JP6308208B2 - Imaging lens and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging lens, and more particularly to an imaging lens using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor, which can obtain high resolution, and an imaging apparatus including the imaging lens.

In recent years, CCD (Charged Coupled Device) type image sensors or CMOS (Complementary)
With the widespread use of mobile terminals equipped with solid-state imaging devices such as Metal Oxide Semiconductor) type image sensors, an imaging device with a high pixel count was used so that higher-quality images could be obtained. Those equipped with an imaging device have been supplied to the market. Conventional image pickup devices having a high number of pixels have been accompanied by an increase in size, but in recent years, pixels have become increasingly thinner and image pickup devices have become smaller. Further, it has become necessary to have five or more lenses in the imaging lens so that a high-quality subject image can be formed on such a high-pixel imaging device.

  On the other hand, particularly in recent years, a thin portable terminal called a smartphone has been developed, and a reduction in the height of an imaging lens used in an imaging apparatus mounted on such a thin portable terminal is required. If an attempt is made to reduce the height of the imaging lens, the power of the object side surface of the first lens closest to the object becomes strong, and the image side surface of the first lens takes a shape close to a flat or concave meniscus. It becomes. Due to this influence, the light incident on the first lens with a large angle tends to generate so-called multiple reflection ghost light in which multiple total reflection occurs between the object side surface and the image side surface of the first lens and reaches the image surface. It has come to be seen.

  In particular, a light beam having an angle larger than the angle of view that contributes to image formation is totally reflected three or more times between both surfaces of the first lens, and therefore reaches the image surface without extremely reducing the intensity of multiple reflection ghost light. Probability is high. When such multiple reflected ghost light is incident on the imaging surface of the image sensor, it causes deterioration in image quality. In particular, the ghost light caused by the luminous flux from a strong light source having an angle larger than the angle of view that contributes to image formation does not appear in the image sensor because the light source that is the main cause of the ghost light does not appear in the image sensor. Easy to stand out.

  On the other hand, Patent Document 1 discloses a condition in which ghost light is not generated. However, in an imaging lens having a large number of lenses, there is a patent for multi-reflection ghost light that is remarkably generated by promoting a reduction in height. It is difficult to solve with the technique of Document 1, and Patent Document 1 does not disclose any countermeasure against multiple reflection ghost light.

JP 2009-294528

  The present invention has been made in view of such problems, and an imaging lens capable of forming a high-quality image by suppressing ghost light while having a relatively large number of lenses and a low profile, and An object is to provide an imaging apparatus using the same.

The imaging lens according to claim 1,
It is composed of a positive first lens, a second lens, a third lens, a fourth lens, and a fifth lens, which are arranged in order from the object side and have a convex surface facing the object side, and the aperture stop is closer to the object side than the third lens. There, at least the first lens antireflection film and the object side optical surface and the image side optical surface of formed, in Zore lens Ta used for forming an object image on the imaging surface of the solid-state imaging device,
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
On the optical axis of the first lens, the thickness of the antireflection film of the object-side optical surface is rather thick than the thickness of the antireflection film of the image side surface,
The thickness of the antireflection film on the object-side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 500 to 750 nm. % Is set to be less than
The film thickness of the antireflection film on the image side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 420 to 650 nm. The thickness is set to be equal to or less than% .

  The inventor studied the characteristics of multiple reflection ghost light while comparing a conventional imaging lens having a relatively long length in the optical axis direction with an imaging lens designed to have a lower height. FIG. 1 is a sectional view of a conventional imaging lens having a relatively long total length in the optical axis direction of 5 mm (L / 2Y = 0.87). FIG. 2 is a cross-sectional view of an imaging lens according to an example of the present invention. The imaging lenses shown in any of the figures are also five balls, L1 to L5 are lenses, S is an aperture stop, CG is a parallel plate such as an IR cut filter, and I is an imaging device. Here, in the imaging lens shown in FIG. 1, even if a light beam having an angle larger than the field angle contributing to image formation is incident and multiple reflection is performed between both surfaces of the first lens L1 closest to the object side, the first lens Since the image side optical surface S2 of L1 is closer to the lens periphery (as it is away from the optical axis), the sag amount becomes a negative value (closer to the object side optical surface S1 of L1). The incident angle of the light beam becomes smaller, and total reflection occurs only twice. Therefore, it was found that the multiple reflection ghost light reaching the image plane is not conspicuous.

  On the other hand, the imaging lens shown in FIG. 2 has a total length in the optical axis that is as short as 3.42 mm (L / 2Y = 0.75) compared to the imaging lens of FIG. The object-side optical surface S1 protrudes in the optical axis direction, and the image-side optical surface S2 has a shape (or concave shape) close to a plane. With such a shape, the image-side optical surface S2 of the first lens L1 does not change greatly (or does not take a large negative value) even at a location away from the optical axis, so that it contributes to image formation. When a light beam having an angle larger than the angle is incident and multiple reflection is performed between both surfaces of the first lens L1 closest to the object side, the incident angle of the light beam after two times of total reflection on the S2 surface is increased to three degrees. Total reflection occurs (especially in the lower marginal ray group). Since the light beam totally reflected three times or more reaches the image sensor, the intensity of the ghost light is very strong and conspicuous.

  Further, when an antireflection film is provided on the optical surface S1, the normal NL of the surface and the optical axis of the object side optical surface S1 of the first lens L1 are closer to the lens periphery (as the distance from the optical axis). The angle α formed by becomes larger. For this reason, the film thickness around the lens tends to decrease compared to that on the axis, and the reflectance on the long wavelength side tends to increase. Therefore, the red ghost light easily reaches the image plane by combining these phenomena. However, when a higher quality image is desired, the red ghost light is more preferable than the blue ghost light. Tend to be hated.

  From the above knowledge, when the imaging lens having a large number of lenses is lowered, the present inventor limits the shape of the first lens L1, and thus it is difficult to significantly suppress the multiple reflection ghost light. The goal was to change the quality instead of reducing the amount of ghost light. More specifically, in order to reduce the most desired red ghost light to be avoided, on the optical axis of the first lens, the film thickness of the antireflection film on the object side optical surface is set to be the same as that of the antireflection film on the image side surface. It was thicker than the film thickness. As a result, only the object-side optical surface of the first lens can shift the minimum reflectance value of the antireflection film to the longer wavelength side, thereby changing the color of the ghost light from red to blue and further reflecting. When the angle between the normal of the optical surface on which the anti-reflection film is deposited and the optical axis increases, the reflectance on the long wavelength side increases, but the minimum value of the anti-reflection film has shifted to the long wavelength side. The reflectance of the light beam reflected at the portion where the angle between the normal line of the optical surface and the optical axis is large can be kept low in the entire visible light region, and the intensity becomes small and can be made inconspicuous. Here, the film thickness refers to the total film thickness.

  The antireflection film may be provided only in the effective diameter range, or may be provided in an area larger than the effective diameter or on the entire surface of the lens. On the other hand, it is not necessary to provide an antireflection film at a joint portion that is joined in contact with another lens.

  The low refractive index layer of the antireflection film preferably refers to a layer having a refractive index of 1.30 or more and less than 1.80 at a wavelength of 587.56 nm. The high refractive index layer of the antireflection film refers to a layer having a refractive index of 1.80 or more and 2.50 or less at a wavelength of 587.56 nm.

  Preferable examples of the low refractive index layer include aluminum fluoride, magnesium fluoride, silicon oxide, aluminum oxide, yttrium oxide, cerium fluoride, and the like, and mixtures thereof. Preferable examples of the high refractive index layer include zirconium oxide, tantalum oxide, titanium oxide, and haonium oxide.

  Examples of the method for providing the antireflection film include a vacuum deposition method, a sputtering method, a CVD method, an atmospheric pressure plasma method, a coating method, and a mist method. In the case where the lens is a glass lens, it is preferable to anneal after forming the antireflection film.

According to a second aspect of the present invention, there is provided the imaging lens according to the first aspect, wherein the distance on the optical axis from the most object-side optical surface to the image-side focal point of the entire imaging lens system is L (mm), and the solid state When the diagonal length of the imaging surface of the imaging device (diagonal length of the rectangular effective pixel region of the solid-state imaging device) is 2Y (mm), the following equation is satisfied.
L / 2Y <0.8 (1)

  When the imaging lens is a five-lens ball, when the imaging lens is low in height such that L / 2Y satisfies the expression (1), the image-side optical surface S2 of the first lens L1 closest to the object side has a shape close to a plane. Since it becomes (or concave), the light beam incident from the outside of the angle of view easily undergoes multiple total reflection between both surfaces of the first lens, so that the configuration of the present invention is particularly effective.

The imaging lens according to claim 3 is a positive first lens, second lens, third lens, fourth lens, fifth lens, and sixth lens that are arranged in order from the object side and have a convex surface facing the object side. The aperture stop is located on the object side of the third lens, an antireflection film is formed on at least the object side optical surface and the image side optical surface of the first lens, and an object image is formed on the imaging surface of the solid-state image sensor. in Zore lens Ta used for imaging,
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
On the optical axis of the first lens, the thickness of the antireflection film of the object-side optical surface is rather thick than the thickness of the antireflection film of the image side surface,
The thickness of the antireflection film on the object-side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 500 to 750 nm. % Is set to be less than
The film thickness of the antireflection film on the image side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 420 to 650 nm. The thickness is set to be equal to or less than% .

  According to the present invention, in order to reduce the most desired red ghost light to be avoided, on the optical axis of the first lens, the film thickness of the antireflection film on the object side optical surface is the same as that of the antireflection film on the image side surface. It was thicker than the film thickness. As a result, the reflectance minimum value of the antireflection film can be shifted to the long wavelength side only on the object side optical surface of the first lens, thereby changing the color of the ghost light from red to blue and further preventing reflection. When the angle between the normal of the optical surface on which the film is deposited and the optical axis is increased, the reflectance on the long wavelength side increases, but the minimum value of the reflectance of the antireflection film is shifted to the long wavelength side. The reflectivity of the light beam reflected at the point where the angle between the surface normal and the optical axis is large can be kept low in the entire visible light range, and the intensity becomes small and can be made inconspicuous.

According to a fourth aspect of the present invention, in the invention of the third aspect, the distance on the optical axis from the most object-side optical surface of the entire imaging lens system to the image-side focal point is L (mm), and the solid state When the diagonal length of the imaging surface of the imaging device (diagonal length of the rectangular effective pixel region of the solid-state imaging device) is 2Y (mm), the following equation is satisfied.
L / 2Y <0.9 (2)

  When the imaging lens is a six-lens lens, when the imaging lens is low in height so that L / 2Y satisfies the expression (2), the image-side optical surface S2 of the first lens L1 closest to the object side has a shape close to a plane. Since it becomes (or concave), the light beam incident from the outside of the angle of view easily undergoes multiple total reflection between both surfaces of the first lens, so that the configuration of the present invention is particularly effective.

Oite the imaging lens according to claim 1 and 3, the film thickness of the antireflection film on the object side optical surface of the first lens on the optical axis, the angle between the optical axis θ is incident at 0 ° The thickness is set so that the reflectance of light is 1% or less within the wavelength band of 500 to 750 nm,
The film thickness of the antireflection film on the image side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 420 to 650 nm. % as to become less, it is configured in thickness.

By setting it as the anti-reflective film which has the said characteristic, the color of ghost light can be changed from red type | system | group to blue type | system | group, and it can make it inconspicuous .

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the object-side optical surface and the image-side optical surface of the first lens have the same film configuration. It is characterized by that.

  By making the antireflection films on the object side optical surface and the image side optical surface have the same film configuration, there is an advantage that the same vapor deposition apparatus can be used at the time of film vapor deposition. The film thickness can be easily adjusted by controlling the heat source of the vapor deposition material and changing the vapor deposition time.

The imaging lens according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the antireflection film has a four-layer structure.

  By making the antireflection film have a four-layer structure, the reflectance can be satisfactorily suppressed in a wide band. Furthermore, by making it less than five layers, cost can be suppressed and generation | occurrence | production of a crack etc. can be suppressed.

The imaging lens according to claim 7 , in the invention according to claim 6 , the antireflection film is formed by laminating the same film material in order of the high refractive index layer and the low refractive index layer from the first lens side, The outermost layer of the antireflection film is a low refractive index layer.

  By repeatedly laminating the same film material in this way, the wavelength range for suppressing reflection can be expanded. Further, by repeating the same film material, it is possible to avoid errors such as erroneous setting of different film materials in the vapor deposition apparatus, and to further improve durability.

According to an eighth aspect of the present invention, in the invention of any one of the first to seventh aspects, the aperture stop is located closer to the object side than the position of the effective diameter of the object-side optical surface of the first lens. Features.

  The present invention is more effective in a compact and low-profile imaging lens with a front diaphragm. In particular, when the aperture stop is positioned on the image side from the vertex on the object side optical surface of the first lens, a light beam outside the angle of view that does not contribute to image formation is likely to enter the lens. It becomes effective.

The imaging lens according to claim 9 is the invention according to any one of claims 1 to 8 , wherein the antireflection film is composed of a Ti-based high refractive index layer and a Si-based low refractive index layer. The low refractive index layer is a mixed film in which two kinds of different inorganic materials are mixed, and the material constituting the mixed film is SiO ₂ and Al ₂ O ₃ , and is used for the Si element in the mixed film. The ratio of the number of elements of Al is 1 to 5%.

Since the low refractive index layer is composed of a mixture of SiO ₂ and Al ₂ O ₃ , stress is relaxed without deteriorating optical properties, and peeling and cracks are prevented from occurring.

An imaging lens according to a tenth aspect is the imaging lens according to any one of the first to ninth aspects, wherein the image-side optical surface of the most image-side lens is an aspheric surface and has an inflection point within an effective diameter. It is characterized by.

  Thereby, the imaging performance in the entire effective field angle can be improved. The “inflection point” means that when the cross section of the image side optical surface of the lens is taken, the inclination of the tangent line drawn on the image side optical surface changes from positive to negative or from negative to positive as the distance from the optical axis increases. The point to do.

An imaging lens according to an eleventh aspect is the invention according to any one of the first to tenth aspects, wherein an antireflection film is formed on the object-side optical surface and the image-side optical surface of all the lenses other than the first lens. It is characterized by being.

  This can further reduce ghosts and flares.

An imaging lens according to a twelfth aspect is characterized in that, in the invention according to any one of the first to eleventh aspects, the second lens has a negative power.

  Thereby, chromatic aberration can be corrected satisfactorily.

According to a thirteenth aspect of the present invention, in the imaging lens according to any one of the first to twelfth aspects, the maximum value Δsagmax of the sag change amount Δsag within the effective diameter of the object-side optical surface of the first lens is It satisfies the following formula.
Δsagmax ≧ 0.4 (3)

  The sag and the sag change amount Δsag will be described. FIG. 3 schematically shows from the center h0 of the surface S1 to the outer peripheral edge as an example of the optical surface of the lens. As shown in FIG. 3, the sag amount (sag) is the optical axis X of the lens center h0 at an arbitrary radius h when the optical axis X of the lens and the lens center h0 of the surface S1 are aligned. The distance (mm) from the perpendicular L to the surface S1, and the direction from the surface S1 toward the image side is positive. The sag change amount Δsag is the sag inclination amount at an arbitrary radius h in the surface S1, that is, the inclination of the tangent line of the surface S1 at the radius h from the straight line L, and the surface S1 at the point of the radius h. Is the same as the angle formed by the normal line and the optical axis X, and its unit is [rad]. However, the case where the sag amount increases from the inner periphery toward the outer periphery is positive, and the case where the sag amount decreases is negative.

If the object-side optical surface of the first lens has a surface shape that satisfies Δsagmax satisfying the expression (3), when the antireflection coating is deposited on the object-side optical surface, Where the angle formed is large (Δsag is large), the film material does not ride on the object-side optical surface by the specified thickness, leading to a decrease in the optical film thickness compared to the center of the lens. In particular, the effect of the present invention is effective. Note that the present invention is further required when the following expression is satisfied.
Δsagmax ≧ 0.6 (3 ′)

An imaging lens according to a fourteenth aspect is the invention according to any one of the first to thirteenth aspects, wherein the sag change amount Δsag on the image side optical surface of the first lens is the image side optical surface of the first lens. The following formula is satisfied in the whole area within 80% of the effective diameter.
−0.05 ≦ Δsag (4)

  On the image side optical surface of the first lens, if Δsag satisfies the formula (4), the surface shape is almost perpendicular to the optical axis within 80% of the effective optical surface diameter. The effect of the present invention is effective because the light beam incident from outside the corner is easily totally reflected on the surface. This is particularly effective because 0 ≦ Δsag is a concave surface in the entire area within 80% of the effective optical surface diameter of the image-side optical surface of the first lens. Since the light beam totally reflected in the peripheral area of the optical surface that exceeds 80% of the effective diameter travels outside the effective diameter of the optical surface, Δsag in that area often does not cause a problem.

The imaging lens according to claim 15 is characterized in that, in the invention according to any one of claims 1 to 14 , the image side optical surface of the first lens is a paraxial concave surface on the image side. To do.

  Since the image-side optical surface of the first lens is a surface having a concave shape on the image side, a light beam incident from outside the angle of view is easily totally reflected by the image-side optical surface. Is effective.

An imaging lens according to a sixteenth aspect is the invention according to any one of the first to fifteenth aspects, wherein sag (mm) on the image side optical surface of the first lens is the same as that of the image side optical surface of the first lens. The following expression is satisfied in the whole area within 80% of the effective diameter.
−0.01 ≦ sag (5)

If the sag on the image-side optical surface of the first lens satisfies the formula (5), the surface shape that is substantially flat with respect to the optical axis within the 80% diameter of the optical surface effective diameter or The effect of the present invention is effective because the light beam entering from the outside of the angle of view is easily totally reflected on the surface because of the concave shape. Note that the present invention is further required when the following expression is satisfied.
−0.004 ≦ sag (5 ′)
However, sag is positive on the object side in the optical axis direction. Since the light beam totally reflected in the peripheral area of the optical surface that exceeds 80% of the effective diameter travels outside the effective diameter of the optical surface, the sag in that area often does not cause a problem.

An imaging device according to a seventeenth aspect includes the imaging lens according to any one of the first to sixteenth aspects and a solid-state imaging device.

  According to the present invention, it is possible to provide an imaging lens capable of forming a high-quality image by suppressing ghost light while having a relatively large number of lenses and a low profile, and an imaging apparatus using the imaging lens. .

It is sectional drawing of the conventional imaging lens. It is sectional drawing of the imaging lens concerning an example of this invention. It is a figure which shows typically from the center h0 of the surface S1 to an outer peripheral end as an example of the optical surface of the lens L1. It is the figure which showed typically the cross section along the optical axis of the imaging optical system of an imaging device. It is the front view (a) of the mobile phone to which the imaging unit is applied, and the rear view (b) of the mobile phone to which the imaging unit is applied. It is a control block diagram of the smart phone of FIG. 3 is a cross-sectional view in the optical axis direction of the imaging lens of Example 1. FIG. FIG. 6 is a cross-sectional view in the optical axis direction of the imaging lens of Example 2. It is a graph which compares and shows the reflection characteristic of the antireflection film of the object side optical surface of a 1st lens, and the antireflection film of an image side optical surface. In Examples 1 and 2, the vertical axis represents Δsag of the object-side optical surface of the first lens L1, and the horizontal axis represents the height from the optical axis (however, the effective diameter is 1). It is. In Examples 1 and 2, the vertical axis represents the sag of the image-side optical surface of the first lens L1, and the horizontal axis represents the height from the optical axis (however, the effective diameter is 1). It is. In Examples 1 and 2, the vertical axis represents Δsag of the image-side optical surface of the first lens L1, and the horizontal axis represents the height from the optical axis (however, the effective diameter is 1). It is. An example of the relationship between reflectance and wavelength when Δsag is changed when an antireflection film is deposited on the optical surface (the angle formed by the normal of the optical surface on which the antireflection film is deposited and the optical axis) is shown. FIG. In the comparative example and Example 1, it is the figure which graphed only the X value of the CIE XYZ coordinate system on the imaging surface which received the multiple reflection ghost light, (a) shows the case of Example 1, (b) The case of a comparative example is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a cross-sectional view along the optical axis of the imaging apparatus 10 according to the present embodiment. The following configuration is a schematic diagram, and some shapes, dimensions, and the like are different from actual ones.

  As shown in FIG. 4, the imaging apparatus 10 includes a CMOS imaging device 11 as a solid-state imaging device including a photoelectric conversion unit 11 a and an imaging lens 12 that forms a subject image on the photoelectric conversion unit 11 a of the imaging device 11. A lens frame 13 that holds the imaging lens 12, an IR cut filter 14 that has a parallel plate shape, and a substrate 15 that supports the imaging element 11.

  As shown in FIG. 4, the image pickup device 11 is an image pickup device in which pixels (photoelectric conversion devices) are two-dimensionally arranged at the center of the light receiving side (upper surface in FIG. 4) on a parallel plate chip. A photoelectric conversion unit 11a as a surface is formed, and a signal processing circuit (not shown) is formed around the photoelectric conversion unit 11a. Such a signal processing circuit includes a drive circuit unit that sequentially drives each pixel to obtain a signal charge, an A / D conversion unit that converts each signal charge into a digital signal, and a signal that forms an image signal output using the digital signal. It consists of a processing unit and the like.

  In addition, a plurality of pads formed in the vicinity of the outer edge on the light receiving surface side of the chip of the image sensor 11 are connected to the substrate 15 by wires (not shown). The image sensor 11 converts the signal charge from the photoelectric conversion unit 11a into an image signal such as a digital YUV signal, and transmits the image signal to an external circuit (not shown) (for example, a control circuit included in a host device on which the image pickup device is mounted). It is like that. In addition, it is possible to receive power and a clock signal for driving the image sensor 11 from an external circuit. Here, Y is a luminance signal, U (= R−Y) is a color difference signal between red and the luminance signal, and V (= BY) is a color difference signal between blue and the luminance signal. Note that the image sensor is not limited to the above CMOS image sensor, and other devices such as a CCD may be used.

  In FIG. 4, an imaging lens 12 having a five-lens configuration is provided inside a lens frame 13. The imaging lens 12 includes, in order from the object side, a positive first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5 having a convex surface directed toward the object side. It is on the object side from the three lenses L3. It is preferable that the optical surfaces of all the lenses are composed of a plurality of layers in which a high refractive index layer and a low refractive index layer are alternately laminated, but at least on the optical axis of the first lens L1, the object side The film thickness of the antireflection film on the optical surface is larger than the film thickness of the antireflection film on the image side surface. Since the method of forming the antireflection film is well known, it will not be described below.

  An annular spacer SP is disposed between the flange portions of the lenses, and the distance between the lenses is maintained with high accuracy. In addition, an IR cut filter 14 is disposed on the flange portion of the fifth lens L5 on the imaging element 11 side via an annular spacer SP. Furthermore, the spacer SP that supports the IR cut filter 14 and the lower end of the lens frame 13 that holds the imaging lens 12 are in contact with the substrate 15.

  The operation of the imaging device 10 described above will be described. 5A and 5B show a state in which the imaging device 10 is mounted on a smartphone 100 as a mobile terminal. FIG. 6 is a control block diagram of the smartphone 100.

  In the imaging device 10, for example, the object side end surface of the lens frame 13 is provided on the back surface of the smartphone 100 (see FIG. 5B), and is disposed at a position corresponding to the lower side of the liquid crystal display unit.

  The imaging device 10 is connected to the control unit 101 of the smartphone 100 via an external connection terminal (an arrow in FIG. 6), and outputs an image signal such as a luminance signal or a color difference signal to the control unit 101 side.

  On the other hand, as shown in FIG. 6, the smartphone 100 controls each unit in an integrated manner, and a control unit (CPU) 101 that executes a program corresponding to each process, a switch such as a power source, a number, and the like using a touch pad. An input unit 60 for inputting instructions, and a display unit 65 for displaying captured images and the like in addition to predetermined data on a liquid crystal panel (however, the touch panel 70 serves as both the liquid crystal panel of the display unit and the touch pad of the input unit) And a wireless communication unit 80 for realizing various information communications with an external server, and a storage unit (ROM) storing necessary data such as a system program, various processing programs, and a terminal ID of the smartphone 100 91, various processing programs and data executed by the control unit 101, processing data, or an image obtained by the imaging device 10. And a temporary storage unit used as a work area for storing data and the like temporarily (RAM) and a 92.

  The smartphone 100 operates by operating the input key unit 60, drives the imaging lens 12 by an actuator (not shown) to perform an autofocus operation, and presses the release button 71 or the like to operate the imaging device 10. Imaging can be performed. The image signal input from the imaging device 10 is stored in the storage unit 92 or displayed on the touch panel 70 by the control system of the smartphone 100, and further transmitted to the outside as video information via the wireless communication unit 80. Is done.

Next, examples suitable for the above-described embodiment will be described. However, the present invention is not limited to the following examples.
f: Focal length of the entire imaging lens system fB: Back focus F: F number 2Y: Diagonal length ENTP on the imaging surface of the solid-state imaging device: Entrance pupil position (distance from the first surface to the entrance pupil position)
EXTP: exit pupil position (distance from imaging surface to exit pupil position)
H1: Front principal point position (distance from first surface to front principal point position)
H2: Rear principal point position (distance from the final surface to the rear principal point position)
R: radius of curvature D: axial top surface spacing Nd: refractive index νd of lens material with respect to d-line: Abbe number of lens material L: distance on the optical axis from the lens surface closest to the object side to the image side focal point of the entire imaging lens system

  In each embodiment, the surface on which the aspheric coefficient is described is a surface having an aspheric shape, and the aspheric shape has an apex at the surface as an origin, an X axis in the optical axis direction, and a direction perpendicular to the optical axis. The height is expressed by the following “Equation 1” where h is the height.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：基準曲率半径
Ｋ ：円錐定数

However,
Ai: i-th order aspheric coefficient R: reference radius of curvature K: conic constant

Example 1
Table 1 shows lens data of Example 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).

(Table 1)
Example 1
f = 2.94mm ENTP = 0mm
fB = 0.32mm EXTP = -1.74mm
F = 2.09 H1 = 1.17mm
2Y = 4.59mm H2 = -2.57mm
L = 3.42mm
L / 2Y = 0.75

Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 (Aperture) ∞ -0.16 0.69
2 1.196 0.39 1.5447 56.2 0.72
3 28.057 0.07 0.73
4 7.081 0.15 1.6347 23.9 0.72
5 1.725 0.27 0.73
6 5.607 0.31 1.5447 56.2 0.83
7 304.977 0.43 0.89
8 -6.894 0.50 1.5447 56.2 1.02
9 -0.751 0.20 1.30
10 -1.783 0.27 1.5447 56.2 1.84
11 1.076 0.39 1.96
12 ∞ 0.11 1.5163 64.1 2.50
13 ∞ 2.50

Aspheric coefficient
2nd surface 3rd surface 4th surface 5th surface 6th surface
K 8.75365E-02 5.01098E + 01 -9.94304E + 00 -4.20559E-01 1.02181E + 01
A4 4.98363E-03 3.46071E-02 -6.91616E-02 -1.59975E-01 -1.63809E-01
A6 1.54519E-02 1.64591E-01 4.96919E-01 1.47025E + 00 -1.56514E-01
A8 -8.59264E-03 -9.39580E-02 -6.79209E-01 -4.96074E + 00 7.37281E-01
A10 1.64097E-01 -8.33916E-01 -1.38166E + 00 1.02873E + 01 -1.50239E + 00
A12 1.88071E-01 -7.29556E-01 -2.10765E-01 -1.26392E + 01 2.50310E + 00
A14 -9.89165E-01 1.43571E + 00 3.02506E + 00 7.32911E + 00 -1.51385E + 00
A16 0.00000E + 00 0.00000E + 00 0.00000E + 00 0.00000E + 00 0.00000E + 00

7th surface 8th surface 9th surface 10th surface 11th surface
K 0.00000E + 00 2.28100E-07 -2.93784E + 00 -5.32419E-01 -1.42366E + 01
A4 -1.93160E-01 -3.14905E-01 -7.66199E-03 -1.84902E-02 -1.29156E-01
A6 -1.56943E-02 1.27573E + 00 -1.57419E-01 8.19765E-02 8.01974E-02
A8 -2.37082E-02 -4.49916E + 00 4.46513E-01 -5.01957E-02 -4.45157E-02
A10 -1.91355E-01 8.51327E + 00 -5.58957E-01 2.42219E-02 1.48987E-02
A12 2.63360E-01 -9.23005E + 00 3.73679E-01 -7.58614E-03 -3.28208E-03
A14 2.21021E-01 5.07538E + 00 -1.20806E-01 1.25912E-03 4.39453E-04
A16 0.00000E + 00 -1.08838E + 00 1.33708E-02 -8.24083E-05 -2.26307E-05

  FIG. 7 is a cross-sectional view of the lens of Example 1 for five balls. In the figure, L1 is a first lens having a positive refractive power and a convex surface facing the object side, and the image side optical surface is concave, L2 is a second lens having a negative refractive power, L3 is a third lens, L4 Is a fourth lens, L5 is a fifth lens whose image side optical surface is paraxial and concave, and has an inflection point within the effective diameter, and S is disposed on the object side from the effective diameter of the first lens L1. An aperture stop, I, indicates an imaging surface. Further, CG is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

In Example 1, a high refractive index layer made of TiO ₂ and a low refractive index layer made of SiO ₂ and Al ₂ O ₃ are alternately laminated on the optical surfaces of all lenses in order from the lens (substrate) side. Thus, an antireflection film consisting of a total of four layers is formed. The ratio of the number of Al elements to the Si elements in the mixed film of the low refractive index layer is 1 to 5%. The outermost layer of the antireflection film is a low refractive index layer. However, as shown in Table 2, the film thickness of the antireflection film on the optical axis on the object side optical surface of the first lens L1 is 294 nm, and as shown in Table 3, on the optical axis on the image side optical surface. The thickness of the antireflection film is 253 nm.

(Example 2)
Table 4 shows lens data of Example 2.

(Table 4)
Example 2
f = 3.47mm ENTP = 0.40mm
fB = 0.30mm EXTP = -2.50mm
F = 1.81 H1 = 0.44mm
2Y = 5.53mm H2 = -3.18mm
L = 4.79mm
L / 2Y = 0.87

Surface number R (mm) D (mm) Nd νd Effective radius (mm)
1 1.719 0.55 1.5447 56.2 1.05
2 (Aperture) -24.146 0.09 0.90
3 4.510 0.20 1.6347 23.9 0.93
4 1.771 0.37 0.94
5 4.427 0.20 1.6347 23.9 0.98
6 2.777 0.09 1.18
7 3.617 0.68 1.5447 56.2 1.44
8 6.274 0.19 1.49
9 132.081 0.78 1.5447 56.2 1.61
10 -0.790 0.09 1.65
11 -4.971 0.52 1.5447 56.2 1.73
12 0.928 0.60 2.41
13 ∞ 0.11 1.5163 64.1 2.72
14 ∞ 2.75

Aspheric coefficient
1st surface 2nd surface 3rd surface 4th surface
K -1.40720E + 00 5.00000E + 01 -4.79559E + 01 -8.24976E + 00
A4 3.89293E-02 7.88563E-02 5.36037E-02 7.99730E-02
A6 1.13045E-02 -1.31489E-02 2.57265E-02 1.33243E-02
A8 1.50160E-02 -1.67135E-01 -1.10479E-01 -3.84373E-02
A10 -5.85923E-02 3.67600E-01 1.24027E-01 3.88155E-02
A12 7.58043E-02 -3.45156E-01 -5.32895E-02 0.00000E + 00
A14 -3.46456E-02 1.15321E-01 0.00000E + 00 0.00000E + 00

5th surface 6th surface 7th surface 8th surface
K 1.67693E + 01 -2.56359E + 01 -5.00000E + 01 0.00000E + 00
A4 -2.22312E-01 -1.66427E-01 -1.21092E-01 -1.08750E-01
A6 1.86310E-01 2.75730E-01 1.36414E-01 -7.41013E-03
A8 -3.82318E-01 -3.79753E-01 -5.52916E-02 -1.35406E-02
A10 3.15515E-01 3.19707E-01 4.30841E-03 1.97316E-02
A12 -1.52109E-01 -1.56133E-01 3.00130E-03 -1.19426E-02
A14 0.00000E + 00 3.25791E-02 -4.69023E-04 3.07881E-03

9th surface 10th surface 11th surface 12th surface
K 5.00000E + 01 -4.03705E + 00 6.87015E + 00 -6.85573E + 00
A4 2.38259E-03 -4.03105E-02 7.15832E-02 -7.03868E-02
A6 -3.92406E-02 -1.39225E-02 -2.48966E-01 2.15814E-02
A8 -3.79075E-02 -3.76763E-03 1.92768E-01 -5.51825E-03
A10 3.85216E-02 4.50081E-03 -7.34751E-02 7.28067E-04
A12 -1.07949E-02 1.61331E-03 1.30428E-02 -3.80863E-05
A14 1.12116E-03 -5.39441E-04 -6.70985E-04 -3.09175E-07

  FIG. 8 is a cross-sectional view of the lens of Example 1 for six balls. In the figure, L1 is a first lens having a positive refractive power, a convex surface facing the object side, and an image-side optical surface close to a flat surface, L2 a second lens having a negative refractive power, and L3 a third lens. L4 is a fourth lens, L5 is a fifth lens, L6 is a sixth lens in which the image side optical surface is a paraxial concave shape and has an inflection point within an effective diameter, and S is a first lens L1. An aperture stop (surface stop) formed on the image-side optical surface, I denotes an imaging surface. Further, CG is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

In Example 2, a high refractive index layer made of TiO ₂ and a low refractive index layer made of SiO ₂ and Al ₂ O ₃ are alternately laminated on the optical surfaces of all lenses in order from the lens (substrate) side. Thus, an antireflection film consisting of a total of four layers is formed. The ratio of the number of Al elements to the Si elements in the mixed film of the low refractive index layer is 1 to 5%. The outermost layer of the antireflection film is a low refractive index layer. However, as shown in Table 2, the film thickness of the antireflection film on the optical axis on the object side optical surface of the first lens L1 is 294 nm, and as shown in Table 3, on the optical axis on the image side optical surface. The thickness of the antireflection film is 253 nm.

  FIG. 9 is a graph showing the reflection characteristics of the antireflection film on the object-side optical surface and the image-side optical surface of the first lens L1 in Examples 1 and 2. As shown in FIG. 9, since the film thickness of the antireflection film on the object-side optical surface of the first lens L1 is as described above on the optical axis, reflection of incident light with an angle θ formed with the optical axis being 0 degrees. The rate is 1% or less within the wavelength range of 500 to 750 nm. Further, since the film thickness of the antireflection film on the image side optical surface of the first lens L1 is as described above, the reflectance of incident light with an angle .theta. The thickness is set to be 1% or less within the range of 650 nm. In Examples 1 and 2, the reflectance of incident light at an angle θ of 0 ° that forms only the object-side optical surface of the first lens L1 with the optical axis is 1% or less within the wavelength band of 500 to 750 nm. However, a similar antireflection film shifted to the longer wavelength side may be deposited on the other optical surfaces. For example, in Example 1, the image side optical surface of the fifth lens L5 has a shape that is concave on the image side in the vicinity of the optical axis and convex on the image side in the peripheral portion, so that Δsag is large. Inter-surface reflection is likely to occur between the optical surfaces. Therefore, as with the object-side optical surface of the first lens L1, an antireflection film is used in which the reflectance of incident light is 0% or less within the wavelength band of 500 to 750 nm when the angle θ formed with the optical axis is 0 degrees. You may do it. Further, in order to change the film thickness ratio with the same film configuration as described above and shift the wavelength band where the reflectance is low to about 100 nm to the longer wavelength side, for example, on the object side optical surface of the first lens L1 The ratio of the physical film thickness of the antireflection film on the optical axis on the image side optical surface of the first lens L1 to the physical film thickness of the antireflection film on the optical axis may be about 0.84 to 0.89. The film design wavelength shift amount may be about 80 to 100 nm on the long wavelength side.

  In FIG. 10, in Examples 1 and 2, the vertical axis represents Δsag of the object-side optical surface of the first lens L1, and the horizontal axis represents the height from the optical axis (where the effective diameter is 1). FIG. The maximum value Δsagmax of the amount Δsag of the object side optical surface in the first lens L1 is about 0.7 in both the first and second embodiments.

  FIG. 11 shows the sag of the image-side optical surface of the first lens L1 on the vertical axis in Examples 1 and 2, and the height from the optical axis on the horizontal axis (however, the effective diameter is 1). FIG. In the entire area within 80% of the effective diameter of the image-side optical surface of the first lens L1, the sag of Example 1 is 0 or more, and the sag of Example 2 is −0.002 or more.

  In FIG. 12, in Examples 1 and 2, the vertical axis indicates Δsag of the image side optical surface of the first lens L1, and the horizontal axis indicates the height from the optical axis (however, the effective diameter is 1). FIG. In the entire area within 80% of the effective diameter of the image side optical surface of the first lens L1, Δsag of Example 1 is 0 or more, and Δsag of Example 2 is −0.01 or more.

  FIG. 13 is a diagram showing an example of the relationship between reflectance and wavelength when Δsag is changed when an antireflection film is deposited on the optical surface. As shown in FIG. 13, when the value of Δsag is increased, that is, the greater the angle between the normal of the optical surface on which the antireflection film is deposited and the optical axis, the lower the reflectance is in the shorter wavelength range. It can be seen that the light on the long wavelength side is easily reflected. As is apparent from FIG. 10, the value of Δsag increases as the height from the optical axis increases, that is, as the distance from the optical surface increases. In other words, when multiple reflection ghost light is generated, for example, a light beam that is reflected four times between both surfaces of L1 and reaches the image surface is finally near the outermost periphery of the S1 surface, that is, at a place where the value of Δsag is large as shown in FIG. Since it is reflected, the reflectance of the light on the long wavelength side becomes high. That is, the ghost light that reaches the image plane may be reddish.

  The inventor has the same lens shape as in Example 1, but the film thickness of the antireflection film on the optical axis of the object-side optical surface in the first lens L1 is set on the optical axis of the image-side optical surface. A comparative example having the same thickness (253 nm) as that of the antireflection film was prepared.

  FIG. 14 shows an example of the XIE of the CIE XYZ coordinate system on the imaging surface that receives the multiple reflection ghost light when a light beam having an angle larger than the field angle contributing to image formation is incident in the comparative example and the first embodiment. Only the values are graphed, and the larger the X value, the stronger the reddish tint. The number of display pixels on the imaging surface is 128 pixels in the horizontal direction and 96 pixels in the vertical direction. The illuminance on the image plane was made substantially equal between the corresponding pixels in the comparative example and Example 1.

  In the comparative example shown in FIG. 14B, there are a wide range of regions where the X value is 1.5 or more, and there are also regions where the X value is 2.0 or more at both ends. On the other hand, in Example 1 shown in FIG. 14 (a), there are few regions where the X value is 1.5 or more, and there are no regions where the X value is 2.0 or more. Therefore, in Example 1, the redness component can be suppressed even when multiple reflection ghost light is generated.

  The present invention is not limited to the embodiments and examples described in the specification, and includes other examples and modifications based on the embodiments, examples, and technical ideas described in the present specification. It will be apparent to those skilled in the art. For example, even when a dummy lens having substantially no refractive power is further provided, it is within the scope of application of the present invention.

  The present invention can provide an imaging lens suitable for a small portable terminal.

DESCRIPTION OF SYMBOLS 10 Image pick-up device 11a Photoelectric conversion part 11 Image pick-up element 12 Image pickup lens 13 Lens frame 14 Parallel plate 15 Substrate 60 Input key part 65 Display part 70 Touch panel 71 Release button 80 Wireless communication part 92 Storage part 100 Smartphone 101 Control part L1-L6 Lens S Aperture stop SP spacer

Claims (17)

It is composed of a positive first lens, a second lens, a third lens, a fourth lens, and a fifth lens, which are arranged in order from the object side and have a convex surface facing the object side, and the aperture stop is closer to the object side than the third lens. There, at least the first lens antireflection film and the object side optical surface and the image side optical surface of formed, in Zore lens Ta used for forming an object image on the imaging surface of the solid-state imaging device,
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
On the optical axis of the first lens, the thickness of the antireflection film of the object-side optical surface is rather thick than the thickness of the antireflection film of the image side surface,
The thickness of the antireflection film on the object-side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 500 to 750 nm. % Is set to be less than
The film thickness of the antireflection film on the image side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 420 to 650 nm. % as to become less, Zore lens shooting, characterized in that is set thickness. The distance on the optical axis from the optical surface closest to the object side to the image-side focal point of the entire imaging lens system is L (mm), the diagonal length of the imaging surface of the solid-state imaging device (the diagonal length of the rectangular effective pixel region of the solid-state imaging device) ) Is 2Y (mm), the imaging lens according to claim 1 satisfying the following formula.
L / 2Y <0.8 (1) A positive first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, which are arranged in order from the object side and have a convex surface directed toward the object side, the aperture stop being the third lens located more object side, at least the first lens object side optical surface and the image side optical surface and the antireflection film is formed, Ta is used for forming an object image on the imaging surface of the solid-state imaging device Zore In
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
On the optical axis of the first lens, the thickness of the antireflection film of the object-side optical surface is rather thick than the thickness of the antireflection film of the image side surface,
The thickness of the antireflection film on the object-side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 500 to 750 nm. % Is set to be less than
The film thickness of the antireflection film on the image side optical surface of the first lens is 1 on the optical axis when the angle θ formed with the optical axis is 0 degree and the reflectance of incident light is in the wavelength range of 420 to 650 nm. % as to become less, Zore lens shooting, characterized in that is set thickness. The distance on the optical axis from the optical surface closest to the object side to the image-side focal point of the entire imaging lens system is L (mm), the diagonal length of the imaging surface of the solid-state imaging device (the diagonal length of the rectangular effective pixel region of the solid-state imaging device) ) Is 2Y (mm), the imaging lens according to claim 3 satisfying the following formula.
L / 2Y <0.9 (2) The antireflection film on the object side optical surface and the image side optical surface of the first lens, the imaging lens according to any one of claims 1 to 4, the same film structure. The antireflection film imaging lens according to any one of claims 1 to 5, which is a stacked structure of four layers. The antireflection film is a high refractive index layer in this order from the first lens side, the same film material in the order of the low refractive index layer are laminated, the outermost layer of the antireflection film according to claim 6, wherein the low refractive index layer Imaging lens. The aperture stop, an imaging lens according to any one of claims 1 to 7 in the object side of the position of the effective diameter of the object-side optical surface of the first lens. The antireflection film is composed of a Ti-based high-refractive index layer and a Si-based low-refractive index layer, and the low-refractive index layer is a mixed film in which two different inorganic materials are mixed. the material constituting the film is a SiO ₂ and Al ₂ O _3, according to any one of claims 1-8 ratio of the number elements of Al to elements of Si in the mixed film is 1-5% Imaging lens. The most image-side optical surface of the image side of the lens is a aspherical, imaging lens according to any one of claims 1 to 9, which has an inflection point in the effective diameter. Wherein the object-side optical surface and the image side optical surface of the all lenses other than the first lens, the imaging lens according to any one of claims 1 to 10, the anti-reflection film is formed. The imaging lens according to any one of claims 1 to 11 and the second lens having a negative power. Wherein the effective diameter of the object side optical surface of the first lens, the imaging lens according to any one of claims 1 to 12 maximum Δsagmax sag variation Δsag is to satisfy the following equation.
Δsagmax ≧ 0.4 (3) Sag variation Δsag at the image side optical surface of the first lens, to any one of claims 1 to 13, satisfying the following formula in 80% diameter inner whole region of the effective diameter of the image-side optical surface of the first lens The imaging lens described.
−0.05 ≦ Δsag (4) The image-side optical surface of the first lens, the imaging lens according to any one of claims 1 to 14 which is a concave surface on the image side in the paraxial. Sag (mm) at the image side optical surface of the first lens, according to any one of claims 1 to 15, satisfying the following formula in 80% diameter inner whole region of the effective diameter of the image-side optical surface of the first lens Imaging lens.
−0.01 ≦ sag (5) An imaging apparatus having an imaging lens; and a solid-state imaging device in any of claims 1-16.

Images