CN105137567A - Imaging lens, imaging module and iris recognition device - Google Patents

Abstract

The invention discloses an imaging lens, an imaging module and an iris recognition device. The imaging lens, the imaging module and the iris recognition device belong to the field of biological recognition. The imaging lens comprises the following components in a light incident direction: a first lens which is a biconvex lens with a positive focal power, wherein the front surface and the back surface of the first lens are convex surfaces; a second lens which is a convexoconcavelens with a positive focal power, wherein the front surface of the second lens is a convex surface and the back surface of the second lens is a recessed surface; a third lens which is a convexoconcave lens with a negative focal power, wherein the front surface of the third lens is a convex surface and the back surface of the third lens is a recessed surface; a fourth lens which is a convexoconcave lens with a positive focal power, wherein the front surface of the fourth lens is a convex surface and the back surface of the fourth lens is a recessed surface; and a fifth lens which is a biconvex lens with a positive focal power, wherein the front surface and the back surface of the fifth lens are convex surfaces. The fourth lens is connected with the fifth lens through an adhesive. The imaging lens has advantages of high imaging quality, wide acquisition range, convenient use, simple structure, convenient assembling and low fabrication cost.

Description

Imaging lens, iris imaging module and iris recognition device

technical field

The invention relates to the field of biological identification, in particular to an imaging lens, an iris imaging module and an iris identification device.

Background technique

Iris recognition is a biometric technology that authenticates user identity based on processing the iris texture information of the eye in an area smaller than 10 mm. The difficulty in realizing this technology lies in how to collect clear and high-quality iris images, that is, high-quality iris image collection optical systems. At present, the existing iris collection optical system can be divided into: zoom optical system and fixed focus optical system, among which the zoom optical system is large in size, complex in structure, high in cost and difficult to assemble; the fixed focus optical system is simple in structure, low in cost and convenient to install At present, the products on the market generally use fixed-focus optical systems, but most of the existing fixed-focus optical systems are monocular acquisition optical systems, which are generally equipped with image sensors with lower pixels (VGA is sufficient).

However, the acquisition of one eye requires a high degree of cooperation from the user, and the acquisition range (depth of field) of the equipment is very narrow, which is extremely inconvenient to use and is not conducive to grasping the distance and alignment.

Contents of the invention

The invention provides an imaging lens, an iris imaging module and an iris recognition device. The lens has good imaging quality, wide collection range, convenient use, simple structure, convenient assembly and low manufacturing cost.

In order to solve the problems of the technologies described above, the present invention provides technical solutions as follows:

An imaging lens, including from front to back along the incident direction of light:

The first lens, the first lens is a biconvex lens with positive refractive power, its front surface is convex, and its rear surface is convex;

The second lens, the second lens is a convex-concave lens with positive refractive power, its front surface is convex, and its rear surface is concave;

The third lens, the third lens is a convex-concave lens with negative refractive power, its front surface is convex, and its rear surface is concave;

The fourth lens, the fourth lens is a convex-concave lens with positive refractive power, its front surface is convex, and its rear surface is concave;

The fifth lens, the fifth lens is a biconvex lens with positive refractive power, its front surface is convex, and its rear surface is convex;

The fourth lens and the fifth lens are glued together.

An iris imaging module includes any of the above imaging lenses and an image sensor located behind the imaging lens, and the image sensor is a CCD or CMOS sensor.

An iris recognition device includes the above-mentioned iris imaging module and a hardware circuit connected with the iris imaging module.

The present invention has the following beneficial effects:

Compared with the prior art, the five lenses of the imaging lens of the present invention from front to back along the incident direction of light are biconvex lens, convex-concave lens, convex-concave lens, convex-concave lens and bi-convex lens, wherein the fourth lens and the fifth lens are cemented on the Together. The imaging lens has high imaging quality in the near-infrared band, and the distortion is small; the depth of field range is wide, and the object distance range is large, so that the acquisition range is wide; the invention is especially suitable for binocular iris acquisition, and has low requirements for user cooperation. Convenient; the five lenses are all spherical lenses without aspherical lenses, the structure is simple, the assembly is convenient, and the cost is low.

Description of drawings

Fig. 1 is the structural representation of imaging lens of the present invention;

FIG. 2 is a schematic structural view of Embodiment 1 of the imaging lens of the present invention;

3 is an optical performance curve diagram of the imaging lens shown in FIG. 2, wherein: 3A is a distortion curve diagram of Embodiment 1; 3B is a field curvature curve diagram of Embodiment 1; 3C is an MTF characteristic curve diagram 1 of Embodiment 1; 3D is the MTF characteristic curve figure two of embodiment one; 3E is the MTF characteristic curve figure three of embodiment one;

Fig. 4 is a schematic structural diagram of Embodiment 2 of the imaging lens of the present invention;

5 is an optical performance curve of the imaging lens shown in FIG. 4, wherein: 5A is the distortion curve of Embodiment 2; 5B is the field curvature curve of Embodiment 2; 5C is the MTF characteristic curve 1 of Embodiment 2; 5D is the second MTF characteristic curve of the second embodiment; 5E is the third MTF characteristic curve of the second embodiment.

Detailed ways

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the drawings and specific embodiments.

On the one hand, the present invention provides an imaging lens, as shown in FIG. 1 , which sequentially includes:

The first lens 1, the first lens 1 is a biconvex lens with positive refractive power, its front surface 11 is a convex surface, and its rear surface 12 is a convex surface;

The second lens 2, the second lens 2 is a convex-concave lens with positive refractive power, its front surface 21 is a convex surface, and its rear surface 22 is a concave surface;

The third lens 3, the third lens 3 is a convex-concave lens with negative power, the front surface 31 is convex, and the rear surface 32 is concave;

The fourth lens 4, the fourth lens 4 is a convex-concave lens with positive refractive power, its front surface 41 is a convex surface, and the rear surface 42 is a concave surface;

The fifth lens 5, the fifth lens 5 is a biconvex lens with positive refractive power, its front surface 51 is a convex surface, and its rear surface 52 is a convex surface;

The fourth lens 4 and the fifth lens 5 are cemented together. In FIG. 1 , 42 and 51 are the same surface, and the number is 42/51.

The front surface of each of the above lenses refers to the surface where the infrared light enters, and the rear surface refers to the surface where the infrared light exits, the same below.

Compared with the prior art, the five lenses of the imaging lens of the present invention from front to back along the incident direction of light are biconvex lens, convex-concave lens, convex-concave lens, convex-concave lens and bi-convex lens, wherein the fourth lens and the fifth lens are cemented on the Together. The imaging lens has high imaging quality in the near-infrared band, and the distortion is small; the depth of field range is wide, and the object distance range is large, so that the acquisition range is wide; the invention is especially suitable for binocular iris acquisition, and has low requirements for user cooperation. Convenient; the five lenses are all spherical lenses without aspherical lenses, the structure is simple, the assembly is convenient, and the cost is low.

As an improvement of the present invention, the focal length of each lens can satisfy: 1.8f≤f1≤2.3f, 0.45f≤f2≤1.1f, -0.55f≤f3≤-0.33f, 1.05f≤f4≤1.35f, 0.9 f≤f5≤1.67f; where, f is the total focal length of the imaging lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is the fifth lens focal length.

When the focal length of each lens satisfies the above relationship, it has higher imaging quality in the near-infrared band and almost no distortion.

Further, 17mm≤f1≤21mm, 4mm≤f2≤9.5mm, -5mm≤f3≤-3mm, 9.5mm≤f4≤12mm, 8mm≤f5≤15mm; 200mm≤h≤400mm, Δh≥110mm; among them, h is the object distance, Δh is the depth of field range of the object side, Δh=the farthest shooting distance of the object side-the shortest shooting distance of the object side. At this time, the imaging lens is suitable for binocular iris image acquisition within the range of 20-40cm, and has a larger depth of field range of the object side.

As another improvement of the present invention, the materials of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4 and the fifth lens 5 satisfy: 1.6≤nd≤1.8, 25≤vd≤55, where , nd is the refractive index of the lens material, vd is the dispersion coefficient of the lens material. Using the material with the above-mentioned refractive index and dispersion coefficient can not only obtain better imaging quality, but also save material cost.

Preferably, as shown in Fig. 1, Fig. 2 and Fig. 4, an aperture 6 (6', 6 ") for controlling the near-infrared light transmission rate is arranged between the third lens 3 and the fourth lens 4. The aperture can Adjust the strength of the passing near-infrared beam, and you can choose different apertures under different lighting environments.

As another improvement of the present invention, a certain surface of a certain lens can be coated with a filter film that can reflect visible light and transmit near-infrared light (such as a narrow-band filter film in the near-infrared band), preferably on the surface of the first lens. The front surface is coated with a filter film; the filter film can avoid the interference of visible light on the imaging lens, and at the same time, the reflected visible light can enable users to see their own eye images from the imaging lens, which is convenient for users to adjust their position and play a role in positioning effect. In addition, the rear surface of the first lens and the front and rear surfaces of the second lens, the third lens, the fourth lens and the fifth lens are all coated with a near-infrared band anti-reflection film that can enhance the transmittance of near-infrared light. The anti-reflection coating can enhance the transmittance of near-infrared light, and can obtain a clearer iris image with a smaller transmission power.

Or, as shown in Figure 4, the imaging lens also includes a plane filter 7 "that can reflect visible light and pass through near-infrared light. The light sheet can avoid the interference of visible light on the imaging lens; the front and rear surfaces of the first lens, the second lens, the third lens, the fourth lens and the fifth lens are all coated with near-infrared light that can enhance the transmittance of near-infrared light. Band anti-reflection coating. The anti-reflection coating can enhance the transmittance of near-infrared light, and can obtain a clearer iris image with a smaller transmission power.

In the present invention, the above-mentioned near-infrared light has a wavelength band of 700-900 nm. The near-infrared light in this band can collect high-quality iris images.

For further cost saving, the material of the first lens, the second lens, the third lens, the fourth lens and the fifth lens can be glass.

The present invention is further elaborated below with two specific embodiments:

Embodiment one:

This embodiment is an imaging lens for binocular iris recognition. As shown in Figure 2, it is composed of five lens groups and a diaphragm 6'. An image sensor 8' is arranged behind the imaging lens, and is sequentially arranged along the light incident direction. It is: the first lens 1' with positive refractive power, which is a biconvex lens, whose front surface 11' is convex, and the rear surface 12' is convex; the second lens 2' with positive refractive power, which is a convex-concave lens, whose The front surface 21' is convex, the back surface 22' is concave; the third lens 3' with negative power is a convex-concave lens, the front surface 31' is convex, and the back surface 32' is concave; the fourth lens 4 'and the fifth lens 5' are cemented lenses, the fourth lens 4' is a convex-concave lens with positive power, its front surface 41' is convex, and the rear surface 42' is concave; the fifth lens 5' is a positive power lens The double-convex lens has a convex front surface 51' and a convex rear surface 52'; the diaphragm 6' is located between the third lens 3' and the fourth lens 4', and the five lenses are made of glass; the imaging surface is an image The sensor surface, which is a CCD or CMOS sensor.

The imaging wavelength of the imaging lens in this embodiment is 700-900nm in the near-infrared band. For the role of infrared light, it is preferable to coat the front surface of the first lens with a narrow-band filter film in the near-infrared band. The filter film can avoid the interference of visible light on the imaging lens. The eye image is convenient for users to adjust their position and play the role of positioning. And in order to increase the transmittance of light in the near-infrared band, all other sides are coated with near-infrared anti-reflection coatings.

For the imaging lens of this embodiment, when the aperture FNO.=5 (FNO. is the ratio of the focal length to the effective aperture, which is used to describe the size of the aperture), and the optimal focus object distance is 300 mm, the specific structural parameters are shown in Table 1, including the lens Surface type, radius of curvature, lens thickness, refractive index, dispersion coefficient, etc. The lens focal length parameters of the optical system of this embodiment are: the focal length of the first lens f1=19.5mm, the focal length of the second lens f2=7.3mm, the focal length of the third lens f3=-4.4mm, the focal length of the fourth lens f4=11.5mm, the fifth lens Focal length f5=12.1mm, Δh=110mm, can collect clear binocular iris images within the range of 250-360mm, and is used for binocular iris image collection in a wider range.

Table 1: Specific structural parameters of Embodiment 1 of the imaging lens of the present invention

Fig. 3 is the optical performance curve diagram of the imaging lens of the present embodiment, 3A shows the distortion curve diagram (%) of the present embodiment, and in the whole field of view, the distortion aberration is all in the range of 0.5%; 3B shows the distortion curve diagram of the present embodiment Field curvature curve (mm), within the full field of view, the field curvature aberration of each light in the meridian plane and sagittal plane is less than 0.05mm; 3C shows the MTF (ModulationTransferFunction, modulation transfer function) characteristic curve of the embodiment of the present invention, It can be seen from the curve that when the object distance is 300mm, the MTF of each field of view is close to the diffraction limit, and the MTF value at the spatial frequency of 100lp/mm is above 0.4; 3D shows the MTF curve of the embodiment of the present invention when the object distance is 250mm, from the figure It can be seen from the figure that the MTF value at the spatial frequency of 100lp/mm is around 0.3; 3E shows the MTF curve of the embodiment of the present invention when the object distance is 360mm, and it can be seen from the figure that the MTF value at the spatial frequency of 100lp/mm is at 0.3 or so; it can be seen from the above optical characteristic curves that the imaging lens of this embodiment has small distortion, high imaging quality, and a wide range of depth of field.

Embodiment two:

This embodiment is an imaging lens for binocular iris recognition, as shown in Figure 4, consisting of five lens groups, a diaphragm 6" and a flat filter 7", and an image sensor 8 is arranged at the rear of the imaging lens ", along the incident direction of the light: the first lens 1" with positive refractive power, which is a biconvex lens, the front surface 11" is convex, and the rear surface 12" is convex; the second lens 2" with positive refractive power , which is a convex-concave lens, its front surface 21 "is a convex surface, and its rear surface 22" is a concave surface; the third lens 3 "with negative power is a convex-concave lens, its front surface 31 "is a convex surface, and its rear surface 32 " It is a concave surface; the fourth lens 4 "and the fifth lens 5" are cemented lenses, and the fourth lens 4 "is a convex-concave lens with positive refractive power, its front surface 41 "is a convex surface, and the rear surface 42 "is a concave surface; the fifth lens 5" is a biconvex lens with positive refractive power, its front surface 51" is convex, and its rear surface 52" is convex; the diaphragm 6" is located between the third lens 3" and the fourth lens 4", and the five lenses are all Glass material; the imaging surface is an image sensor surface, which is a CCD or CMOS sensor.

The imaging lens of this embodiment has an imaging wavelength of 700-900nm in the near-infrared band, and uses a plane filter 7 "to filter out stray light interference. The front surface of the plane filter 7" is 71", and the rear surface is 72". The material of the sheet 7" meets 1.4≤nd≤1.6, 60≤vd≤70, the flat filter 7" can be located at the front end or the rear end of the entire imaging lens, preferably the rear end is located at the fifth lens 5" and the image sensor 8" Among them, it is a near-infrared band narrow-band filter with a transmission wavelength of 700-900nm. The front surface and the rear surface of each lens are coated with an anti-reflection film in the near infrared band to enhance the transmittance of light in the near infrared band.

When the imaging mirror of the present embodiment has an aperture FNO.=5.1 (FNO. is the ratio of the focal length to the effective aperture, and is used to describe the size of the aperture), and the optimum focus-object distance is 300 mm, the specific structural parameters are shown in Table 2, including the lens Surface type, radius of curvature, lens thickness, refractive index, dispersion coefficient, etc. The lens focal length parameters of the optical system of this embodiment are: the focal length of the first lens f1=18.9mm, the focal length of the second lens f2=6.85mm, the focal length of the third lens f3=-4.8mm, the focal length of the fourth lens f4=10.9mm and the fifth lens Focal length f5=13.2mm, Δh=110mm, can collect clear binocular iris images in the range of 250-360mm, and is used for binocular iris image collection in a wider range.

Table 2: Specific structural parameters of Embodiment 2 of the imaging lens of the present invention

Fig. 5 is the optical performance curve diagram of the imaging lens of this embodiment, 3A shows the distortion curve diagram (%) of this embodiment, and in the whole field of view, the distortion aberration is all in the range of 0.5%; 3B shows the distortion curve diagram of this embodiment Field curvature curve (mm), within the full field of view, the field curvature aberration of each light in the meridian plane and sagittal plane is less than 0.05mm; 3C shows the MTF characteristic curve of the embodiment of the present invention, and it can be seen from the curve that the object distance At 300mm, the MTF of each field of view reaches the diffraction limit, and the MTF value at the spatial frequency of 100lp/mm is above 0.4; 3D shows the MTF curve of the embodiment of the present invention when the object distance is 250mm, and it can be seen from the figure that at this time in space The MTF value at the frequency of 100lp/mm is about 0.3; 3E shows the MTF curve of the embodiment of the present invention when the object distance is 360mm, and it can be seen from the figure that the MTF value at the spatial frequency of 100lp/mm is about 0.3; from the above optical characteristics It can be seen from the graph that the imaging lens of this embodiment has small distortion, high imaging quality, and a wide range of depth of field.

On the other hand, the present invention provides an iris imaging module, as shown in Figure 2 and Figure 4, comprising any of the above-mentioned imaging lenses and an image sensor 8' (8") positioned behind the imaging lens, the image sensor 8 '(8") is a CCD or CMOS sensor. The iris imaging module of the present invention has high imaging quality in the near-infrared band, small distortion, simple structure, convenient assembly, and low manufacturing cost; it is especially suitable for binocular iris collection and requires low user cooperation.

In yet another aspect, the present invention provides an iris recognition device, comprising the above-mentioned iris imaging module and a hardware circuit connected to the iris imaging module. The iris recognition device of the present invention has high imaging quality in the near-infrared band, small distortion, simple structure, convenient assembly, and low manufacturing cost; it is especially suitable for binocular iris collection and requires low user cooperation.

The above description is a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (10)

1. an imaging lens, is characterized in that, comprises successively from front to back along light direction:

First lens, described first lens are the biconvex lens with positive light coke, and its front surface is convex surface, and rear surface is convex surface;

Second lens, described second lens are the meniscus with positive light coke, and its front surface is convex surface, and rear surface is concave surface;

3rd lens, described 3rd lens are the meniscus with negative power, and its front surface is convex surface, and rear surface is concave surface;

4th lens, described 4th lens are the meniscus with positive light coke, and its front surface is convex surface, and rear surface is concave surface;

5th lens, described 5th lens are the biconvex lens with positive light coke, and its front surface is convex surface, and rear surface is convex surface;

Described 4th lens and the 5th lens glue are combined.

2. imaging lens according to claim 1, is characterized in that, 1.8f≤f1≤2.3f, 0.45f≤f2≤1.1f ,-0.55f≤f3≤-0.33f, 1.05f≤f4≤1.35f, 0.9f≤f5≤1.67f; Wherein, f is total focal length of imaging lens, and f1 is first focal length of lens, and f2 is second focal length of lens, and f3 is the 3rd focal length of lens, and f4 is the 4th focal length of lens, and f5 is the 5th focal length of lens.

3. imaging lens according to claim 1, is characterized in that, 17mm≤f1≤21mm, 4mm≤f2≤9.5mm ,-5mm≤f3≤-3mm, 9.5mm≤f4≤12mm, 8mm≤f5≤15mm; 200mm≤h≤400mm, Δ h >=110mm; Wherein, h is object distance, and Δ h is object space field depth, Δ h=object space shooting distance farthest-object space minimum photographic distance.

4. imaging lens according to claim 1, is characterized in that, the material of described first lens, the second lens, the 3rd lens, the 4th lens and the 5th lens meets: 1.6≤nd≤1.8,25≤vd≤55, wherein, nd is the refractive index of lens material, and vd is the abbe number of lens material.

5. the imaging lens according to the arbitrary claim of claim 1-4, is characterized in that, is provided with the diaphragm for controlling near infrared light percent of pass between described 3rd lens and the 4th lens.

6. imaging lens according to claim 5, is characterized in that, the front surface of described first lens is coated with can reflect visible light through the filter coating of near infrared light; Front surface and the rear surface of the rear surface of described first lens and described second lens, the 3rd lens, the 4th lens and the 5th lens are all coated with the near-infrared band anti-reflection film that can strengthen near infrared light transmitance.

7. imaging lens according to claim 5, is characterized in that, or described imaging lens also comprises can reflect visible light through the optically flat filter of near infrared light; Front surface and the rear surface of described first lens, the second lens, the 3rd lens, the 4th lens and the 5th lens are all coated with the near-infrared band anti-reflection film that can strengthen near infrared light transmitance.

8. imaging lens according to claim 5, is characterized in that, the material of described first lens, the second lens, the 3rd lens, the 4th lens and the 5th lens is glass.

9. an iris imaging module, is characterized in that, comprise the imaging lens described in the arbitrary claim of claim 1-8 and be positioned at the imageing sensor at described imaging lens rear, described imageing sensor is CCD or cmos sensor.

10. an iris identification device, is characterized in that, the hardware circuit comprising iris imaging module according to claim 9 and be connected with described iris imaging module.