group. The aperture stop S is located near the front focal plane of the rear lens group.

[0046] The first lens L1 is a negative meniscus lens convex toward the object side, and the absolute value of the optical focal length is in the range of [0.0025, 0.005]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.0031, or another optical focal length within the range.

[0047] The second lens L2 is a negative meniscus lens convex toward the object side, and the absolute value of the optical focal length is in the range of [0.01, 0.03]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.017, or another optical focal length within the range.

[0048] The third lens L3 is a biconvex lens, and the absolute value of the optical focal length is in the range of [0.006, 0.01]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.007, or another optical focal length value within the optical focal length range is preferred.

[0049] The fourth lens L4 is a negative meniscus lens convex toward the object side, and the absolute value of the optical focal length is in the range of [0.03, 0.05]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.034, or another optical focal length within the range.

[0050] The fifth lens L5 is a biconcave lens, and the absolute value of the optical focal length is in the range of [0.02, 0.04]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.024, or another optical focal length within the range.

[0051] The sixth lens L6 is a biconvex lens, and the absolute value of the optical focal length is in the range of [0.03, 0.05]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.034, or another optical focal length within the range.

[0052] The seventh cemented lens L7 is composed of a seventh cemented positive lens L700 and a seventh cemented meniscus negative lens L701 coaxially arranged along the incident direction of light. The absolute value of the optical focal length is in the range of [0.01, 0.04]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.019, or another optical focal length value within the optical focal length range is preferred.

[0053] The eighth cemented lens L8 is composed of an eighth cemented meniscus negative lens L800 convex toward the object side, an eighth cemented positive lens L801, and an eighth cemented meniscus negative lens L802 convex toward the image side, which are coaxially arranged in sequence along the incident direction of light. The absolute value of the optical focal length is in the range of [0.01, 0.04]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.015, or another optical focal length value within the optical focal length range is preferred.

[0054] The ninth lens L9 is a biconvex lens, and the absolute value of the optical focal length is in the range of [0.02, 0.05]. In the embodiment of the present invention, the absolute value of the optical focal length is preferably 0.025, or another optical focal length value within the optical focal length range.

[0055] In this embodiment, the first lens L1 is made of fused quartz; the second lens L2 is made of radiation-resistant heavy crown glass, with a refractive index in the range of [1.60, 1.70] and a dispersion in the range of [50, 65]. In this embodiment, H-ZK6 glass is preferably used, with a refractive index of 1.613 and a dispersion of 58.577. Alternatively, radiation-resistant glass materials within other refractive index and dispersion ranges are preferred.

[0056] The refractive index of the third lens element L3 is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60]. In this embodiment of the present invention, N-KZFS2 glass material is preferably used, with a refractive index of 1.558 and a dispersion of 54.008. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0057] The refractive index of the fourth lens element L4 is in the range of [1.70, 1.80], and the dispersion is in the range of [40, 55]. In this embodiment of the present invention, H-LAF3B glass material is preferably used, with a refractive index of 1.744 and a dispersion of 44.904. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0058] The refractive index of the fifth lens element L5 is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28]. In this embodiment of the present invention, N-SF10 glass material is preferably used, with a refractive index of 1.785 and a dispersion of 25.68. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0059] The refractive index of the sixth lens L6 is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28]. In this embodiment of the present invention, N-SF10 glass material is preferably used, with a refractive index of 1.785 and a dispersion of 25.68. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0060] The refractive index of the seventh cemented positive lens L700 is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90]. In this embodiment of the present invention, H-FK61 glass material is preferably used, with a refractive index of 1.497 and a dispersion of 81.613. Alternatively, glass materials within other refractive index and dispersion ranges are preferred.

[0061] The refractive index of the seventh cemented meniscus negative lens L701 is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60]. In this embodiment of the present invention, N-KZFS2 glass material is preferably used, with a refractive index of 1.558 and a dispersion of 54.008. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0062] The refractive index of the eighth cemented meniscus negative lens (L800) is in the range of [1.70, 1.75], and the dispersion is in the range of [30, 40]. In the embodiment of the present invention, the glass material of the N-KZFS8 model is preferably used, with a refractive index of 1.720 and a dispersion of 34.700. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0063] The refractive index of the eighth cemented positive lens L801 is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90]. In this embodiment of the present invention, H-FK61 glass material is preferably used, with a refractive index of 1.497 and a dispersion of 81.613. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0064] The refractive index of L802 of the eighth cemented meniscus negative lens is in the range of [1.80, 1.85], and the dispersion is in the range of [40, 50]. In this embodiment of the present invention, N-LASF41 glass material is preferably used, with a refractive index of 1.835 and a dispersion of 43.129. Alternatively, glass materials within other refractive index and dispersion ranges are preferably used.

[0065] The refractive index of the ninth lens L9 is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90]. In this embodiment of the present invention, H-FK61 glass material is preferably used, with a refractive index of 1.497 and a dispersion of 81.613, or other glass materials within the refractive index and dispersion ranges are preferably used.

[0066] The surface parameters of all lenses in the embodiment of the present invention are as follows:

[0067]

[0068] In this embodiment of the present invention, the image-facing surface of the second lens L2 and the object-facing surface of the sixth lens L6 are both aspherical surfaces, and the aspherical surface equations are:

[0069]

[0070] Among them, z is the aspheric surface height, c is the aspheric surface vertex curvature, y is the aperture, k is the cone coefficient, A4 is the 4th aspheric surface coefficient, A6 is the 6th aspheric surface coefficient, A8 is the 8th aspheric surface coefficient, A 10 is the 10th-order aspheric coefficient.

[0071] In this embodiment, the two aspheric coefficients are as follows:

[0072]

[0073] The effective focal length of the optical system of this embodiment is The full field of view angle is 119°, the operating band is 550-910nm, the relative aperture is 1:4.5, the total optical length is 235mm, the clear aperture of the first lens is 180mm, and the incident angle of the principal ray of the edge field of view on the image plane is 2.5°, achieving a large field of view and image telecentricity. The illumination of the image plane in the edge field of view is better than 85%. The optical system of this embodiment can be applied to space remote sensing fields such as the front optical system of satellite-borne high-resolution and wide-coverage imaging spectrometers and multi-angle and multi-spectral polarization cameras.

[0074] like Figure 2Figure 2 shows the modulation transfer function (MTF) curve for the wide-band, large-field-of-view, low-distortion optical system of this embodiment. The abscissa represents spatial frequency in line pairs per millimeter (lp / mm), while the ordinate represents the MTF value. The graph shows that at a spatial frequency of 20 lp / mm, the MTF at the maximum field of view exceeds 0.70, indicating that the optical system has excellent imaging quality across the entire image plane.

[0075] like Figure 3 The left figure in FIG shows the field curvature curve of the wide-band, large-field-of-view, low-distortion optical system of this embodiment. The horizontal axis is the field curvature and the vertical axis is the normalized field of view. The figure shows that the maximum field curvature of the embodiment of the present invention is less than 0.3 mm. Figure 3 The right figure in the figure shows the distortion curve of the wide-band, large-field-of-view, low-distortion optical system of this embodiment. The horizontal axis is the relative distortion and the vertical axis is the normalized field of view. The figure shows that the distortion of all fields of view in the embodiment of the present invention is less than 2%.

[0076] like Figure 4 Figure 2 shows the lateral chromatic aberration curve for the wide-band, large-field-of-view, low-distortion optical system of this embodiment. The abscissa represents lateral chromatic aberration, and the ordinate represents the normalized field of view. The figure demonstrates that the lateral chromatic aberration of this embodiment is less than 16 μm, providing strong support for spectral registration in optical remote sensing instruments.

Claims

1. A wide-band, large-field-of-view, low-distortion optical system, characterized in that: The invention comprises a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6), an aperture stop (S), a seventh cemented lens (L7), an eighth cemented lens (L8), and a ninth lens (L9), which are coaxially arranged in sequence along the incident direction. The first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) constitute a front lens group, the seventh cemented lens (L7), the eighth cemented lens (L8), and the ninth lens (L9) constitute a rear lens group, and the aperture stop (S) is located near the front focal plane of the rear lens group. The first lens (L1) is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the first lens (L1) is in the range of [0.0025, 0.005]; The second lens (L2) is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the second lens (L2) is in the range of [0.01, 0.03]; The third lens (L3) is a biconvex lens, and the absolute value of the focal length of the third lens (L3) is in the range of [0.006, 0.01]; The fourth lens (L4) is a negative meniscus lens convex toward the object side, and the absolute value of the focal length of the fourth lens (L4) is in the range of [0.03, 0.05]; The fifth lens (L5) is a biconcave lens, and the absolute value of the focal length of the fifth lens (L5) is in the range of [0.02, 0.04]; The sixth lens (L6) is a biconvex lens, and the absolute value of the focal length of the sixth lens (L6) is in the range of [0.03, 0.05]; The seventh cemented lens (L7) is composed of a seventh cemented positive lens (L700) and a seventh cemented meniscus negative lens (L701) coaxially arranged in sequence along the incident direction of light, and the absolute value of the optical focus of the seventh cemented lens (L7) is in the range of [0.01, 0.04]; The eighth cemented lens (L8) is composed of an eighth cemented meniscus negative lens (L800) convex to the object side, an eighth cemented positive lens (L801), and an eighth cemented meniscus negative lens (L802) convex to the image side, which are coaxially arranged in sequence along the incident direction of light, and the absolute value of the optical focal length of the eighth cemented lens (L8) is in the range of [0.01, 0.04]. The ninth lens (L9) is a biconvex lens, and the absolute value of the focal length of the ninth lens (L9) is in the range of [0.02, 0.05].

2. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The first lens (L1) is made of fused quartz material; the second lens (L2) is made of radiation-resistant heavy crown glass material.

3. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The refractive index of the second lens (L2) is in the range of [1.60, 1.70], and the dispersion is in the range of [50, 65]; The refractive index of the third lens (L3) is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60]; The refractive index of the fourth lens (L4) is in the range of [1.70, 1.80], and the dispersion is in the range of [40, 55]; The refractive index of the fifth lens (L5) is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28]; The refractive index of the sixth lens (L6) is in the range of [1.75, 1.85], and the dispersion is in the range of [20, 28]; The refractive index of the seventh cemented positive lens (L700) is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90]; The refractive index of the seventh cemented meniscus negative lens (L701) is in the range of [1.50, 1.65], and the dispersion is in the range of [50, 60]; The refractive index of the eighth cemented meniscus negative lens (L800) is in the range of [1.70, 1.75], and the dispersion is in the range of [30, 40]; The refractive index of the eighth cemented positive lens (L801) is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90]; The refractive index of the eighth cemented meniscus negative lens (L802) is in the range of [1.80, 1.85], and the dispersion is in the range of [40, 50]; The refractive index of the ninth lens (L9) is in the range of [1.45, 1.55], and the dispersion is in the range of [75, 90].

4. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The second lens (L2) and the sixth lens (L6) are both aspherical.

5. The wide-band, large-field-of-view, low-distortion optical system according to claim 4, characterized in that: The equation of the aspheric surface is constructed using formula (1): (1) In formula (1), z is the aspheric height, c is the vertex curvature of the aspheric surface, y is the aperture of the aspheric surface, k is the cone coefficient, A4 is the fourth-order aspheric coefficient, A6 is the sixth-order aspheric coefficient, A8 is the eighth-order aspheric coefficient, and A 10 is the 10th-order aspheric coefficient.

6. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The operating band is from visible light to near infrared.

7. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The clear aperture of the first lens (L1) is less than 200 mm.

8. The wide-band, large-field-of-view, low-distortion optical system according to claim 1, characterized in that: The incident angle of the chief ray at the focal plane is less than 3° for all fields of view.

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