JP2021096283A - Lens system - Google Patents

Abstract

To provide a lens system which materializes reduction of the occurrence of a ghost attributed to near-infrared light.SOLUTION: An IR cut coating layer (infrared cut filter) 40 is formed on an image-side surface L5R2 of a fifth lens L5. The radius of curvature (Ra) of the image-side surface L5R2 in the fifth lens L5 is set to be small, so that the angle, to an optical axis A, of reflected light RL from an IR cut coating layer 40, specifically in a portion apart from the optical axis A, can be made large. Thus, reflected light RL directing toward an object-side optical system OA is easily cut off by a diaphragm 20, or the probability of reflected light RL entering the object-side optical system OA from the image side is reduced.SELECTED DRAWING: Figure 3

Description

The present invention relates to a lens system including a plurality of lenses.

For example, as an optical system used in an image pickup device mounted on an automobile, a surveillance camera, etc., a lens unit (a lens unit in which a plurality of lenses are arranged in the optical axis direction from the object side to the image side (image sensor side)). Lens system) is used. Since the image pickup device generally used captures an image of visible light, the above lens unit is designed so as to satisfactorily image the image of visible light on the image pickup device. However, in reality, the image sensor (CMOS sensor or the like) has sensitivity over a wide wavelength range from visible light to near-infrared light, and near-infrared light also passes through the lens unit. On the other hand, since the optical characteristics of each lens in the lens unit are different between visible light and near-infrared light, the near-infrared light that has passed through the lens unit optimized for visible light forms a good image on the image pickup element. do not. Therefore, when the near-infrared light is detected by the image sensor in the same manner as the visible light, the image obtained by the image sensor is not good, and the visible light does not pass through the near-infrared light in the lens unit. An infrared (IR) cut filter that allows only light to pass through is provided.

Patent Document 1 describes that such an IR cut filter in a lens unit is formed as a thin film (coating) on the surface (lens surface) of one of the lenses constituting the lens unit, and a location where the lens is provided. Is described. The IR cut coating layer is set to transmit light having a wavelength shorter than the cutoff wavelength (visible light) and to reflect light having a wavelength longer than this (near infrared light). In this case, ideally, the transmittance of visible light is 100% (reflectance is 0%), and the transmittance of near-infrared light is 0% (reflectance is 100%).

For example, when this IR cut coating layer is formed on the side close to the image sensor (image side), for example, on the cover glass, the reflected near-infrared light is incident on the lens unit in the opposite direction, and after this is reflected. It may go to the image sensor side again. However, if this light does not finally pass through the IR cut coating layer, this light will not be detected by the image sensor. Therefore, most of the near-infrared light is not detected by the image sensor, and the obtained image is not affected by most of the near-infrared light.

Here, particularly for light having a wavelength near the cutoff wavelength in the IR cut coating layer, both the transmittance and the reflectance are non-negligible values (for example, the transmittance is 50% and the reflectance is 50%). In this case, after the reflected light is incident on the lens unit in the opposite direction, it is reflected again toward the image sensor side, and then the component transmitted through the IR cut coating layer and detected by the image sensor cannot be ignored. Since the optical path in the lens unit in this case is significantly different from the original one, the image caused by this component becomes a ghost that is a component other than the original image in the image sensor. That is, light having a wavelength close to the cutoff wavelength causes ghosting.

In the lens unit described in Patent Document 1, such an IR cut coating layer is provided on the lens surface closest to the diaphragm on the downstream side of the diaphragm provided near the center in the optical axis direction of the lens unit. The near-infrared light is removed with high efficiency. As a result, in this lens unit, the near-infrared light reaching the image sensor can be greatly reduced, and the generation of ghosts caused by this can be reduced.

Patent Gazette Patent No. 5896061

Also in the lens unit described in Patent Document 1, light having a wavelength particularly close to the cutoff wavelength is reflected by the IR cut coating layer, and this reflected light is incident on the portion of the lens unit on the object side in the opposite direction. It is the same that it goes to the image pickup element side and causes ghost. Therefore, in the technique described in Patent Document 1, although the ghost is reduced, the degree of the reduction is not sufficient.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a lens system in which the generation of ghosts caused by near-infrared light is reduced.

The lens system according to the present invention is configured by laminating a plurality of lenses including the first lens, which is the most object side, along the optical axis from the object side to the image side, and is located on the image side most. An intermediate glass lens which is one of the lenses other than the first lens and is made of glass, which is a lens system for forming an image of an image to be imaged on an image plane on the image side of the lens, and is on the object side. On one of the first surface, which is the surface, and the second surface, which is the surface on the image side, a thin-film infrared cut filter that blocks light having a longer wavelength than the light to be imaged is provided. When it is formed and the radius of curvature of one of the surfaces is Ra,
2.00 ≦ | Ra ｜ ≦ 4.00
It is said to be in the range of.

In this configuration, light having a wavelength near the cutoff wavelength of the infrared cut filter is reflected by the lens surface of the intermediate glass lens. However, by setting the radius of curvature of the lens surface of the intermediate glass lens in this way, it is possible to prevent the reflected light from finally reaching the image surface. Therefore, most of the near-infrared light is removed by the infrared cut filter, and the generation of ghosts caused by the reflected light is suppressed.

The aperture may be arranged adjacent to the object side of the intermediate glass lens.
In this case, the reflected light is easily excluded by the diaphragm, so that the generation of ghosts is further suppressed.
Here, the first surface of the intermediate glass lens may have a convex shape toward the object side, and the second surface of the intermediate glass lens may have a convex shape toward the image side.

The intermediate glass lens is a lens other than the first lens and the lens closest to the image side, and is a surface facing the one surface of the lens adjacent to the one surface side of the intermediate glass lens. When the radius of curvature of
1.20 << | Rb / Ra | <4.00
It may be in the range of.
Since | Rb / Ra | exceeds 1.20, it is possible to suppress the generation of ghosts due to the reflection between these surfaces. Further, since | Rb / Ra | is less than 4.00, it becomes easy to correct the aberration of the lens system.

The intermediate glass lens is a lens other than the first lens and the lens closest to the image side, and one surface of the intermediate glass lens has a convex shape, and the one surface of the intermediate glass lens is convex. When the surface of the lens adjacent to the lens facing the one surface is concave and the radius of curvature is Rb,
1.20 <Rb / Ra <4.00
It may be in the range of.
In this case, since the surface on which the infrared cut filter is formed and the opposite surface are configured to be a combination of a convex curved surface and a concave curved surface, the lens having these surfaces is brought close to each other to be compact. Lens system can be configured. In particular, since Rb / Ra exceeds 1.20, the radius of curvature Rb is larger than Ra, and it becomes easy to bring them close to each other. Further, since Rb / Ra is less than 4.00, it is possible to easily correct the aberration while suppressing the occurrence of ghost, as described above.

Both the first surface and the second surface of the intermediate glass lens may have a spherical shape.
With such a configuration, the intermediate glass lens can be inexpensive, and the entire lens system or an imaging device using the lens system can be inexpensive.

In the plurality of the lenses, the first lens is a negative lens having the second surface which is concave when viewed from the image side, and is concave when viewed from the image side between the first lens and the intermediate glass lens. A second lens that is a negative lens having the second surface, a third lens that is a positive lens, and a fourth lens that is a positive lens having the second surface that is convex toward the image side. A sixth lens, which is a negative lens having the second surface having a concave shape when viewed from the image side on the image side of the intermediate glass lens, and an object. The first surface having a convex shape toward the side and a seventh lens having the second surface having a convex shape toward the image side are sequentially provided, and the second surface of the sixth lens is provided. A bonded lens may be formed in which the lens and the first surface of the seventh lens are bonded to each other.

The first lens may be made of glass, and the second lens, the third lens, the fourth lens, the sixth lens, and the seventh lens may be made of a resin material.
With such a configuration, while the first lens exposed to the outside has high strength, each lens other than the first lens and the intermediate glass lens can be made inexpensive, which enhances the reliability of the lens system and makes it inexpensive. Can be.

According to the present invention, this lens system is used because it is suppressed that light having a wavelength near the cutoff wavelength of the infrared cut filter is reflected by the infrared cut filter toward the object side and then reaches the image plane again. In the image pickup device, the ghost generated due to this reflection is suppressed. Further, a lens system having this configuration can be realized at low cost.

It is sectional drawing of the lens system which concerns on embodiment. It is a design value of each lens and the like in Example 1. It is an enlarged figure which shows the structure of the vicinity of the intermediate glass lens in the lens system which concerns on embodiment. It is a design value of each lens and the like in Example 2. It is a design value of each lens and the like in Example 3. It is a design value of each lens and the like in Example 4. It is a design value of each lens and the like in Example 5. In Example 1, it is a two-dimensional intensity distribution (a) and a one-dimensional intensity distribution (b) of an image plane when a spot-shaped light beam having an incident angle of 0 ° is incident. In Example 1, it is a two-dimensional intensity distribution (a) and a one-dimensional intensity distribution (b) of an image plane when a spot-shaped light beam having an incident angle of 30 ° is incident. In Example 1, it is a two-dimensional intensity distribution (a) and a one-dimensional intensity distribution (b) of an image plane when a spot-shaped light beam having an incident angle of 60 ° is incident. In Example 1, it is a two-dimensional intensity distribution (a) and a one-dimensional intensity distribution (b) of an image plane when a spot-shaped light beam having an incident angle of 90 ° is incident.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of the entire optical system including the lens system 1 according to the present embodiment in a cross section along the optical axis A. Here, the object side is the upper side in the figure, and the image sensor 100 is located at the lowermost part in the figure. In FIG. 1, only the optically functioning portion of each component corresponding to the first embodiment described later is shown. In reality, each component is fixed inside the lens barrel so as to maintain the positional relationship shown in FIG. 1, so that the structure required for this fixing or the positional relationship between the components is maintained. Although a structure for fixing the mirror is provided, the description thereof is omitted in FIG.

The image sensor 100 is a two-dimensional CMOS image sensor, and each pixel is arranged two-dimensionally in a plane perpendicular to the optical axis A. Further, on the object side of the image pickup device 100, a flat cover glass 110 orthogonal to the optical axis A is provided. In FIG. 1, a lens system 1 including a first lens L1 to a seventh lens L7 is configured. The lens system 1 is configured to form an image to be imaged on the image pickup device 100 (image plane) in a desired field of view and in a desired form. In reality, near-infrared light or the like is emitted from the imaging target in addition to visible light, but the lens system 1 is designed so that this imaging condition is satisfied in the case of visible light. The optically functional region (the portion shown in FIG. 1) of each lens in the lens system 1 has a substantially disk-shaped outer shape symmetrical about the optical axis A.

(Example 1)
The configuration of FIG. 1 corresponds to the first embodiment, and FIG. 2 shows the design values of each lens used in the first embodiment. Here, FIG. 2A shows the effective focal length of the entire lens system (Effective Focal Lens: f0 = 1.011 mm) and the total length along the optical axis A (Total Track = 13.404 mm) as the design values of the lens system. ), F value (F-number = 2.03), and angle of view (Half Field of Angle = 109 °). In FIG. 2B, in addition to the first lens L1 to the seventh lens L7, the aperture 20 and the cover glass 110 are also shown. For each lens, the refractive index Nd (corresponding to a wavelength of 587 nm) and the Abbe number νd are also described. Further, the numerical value indicated by f in FIG. 2B is the focal length in each lens or the combination of lenses corresponding to the indicated range. Further, here, there are two types of lens surface shapes, spherical and aspherical, and when the lens surface is aspherical, the radius of curvature (Radius) shown in this table is the center (optical axis). It is the value in (A).

In FIG. 1, the first lens L1 provided on the most object (Obj) side (upper side in the drawing) is a fisheye lens, which mainly determines the field of view and the like. The second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are sequentially arranged on the image pickup element 100 side (image (Img) side). There is. Further, the diaphragm 20 for limiting the luminous flux used for imaging is between the fourth lens L4 and the fifth lens L5, and the light-shielding plate 30 for removing unnecessary light is between the second lens L2 and the fifth lens L5. It is provided between each of the three lenses L3. The shapes of the opening and the light-shielding plate 30 provided in the diaphragm 20 are set according to the purpose.

The lens surface on the object side and the lens surface on the image side of each lens are appropriately curved (convex curved surface, concave curved surface) so that the lens system 1 brings about desired imaging characteristics. Hereinafter, the lens surface on the object side of each lens is referred to as a first surface R1, and the lens surface on the image side is referred to as a second surface R2. Further, as the shape of the lens surface (convex curved surface or concave curved surface), the shape of the first surface R1 means the shape seen from the object side, and the shape of the second surface R2 means the shape seen from the image side. To do.

The first lens L1 is a negative lens (meniscus lens) in which the first surface R1 on the object side is a convex curved surface and R2 on the image side is a concave curved surface. The second lens L2 is a negative lens in which the first surface R1 on the object side is a convex curved surface and the second surface R2 on the image side is a concave curved surface. The third lens L3 is a positive lens in which the first surface R1 on the object side is a concave curved surface and the second surface R2 on the image side is a convex curved surface. The fourth lens L4 is a positive lens in which the first surface R1 on the object side is a concave curved surface and the second surface R2 on the image side is a convex curved surface. The fifth lens L5 is a positive lens in which the first surface R1 on the object side is a convex curved surface and the second surface R2 on the image side is a convex curved surface.

The sixth lens L6 is a negative lens in which the first surface R1 on the object side is a concave curved surface and the second surface R2 on the image side is a concave curved surface. The seventh lens L7 is a positive lens in which the first surface R1 on the object side is a convex curved surface and the second surface R2 on the image side is a convex curved surface. Further, the sixth lens L6 and the seventh lens L7 are set so as to form a bonded lens by fitting the opposing optical surfaces (surfaces). That is, the second surface R2 on the image side of the sixth lens L6 and the first surface R1 on the object side of the seventh lens L7 are configured to fit. The first surface R1 on the object side and the second surface R2 on the image side of each of the above lenses are set so that desired imaging characteristics can be obtained on the image plane (image sensor 100) with respect to visible light. There is.

Further, in general, there are two types of materials constituting a lens in such a small image pickup apparatus, glass and resin material. The former has high mechanical strength but is expensive, and the latter has low mechanical strength but is inexpensive. Since the first lens L1 is located on the outermost surface of the image pickup apparatus 1 and has the largest diameter, a glass lens that is not easily scratched is preferably used. As many other lenses smaller than this, one made of an inexpensive resin material can be used. In the first embodiment, the first lens L1 and the fifth lens are made of glass, the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are made of plastic (resin). It is said that.

Since the coefficient of thermal expansion of glass is smaller than that of the resin material, glass is used for lenses in which minute changes in shape and position due to thermal expansion at high temperatures have a large effect on imaging characteristics (changes in focal position). It is preferably made of. Therefore, in the first embodiment, the fifth lens (intermediate glass lens) L5 is made of glass like the first lens L1. As described above, the second surface R2 on the image side of the fifth lens L1 has a convex shape toward the image side, and the first surface R1 on the object side has a convex shape toward the object side. Further, particularly for a lens adjacent to the aperture 20 on the object side and the image side, a change in the focal position due to a change in the surface position due to thermal expansion during a temperature change has a particularly large effect on the imaging characteristics. Therefore, it is preferable that one of these is made of glass. Further, by making the lens adjacent to the aperture 20 on the image side made of glass, the fluctuation of the angle of view due to the temperature change is suppressed. Therefore, in the present embodiment, the fifth lens L5 is made of glass.

In FIG. 2B, the glass lenses L1 and L5 are spherical lenses, and the other plastic lenses L2 to L4, L6 and L7 are aspherical lenses. An aspherical lens is relatively difficult to manufacture as compared with a spherical lens, but in a plastic lens, an aspherical shape can be easily manufactured by resin molding. Therefore, while it is easy to make the lenses L2 to L4, L6, and L7 aspherical, the glass lenses L1 and L5, which are relatively difficult to have an aspherical shape, are made spherical. .. Therefore, such a combination makes it possible to improve the performance of the lens system 1 because it is inexpensive, the change in the focal position due to the temperature change can be suppressed, and the aberration can be appropriately corrected. Here, for all lenses (planes), the radius of curvature is set to be positive when the center of curvature is on the image side and negative when the center of curvature is on the object side. Therefore, as described above, the shape of the curved surface (convex curved surface, concave curved surface) is defined as the case where the shape of the first surface R1 is viewed from the object side and the shape of the second surface R2 is defined as the case where the shape is viewed from the image side. In FIG. 2B, the first surface R1 has a convex curved surface (negative case is a concave curved surface) when the radius of curvature is positive, and the second surface R2 has a concave curved surface (negative case) when the radius of curvature is positive. The case is a convex curved surface).

Further, the shape when the surface shown in FIG. 2 (b) is an aspherical surface is represented by the following equation (1), and each parameter (aspherical coefficient) is shown in the table of FIG. 2 (c). It is shown.

Here, since this shape is symmetrical around the optical axis A, the relationship between Z (sag amount: height along the optical axis A) and r (diameter distance from the optical axis A). It is shown. Further, c is the reciprocal of the radius of curvature (Radius) at the center shown in the table of FIG. 2 (b).

In this lens system 1, the IR cut coating layer (infrared cut filter) 40 is formed on the second surface R2 on the image side of the fifth lens L5. The IR cut coating layer 40 can remove near-infrared light toward the image sensor 100 side. The IR cut coating layer 40 is formed as a thin film, for example, by vapor deposition or the like, as a multilayer film that transmits light having a wavelength shorter than the cutoff wavelength and does not transmit (reflects) light having a wavelength longer than this. .. At this time, both the reflectance and the transmittance are non-negligible values especially for light having a wavelength close to the cutoff wavelength. Therefore, in the conventional lens unit, the reflected light having a wavelength closer to the cutoff wavelength is reflected toward the image side on the object side, and then passes through the IR cut coating layer 40 and is incident on the image sensor 100. The ingredients could not be ignored, and ghosts caused by this occurred. On the other hand, in this lens system 1, the component that is reflected by the IR cut coating layer 40 toward the object side and then reflected again toward the image side and incident on the image sensor 100 is reduced. Ghosts caused by are reduced. This point will be described below.

FIG. 3 is a diagram schematically showing the effect of this in an enlarged configuration of FIG. 1. Here, the component on the object side (upper side in the figure) of the aperture 20 is the object side optical system OA, and the component on the image side (lower side in the figure) of the fifth lens L5 is the image side optical system OB. Shown as one. As described above, the IR cut coating layer 40 is formed on the second surface R2 on the image side of the fifth lens L5. Here, when the radius of curvature Ra of the second surface R2 on the image side of the fifth lens L5 is shown as an absolute value, the radius of curvature Ra is set small.

In FIG. 3, the state of reflection from the IR cut coating layer 40 in this configuration is schematically shown. By setting the radius of curvature (Ra) of the second surface R2 on the image side of the fifth lens L5 to be small, the optical axis A of the reflected light RL from the IR cut coating layer 40 is set particularly at a portion away from the optical axis A. The angle with respect to can be increased. As a result, the reflected light RL toward the object-side optical system OA is easily blocked by the diaphragm 20, or the probability that the reflected light RL is incident on the object-side optical system OA from the image side is reduced.

Specifically, the radius of curvature Ra is preferably in the range of 2.00 mm ≦ | Ra | ≦ 4.00 mm. By reducing the absolute value of the radius of curvature Ra to 4.00 mm or less, the occurrence of flare and ghost can be suppressed as described above. If the absolute value of the radius of curvature Ra exceeds 4.00 mm, the second surface R2 on the image side of the fifth lens L5 becomes close to a flat surface, so that the reflected light easily reaches the image plane, and flares and ghosts occur. It becomes a factor of occurrence. Further, by setting the absolute value of the radius of curvature Ra to 2.00 mm or more, the IR cut coating layer 40 can be uniformly formed on the second surface R2 on the image side of the fifth lens L5. If the absolute value of the radius of curvature Ra is less than 2.00 mm, the radius of curvature of the lens becomes too small, and the IR cut coating layer 40 on the central portion and the end side of the second surface R2 on the image side is uniformly applied. It becomes difficult to form the image and obtain its optical characteristics uniformly, and there is a possibility that there is a difference in hue between the central portion and the peripheral portion of the image.

Further, in FIG. 3, the radius of curvature Rb of the first surface R1 on the object side of the sixth lens L6 facing the second surface R2 on the image side of the fifth lens L5, and the second surface on the image side of the fifth lens L5. The radius of curvature Ra of R2 is in the range of 1.20 << Rb / Ra | <4.00. Since | Rb / Ra | exceeds 1.20, the difference between the radius of curvature Ra and the radius of curvature Rb can be obtained, so that the generation of ghosts due to the reflection between these surfaces can be suppressed. Further, since | Rb / Ra | is less than 4.00, it becomes easy to correct the aberration of the lens system, so that it is possible to provide a high-performance lens system.

Further, in general, the IR cut coating layer 40 is formed by vapor deposition or the like as a multilayer film containing _{SiO 2.} At this time, it is generally difficult to form such an IR cut coating layer 40 on a plastic (organic material) with a high bonding strength, whereas such a layer is formed on a glass material with a high bonding strength. It's easy to do. Further, since the main component of the glass material is SiO ₂ , the difference in the coefficient of thermal expansion between the glass material and the IR cut coating layer 40 is also small. Therefore, it is particularly preferable that the fifth lens L5 is made of glass as described above.

In addition to the above-mentioned Example 1, similarly, other specific configurations (Examples 2 to 5) of the lens system 1 are shown in FIGS. 4 to 7 as in FIG. 2. Here, not only the radius of curvature but also some shapes (convex curved surface, concave curved surface) are changed from the lens system of the first embodiment. In any of the embodiments, the total number of lenses is seven as in the first embodiment, and the sixth lens L6 and the seventh lens L7 are similarly bonded lenses. Similarly, the first lens L1 and the fifth lens L5 are made of glass, and the other lenses are made of plastic. The same applies to the point that the aperture 20 is located between the fourth lens L4 and the fifth lens L5.

In the second embodiment, as compared with the first embodiment, the first surface R1 on the object side of the second lens L2 is a concave curved surface, the first surface R1 on the object side of the third lens L3 is a convex curved surface, and the image side thereof is the first surface R1. The 2 surface R2 is changed to be a concave curved surface, the first surface R1 on the object side of the 4th lens L4 is changed to be a convex curved surface, and the radius of curvature of the convex curved surface of the 2nd surface R2 on the image side of the 5th lens L5 is set large. Has been done. In the third embodiment, the angle of view is set wider than that in the first embodiment, and in particular, the radius of curvature of the convex curved surface of the first surface R1 on the object side of the fifth lens L5 is set to be large.

In the fourth embodiment, the angle of view is set wider than that of the first embodiment, the radius of curvature of the convex curved surface of the first surface R1 on the object side of the second lens L2, and the first surface R1 on the object side of the fifth lens L5. The radius of curvature on the convex curved surface of is set large. In the fifth embodiment, the radius of curvature of the convex curved surface of the first surface R1 on the object side of the fifth lens L5 is set to be particularly large. The characteristics of the entire lens system in Examples 2 to 5 are shown in FIGS. 4 to 7 (a), and the aspherical lenses used (second lens L2, third lens L3, fourth lens L4, sixth lens L6) are shown in FIGS. , The aspherical coefficient in the seventh lens L7) is shown in (c) of FIGS. 4 to 7.

In the table (b) of FIGS. 2, 4 to 7, the radius of curvature of the first surface R1 on the object side of the fifth lens L5, the radius of curvature Ra of the second surface R2 on the image side of the fifth lens L5, and the sixth lens. The radius of curvature Rb of the first surface R1 on the object side of L6 is shown by hatching. In this way, the lens system 1 having the configuration shown in FIG. 1 can be realized with Ra and Rb as the above ranges.

Next, the light intensity on the image sensor 100 in Example 1 was actually calculated by simulation, and the state of ghost generation was investigated. 8 to 11 show the intensities on the image sensor 100 when the light rays on the spot are incident on the lens system 1 with the incident angles of 0 °, 30 °, 60 °, and 90 ° with respect to the optical axis A, respectively. This is the result of calculating the distribution. In each figure, (a) shows a two-dimensional intensity distribution, and (b) shows a one-dimensional intensity distribution in the horizontal direction at the center in the vertical direction. The highest sharp peak recognized in (b) corresponds to this light source, and the other locally high intensity portions correspond to ghosts. The characteristic of (b) is standardized with the peak intensity as 1, and from the sensitivity characteristic of the image sensor 100, when the intensity in this case is 1E-6 (1 × ^10-6 ) or less, the intensity is substantially increased. It can be regarded as zero. That is, if there is a portion having an intensity exceeding 1E-6 at a portion other than the portion corresponding to the single peak in (b), this portion is recognized as a ghost in the imaging apparatus.

In this result, when the incident angle is 0 ° (FIG. 8), peaks other than a single peak are not observed, including those having an intensity of 1E-6 or less. That is, the generation of ghosts is suppressed. As the angle of incidence increases, the occurrence of peaks other than the original peak is observed, but the intensity of most of them is 1E-6 or less. That is, in the examples, the generation of ghosts is suppressed. Moreover, in any case, the original peak is recognized by the same sharp shape.

Therefore, it was confirmed that the imaging optical system with reduced ghost can be realized by using the lens system 1 of FIG.

(Main features of this form)
The features of this embodiment are briefly summarized as follows.
(1) The lens system 1 is configured by laminating a plurality of lenses including the first lens L1 which is the most object side along the optical axis A from the object side to the image side, including the aperture 20, and is most on the image side. The image to be imaged is formed on the image plane on the image side of the seventh lens L7 located in the above, and the intermediate glass lens L5, which is one of the lenses other than the first lens L1 and is made of glass, is on the object side. On one of the first surface R1 which is the surface of the lens and the second surface R2 which is the surface on the image side, a thin film of infrared rays that blocks light having a longer wavelength than the light to be imaged is formed. When the cut filter 40 is formed and the radius of curvature Ra of one of the surfaces is set,
2.00 ≦ | Ra ｜ ≦ 4.00
It is said to be in the range of.

In this configuration, the IR cut coating layer 40 suppresses light having a wavelength longer than the cutoff wavelength from reaching the image plane (image sensor 100). However, since both the reflectance and the transmittance of light having a wavelength close to the cutoff wavelength are not negligible, this light generally reaches the image plane and causes ghosting. On the other hand, in this lens system 1, the second surface on the image side of the fifth lens L5, which is one surface of the intermediate glass lens L5 in which the absolute value Ra of the radius of curvature is 2.0 mm or more and 4.0 mm or less. By forming the IR cut coating layer 40 on R2, the angle between the reflected light RL from the IR cut coating layer 40 and the optical axis A is increased, so that light having a wavelength close to the cutoff wavelength reaches the image plane. Is suppressed.

(2) At this time, the diaphragm 20 is arranged adjacent to the object side of the intermediate glass lens L5. As a result, light having a wavelength close to the cutoff wavelength is easily removed by the diaphragm 20 after being reflected by the second surface R2 on the image side of the fifth lens L5 toward the object side.
(3) At this time, the first surface R1 of the intermediate glass lens L5 has a convex shape toward the object side, and the second surface R2 of the intermediate glass lens L5 has a convex shape toward the image side. It was shown in each Example that a lens system having good imaging characteristics can be constructed by using such an intermediate glass lens L5.

(4) The intermediate glass lens L5 is a lens other than the first lens L1 and the seventh lens L7 closest to the image side, and one surface (second surface R2) of the intermediate glass lens L5 has a convex shape. The surface (first surface R1) of the sixth lens L6 adjacent to one surface of the intermediate glass lens L5 is concave, and the ratio of the radius of curvature Rb of this surface L6R1 to Ra is absolute. The value is in the range of 1.20 << Rb / Ra | <4.00.
Within such a range, the radius of curvature of the surface on which the IR cut coating layer 40 is formed and the surface L6R1 facing the IR cut coating layer 40 are made different so as to be 1.20 << Rb / Ra | (L6R1 is flatter than L5R2). By making the shape close to), it is possible to suppress the generation of ghosts due to reflection between these surfaces. At this time, by making the surface facing the surface on which the infrared cut filter is formed a curved surface such that Rb is in the range of | Rb / Ra | <4.00, it becomes easy to correct the aberration of the lens system. ..

(5) The surface L6R1 of the sixth lens L6 adjacent to the intermediate glass lens L5 on one surface side facing the one surface is a concave curved surface having a radius of curvature Rb, and the ratio of Rb to Ra is 1.20. The range is <Rb / Ra <4.00.
In this case, since the surface L5R2 on which the IR cut coating layer 40 is formed and the surface L6R1 facing the surface L5R2 are configured to be a combination of a convex curved surface and a concave curved surface, respectively, the intermediate glass lens L5 and the first The lens system 1 can be made smaller by bringing the 6 lenses L6 close to each other. In particular, by making the radius of curvature Rb of the surface L6R1 larger than Ra, it becomes easy to bring them close to each other. At this time, by setting Rb / Ra in the above range, it is possible to easily correct the aberration while suppressing the occurrence of ghosts, as described above.

(6) In the intermediate glass lens L5, both L5R1 and L5R2 have a spherical shape. As a result, the intermediate glass lens L5 can be made inexpensive, and the entire lens system 1 can be made inexpensive.

(7) Further, the first lens L1 is a negative lens having a second surface R2 having a concave shape when viewed from the image side, and has a concave shape when viewed from the image side between the first lens L1 and the intermediate glass lens L5. A fourth lens having a second lens L2, which is a negative lens having a second surface R2, a third lens L3, which is a positive lens, and a second surface R2 having a convex shape toward the image side. A sixth lens L6 which is a negative lens having a second surface R2 which is sequentially provided with a lens L4 from an object side toward an image side and has a concave shape when viewed from the image side on the image side of the intermediate glass lens L5. And a seventh lens L7 having a first surface R1 having a convex shape toward the object side and a second surface R2 having a convex shape toward the image side, and the sixth lens L6 A bonded lens is formed in which the second surface R2 and the first surface R1 of the seventh lens L7 are bonded.
It was confirmed by Examples that ghosts are reduced by such a specific lens configuration.

(8) The first lens L1 is made of glass, and the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are made of a resin material. With such a configuration, while the first lens L1 exposed to the outside has high strength, each lens other than the first lens L1 and the intermediate glass lens L5 can be made inexpensive, and the reliability of the lens system 1 is enhanced. , This can be cheap.

Even in configurations other than the above examples, when an intermediate glass lens as described above is used, the reflected light of the infrared cut filter is incident on the optical system on the object side of the lens, and this is again the image plane ( It is suppressed toward the image sensor) side. Therefore, for example, the configuration of the lens on the object side and the image side of the intermediate glass lens is arbitrary. Further, the lens barrel accommodating the above lens system and the structure other than the optically functioning part of each lens, for example, the structure for fixing the lens to the lens barrel and the structure for fixing the positional relationship between the lenses are It is optional.

The present invention has been described based on an embodiment and a modified example thereof, but this embodiment is an example, and various modified examples are possible for the combination of each component thereof, and such a modified example is also described in the present invention. It will be understood by those skilled in the art that it is within the scope of the invention.

1 Lens system 20 Aperture 30 Shading plate 40 IR cut coating layer (infrared cut filter)
100 Image sensor 110 Cover glass A Optical axis Img image (side)
L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens (intermediate glass lens)
L6 6th lens L7 7th lens OA Object side optical system OB Image side optical system Obj Object (side)
R1 1st surface R2 2nd surface RL Reflected light

Claims (8)

Along the optical axis from the object side to the image side, a plurality of lenses including the first lens, which is the most object side, are laminated including the diaphragm, and are located on the image side of the lens located on the image side most. A lens system that forms an image of an image to be imaged on the image plane.
In an intermediate glass lens which is one of the lenses other than the first lens and is made of glass,
On one of the first surface, which is the surface on the object side, and the second surface, which is the surface on the image side, a thin-film infrared ray that blocks light having a wavelength longer than the light to be imaged is formed. A cut filter is formed,
When the radius of curvature of one of the surfaces is Ra,
2.00 ≦ | Ra ｜ ≦ 4.00
A lens system characterized by being in the range of. The lens system according to claim 1, wherein the aperture is arranged adjacent to the object side of the intermediate glass lens. The second aspect of the invention, wherein the first surface of the intermediate glass lens has a convex shape toward an object side, and the second surface of the intermediate glass lens has a convex shape toward an image side. Lens system. The intermediate glass lens is a lens other than the first lens and the lens closest to the image side.
When the radius of curvature of the surface of the intermediate glass lens facing the one surface of the adjacent lens on the side of the one surface is Rb,
1.20 << | Rb / Ra | <4.00
The lens system according to any one of claims 1 to 3, wherein the lens system is in the range of the above. The intermediate glass lens is a lens other than the first lens and the lens closest to the image side.
One surface of the intermediate glass lens has a convex shape.
When the surface of the intermediate glass lens facing the one surface of the adjacent lens on the side of the one surface is concave and the radius of curvature is Rb,
1.20 <Rb / Ra <4.00
The lens system according to any one of claims 1 to 3, wherein the lens system is in the range of the above. The lens system according to any one of claims 1 to 5, wherein both the first surface and the second surface of the intermediate glass lens have a spherical shape. In the plurality of lenses
The first lens is a negative lens having the second surface having a concave shape when viewed from the image side.
Between the first lens and the intermediate glass lens
A second lens, which is a negative lens having the second surface having a concave shape when viewed from the image side,
The third lens, which is a positive lens,
A fourth lens, which is a positive lens having the second surface having a convex shape toward the image side,
From the object side to the image side.
On the image side of the intermediate glass lens
A sixth lens, which is a negative lens having the second surface and has a concave shape when viewed from the image side,
A seventh lens having the first surface having a convex shape toward the object side and the second surface having a convex shape toward the image side are sequentially provided.
A bonded lens was formed in which the second surface of the sixth lens and the first surface of the seventh lens were bonded.
The lens system according to any one of claims 1 to 6, wherein the lens system is characterized by the above. The seventh aspect of claim 7, wherein the first lens is made of glass, and the second lens, the third lens, the fourth lens, the sixth lens, and the seventh lens are made of a resin material. Lens system.

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