A large-aperture optical system applied to ultra-low illumination

Abstract

The application discloses a large-aperture optical system applied to ultra-low illumination, which comprises a first lens group, a second lens group and a third lens group arranged in sequence from an object side to an image side; the first lens group comprises a first spherical lens with positive focal power, a second spherical lens with positive focal power, a third spherical lens with negative focal power, a fourth spherical lens with positive focal power and a fifth spherical lens with negative focal power; the second lens group comprises a sixth spherical lens, a seventh spherical lens and an eighth spherical lens; and the third lens group comprises a ninth spherical lens, a tenth spherical lens, an eleventh spherical lens and a twelfth spherical lens. Through reasonable selection of glass spherical lens combination, the optical aberration of each stage is balanced and corrected, the focal power and focal length relationship of each lens is reasonably distributed, the effects of super-large aperture, low distortion, high relative illumination and high resolving power are realized, the number of lenses is small, the optical system structure is compact and the cost is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and in particular to a large-aperture optical system for use in ultra-low illumination. Background Technology

[0002] In the current surveillance and security field, active infrared illumination accounts for a large share. However, with the development of ultra-low-light cameras and their use in special fields, existing optical lenses on the market cannot meet the needs of ultra-low-light applications. Specifically: 1. Similar products have small apertures, requiring additional infrared illumination; 2. Similar products are expensive, relying on a large number of aspherical lenses with poor physical properties; 3. Similar products have large chromatic aberrations, requiring the use of filters of different thicknesses to correct chromatic aberrations during day and night cycles. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a large-aperture optical system for ultra-low illumination that requires no additional lighting and is low in cost.

[0004] According to an embodiment of the present invention, a large-aperture optical system for ultra-low illumination includes a first lens group, a second lens group, and a third lens group arranged sequentially from the object side to the image side;

[0005] The first lens group includes a first spherical lens with positive optical power, a second spherical lens with positive optical power, a third spherical lens with negative optical power, a fourth spherical lens with positive optical power, and a fifth spherical lens with negative optical power.

[0006] The second lens group includes a sixth spherical lens with positive optical power, a seventh spherical lens with negative optical power, and an eighth spherical lens with positive optical power;

[0007] The third lens group includes a ninth spherical lens with negative optical power, a tenth spherical lens with positive optical power, an eleventh spherical lens with negative optical power, and a twelfth spherical lens with positive optical power.

[0008] The focal lengths of the above spherical lenses satisfy the following relationship:

[0009] 0.5≤f1 / f≤1.5; 1.0≤f2 / f≤4.0; -1≤f3 / f≤-0.4; 0.4≤f4 / f≤0.8;

[0010] -0.7≤f5 / f≤-0.3;0.3≤f6 / f≤0.8;-0.5≤f7 / f≤-0.2;0.2≤f8 / f≤0.8;

[0011] -0.5≤f9 / f≤-0.3;0.5≤f10 / f≤1.0;-0.6≤f11 / f≤-0.2;0.15≤f12 / f≤0.5;

[0012] Where f is the effective focal length of the large aperture optical system, f1 is the focal length of the first spherical lens, f2 is the focal length of the second spherical lens, f3 is the focal length of the third spherical lens, f4 is the focal length of the fourth spherical lens, f5 is the focal length of the fifth spherical lens, f6 is the focal length of the sixth spherical lens, f7 is the focal length of the seventh spherical lens, f8 is the focal length of the eighth spherical lens, f9 is the focal length of the ninth spherical lens, f10 is the focal length of the tenth spherical lens, f11 is the focal length of the eleventh spherical lens, and f12 is the focal length of the twelfth spherical lens.

[0013] A large-aperture optical system for ultra-low illumination according to an embodiment of the present invention has at least the following beneficial effects:

[0014] This technical solution achieves effects such as ultra-large aperture, low distortion, high relative illumination, and high resolution by rationally selecting a combination of glass spherical lenses to balance and correct various levels of optical aberrations and rationally allocating the optical power and focal length relationship of each lens. Moreover, the number of lenses is small, the entire optical system has a compact structure, and the cost is greatly reduced.

[0015] According to some embodiments of the present invention, the second spherical lens and the third spherical lens form a first cemented lens group with high and low dispersion coefficients, wherein the dispersion coefficient range of the second spherical lens is (62.0, 71.5) and the dispersion coefficient range of the third spherical lens is (32.0, 40.0), and the focal length f23 of the first cemented lens group satisfies: -1.8≤f23 / f≤-1.2.

[0016] According to some embodiments of the present invention, the second spherical lens is a biconvex positive lens and the third spherical lens is a biconcave negative lens.

[0017] According to some embodiments of the present invention, the fourth spherical lens and the fifth spherical lens form a second cemented lens group with high and low dispersion coefficients, wherein the dispersion coefficient range of the fourth spherical lens is (62.0, 71.5) and the dispersion coefficient range of the fifth spherical lens is (15.0, 23.0), and the focal length f45 of the second cemented lens group satisfies: 4.0≤f45 / f≤8.0.

[0018] According to some embodiments of the present invention, the fourth spherical lens is a biconvex positive lens and the fifth spherical lens is a biconcave negative lens.

[0019] According to some embodiments of the present invention, the first lens group is a fixed lens group whose relative distance to the image plane remains constant, and the second and third lens groups are both actuating groups that can move along the optical axis.

[0020] According to some embodiments of the present invention, an image sensor disposed on the image side is also included, the image sensor being 1 / 1.8 inch in size, having a display resolution of 1920×1080, a pixel pitch of 4 μm, and a Nyquist frequency of 125 lp / mm.

[0021] According to some embodiments of the present invention, an IR filter group is disposed between the third lens group and the image sensor.

[0022] According to some embodiments of the present invention, a protective glass is disposed between the filter group (IR) and the image sensor.

[0023] According to some embodiments of the present invention, the focal length EFL of the large aperture optical system is 50mm and the aperture value Fno is 1.2.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0026] Figure 1 This is a schematic diagram of the large aperture optical system structure according to an embodiment of the present invention;

[0027] Figure 2 The diagram shows the chromatic aberration, astigmatism, and distortion of the large-aperture optical system according to an embodiment of the present invention.

[0028] Figure 3 This is a ray aberration diagram of the large aperture optical system according to an embodiment of the present invention;

[0029] Figure 4 This is the MTF diagram of the large aperture optical system according to an embodiment of the present invention;

[0030] Figure 5 This is a relative illumination diagram of the large aperture optical system according to an embodiment of the present invention.

[0031] Icon labels:

[0032] First lens group G1, first spherical lens L1, second spherical lens L2, third spherical lens L3, fourth spherical lens L4, fifth spherical lens L5

[0033] Second lens group G2, sixth spherical lens L6, seventh spherical lens L7, eighth spherical lens L8

[0034] Third lens group G3, ninth spherical lens L9, tenth spherical lens L10, eleventh spherical lens L11, twelfth spherical lens L12.

[0035] Image sensor (IMG), filter group (IR), protective glass (CG). Detailed Implementation

[0036] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0037] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0038] In the description of this invention, "multiple" refers to two or more. The use of "first" and "second" is for distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or the order in which the indicated technical features are presented.

[0039] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0040] Reference Figure 1 As shown, this is an embodiment of the present invention of a large aperture optical system applied in ultra-low illumination, including a first lens group G1, a second lens group G2, and a third lens group G3 arranged sequentially from the object side to the image side;

[0041] The first lens group G1 includes a positive optical power first spherical lens L1, a positive optical power second spherical lens L2, a negative optical power third spherical lens L3, a positive optical power fourth spherical lens L4, and a negative optical power fifth spherical lens L5. The first spherical lens L1 controls the incident angle of the optical system and reduces the height of light rays, but it will bring about large spherical aberration and on-axis chromatic aberration. The second spherical lens L2 and the third spherical lens L3 are cemented lenses made of high and low dispersion materials, which have the function of correcting spherical aberration and chromatic aberration. The fourth spherical lens L4 and the fifth spherical lens L5 are cemented lenses made of low refractive index low dispersion positive lens and high refractive index high dispersion negative lens materials, which further correct the spherical aberration and chromatic aberration of the system.

[0042] The second lens group G2 includes a sixth spherical lens L6 with positive optical power, a seventh spherical lens L7 with negative optical power, and an eighth spherical lens L8 with positive optical power. The cemented lens of L6 and L7, made of high and low dispersion materials, reduces the height of light rays and does not introduce too much chromatic aberration. The eighth spherical lens L8, made of high refractive index material, has a large positive optical power and shortens the optical path of the system, but it will bring greater coma and astigmatism.

[0043] The third lens group G3 includes a ninth spherical lens L9 with negative optical power, a tenth spherical lens L10 with positive optical power, an eleventh spherical lens L11 with negative optical power, and a twelfth spherical lens L12 with positive optical power. The ninth spherical lens L9 has the characteristics of negative optical power with high refractive index and high dispersion, which can correct and balance the coma and astigmatism introduced by L8, but will introduce chromatic aberration. The tenth spherical lens L10 and the eleventh spherical lens L11 are high refractive index and low dispersion positive optical power materials and low refractive index and high dispersion negative optical power materials, respectively, which can correct the spherical aberration and chromatic aberration introduced by L12. The twelfth spherical lens L12 has positive optical power. L12 is a high refractive index and high dispersion material with a large positive optical power, which modulates the emitted light to achieve the focal length magnification required by the system.

[0044] The focal lengths of the above spherical lenses satisfy the following relationship:

[0045] 0.5≤f1 / f≤1.5; 1.0≤f2 / f≤4.0; -1≤f3 / f≤-0.4; 0.4≤f4 / f≤0.8;

[0046] -0.7≤f5 / f≤-0.3;0.3≤f6 / f≤0.8;-0.5≤f7 / f≤-0.2;0.2≤f8 / f≤0.8;

[0047] -0.5≤f9 / f≤-0.3;0.5≤f10 / f≤1.0;-0.6≤f11 / f≤-0.2;0.15≤f12 / f≤0.5;

[0048] Where f is the effective focal length of the large aperture optical system, f1 is the focal length of the first spherical lens L1, f2 is the focal length of the second spherical lens L2, f3 is the focal length of the third spherical lens L3, f4 is the focal length of the fourth spherical lens L4, f5 is the focal length of the fifth spherical lens L5, f6 is the focal length of the sixth spherical lens L6, f7 is the focal length of the seventh spherical lens L7, f8 is the focal length of the eighth spherical lens L8, f9 is the focal length of the ninth spherical lens L9, f10 is the focal length of the tenth spherical lens L10, f11 is the focal length of the eleventh spherical lens L11, and f12 is the focal length of the twelfth spherical lens L12.

[0049] As can be seen from the above, this technical solution achieves effects such as ultra-large aperture, low distortion, high relative illumination, and high resolution by rationally selecting the combination of glass spherical lenses to balance and correct various levels of optical aberrations and rationally allocating the optical power and focal length relationship of each lens. Moreover, the number of lenses is small, the entire optical system has a compact structure and small size, and is easy to carry and transport. Compared with aspherical lenses, the cost is greatly reduced.

[0050] Because existing fixed-focus lenses require switching between filters of different thicknesses to compensate for the inconsistency in focus between visible light and near-infrared light, i.e., chromatic aberration, in some embodiments of this invention, a second spherical lens L2 and a third spherical lens L3 form a first cemented lens group with a combination of high and low dispersion coefficients. The dispersion coefficient range of the second spherical lens L2 is (62.0, 71.5), and the dispersion coefficient range of the third spherical lens L3 is (32.0, 40.0). The focal length f23 of the first cemented lens group satisfies: -1.8 ≤ f23 / f ≤ -1.2. This embodiment, through the reasonable combination of cemented lens groups with high and low dispersion coefficients, can effectively correct chromatic aberration, achieving a confocal effect in both day and night, thus eliminating the need to switch filters.

[0051] In some embodiments of the present invention, the second spherical lens L2 is a biconvex positive lens, and the third spherical lens L3 is a biconcave negative lens. The biconvex positive lens and the biconcave negative lens are cemented together to form a first cemented lens group. It should be noted that the cemented structure is only one embodiment of the present invention, and similar technical effects can also be achieved by controlling the gap between the biconvex positive lens and the biconcave negative lens to be extremely small.

[0052] Furthermore, in some embodiments of the present invention, the fourth spherical lens L4 and the fifth spherical lens L5 form a second cemented lens group with a combination of high and low dispersion coefficients. The dispersion coefficient range of the fourth spherical lens L4 is (62.0, 71.5), and the dispersion coefficient range of the fifth spherical lens L5 is (15.0, 23.0). The focal length f45 of the second cemented lens group satisfies: 4.0 ≤ f45 / f ≤ 8.0. This embodiment, through the reasonable combination of cemented lens groups with high and low dispersion coefficients, can effectively correct chromatic aberration, achieving a confocal effect for both day and night, thus eliminating the need to switch filters. It should be noted that the second cemented lens group can be used alone or simultaneously with the first cemented lens group to further correct chromatic aberration.

[0053] In some embodiments of the present invention, the fourth spherical lens L4 is a biconvex positive lens, and the fifth spherical lens L5 is a biconcave negative lens. The biconvex positive lens and the biconcave negative lens are cemented together to form a second cemented lens group. It should be noted that the cemented structure is only one embodiment of the present invention, and similar technical effects can also be achieved by controlling the gap between the biconvex positive lens and the biconcave negative lens to be extremely small.

[0054] The following table shows the specific parameters of the embodiments of the present invention:

[0055]

[0056]

[0057] Table 1

[0058] like Figure 1 As shown, in some embodiments of the present invention, the first lens group G1 is a fixed lens group whose distance from the image plane remains constant, while the second lens group G2 and the third lens group G3 are both actuating groups that can move along the optical axis. At different distances from the object plane, focusing is achieved by moving the two actuating groups along the optical axis. The following table shows the focusing interval data for specific embodiments of the present invention:

[0059]

[0060] Table 2

[0061] Where D0 is the distance between the first lens group G1 and the object plane, D1 is the distance between the first lens group G1 and the second lens group G2, D2 is the distance between the second lens group G2 and the third lens group G3, and D3 is the focal length between the third lens group G3 and the image plane.

[0062] It can be seen that during the focusing process, as the projection distance gradually increases, the air gap between the second lens group G2 and the first lens group G1 continuously increases, while the air gap between the third lens group G3 and the second lens group G2 continuously decreases.

[0063] In some embodiments of the present invention, an image sensor (IMG) disposed on the image side is also included. The image sensor IMG has a size of 1 / 1.8 inch, a display resolution of 1920×1080, a pixel pitch of 4 μm, and a Nyquist frequency of 125 lp / mm. It should be noted that the invention is not limited to a specific type of sensor (image sensor, such as CMOS, CCD, etc.).

[0064] In some embodiments of the present invention, a filter group IR is disposed between the third lens group G3 and the image sensor IMG. The filter group IR is a parallel plate with a certain thickness, and its optical surface is coated with different bandwidth films depending on whether it is day or night. The filter group IR can be an infrared cutoff or absorption filter, or a full-transmission spectral filter, which can filter out interfering light and enable the image sensor IMG to obtain the best imaging effect.

[0065] Furthermore, in some embodiments of the present invention, a protective glass CG is provided between the filter group IR and the image sensor IMG, which can protect the image sensor IMG from direct damage by external forces.

[0066] In some embodiments of the present invention, the focal length EFL of the large-aperture optical system is 50mm, and the aperture value Fno is 1.2. The long focal length is suitable for long-distance monitoring and shooting, especially for military equipment, and the large aperture is suitable for ultra-low light environments. The optimal imaging target surface supported by the above large-aperture optical system is 9mm (half-image height 4.5mm).

[0067] Figures 2 to 5 This is an optical evaluation diagram of an embodiment of the present invention. Figure 2 The image shown is a spherical aberration field curve according to an embodiment of the present invention. It can be seen that the axial chromatic aberration of red and green light is corrected and the secondary spectrum is small. The optical distortion is less than 1% and the image distortion is small. Figure 3 The light aberration diagram of this embodiment of the invention shows that the aberrations are well balanced and corrected, the magnification color difference is about half a pixel, and the color difference effect of the actual captured image is good. Figure 4 The MTF diagram of this embodiment of the invention shows that an average MTF greater than 0.45 can be achieved at the Nyquist frequency with a large aperture of F1.2. Figure 5 The relative illuminance curve of this embodiment of the invention shows that the ratio of the brightness of the peripheral area to the brightness of the central area is greater than 90%, indicating good uniformity of brightness in the image.

[0068] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A large-aperture optical system for ultra-low illumination, characterized in that, It includes a first lens group (G1), a second lens group (G2), and a third lens group (G3) arranged sequentially from the object side to the image side; The first lens group (G1) includes a first spherical lens with positive optical power, a second spherical lens with positive optical power, a third spherical lens with negative optical power, a fourth spherical lens with positive optical power, and a fifth spherical lens with negative optical power. The second lens group (G2) includes a sixth spherical lens with positive optical power, a seventh spherical lens with negative optical power, and an eighth spherical lens with positive optical power; The third lens group (G3) includes a ninth spherical lens with negative optical power, a tenth spherical lens with positive optical power, an eleventh spherical lens with negative optical power, and a twelfth spherical lens with positive optical power. The focal lengths of the above spherical lenses satisfy the following relationship: 0.5≤f1 / f≤1.5; 1.0≤f2 / f≤4.0; -1≤f3 / f≤-0.4; 0.4 ≤ f4 / f ≤ 0.8; -0.7≤f5 / f≤-0.3;0.3≤f6 / f≤0.8;-0.5≤f7 / f≤-0.2;0.2≤f8 / f≤0.8; -0.5≤f9 / f≤-0.3;0.5≤f10 / f≤1.0;-0.6≤f11 / f≤-0.2;0.15≤f12 / f≤0.5; Where f is the effective focal length of the large aperture optical system, f1 is the focal length of the first spherical lens, f2 is the focal length of the second spherical lens, f3 is the focal length of the third spherical lens, f4 is the focal length of the fourth spherical lens, f5 is the focal length of the fifth spherical lens, f6 is the focal length of the sixth spherical lens, f7 is the focal length of the seventh spherical lens, f8 is the focal length of the eighth spherical lens, f9 is the focal length of the ninth spherical lens, f10 is the focal length of the tenth spherical lens, f11 is the focal length of the eleventh spherical lens, and f12 is the focal length of the twelfth spherical lens.

2. The large-aperture optical system for ultra-low illumination according to claim 1, characterized in that: The second spherical lens and the third spherical lens form a first cemented lens group with high and low dispersion coefficients. The dispersion coefficient range of the second spherical lens is (62.0, 71.5), and the dispersion coefficient range of the third spherical lens is (32.0, 40.0). The focal length f23 of the first cemented lens group satisfies: -1.8≤f23 / f≤-1.

2.

3. The large-aperture optical system for ultra-low illumination according to claim 2, characterized in that: The second spherical lens is a biconvex positive lens, and the third spherical lens is a biconcave negative lens.

4. The large-aperture optical system for ultra-low illumination according to claim 1 or 2 or 3, characterized in that: The fourth and fifth spherical lenses form a second cemented lens group with high and low dispersion coefficients. The dispersion coefficient range of the fourth spherical lens is (62.0, 71.5), and the dispersion coefficient range of the fifth spherical lens is (15.0, 23.0). The focal length f45 of the first cemented lens group satisfies: 4.0 ≤ f45 / f ≤ 8.

0.

5. The large-aperture optical system for ultra-low illumination according to claim 4, characterized in that: The fourth spherical lens is a biconvex positive lens, and the fifth spherical lens is a biconcave negative lens.

6. The large-aperture optical system for ultra-low illumination according to claim 1, characterized in that: The first lens group (G1) is a fixed lens group that maintains a constant distance from the image plane, while the second lens group (G2) and the third lens group (G3) are both actuated groups that can move along the optical axis.

7. The large-aperture optical system for ultra-low illumination according to claim 1, characterized in that: It also includes an image sensor (IMG) located on the image side, which is 1 / 1.8 inch in size, has a display resolution of 1920×1080, a pixel pitch of 4µm, and a Nyquist frequency of 125lp / mm.

8. The large-aperture optical system for ultra-low illumination according to claim 7, characterized in that: A filter group (IR) is disposed between the third lens group (G3) and the image sensor (IMG).

9. The large-aperture optical system for ultra-low illumination according to claim 8, characterized in that: A protective glass (CG) is disposed between the filter group (IR) and the image sensor (IMG).

10. The large-aperture optical system for ultra-low illumination according to claim 1, characterized in that: The large aperture optical system has a focal length EFL of 50mm and an aperture value Fno of 1.2.

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