Imaging lens

Abstract

The present invention relates to an imaging lens, which includes a first lens group (1), a diaphragm (2), and a second lens group (3) arranged in sequence along the optical axis from the object side to the image side. The first lens group (1) includes at least five lenses, the second lens group (3) includes four lenses, the first lens group (1) is a fixed group, and the second lens group (3) is a focusing group. The imaging lens of the present invention has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the smaller distortion characteristics of the lens itself, the lens has a wider field of view.

Description

Technical Field

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

[0002] Machine vision is a comprehensive technology, including image processing, mechanical engineering technology, control, electric light source illumination, optical imaging, sensors, analog and digital video technology, computer software and hardware technology (image enhancement and analysis algorithms, image cards, I / O cards, etc.). A typical machine vision application system includes image capture, light source system, image digitization module, digital image processing module, intelligent judgment and decision-making module, and mechanical control execution module. With the development of the imaging lens industry, various imaging lenses have emerged. However, these imaging lenses have poor optical resolution and large imaging distortion. It can be seen that although the imaging lenses in the prior art have a wide shooting range, their imaging is not delicate enough, the dynamic range during imaging is not high, the color and contrast are not good enough, and at the same time, their transmittance deviation is relatively large. Therefore, the application fields of such lenses are limited, especially in some high-precision and high-tech fields. Summary of the Invention

[0003] The purpose of the present invention is to provide an imaging lens applicable to machine vision technology.

[0004] To achieve the above-mentioned invention purpose, the present invention provides an imaging lens, which includes a first lens group, a diaphragm, and a second lens group arranged in sequence from the object side to the image side along the optical axis. The first lens group includes at least five lenses, the second lens group includes four lenses, the first lens group is a fixed group, and the second lens group is a focusing group.

[0005] According to one aspect of the present invention, the second lens group has a positive optical power and moves along the optical axis direction for focusing when imaging from infinity to a short distance.

[0006] According to one aspect of the present invention, the first lens group includes at least two negative lenses and two positive lenses, and the second lens group includes one negative lens and three positive lenses.

[0007] According to one aspect of the present invention, in the first lens group, the lenses closest to the object side and the image side are both convex-concave type;

[0008] Among the two negative lenses of the first lens group, one is double concave type and the other is convex-concave type.

[0009] According to one aspect of the present invention, the second lens group includes three double convex lenses and one double concave lens, and has a cemented lens group.

[0010] According to one aspect of the present invention, the focal length F1 of the first lens group and the focal length F of the imaging lens satisfy the following relational expression:

[0011] -20 < F1 / F < 20.

[0012] According to one aspect of the present invention, the focal length F2 of the second lens group and the focal length F of the imaging lens satisfy the following relational expression:

[0013] 1 < F2 / F < 2.

[0014] According to one aspect of the present invention, the total length L of the imaging lens and the focal length F satisfy the following relational expression:

[0015] 2 < L / F < 8.

[0016] According to one aspect of the present invention, one lens in the cemented lens group of the second lens group uses a low-dispersion glass material, and its refractive index ND and Abbe number VD respectively satisfy the following relational expressions:

[0017] 1.40 ≤ ND ≤ 1.53;

[0018] And

[0019] 64 ≤ VD ≤ 96.

[0020] According to the present invention, an imaging lens is provided, which has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the smaller distortion characteristics of the lens itself, the lens has a wider field of view.

[0021] According to one solution of the present invention, the first lens group is used as a fixed group, which mainly functions to turn the optical path and expand the aperture, so that light can smoothly enter the imaging system while ensuring the aperture size, thereby reducing the tolerance sensitivity of the system. Secondly, the combination of multiple positive and negative lenses is convenient for correcting the high and low temperatures of the system. The second lens group is used as a focusing lens group, and its main function is to enable the optical system to achieve clear imaging at different object distances, correct the monochromatic aberration of the system, ensure the consistency of image quality under the condition of low distortion, and at the same time correct chromatic aberration to ensure good color reproducibility. And the setting that the first lens group is a fixed group and the second lens group is a focusing group can make the imaging more delicate and the lens has smaller distortion characteristics.

[0022] According to one solution of the present invention, the first lens group uses a combination of multiple positive and negative lenses to facilitate the correction of the high and low temperatures of the system; and uses multiple convex and concave lenses to facilitate the correction of the aberration of the system, reduce the tolerance sensitivity of the imaging system, and improve the image clarity.

[0023] According to an aspect of the present invention, the second lens group adopts the combination of positive and negative lens optical powers and the use of cemented lenses, which is beneficial to correcting the monochromatic aberration and chromatic aberration of the entire second lens group, can reduce the tolerance sensitivity of the optical system, and improve the imaging quality of the optical system.

[0024] According to an aspect of the present invention, by reasonably matching the positive and negative optical powers and the magnitudes of the optical powers of the first lens group and the entire lens, low distortion can be well ensured and the tolerance sensitivity can be reduced.

[0025] According to an aspect of the present invention, by reasonably matching the positive and negative optical powers and the magnitudes of the optical powers of the second lens group and the entire lens, the deterioration of the focusing performance at different object distances can be well avoided and the tolerance sensitivity is easily reduced.

[0026] According to an aspect of the present invention, by reasonably controlling the overall length of the system, the volume of the entire lens can be balanced to control costs, the imaging quality of the optical system can be ensured, and the image quality contrast can be made high.

[0027] According to an aspect of the present invention, one of the cemented lenses in the second lens group adopts a low-dispersion material, which is beneficial to correcting chromatic aberration. At the same time, the deterioration of the focusing performance at different object distances can be avoided, and the high and low temperature performance is easily corrected. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram showing the structure of an imaging lens according to the first embodiment of the present invention;

[0029] Figure 2 Schematic diagram showing the resolution diagram of an imaging lens according to the first embodiment of the present invention;

[0030] Figure 3 Schematic diagram showing the distortion diagram of an imaging lens according to the first embodiment of the present invention;

[0031] Figure 4 Schematic diagram showing the defocus curve diagram of an imaging lens according to the first embodiment of the present invention;

[0032] Figure 5 Schematic diagram showing the structure of an imaging lens according to the second embodiment of the present invention;

[0033] Figure 6 Schematic diagram showing the resolution diagram of an imaging lens according to the second embodiment of the present invention;

[0034] Figure 7 Schematic diagram showing the distortion diagram of an imaging lens according to the second embodiment of the present invention;

[0035] Figure 8Schematically showing the defocus curve diagram of an imaging lens according to the second embodiment of the present invention;

[0036] Figure 9 Schematically showing the structural diagram of an imaging lens according to the third embodiment of the present invention;

[0037] Figure 10 Schematically showing the resolution force diagram of an imaging lens according to the third embodiment of the present invention;

[0038] Figure 11 Schematically showing the distortion diagram of an imaging lens according to the third embodiment of the present invention;

[0039] Figure 12 Schematically showing the defocus curve diagram of an imaging lens according to the third embodiment of the present invention;

[0040] Figure 13 Schematically showing the structural diagram of an imaging lens according to the fourth embodiment of the present invention;

[0041] Figure 14 Schematically showing the resolution force diagram of an imaging lens according to the fourth embodiment of the present invention;

[0042] Figure 15 Schematically showing the distortion diagram of an imaging lens according to the fourth embodiment of the present invention;

[0043] Figure 16 Schematically showing the defocus curve diagram of an imaging lens according to the fourth embodiment of the present invention;

[0044] Figure 17 Schematically showing the structural diagram of an imaging lens according to the fifth embodiment of the present invention;

[0045] Figure 18 Schematically showing the resolution force diagram of an imaging lens according to the fifth embodiment of the present invention;

[0046] Figure 19 Schematically showing the distortion diagram of an imaging lens according to the fifth embodiment of the present invention;

[0047] Figure 20 Schematically showing the defocus curve diagram of an imaging lens according to the fifth embodiment of the present invention. Detailed implementation manners

[0048] 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, without creative efforts, other drawings can also be obtained based on these drawings.

[0049] When describing the embodiments of the present invention, the orientation or positional relationships expressed by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" are based on the orientation or positional relationships shown in the relevant drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0050] The present invention will be described in detail below in conjunction with the drawings and specific embodiments. The embodiments cannot be described in detail here one by one, but the embodiments of the present invention are not limited to the following embodiments.

[0051] See Figure 1 , the imaging lens of the present invention includes a first lens group 1, a diaphragm 2, and a second lens group 3 arranged in sequence along the optical axis from the object side to the image side. The first lens group 1 includes at least five lenses, the second lens group 3 includes four lenses, the first lens group 1 is a fixed group, and the second lens group 3 is a focusing group. The first lens group 1 has a positive or negative optical power, and the second lens group 3 both have positive optical powers. When imaging from infinity to a short distance, the second lens group 3 moves along the optical axis direction for focusing. A filter / color filter is also provided on the image side of the second lens group 3, and the image plane 4 is located on the image side of the filter / color filter. The first lens group 1 includes at least two negative lenses and two positive lenses, and the second lens group 3 includes one negative lens and three positive lenses. As a fixed group, the first lens group 1 mainly plays the role of turning the optical path and expanding the aperture, enabling light to smoothly enter the imaging system while ensuring the aperture size, thereby reducing the tolerance sensitivity of the system. Secondly, the combination of multiple positive and negative lenses is convenient for correcting the high and low temperatures of the system. As a focusing lens group, the second lens group 3 mainly functions to enable the optical system to clearly image at different object distances, correct the monochromatic aberration of the system, ensure the consistency of image quality under low distortion conditions, and at the same time correct chromatic aberration to ensure good color reproducibility.

[0052] In the first lens group 1, the lenses closest to the object side and the image side are both convex-concave lenses. Among them, the object side surface of the lens located on the object side is convex, and the image side surface of the lens located on the image side is concave. Among the two negative lenses of the first lens group 1, one is a double concave lens and the other is a convex-concave lens. Thus, by using a combination of multiple positive and negative lenses, the first lens group 1 facilitates the correction of the high and low temperatures of the system, and by using multiple convex-concave lenses, it facilitates the correction of the aberration of the system, reduces the tolerance sensitivity of the imaging system, and improves the image clarity.

[0053] In the present invention, the second lens group 3 includes three double convex lenses and one double concave lens, and has a cemented lens group. In this way, by using the combination of the optical powers of positive and negative lenses and the use of cemented lenses, it is beneficial to correct the monochromatic aberration and chromatic aberration of the entire second lens group 3, can reduce the tolerance sensitivity of the optical system, and improve the imaging quality of the optical system.

[0054] In the present invention, the focal length F1 of the first lens group 1 and the focal length F of the imaging lens satisfy the following relational expression: -20 < F1 / F < 20. In this way, by reasonably matching the positive and negative optical powers and the magnitudes of the optical powers of the first lens group 1 and the entire lens, it is possible to well ensure low distortion and reduce the tolerance sensitivity. The focal length F2 of the second lens group 3 and the focal length F of the imaging lens satisfy the following relational expression: 1 < F2 / F < 2. In this way, by reasonably matching the positive and negative optical powers and the magnitudes of the optical powers of the second lens group 3 and the entire imaging lens, it is possible to well avoid the deterioration of the focusing performance at different object distances and is easy to reduce the tolerance sensitivity. The total length L of the imaging lens (i.e., the distance from the first lens to the image plane) and the focal length F of the imaging lens satisfy the following relational expression: 2 < L / F < 8. In this way, by reasonably controlling the total length of the system, the volume of the entire lens can be balanced to control the cost, ensure the imaging quality of the optical system, and make the image quality have a high contrast. One of the lenses in the cemented lens group of the second lens group 3 uses a low-dispersion glass material, and its refractive index ND and Abbe number VD respectively satisfy the following relational expressions: 1.40 ≤ ND ≤ 1.53; 64 ≤ VD ≤ 96. Using a low-dispersion material for one of the lenses of the cemented lens of the second lens group 3 is beneficial to correcting chromatic aberration, and at the same time can avoid the deterioration of the focusing performance at different object distances and is easy to correct the high and low temperature performance.

[0055] In summary, through the above settings, the imaging lens of the present invention has a more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the smaller distortion characteristics of the lens itself, the lens has a wider field of view.

[0056] The following are five sets of embodiments based on the above settings of the present invention to specifically illustrate the imaging lens of the present invention. In the following embodiments, S1, S2, …, SN are used to represent the surfaces of each lens, where the cemented surface of the cemented lens group is denoted as one surface, and the aperture stop is denoted as STO. The parameter settings of each embodiment satisfy Table 1 below:

[0057]

[0058] Table 1

[0059] The first embodiment:

[0060] Referring to Figure 1 , in this embodiment, along the optical axis from the object side to the image side, the first lens group 1 includes the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 arranged in sequence. The second lens group 3 includes the sixth lens L6, the seventh lens L7, the eighth lens L8, and the ninth lens L9, wherein the sixth lens L6 and the seventh lens L7 form a cemented lens group. The focal length f of the imaging lens in this embodiment is 13.4 mm, and the aperture value FNO = 2.4. Other parameters are shown in Table 2 below:

[0061]

[0062] Table 2

[0063] Combined with Figures 2 to 4 , the imaging lens in this embodiment has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the smaller distortion characteristics of the lens itself, the lens has a wider field of view.

[0064] The second embodiment:

[0065] Referring to Figure 5 , in this embodiment, along the optical axis from the object side to the image side, the first lens group 1 includes the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 arranged in sequence. The second lens group 3 includes the sixth lens L6, the seventh lens L7, the eighth lens L8, and the ninth lens L9, wherein the sixth lens L6 and the seventh lens L7 form a cemented lens group. The focal length f of the imaging lens in this embodiment is 15.2 mm, and the aperture value FNO = 1.6. Other parameters are shown in Table 3 below:

[0066]

[0067] Table 3

[0068] Combined with Figures 6 to 8, the imaging lens of this embodiment has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the relatively small distortion characteristics of the lens itself, the lens has a wider field of view.

[0069] The third embodiment:

[0070] Refer to Figure 9 , in this embodiment, along the optical axis from the object side to the image side, the first lens group 1 includes the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 arranged in sequence. The second lens group 3 includes the sixth lens L6, the seventh lens L7, the eighth lens L8, and the ninth lens L9. Among them, the sixth lens L6 and the seventh lens L7 form a cemented lens group. The focal length f of the imaging lens of this embodiment is 16.8 mm, and the aperture value FNO = 2.4. Other parameters are shown in Table 4 below:

[0071]

[0072] Table 4

[0073] Combined with Figures 10 to 12 , the imaging lens of this embodiment has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the relatively small distortion characteristics of the lens itself, the lens has a wider field of view.

[0074] The fourth embodiment:

[0075] Refer to Figure 13 , in this embodiment, along the optical axis from the object side to the image side, the first lens group 1 includes the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 arranged in sequence. The second lens group 3 includes the sixth lens L6, the seventh lens L7, the eighth lens L8, and the ninth lens L9. Among them, the sixth lens L6, the seventh lens L7, and the eighth lens L8 form a cemented lens group. The focal length f of the imaging lens of this embodiment is 17.0 mm, and the aperture value FNO = 1.8. Other parameters are shown in Table 5 below:

[0076]

[0077] Table 5

[0078] Combined with Figures 14 to 16 , the imaging lens of this embodiment has more delicate imaging, a higher dynamic imaging range, a larger depth of field, good color and contrast, good high and low temperature performance, a wider application range, and at the same time, due to the relatively small distortion characteristics of the lens itself, the lens has a wider field of view.

[0079] The fifth embodiment:

[0080] See Figure 17 Figure 17 , in this embodiment, along the optical axis from the object side to the image side, the first lens group 1 includes 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 arranged in sequence. The second lens group 3 includes the seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10. Among them, the seventh lens L7 and the eighth lens L8 form a cemented lens group. The focal length f of the imaging lens in this embodiment is 8.6 mm, and the aperture value FNO = 2.0. Other parameters are shown in Table 6 below:

[0081]

[0082] Table 6

[0083] Combined with Figures 18 to 20 Figures 18 to 20 , the imaging of the imaging lens in this embodiment is more delicate, the dynamic imaging range is higher, the depth of field is larger, the color and contrast are also good, the high and low temperature performance is better, its application range is wider, and at the same time, due to the smaller distortion characteristics of the lens itself, the lens has a wider field of view.

[0084] The above is only one solution of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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 lens, comprising a first lens group (1), a diaphragm (2), and a second lens group (3) arranged in sequence from the object side to the image side along the optical axis, with a total of two lens groups, characterized in that, The first lens group (1) is a fixed group, and the second lens group (3) is a focusing group; The first lens group (1) has a positive or negative optical power. The first lens group (1) includes a first lens, a second lens, a third lens with negative optical power, a fourth lens with positive optical power, and a fifth lens with positive optical power, which are arranged in sequence along the optical axis from the object side to the image side, totaling five lenses; the first lens and the second lens have positive or negative optical power, and the optical powers of the first lens and the second lens are opposite; Or the first lens group (1) includes a first lens with positive optical power, a second lens with negative optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with negative optical power, and a sixth lens with positive optical power, which are arranged in sequence along the optical axis from the object side to the image side, totaling six lenses; The second lens group (3) has positive optical power. When imaging from infinity to a close distance, it moves along the optical axis direction for focusing. The second lens group (3) includes a positive lens, a negative lens, a positive lens, and a positive lens, which are arranged in sequence along the optical axis from the object side to the image side, totaling four lenses.

2. The imaging lens according to claim 1, wherein, In the first lens group (1), the lenses closest to the object side and the image side are both convex-concave types; When the first lens group (1) has a total of five lenses, among the two negative lenses of the first lens group (1), one is a double-concave type and the other is a convex-concave type; When the first lens group (1) has a total of six lenses, among the three negative lenses of the first lens group (1), two are double-concave types and the other is a convex-concave type.

3. The imaging lens according to claim 1, wherein Among the four lenses of the second lens group (3), three are double-convex lenses and the other is a double-concave lens; The second lens group (3) has a cemented lens group. The first two lenses in the second lens group (3) are cemented to form a doublet lens group, or the first three lenses in the second lens group (3) are cemented to form a triplet lens group.

4. The imaging lens according to any one of claims 1-3, characterized in that, The focal length F1 of the first lens group (1) and the focal length F of the imaging lens satisfy the following relationship: -20 < F1 / F < 20.

5. The imaging lens according to any one of claims 1-3, characterized in that, The focal length F2 of the second lens group (3) and the focal length F of the imaging lens satisfy the following relationship: 1 < F2 / F < 2.

6. The imaging lens according to any one of claims 1-3, characterized in that, The total length L of the imaging lens and the focal length F satisfy the following relationship: 2 < L / F < 8.

7. The imaging lens according to claim 3, wherein One of the lenses in the cemented lens group of the second lens group (3) uses a low-dispersion glass material, and its refractive index ND and Abbe number VD respectively satisfy the following relationships: 1.40 ≤ ND ≤ 1.53; And 64 ≤ VD ≤ 96.

Images