An imaging system

Abstract

The present invention relates to an imaging system which, from the object side to the image side, sequentially includes a first fixed lens group (G1) with positive optical power, a second focusing lens group (G2) with positive optical power, and a third fixed lens group (G3) with positive or negative optical power. The focal length f1 of the first fixed lens group (G1) and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.55. The imaging system of the present invention has the advantages of low distortion, large depth of field, uniform image quality, good color restoration, high contrast, high resolution, and low chromatic aberration, and at the same time has a temperature drift correction function.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and particularly relates to an optical imaging system. Background Art

[0002] Machine vision refers to collecting optical signals through a machine vision lens and giving them to a camera, and then the camera converts the optical signals into electrical signals and transmits them to an image processing system. Various operations are performed based on the collected image information to extract the features of the target, and then the on-site equipment actions are controlled according to the discrimination results. In the era of industrial automation, the demand for machine vision has been increasing year by year, and it has been widely used in fields such as electronic manufacturing, defect detection, and precision testing.

[0003] The imaging system applied to machine vision has very high requirements for pixels, picture uniformity, distortion, brightness, color restoration degree, etc. At present, the machine vision lenses on the market have large distortion, uneven brightness, difficult-to-show imaging details, low dynamic range, and poor color and contrast. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide an imaging system with low distortion, large depth of field, uniform image quality, good color restoration degree, good resolution, and low chromatic aberration.

[0005] To achieve the above purpose, the present invention provides an imaging system. Along the object side to the image side, it sequentially includes a first fixed lens group with positive optical power, a second focusing lens group with positive optical power, and a third fixed lens group with positive or negative optical power. The focal length f1 of the first fixed lens group and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.55.

[0006] According to one aspect of the present invention, the first fixed lens group includes four lenses, at least two of which are positive optical power lenses, and at least one is a negative optical power lens.

[0007] According to one aspect of the present invention, the refractive index nd and Abbe number vd of at least one positive optical power lens in the first fixed lens group satisfy the relationship:

[0008] 1.4 ≤ nd ≤ 1.5, 70 ≤ vd ≤ 80.

[0009] According to one aspect of the present invention, along the object side to the image side direction, the object side surface of the first lens in the first fixed lens group is a convex surface.

[0010] According to one aspect of the present invention, along the object side to the image side direction, the second lens and the third lens in the first fixed lens group form a doublet.

[0011] According to one aspect of the present invention, the third lens in the first fixed lens group is a concave-concave lens.

[0012] According to one aspect of the present invention, the second focusing lens group includes at least two positive refractive power lenses and at least one negative refractive power lens.

[0013] According to one aspect of the present invention, the third fixed lens group includes a positive refractive power or negative refractive power lens.

[0014] According to one aspect of the present invention, the imaging system further includes a diaphragm, and the diaphragm is located in the first fixed lens group or between the first fixed lens group and the second focusing lens group.

[0015] According to one aspect of the present invention, the focal length f2 of the second focusing lens group and the focal length f of the imaging system satisfy the relationship: 1.38 ≤ |f2 / f| ≤ 2.82.

[0016] According to one aspect of the present invention, the distance from the object side surface of the first lens in the first fixed lens group to the image surface is L, and it satisfies the relationship with the focal length f of the imaging system: 1.3 ≤ |L / f| ≤ 1.61.

[0017] In the imaging system of the present invention, the first fixed lens group, as a fixed group, mainly functions to collect light, enabling light to enter the imaging system smoothly, thereby reducing the sensitivity of the system to tolerances. Secondly, it can correct the chromatic aberration of the system, ensure good color reproducibility, and improve the image quality of the imaging system. The second focusing lens group, as a focusing group, mainly functions to enable the optical system to form a clear image at different object distances, while correcting the system aberration and distortion, reducing the sensitivity of the system to tolerances, so as to ensure the high image quality and uniform image quality of the imaging system. The third fixed lens group, as a fixed group, can make the light reach gently, ensuring a small chief ray angle of the imaging system. According to an embodiment of the present invention, the third fixed lens group G3 of the present invention includes a positive refractive power or negative refractive power lens.

[0018] In addition, the focal length f1 of the first fixed lens group and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.55. With such a setting, by reasonably matching the positive and negative refractive powers and the refractive power magnitudes of the first fixed lens group, the sensitivity of the imaging system to tolerances can be reduced, and the imaging quality at different object distances can be ensured.

[0019] In the imaging system of the present invention, the refractive index nd and Abbe number vd of at least one positive-power lens in the first fixed lens group satisfy the relational expressions: 1.4 ≤ nd ≤ 1.5, 70 ≤ vd ≤ 80. With such settings, chromatic aberration of the imaging system can be effectively corrected, the imaging quality of the imaging system can be improved, and at the same time, it is beneficial to the temperature drift correction of the athermalized system.

[0020] The second focusing lens group of the present invention includes at least two positive-power lenses and at least one negative-power lens. With such settings, through the reasonable combination of positive and negative power lenses, it is beneficial to correct the aberrations inside the second focusing lens group, and the correction of the aberrations inside the second focusing lens group is beneficial to reducing the burden of the first fixed lens group and the third fixed lens group on aberration correction, can reduce the tolerance sensitivity of the imaging system, and comprehensively improve the imaging quality of the imaging system.

[0021] In the imaging system of the present invention, the distance from the object side surface of the first lens in the first fixed lens group to the image surface is L, and it satisfies the relational expression with the focal length f of the imaging system: 1.3 ≤ |L / f| ≤ 1.61. Meeting the above requirements can ensure the imaging quality of the optical system, making the picture quality delicate, the image quality uniform, and the contrast high.

[0022] In the imaging system of the present invention, the focal length f2 of the second focusing lens group and the focal length f of the imaging system satisfy the relational expression: 1.38 ≤ |f2 / f| ≤ 2.82. With such settings, it is beneficial to balance the tolerance sensitivity and focusing performance of the optical system. Description of the Drawings

[0023] Figure 1 Schematic diagram showing the structural composition of the imaging system according to Embodiment 1 of the present invention;

[0024] Figure 2 Schematic diagram showing the distortion diagram of the imaging system according to Embodiment 1 of the present invention when focusing at the optimal working object distance;

[0025] Figure 3 Schematic diagram showing the high-temperature defocus MTF curve of the imaging system according to Embodiment 1 of the present invention when focusing at the optimal working object distance;

[0026] Figure 4 Schematic diagram showing the low-temperature defocus MTF curve of the imaging system according to Embodiment 1 of the present invention when focusing at the optimal working object distance;

[0027] Figure 5 Schematic diagram showing the main object distance MTF curve of the imaging system according to Embodiment 1 of the present invention;

[0028] Figure 6 Schematic diagram showing the defocus MTF curve of the imaging system according to Embodiment 1 of the present invention;

[0029] Figure 7 Schematic diagram showing the structural composition of the imaging system according to Embodiment 2 of the present invention;

[0030] Figure 8 Schematic diagram showing the distortion map of the imaging system according to Embodiment 2 of the present invention when focused at the optimal working object distance;

[0031] Figure 9 Schematic diagram showing the high-temperature defocus MTF curve of the imaging system according to Embodiment 2 of the present invention when focused at the optimal working object distance;

[0032] Figure 10 Schematic diagram showing the low-temperature defocus MTF curve of the imaging system according to Embodiment 2 of the present invention when focused at the optimal working object distance;

[0033] Figure 11 Schematic diagram showing the main object distance MTF curve of the imaging system according to Embodiment 2 of the present invention;

[0034] Figure 12 Schematic diagram showing the defocus MTF curve of the imaging system according to Embodiment 2 of the present invention;

[0035] Figure 13 Schematic diagram showing the structural composition of the imaging system according to Embodiment 3 of the present invention;

[0036] Figure 14 Schematic diagram showing the distortion map of the imaging system according to Embodiment 3 of the present invention when focused at the optimal working object distance;

[0037] Figure 15 Schematic diagram showing the high-temperature defocus MTF curve of the imaging system according to Embodiment 3 of the present invention when focused at the optimal working object distance;

[0038] Figure 16 Schematic diagram showing the low-temperature defocus MTF curve of the imaging system according to Embodiment 3 of the present invention when focused at the optimal working object distance;

[0039] Figure 17 Schematic diagram showing the main object distance MTF curve of the imaging system according to Embodiment 3 of the present invention;

[0040] Figure 18 Schematic diagram showing the defocus MTF curve of the imaging system according to Embodiment 3 of the present invention;

[0041] Figure 19 Schematic diagram showing the structural composition of the imaging system according to Embodiment 4 of the present invention;

[0042] Figure 20 Schematic diagram showing the distortion map of the imaging system according to Embodiment 4 of the present invention when focused at the optimal working object distance;

[0043] Figure 21 Schematically showing the high-temperature defocus MTF curve when the imaging system according to Embodiment 4 of the present invention is focused at the optimal working object distance;

[0044] Figure 22 Schematically showing the low-temperature defocus MTF curve when the imaging system according to Embodiment 4 of the present invention is focused at the optimal working object distance;

[0045] Figure 23 Schematically showing the main object distance MTF curve in the imaging system according to Embodiment 4 of the present invention;

[0046] Figure 24 Schematically showing the defocus MTF curve of the imaging system according to Embodiment 4 of the present invention;

[0047] Figure 25 Schematically showing the structural composition diagram of the imaging system according to Embodiment 5 of the present invention;

[0048] Figure 26 Schematically showing the distortion diagram when the imaging system according to Embodiment 5 of the present invention is focused at the optimal working object distance;

[0049] Figure 27 Schematically showing the high-temperature defocus MTF curve when the imaging system according to Embodiment 5 of the present invention is focused at the optimal working object distance;

[0050] Figure 28 Schematically showing the low-temperature defocus MTF curve when the imaging system according to Embodiment 5 of the present invention is focused at the optimal working object distance;

[0051] Figure 29 Schematically showing the main object distance MTF curve in the imaging system according to Embodiment 5 of the present invention;

[0052] Figure 30 Schematically showing the defocus MTF curve of the imaging system according to Embodiment 5 of the present invention. Detailed implementation manners

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0054] The present invention will be described in detail below in conjunction with the drawings and specific implementation manners. The implementation manners cannot be elaborated one by one here, but the implementation manners of the present invention are not limited to the following implementation manners.

[0055] Refer toFigure 1 As shown, the present invention provides an imaging system which, in the direction from the object side to the image side, sequentially includes a first fixed lens group G1 with positive optical power, a second focusing lens group G2 with positive optical power, and a third fixed lens group G3 with positive or negative optical power. When imaging an object from an infinitely distant object to a close-range object, the second focusing lens group G2 moves along the optical axis of the imaging system. In the imaging system of the present invention, the focal length f1 of the first fixed lens group G1 and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.55.

[0056] In the imaging system of the present invention, the first fixed lens group G1, as a fixed group, mainly functions to collect light, enabling light rays to enter the imaging system smoothly, thereby reducing the sensitivity of the system to tolerances. Secondly, it can correct the chromatic aberration of the system, ensure good color reproducibility, and improve the image quality of the imaging system. The second focusing lens group G2, as a focusing group, mainly functions to enable the optical system to form a clear image at different object distances, while correcting the aberrations and distortions of the system, reducing the tolerance sensitivity of the system, and thus ensuring high image quality and uniform image quality of the imaging system. The third fixed lens group G3, as a fixed group, can make the light rays reach gently, ensuring a small chief ray angle of the imaging system. According to an embodiment of the present invention, the third fixed lens group G3 of the present invention includes a lens with positive or negative optical power.

[0057] In addition, the focal length f1 of the first fixed lens group G1 and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.55. With such a setting, by reasonably matching the positive and negative optical powers and the magnitude of the optical power of the first fixed lens group G1, the tolerance sensitivity of the imaging system can be reduced, and the imaging quality at different object distances can be ensured.

[0058] In the imaging system of the present invention, the first fixed lens group G1 includes four lenses, at least two of which are positive-power lenses, and at least one is a negative-power lens. And at least one positive-power lens in the first fixed lens group G1 has a refractive index nd and an Abbe number vd that satisfy the relationship:

[0059] 1.4 ≤ nd ≤ 1.5, 70 ≤ vd ≤ 80. With such a setting, the chromatic aberration of the imaging system can be effectively corrected, the imaging quality of the imaging system can be improved, and at the same time, it is beneficial to the temperature drift correction of the athermalized system.

[0060] In the imaging system of the present invention, in the direction from the object side to the image side, the object side surface of the first lens in the first fixed lens group G1 is a convex surface. In the direction from the object side to the image side, the second and third lenses in the first fixed lens group G1 form a doublet, and the third lens is a concave-concave lens.

[0061] The first fixed lens group G1 of the present invention is arranged according to the above limitations. Through the reasonable combination of positive and negative focal length lenses, it is beneficial to ensure that the light beam smoothly enters the imaging system and corrects the chromatic aberration of the system, thereby reducing the tolerance sensitivity of the imaging system, ensuring the color restoration degree of the picture, and improving the imaging quality.

[0062] According to an embodiment of the present invention, the second focusing lens group G2 of the present invention includes at least two positive focal length lenses and at least one negative focal length lens. With such a setting, through the reasonable combination of positive and negative focal length lenses, it is beneficial to correct the aberration inside the second focusing lens group G2. The correction of the aberration inside the second focusing lens group G2 is beneficial to reducing the burden of the first fixed lens group G1 and the third fixed lens group G3 on aberration correction, can reduce the tolerance sensitivity of the imaging system, and comprehensively improve the imaging quality of the imaging system.

[0063] According to an embodiment of the present invention, the imaging system of the present invention further includes a diaphragm STOP, and the diaphragm STOP is located in the first fixed lens group G1 or between the first fixed lens group G1 and the second focusing lens group G2. With such a setting, it is beneficial to improve the image quality of the imaging system, make it close to the diffraction limit and ensure the uniformity of the picture.

[0064] For the imaging system of the present invention, the focal length f2 of the second focusing lens group G2 and the focal length f of the imaging system satisfy the relational expression: 1.38 ≤ |f2 / f| ≤ 2.82. With such a setting, it is beneficial to balance the tolerance sensitivity and focusing performance of the optical system.

[0065] For the imaging system of the present invention, the distance from the object side surface of the first lens in the first fixed lens group G1 to the image surface is L, and it satisfies the relational expression with the focal length f of the imaging system: 1.3 ≤ |L / f| ≤ 1.61. Meeting the above requirements can ensure the imaging quality of the optical system, making the picture quality delicate, the image quality uniform, and the contrast high.

[0066] In summary, the imaging system of the present invention, arranged according to the above limitations, has the advantages of low distortion, large depth of field, uniform picture quality, good color restoration degree, high contrast, high resolution, and low chromatic aberration, and at the same time has a temperature drift correction function.

[0067] The following gives 5 specific embodiments according to the above settings of the present invention to specifically illustrate the lens according to the present invention.

[0068] The data of the five groups of embodiments are as follows in Table 1:

[0069] Conditional Example 1 Example 2 Example 3 Example 4 Example 5 1.4 ≤ |f1 / f| ≤ 3.55 2.50 2.78 3.02 3.55 1.47 1.38 ≤ |f2 / f| ≤ 2.82 1.96 1.69 1.5 1.38 2.82 1.3 ≤ |L / f| ≤ 1.61 1.41 1.43 1.61 1.61 1.34 1.4 ≤ nd ≤ 1.5 1.49 1.48 1.48 1.49 1.5 70 ≤ vd ≤ 80 70 70 80 70 70

[0070] Table 1

[0071] Embodiment 1:

[0072] Figure 1 It is a structural diagram schematically showing an imaging system according to Embodiment 1 of the present invention.

[0073] The following Table 2 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, Abbe number:

[0074]

[0075]

[0076] Table 2

[0077] In this embodiment, the total length L of the imaging system is 63.3 mm, the system focal length f is 45.02 mm, the object distance range of the imaging system is 0.04 m - inf, and the aperture number F is 2.8. Among them, the first fixed lens group G1 contains a total of four lenses (L1 - L4), the lens L2 and the lens L3 form a doublet lens, and the aperture STOP is located between the lens L3 and the lens L4. In this embodiment, the lenses with positive optical power in the first fixed lens group G1 are L1, L2, and L4, and the lens with negative optical power is L3. The second focusing lens group G2 contains a total of three lenses (L5 - L7). In this embodiment, the lenses with positive optical power are L5 and L6, and the lens with negative optical power is L7. The third fixed lens group G3 contains a lens L8. In this embodiment, its optical power is positive.

[0078] Figures 2 - 6 They respectively schematically show the distortion diagram, high - temperature defocus MTF curve diagram, low - temperature defocus MTF curve diagram, main object distance MTF curve diagram, and defocus MTF curve diagram of the imaging system in Example 1 when focused at the best working object distance. Combining with the attached drawings, it can be known that for the imaging system obtained according to Embodiment 1 of the present invention, the distortion is controlled within 0.8, and at the same time, it has the advantages of large depth of field, uniform image quality, good color restoration, high contrast, high resolution, low chromatic aberration, and temperature drift correction function.

[0079] Embodiment 2:

[0080] Figure 7 It is a structural diagram schematically showing an imaging system according to Embodiment 2 of the present invention.

[0081] The following Table 3 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, Abbe number:

[0082]

[0083]

[0084] Table 3

[0085] In this embodiment, the total length L of the imaging system is 71.3 mm, the system focal length f is 49.7 mm, the object distance range of the imaging system is 0.05 m - inf, and the aperture number F is 3. A total of four lenses (L1 - L4) are included in the first fixed lens group G1. Lenses L2 and L3 form a doublet. The aperture STOP is located between the first fixed lens group G1 and the second fixed lens group G2. In this embodiment, the lenses with positive optical power in the first fixed lens group G1 are L1 and L2, and the lenses with negative optical power are L3 and L4. A total of three lenses (L5 - L7) are included in the second focusing lens group G2. In this embodiment, the lenses with positive optical power are L5 and L6, and the lens with negative optical power is L7. The third fixed lens group G3 includes one lens L8. In this embodiment, its optical power is positive.

[0086] Figures 8 - 12 They respectively schematically show the distortion diagram, high - temperature defocus MTF curve diagram, low - temperature defocus MTF curve diagram, main object distance MTF curve diagram, and defocus MTF curve diagram when the imaging system of Example 2 is focused at the optimal working object distance. It can be learned from the accompanying drawings that for the imaging system obtained according to Embodiment 2 of the present invention, the distortion is controlled within 0.4, and at the same time, it has the advantages of large depth of field, uniform image quality, good color restoration, high contrast, high resolution, low chromatic aberration, and a temperature drift correction function.

[0087] Embodiment Three:

[0088] Figure 13 It is a schematic diagram showing the structure of the imaging system according to Embodiment Three of the present invention.

[0089] The following Table 4 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0090]

[0091]

[0092] Table 4

[0093] In this embodiment, the total length L of the imaging system is 61.8 mm, the system focal length f is 38.4 mm, the object distance range of the imaging system is 0.04 m - inf, and the f-number F is 3. A total of four lenses (L1 - L4) are included in the first fixed lens group G1. Lenses L2 and L3 form a doublet lens, and the aperture STOP is located between lenses L3 and L4. In this embodiment, the lenses with positive optical power in the first fixed lens group G1 are L1 and L2, and the lenses with negative optical power are L3 and L4. A total of three lenses (L5 - L7) are included in the second focusing lens group G2. In this embodiment, the lenses with positive optical power are L5 and L6, and the lens with negative optical power is L7. Lenses L6 and L7 form a doublet lens. The third fixed lens group G3 includes one lens L8, and in this embodiment, its optical power is positive.

[0094] Figures 14 - 18 Schematically show the distortion diagram, high-temperature defocus MTF curve diagram, low-temperature defocus MTF curve diagram, main object distance MTF curve diagram, and defocus MTF curve diagram of the imaging system in Embodiment 3 when focusing at the optimal working object distance. It can be known from the accompanying drawings that for the imaging system obtained according to Embodiment 3 of the present invention, the distortion is controlled within 0.4, and at the same time, it has the advantages of large depth of field, uniform image quality, good color restoration, high contrast, high resolution, low chromatic aberration, and a temperature drift correction function.

[0095] Embodiment Four

[0096] Figure 19 Schematically show the structural diagram of the imaging system according to Embodiment Four of the present invention.

[0097] The following Table 5 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0098]

[0099] Table 5

[0100] In this embodiment, the total length L of the imaging system is 62.7 mm, the system focal length f is 39 mm, the object distance range of the imaging system is 0.04 m - inf, and the f-number F is 2.8. A total of four lenses (L1 - L4) are included in the first fixed lens group G1. Lenses L2 and L3 form a doublet. The aperture STOP is located between lenses L3 and L4. In this embodiment, the lenses with positive optical power in the first fixed lens group G1 are L1 and L2, and the lenses with negative optical power are L3 and L4. A total of four lenses (L5 - L8) are included in the second focusing lens group G2. In this embodiment, the lenses with positive optical power are L5, L6, and L8, and the lens with negative optical power is L7. Lenses L6 and L7 form a doublet. The third fixed lens group G3 includes one lens L9. In this embodiment, its optical power is positive.

[0101] Figures 20 - 24 Schematically show the distortion diagram, high-temperature defocus MTF curve diagram, low-temperature defocus MTF curve diagram, main object distance MTF curve diagram, and defocus MTF curve diagram of the imaging system in Embodiment 4 when focusing at the optimal working object distance. It can be learned from the accompanying drawings that for the imaging system obtained according to Embodiment 4 of the present invention, the distortion is controlled within 0.4, and at the same time, it has the advantages of large depth of field, uniform image quality, good color restoration, high contrast, high resolution, low chromatic aberration, and the function of temperature drift correction.

[0102] Embodiment Five

[0103] Figure 25 Schematically shows the structural diagram of the imaging system according to Embodiment Five of the present invention.

[0104] The following Table 6 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0105] # Type Radius Thickness Nd Vd sur1 standard 99.3 2.69 1.50 66 sur2 standard -62 5.62 sur3 standard 13.2 4.47 1.5 70 sur4 standard -22.1 0.59 1.78 44 sur5 standard 13.9 7.55 Stop standard Inf 2.26 sur7 standard -21.8 2.05 1.90 31 sur8 standard -12.9 2.05 (movable) sur9 standard 54.8 4.01 1.83 43 sur10 standard 156.7 0.12 sur11 standard 14.1 2.59 1.62 60 sur12 standard 1776 0.45 sur13 standard -153 3.04 1.63 36 sur14 standard 14.5 14.2 (movable) sur15 standard -26.5 1.12 1.78 44 sur16 standard -33.3 14.02 Image standard Inf

[0106] Table 6

[0107] In this embodiment, the total length L of the imaging system is 67 mm, the system focal length f is 49.9 mm, the object distance range of the imaging system is 0.04 m - inf, and the aperture number F is 2.8. A total of four lenses (L1 - L4) are included in the first fixed lens group G1. Lenses L2 and L3 form a doublet lens, and the aperture STOP is located between lenses L3 and L4. In this embodiment, the lenses with positive optical power in the first fixed lens group G1 are L1, L2, and L4, and the lens with negative optical power is L3. A total of three lenses (L5 - L7) are included in the second focusing lens group G2. In this embodiment, the lenses with positive optical power are L5 and L6, and the lens with negative optical power is L7. The third fixed lens group G3 includes one lens L8, and in this embodiment, its optical power is negative.

[0108] Figures 26 - 30 Schematically show the distortion diagram, high - temperature defocus MTF curve diagram, low - temperature defocus MTF curve diagram, main object distance MTF curve diagram, and defocus MTF curve diagram of the imaging system in Example 5 when focusing at the best working object distance. It can be known from the accompanying drawings that for the imaging system obtained according to Embodiment 5 of the present invention, the distortion is controlled within 0.8, and at the same time, it has the advantages of large depth of field, uniform image quality, good color restoration, high contrast, high resolution, low chromatic aberration, and the function of temperature drift correction.

[0109] The above description is only one embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An imaging system, characterized in that, along the object side to the image side, it successively includes a first fixed lens group (G1) with positive optical power, a second focusing lens group (G2) with positive optical power, and a third fixed lens group (G3) with positive or negative optical power, a total of three lens groups, the first fixed lens group (G1) only includes four lenses; the optical powers of the lenses in the first fixed lens group (G1) are positive, positive, negative, negative respectively along the object side to the image side, or the optical powers of the lenses in the first fixed lens group (G1) are positive, positive, negative, positive respectively along the object side to the image side; the second focusing lens group (G2) only includes three lenses, and the optical powers of the lenses in the second focusing lens group (G2) are positive, positive, negative respectively along the object side to the image side; alternatively, the second focusing lens group (G2) only includes four lenses, and the optical powers of the lenses in the second focusing lens group (G2) are positive, positive, negative, positive respectively along the object side to the image side; the focal length f1 of the first fixed lens group (G1) and the focal length f of the imaging system satisfy the relationship: 1.4 ≤ |f1 / f| ≤ 3.

55.

2. The imaging system according to claim 1, characterized in that, the refractive index nd and Abbe number vd of at least one positive optical power lens in the first fixed lens group (G1) satisfy the relationship: 1.4 ≤ nd ≤ 1.5, 70 ≤ vd ≤ 80.

3. The imaging system according to claim 1, characterized in that, along the object side to the image side direction, the object side surface of the first lens in the first fixed lens group (G1) is a convex surface.

4. The imaging system according to claim 3, characterized in that, along the object side to the image side direction, the second lens and the third lens in the first fixed lens group (G1) form a cemented doublet.

5. The imaging system according to claim 4, characterized in that, the third lens in the first fixed lens group (G1) is a concave-concave lens.

6. The imaging system according to claim 1, characterized in that, the third fixed lens group (G3) includes one positive or negative optical power lens.

7. The imaging system according to claim 1, characterized in that, the imaging system further includes a stop (STOP), and the stop (STOP) is located in the first fixed lens group (G1) or between the first fixed lens group (G1) and the second focusing lens group (G2).

8. The imaging system according to any one of claims 1-7, characterized in that, the focal length f2 of the second focusing lens group (G2) and the focal length f of the imaging system satisfy the relationship: 1.38 ≤ |f2 / f| ≤ 2.

82.

9. The imaging system according to any one of claims 1-7, characterized in that, the distance from the object side surface of the first lens in the first fixed lens group (G1) to the image surface is L, and it satisfies the relationship with the focal length f of the imaging system: 1.3 ≤ |L / f| ≤ 1.61.

Images