JP2015127741A - Endoscope camera lens and endoscope camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endoscope camera lens of a small diameter capable of ensuring required optical performance at a low cost.SOLUTION: An endoscope camera lens 10 is constituted of a single structured lens 11 with a convex lens part 15 having a flat surface on a first plane at the object side and a convex aspheric surface on a second plane at the image side; and a cylindrical frame part 14 at the periphery thereof, which are integrally formed with each other. The endoscope camera lens 10 is arranged so that a waterproof glass 12 is bonded on the first plane of the lens 11 and a cover glass 22 of an imaging element 20 is bonded on the end face at the image side of the frame part 14 of the lens 11. The lens 11 is formed with the thickness of 0.3 mm or less; the refractive index nd on a d-line is 1.6 or less; and Abbe number νd calculated from an F-line, the d-line and a C-line is 55 or more.

Description

  The present invention relates to an endoscope camera lens and an endoscope camera.

  In recent years, surgery using an endoscopic camera has become widespread because the burden on patients is small. Furthermore, when using an endoscopic camera in a thin part, or for the use of an auxiliary camera that takes images from two or more locations in order to ensure endoscopic surgery, there is a need for an endoscopic camera with a further small diameter. It is growing. As a small-diameter endoscopic camera, for example, an ultra-thin camera having a diameter of about 1 mm has been required.

  When an ultra-thin diameter camera is configured, the processing of lens balls of the imaging optical system is limited to a diameter of about 1 mm, and thus usually has a lens configuration of about 3 to 4 lenses. For this reason, there exists a subject that the cost of a lens becomes high. In addition, since the optical total length with respect to the lens diameter becomes longer, the distortion aberration increases, and the focal length varies, so it is necessary to adjust the back focus for each individual lens at the time of assembly before bonding to the image sensor. Has a problem.

  In a conventional endoscope camera lens, in order to simplify the lens configuration as much as possible in order to reduce the diameter, a configuration having about three lenses, a diaphragm, and a lens barrel for storing the lens is generally used ( For example, see Patent Document 1). Further, as an example in which the optical performance is improved along with the reduction in the diameter of the lens, an endoscope objective optical system having a two-group configuration using four lenses is disclosed (Patent Document 2).

JP 2001-286436 A (FIGS. 1 and 10) International Publication No. 2013/071139 (Figure 1)

  A conventional endoscope camera lens having a small diameter has a problem that the number of lenses constituting the lens is large and glass is used as the material of the lens, which increases the cost. In addition, when the diameter is reduced, chromatic aberration, spherical aberration, and the like increase, and the required optical performance may not be satisfied. Further, in the configuration of a plurality of lenses, there is a problem that spherical aberration, chromatic aberration, and distortion become large because the optical total length becomes long.

  An object of the present invention is to provide a lens for an endoscope camera and an endoscope camera that can sufficiently obtain the required optical performance even at a small diameter at a low cost.

  The present invention has a one-piece structure in which a first surface on the object side has a flat surface, an aspherical convex surface on the second surface on the image side, and a cylindrical frame portion is integrally formed on the outer peripheral portion. There is provided an endoscope camera lens that is configured to be capable of bonding a waterproof glass on a first surface of the lens and an image sensor on an image side end surface of the lens frame.

  The present invention also includes an endoscope camera having the above-described endoscope camera lens and an image sensor, wherein a cover glass of the image sensor is bonded and fixed to an image side end surface of the frame portion of the lens. I will provide a.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a small diameter, the lens for endoscope cameras and endoscope camera which can fully obtain desired optical performance at low cost are realizable.

Sectional drawing which shows the structure of the lens for endoscope cameras which concerns on embodiment of this invention, and an endoscope camera A perspective view of an endoscope camera lens and an endoscope camera of the present embodiment FIG. 5 is a characteristic diagram showing the aberration of an endoscope camera lens as the optical characteristics of Example 1 Characteristic diagram showing MTF of an endoscope camera lens as an optical characteristic of Example 1 The characteristic view which shows the influence of the iris diaphragm in the lens for endoscope cameras of this embodiment Characteristic chart showing aberration of lens for endoscope camera as optical characteristic of embodiment 2 Characteristic diagram showing MTF of an endoscope camera lens as an optical characteristic of Example 2 Sectional drawing which shows the structure of the lens for endoscope cameras which concerns on the comparative example 1. The characteristic view which shows the aberration of the lens for endoscope cameras as an optical characteristic of the comparative example 1 The characteristic view which shows MTF of the lens for endoscope cameras as an optical characteristic of the comparative example 1 The characteristic view which shows the aberration of the lens for endoscope cameras as an optical characteristic of the comparative example 2 The characteristic view which shows MTF of the lens for endoscope cameras as an optical characteristic of the comparative example 2

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an endoscope camera lens and an endoscope camera according to the present invention (hereinafter referred to as “this embodiment”) will be described in detail with reference to the accompanying drawings.

  The endoscopic camera of the present embodiment is a thin camera used for surgery, for example, and constitutes an ultra-thin camera having an outer diameter of, for example, about 1 mm. The endoscopic camera of the present embodiment is suitable for use as an auxiliary camera that is used by being inserted into a thin site or that captures images from two or more locations in order to ensure endoscopic surgery. The lens for an endoscope camera according to this embodiment can be applied to an endoscope camera having a diameter of 2 mm or less.

  FIG. 1 is a cross-sectional view showing a configuration of an endoscope camera lens and an endoscope camera according to an embodiment of the present invention. FIG. 2 is a perspective view of the endoscope camera lens and the endoscope camera of the present embodiment.

  The endoscope camera includes an endoscope camera lens 10 as an imaging optical system, and an imaging element 20 such as a CMOS image sensor that captures a subject image formed by the endoscope camera lens 10.

  The endoscope camera lens 10 has a single lens 11 in which a cylindrical frame portion 14 on the outer peripheral portion and a convex lens portion 15 having a positive power on the center side are integrally formed. . A waterproof glass 12 is bonded and fixed to the object side (subject side, front side) of the lens 11, and a diaphragm 13 is provided between the lens 11 and the waterproof glass 12.

  In the lens 11, one surface (first surface) on the object side (subject side) is a flat surface, and the other surface (second surface) on the image side (imaging device side, rear) of the convex lens portion 15 is aspheric. It is convex. The lens 11 has a shape in which a cylindrical frame portion 14 is connected to an outer peripheral portion of a convex lens portion 15 having a flat outer surface toward the image side, and has a cylindrical shape with one end closed by a flat surface, and is a cross section cut in the optical axis direction. Is substantially U-shaped (U-shaped).

  The lens 11 has a single lens structure having a flat surface on the first surface on the object side and an aspheric convex surface on the second surface on the image side. However, in the outer structure of the lens 11, the entire surface of the first surface is provided. Is not limited to a continuous plane, and there may be different surfaces such as a curved surface and an inclined surface in the outer peripheral portion and the like. Further, the second surface on the image side of the lens 11 is formed in the convex lens portion 15 having an aspheric surface at the center side, and a frame portion 14 is formed in the outer peripheral portion, and therefore includes a surface different from the aspheric surface such as a flat surface. Yes.

  In the lens 11, the thickness of the convex lens portion 15 is 0.3 mm or less. The material of the lens 11 has a refractive index (nd) of d-line (yellow, wavelength of about 587 nm) of 1.6 or less, and F-line (blue, wavelength of about 486 nm), d-line and C-line (red, wavelength of about The Abbe number (νd) determined from 656 nm is 55 or more. Here, the “Abbe number” is a constant of the optical medium indicated by the ratio of the refractive index to the dispersion. The larger the Abbe number, the smaller the chromatic aberration. The angle of view of the lens 11 is 100 degrees or more, preferably 110 degrees or more. The detailed configuration of the lens 11 will be described later.

  As a material of the lens 11, for example, a transparent plastic material, more specifically, a heat-resistant acrylic resin is used. As the heat-resistant acrylic resin, for example, there is a resin having resistance to a temperature of up to about 117 degrees in a molded product. This type of plastic material can be injection-molded, and a lens having a very small diameter and a desired shape can be produced by molding. Note that other resin materials may be used as long as the same conditions are satisfied. Moreover, even if it is a glass material, if there exists what can be injection-molded, it is applicable.

  The waterproof glass 12 is a disk-shaped transparent glass member having a flat surface on both sides, and has a protection function and a waterproof function for the lens 11. The waterproof glass 12 is attached and fixed to the lens 11 with one surface (rear end surface) adhered to the object-side surface of the lens 11.

  The diaphragm 13 has, for example, a circular opening, allows light in the central part including the optical axis to pass therethrough, and blocks light in the peripheral part. In the present embodiment, the diaphragm 13 is disposed on the waterproof glass 12 by providing the diaphragm 13 on the lens 11 side surface (rear end surface) of the waterproof glass 12 using, for example, a thin plate or a thin film. As a specific example of the diaphragm 13, it is formed of a stainless steel (SUS) thin plate and bonded to the waterproof glass 12. In addition, as another configuration example, a configuration in which the film-like diaphragm 13 is disposed by being bonded to the waterproof glass 12 and provided between the lens 11 may be used.

  The imaging device 20 includes an imaging chip 21 made of a CMOS image sensor or the like, and a cover glass 22 provided on the imaging surface side of the imaging chip 21. The imaging chip 21 is configured by a semiconductor chip whose imaging surface is square, for example. The cover glass 22 is a rectangular plate-like transparent glass member having a flat surface on both sides, and has a protection function for the imaging chip 21.

  The image-side end surface of the frame portion 14 of the lens 11 and the lens-side surface of the cover glass 22 are bonded, and the endoscope camera lens 10 and the image sensor 20 are attached and fixed, so that the endoscope camera An imaging unit is configured. When the endoscope camera lens 10 and the image sensor 20 are attached, the diaphragm position of the endoscope camera lens 10 is adjusted while displaying the output of the image sensor 20 and displaying the image. The image sensor 20 is bonded to the camera lens 10.

  As an assembly procedure of the lens for the endoscope camera, first, the positions of the imaging surfaces of the lens 11 and the imaging device 20 are aligned, the image side end surface of the frame portion 14 of the lens 11, the cover glass 22 of the imaging device 20, May be adhered and fixed. In this case, secondly, the imaging optical system is centered by adjusting the position of the diaphragm 13 provided in the waterproof glass 12 while confirming the captured image by imaging from the imaging element 20. The object side plane and the image side end surface of the waterproof glass 12 may be bonded and fixed.

  Below, some specific structural examples are illustrated about the lens 10 for endoscope cameras which concerns on this embodiment.

<Example 1>
As Example 1, a first example of the configuration of an endoscope camera lens 10 is shown.

[Lens data]
Focal length f = 0.5 mm, F-number = 3.5, aperture diameter Da = 0.15 mm, image height = 0.5 mm, field angle = 110 degrees, object distance = ∞

Surface number Curvature radius r (mm) Distance d (mm) Refractive index n Abbe number ν
1 r1 = ∞ d1 = 0.2 n1 = 1.5168 ν1 = 64.1
2 r2 = ∞ d2 = 0
3 r3 = ∞ d3 = 0.2 n2 = 1.4941 ν2 = 58.1
4 r4 = −0.25 d4 = 0.24
(Aspherical)
5 r5 = ∞ d5 = 0.4 n3 = 1.5168 ν3 = 64.1
6 r6 = ∞ d6 = 0
7 Imaging surface

(1) About waterproof glass 12 The front end surface of the waterproof glass 12 is surface number 1, the rear end surface of the lens 11 side is surface number 2, the refractive index of the waterproof glass 12 is n1, and the Abbe number is ν1. And the thickness of the waterproof glass 12 is d1, and the space | interval of the waterproof glass 12 and the lens 11 is d2. That is, the waterproof glass 12 has a thickness d1 = 0.2 mm, a refractive index n1 = 1.5168, and an Abbe number ν1 = 64.1.

(2) Lens 11 The object side (waterproof glass 12 side) surface (front end surface) of lens 11 is surface number 3, the image side (imaging device 20 side) surface (rear end surface) is surface number 4, and the lens The refractive index of 11 is n2, and the Abbe number is ν2. The thickness of the convex lens portion 15 of the lens 11 is d3, and the distance between the convex lens portion 15 of the lens 11 and the cover glass 22 is d4. That is, the lens 11 has a thickness d3 = 0.2 mm, a refractive index n2 = 1.4941, and an Abbe number ν2 = 58.1. The first surface (surface number 3) of the lens 11 is a flat surface with an infinite curvature radius r3. In Example 1, a heat-resistant acrylic resin material is used as the lens material. The outer diameter of the lens 11 including the frame portion 14 is Φ1.0 mm.

  In the lens 11, the radius of curvature r4 of the second aspheric surface (surface number 4) is defined by the aspherical surface definition formula Z expressed by the following formula (1), and the radius of curvature r4 on the optical axis is -0.25. It is.

Z = [ch ² / {1 + √ (1− (1 + K) c ² h ² )}] + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰
... (1)
Here, the constants are K = 0, A = 0.15884 × 10 ⁻² , B = −0.1974 × 10 ⁻³ , C = 0, D = 0, c = 1 / r, h = image. High (radial direction).

(3) Cover Glass 22 The surface 11 of the cover glass 22 on the lens 11 side is surface number 5, the surface on the imaging chip 21 side is surface number 6, the refractive index of the cover glass 22 is n3, and the Abbe number is ν3. The thickness of the cover glass 22 is d5, and the distance between the cover glass 22 and the imaging chip 21 is d6. That is, the cover glass 22 has a thickness d5 = 0.4 mm, a refractive index n3 = 1.5168, and an Abbe number ν3 = 64.1. In this embodiment, the same glass material is used for the waterproof glass 12 and the cover glass 22.

  FIG. 3 is a characteristic diagram showing the aberration of the lens for an endoscope camera as the optical characteristic of Example 1, (A) shows spherical aberration, (B) shows astigmatism, and (C) shows distortion aberration. ing. Here, the spherical aberration corresponds to the characteristic of the d-line (wavelength 587.6 nm) in FIG. 3A, and the axial chromatic aberration is the characteristic of the F-line (wavelength 486.1 nm) in FIG. And the difference between the characteristics of C-line (wavelength 656.3 nm). In FIG. 3 (B) astigmatism, R represents radial characteristics and T represents tangential characteristics.

  FIG. 4 is a characteristic diagram showing MTF (Modulation Transfer Function) of the lens for an endoscope camera as the optical characteristics of Example 1, and the image height with respect to the spatial frequency is 0% (effective image height ratio 0.0, on the optical axis). ) Each MTF in the case of 40% (0.4), 80% (0.8), and 10% (1.0) is shown. In the MTF of FIG. 4, the image height of 0% (on the optical axis) corresponds to the center characteristic (center MTF), and the image height of 80% (0.8) corresponds to the periphery characteristic (peripheral MTF). Represents radial characteristics, and T represents tangential characteristics in each direction.

  As shown in FIGS. 3 and 4, the endoscope camera lens of Example 1 has spherical aberration, chromatic aberration, distortion, and MTF even when the angle of view is 100 degrees or more (110 degrees in this example). For each, sufficient optical properties are obtained for use in an endoscope. Specifically, the spherical aberration is −0.008 mm or less, and the longitudinal chromatic aberration is −0.008 mm or less. Although not shown, the lateral chromatic aberration is −0.004 mm or less. The distortion is 30% or less. The MTF has a center MTF of 72% and a peripheral MTF of 20% at a spatial frequency of 100 (cycles / mm).

  In Example 1, an acrylic resin material having a refractive index n3 = 1.4941 and an Abbe number ν3 = 58.1 is used, but the refractive index nd of d-line is 1.5 or less, and F-line and d-line. The Abbe number νd obtained from the C line is not limited to 58 or more, and if nd ≦ 1.6 and νd ≧ 55, practically sufficient optical characteristics can be obtained.

  FIG. 5 is a characteristic diagram showing the influence of the diaphragm in the endoscope camera lens of the present embodiment, and shows changes in the peripheral MTF and the peripheral light amount with respect to the thickness of the diaphragm.

  In the present embodiment, the diaphragm 13 has a thickness of 20 ± 10 μm. Although the peripheral MTF increases as the diaphragm thickness increases, wavefront aberration occurs when the diaphragm is too thick. Further, as the thickness of the stop increases, the peripheral light amount decreases and the peripheral portion becomes dark. By setting the thickness of the diaphragm 13 to 20 ± 10 μm, the influence of the thickness of the diaphragm 13 can be minimized. In Example 1, the diaphragm 13 having a thickness of 20 μm is formed by a thin plate of stainless steel (SUS).

<Example 2>
Example 2 shows an example in which the thickness of the lens 11 in Example 1 is changed to 0.3 mm as a second example of the configuration of the endoscope camera lens 10.

[Lens data]
Focal length f = 0.5 mm, F-number = 3.5, aperture diameter Da = 0.15 mm, image height = 0.5 mm, field angle = 110 degrees, object distance = ∞

Surface number Curvature radius r (mm) Distance d (mm) Refractive index n Abbe number ν
1 r1 = ∞ d1 = 0.2 n1 = 1.5168 ν1 = 64.1
2 r2 = ∞ d2 = 0
3 r3 = ∞ d3 = 0.3 n2 = 1.4941 ν2 = 58.1
4 r4 = −0.25 d4 = 0.24
(Aspherical)
5 r5 = ∞ d5 = 0.4 n3 = 1.5168 ν3 = 64.1
6 r6 = ∞ d6 = 0
7 Imaging surface

(1) About waterproof glass 12 It is the same as Example 1.

(2) Lens 11 The lens 11 has a thickness d3 = 0.3 mm, a refractive index n2 = 1.4941, and an Abbe number ν2 = 58.1.

In the lens 11, the radius of curvature r4 of the second aspherical surface (surface number 4) is defined by the aspherical surface defining formula Z expressed by the above mathematical formula (1) as in the first embodiment, and the radius of curvature on the optical axis. r4 is -0.25. However, in Example 2, the constants in Equation (1) are K = 0, A = 0.7573 × 10 ⁻¹ , B = −0.4202 × 10 ⁻² , C = 0, and D = 0. .

(3) Cover glass 22 The same as in the first embodiment.

  FIG. 6 is a characteristic diagram showing the aberration of the endoscope camera lens as the optical characteristics of Example 2, where (A) shows spherical aberration, (B) shows astigmatism, and (C) shows distortion. ing. Here, the spherical aberration corresponds to the characteristic of the d-line (wavelength 587.6 nm) in FIG. 6A, and the axial chromatic aberration is the characteristic of the F-line (wavelength 486.1 nm) in FIG. And the difference between the characteristics of C-line (wavelength 656.3 nm). In the astigmatism shown in FIG. 6B, R represents radial characteristics and T represents tangential characteristics.

  FIG. 7 is a characteristic diagram showing the MTF of the lens for an endoscope camera as the optical characteristics of Example 2, and the image height with respect to the spatial frequency is 0% (effective image height ratio 0.0, on the optical axis), 40% ( 0.4), 80% (0.8), and 10% (1.0). In the MTF of FIG. 7, the image height of 0% (on the optical axis) corresponds to the center characteristic (center MTF), and the image height of 80% (0.8) corresponds to the peripheral characteristic (peripheral MTF). Represents radial characteristics, and T represents tangential characteristics in each direction.

  As shown in FIGS. 6 and 7, the endoscope camera lens of Example 2 has spherical aberration, chromatic aberration, distortion, and MTF even when the angle of view is 100 degrees or more (110 degrees in this example). For each, sufficient optical properties are obtained for use in an endoscope. The spherical aberration is -0.025 mm or less, which is inferior to that of Example 1, but is a sufficient characteristic for practical use. The longitudinal chromatic aberration is −0.008 mm or less, the lateral chromatic aberration is −0.005 mm or less (not shown), and the distortion is 30% or less. The MTF has a center MTF of 65% and a peripheral MTF of 11% at a spatial frequency of 100 (cycles / mm). Although the peripheral MTF is inferior to that of the first embodiment, it is a practically sufficient characteristic.

<Comparative Example 1>
As a comparative example 1 with respect to the example of the present embodiment, a configuration of an endoscope camera lens having a general three-lens configuration lens is shown.

  FIG. 8 is a cross-sectional view illustrating a configuration of an endoscope camera lens according to Comparative Example 1. The endoscope camera of Comparative Example 1 includes an endoscope camera lens 50 and an imaging element 60 such as a CMOS image sensor that captures a subject image formed by the endoscope camera lens 50.

  An endoscope camera lens 50 includes a first lens 51 having a concave surface and the other surface being flat, a second lens 52 having a flat surface and the other surface being convex, and a third lens having both surfaces convex. 53. A waterproof glass 54 is bonded and fixed to the object side (subject side, front side) of the first lens 51. A diaphragm 55 is provided between the first lens 51 and the second lens 52, and the first lens 51, the second lens 52, the third lens 53, and the diaphragm 55 are housed and fixed inside the lens barrel 56. .

  The imaging element 60 includes an imaging chip 61 made of a CMOS image sensor or the like, and a cover glass 62 provided on the imaging surface side of the imaging chip 61. The endoscope camera lens 50 and the image sensor 60 are subjected to back focus adjustment for each lens, and then the image side end surface (image sensor side, rear side) of the lens barrel 56 and the lens side surface of the cover glass 62. Is glued. Thereby, the endoscope camera lens 50 and the imaging device 60 are attached and fixed, and the imaging unit of the endoscope camera is configured.

[Lens data]
Focal length f = 0.65 mm, F-number = 3.5, image height = 0.5 mm, angle of view = 110 degrees, object distance = ∞

Surface number Curvature radius r (mm) Distance d (mm) Refractive index n Abbe number ν
1 r1 = ∞ d1 = 0.25 n1 = 1.5168 ν1 = 64.1
2 r2 = ∞ d2 = 0.1
3 r3 = −1.0 d3 = 0.57 n2 = 1.8540 ν2 = 40.4
4 r4 = ∞ d4 = 0.05
5 r5 = ∞ d5 = 0.55 n3 = 1.8100 ν3 = 41.0
6 r6 = −0.65 d6 = 0.0
(Aspherical)
7 r7 = + 1.0 d7 = 0.6 n4 = 1.72020 ν4 = 50.0
(Aspherical)
8 r8 = + 0.8 d8 = 0.23
(Aspherical)
9 r9 = ∞ d9 = 0.4 n5 = 1.5168 ν5 = 64.1
10 r10 = ∞ d10 = 0
11 Imaging surface

(1) Waterproof Glass 54 The front end surface of the waterproof glass 54 is surface number 1, the rear end surface of the first lens 51 side is surface number 2, the refractive index of the waterproof glass 54 is n1, and the Abbe number is ν1. The thickness of the waterproof glass 54 is d1, and the distance between the waterproof glass 54 and the first lens 51 is d2. That is, the waterproof glass 54 has a wall thickness d1 = 0.25 mm, a refractive index n1 = 1.5168, and an Abbe number ν1 = 64.1.

(2) Regarding the first lens 51 The surface of the first lens 51 on the object side (waterproof glass 54 side) is surface number 3, the surface of the second lens 52 side is surface number 4, and the refractive index of the first lens 51 is n2 and Abbe number is ν2. The thickness of the first lens 51 is d3, and the distance between the first lens 51 and the second lens 52 is d4. That is, the first lens 51 has a thickness d3 = 0.57 mm, a refractive index n2 = 1.8540, and an Abbe number ν2 = 40.4. In the first lens 51, the first surface (surface number 3) is a concave surface with a radius of curvature r = −1.0, and the second surface (surface number 4) is a plane with an infinite curvature radius r4.

(3) About the second lens 52 The surface of the second lens 52 on the first lens 51 side is surface number 5, the surface of the third lens 53 side is surface number 6, and the refractive index of the second lens 52 is n3. The number is ν3. The thickness of the second lens 52 is d5, and the distance between the second lens 52 and the third lens 53 is d6. That is, the second lens 52 has a thickness d5 = 0.55 mm, a refractive index n3 = 1.8100, and an Abbe number ν3 = 41.0. In the second lens 52, the first surface (surface number 5) is a plane with an infinite curvature radius r5, and the curvature radius r6 of the aspherical second surface (surface number 6) is expressed by the above equation (1). It is defined by the aspherical definition formula Z shown, and the radius of curvature r6 at the optical axis is -0.65. However, each constant in Formula (1) is K = 0, A = 0.1000 × 10 ⁻⁴ , B = 0, C = 0, and D = 0.

(4) About the third lens 53 The surface of the third lens 53 on the second lens 52 side is surface number 7, the surface of the image sensor 60 side is surface number 8, the refractive index of the third lens 53 is n4, and the Abbe number. Is ν4. The thickness of the third lens 53 is d7, and the distance between the third lens 53 and the cover glass 62 is d8. That is, the third lens 53 has a thickness d7 = 0.6 mm, a refractive index n4 = 1.7720, and an Abbe number ν4 = 50.0. In the third lens 53, the radius of curvature r7 of the first aspheric surface (surface number 7) and the radius of curvature r8 of the second surface (surface number 8) are defined by the aspherical surface defined by the above equation (1). Defined by Z. The curvature radius r7 is the curvature radius r7 on the optical axis, and the constants in the formula (1) are K = 0, A = −0.301963 × 10 ⁻¹ , B = −0.364008 × 10, respectively. ^-0 , C = 0, D = 0. The radius of curvature r8 is the radius of curvature r8 on the optical axis is +0.8, and the constants in the equation (1) are K = 0, A = 0.2200094 × 10 ⁻⁰ , B = −0.287774 × 10 ⁻¹ , C = 0, D = 0.

(5) Cover glass 62 The surface of the cover glass 62 on the third lens 53 side is surface number 9, the surface of the imaging chip 61 side is surface number 10, the refractive index of the cover glass 62 is n5, and the Abbe number is ν5. is there. The thickness of the cover glass 62 is d9, and the distance between the cover glass 62 and the imaging chip 61 is d10. That is, the cover glass 62 has a thickness d9 = 0.4 mm, a refractive index n5 = 1.5168, and an Abbe number ν3 = 64.1.

  In Comparative Example 1, different glass materials are used for the first lens 51, the second lens 52, and the third lens 53, respectively. Further, the waterproof glass 54 and the cover glass 62 are made of the same glass material.

  FIG. 9 is a characteristic diagram showing the aberration of the endoscope camera lens 50 as the optical characteristics of Comparative Example 1, where (A) shows spherical aberration, (B) shows astigmatism, and (C) shows distortion. Show. Here, the spherical aberration corresponds to the characteristic of the d-line (wavelength 587.6 nm) in FIG. 9A, and the axial chromatic aberration is the characteristic of the F-line (wavelength 486.1 nm) in FIG. And the difference between the characteristics of C-line (wavelength 656.3 nm). In the astigmatism of FIG. 9B, R represents radial characteristics and T represents tangential characteristics.

  FIG. 10 is a characteristic diagram showing the MTF of the endoscope camera lens 50 as the optical characteristics of Comparative Example 1, with an image height of 0% (effective image height ratio 0.0, on the optical axis) and 40% of the spatial frequency. Each MTF in the case of (0.4), 80% (0.8), and 10% (1.0) is shown. In the MTF of FIG. 10, the image height of 0% (on the optical axis) corresponds to the center characteristic (center MTF), and the image height of 80% (0.8) corresponds to the peripheral characteristic (peripheral MTF). Represents radial characteristics, and T represents tangential characteristics in each direction.

  As shown in FIGS. 9 and 10, the optical camera lens of Comparative Example 1 is partially degraded in optical characteristics as compared to Example 1. The spherical aberration is −0.04 mm or less, the longitudinal chromatic aberration is −0.025 mm or less, the lateral chromatic aberration is −0.008 mm or less (not shown), and a color shift of 2 pixels (8 μm) or more occurs. Distortion is 50% or less, and the TV resolution at the periphery is about half. The MTF has a center MTF of 50%, which is worse than that of the first embodiment at a spatial frequency of 100 (cycle / mm), but the peripheral MTF is 30%, which is a better value than that of the first embodiment.

  Table 1 shows a list of optical characteristics of Example 1 and Comparative Example 1 described above.

  Example 1 according to the present embodiment has a configuration in which the number of lenses is one in one group. Compared to the configuration in three groups of three in Comparative Example 1, a small-sized endoscope camera lens can be realized. . In Example 1, the total track (distance from the object side surface of the waterproof glass to the imaging surface of the image sensor) and the front lens effective diameter (effective diameter of the waterproof glass) are both less than half of those in Comparative Example 1. is there.

  In addition, since the first embodiment includes a cylindrical frame portion in one lens, the configuration is simple and does not require a lens barrel, and further cost reduction can be realized. It is only necessary to adhere to the cover glass of the element, and assembly is easy. On the other hand, in Comparative Example 1, a lens barrel that houses three lenses is required, and assembly accuracy is required to obtain predetermined optical performance.

  Regarding the lens aberration, the endoscope camera lens of Example 1 has smaller spherical aberration, chromatic aberration, and distortion than the three-lens configuration lens shown in Comparative Example 1, and the MTF except for the image height of 100%. Almost the same performance is obtained. The decentering peripheral MTF shows the peripheral MTF when the lens center is decentered by shifting by 10 μm. Since the endoscope camera lens of Example 1 has small chromatic aberration, an achromatic lens is unnecessary, and sufficient optical performance can be obtained with a single lens.

  As for the peripheral light amount ratio, Comparative Example 1 is 62% and the light amount suddenly decreases and darkens in the peripheral portion, but Example 1 is 58% and gradually decreases from the center toward the periphery. It is difficult to perceive a decrease in ambient light.

<Comparative Example 2>
As a comparative example 2 with respect to the example of the present embodiment, an example in which the Abbe number of the lens 11 in the example 1 is changed to about 30 is shown.

[Lens data]
Focal length f = 0.5 mm, F-number = 3.5, aperture diameter Da = 0.15 mm, image height = 0.5 mm, field angle = 110 degrees, object distance = ∞

Surface number Curvature radius r (mm) Distance d (mm) Refractive index n Abbe number ν
1 r1 = ∞ d1 = 0.2 n1 = 1.5168 ν1 = 64.1
2 r2 = ∞ d2 = 0
3 r3 = ∞ d3 = 0.2 n2 = 1.5855 ν2 = 29.9
4 r4 = −0.29 d4 = 0.23
(Aspherical)
5 r5 = ∞ d5 = 0.4 n3 = 1.5168 ν3 = 64.1
6 r6 = ∞ d6 = 0
7 Imaging surface

(1) About waterproof glass 12 It is the same as Example 1.

(2) Lens 11 The lens 11 has a thickness d3 = 0.2 mm, a refractive index n2 = 1.5855, and an Abbe number ν2 = 29.9. In Comparative Example 2, a polycarbonate resin material is used as the lens material.

In the lens 11, the radius of curvature r4 of the second aspherical surface (surface number 4) is defined by the aspherical surface defining formula Z expressed by the above mathematical formula (1) as in the first embodiment, and the radius of curvature on the optical axis. r4 is -0.29. However, in Example 3, the constants in Equation (1) are K = 0, A = 0.1865 × 10 ⁻² , B = −0.3124 × 10 ⁻³ , C = 0, and D = 0. .

(3) Cover glass 22 The same as in the first embodiment.

  FIG. 11 is a characteristic diagram showing the aberration of an endoscope camera lens as the optical characteristics of Comparative Example 2, wherein (A) shows spherical aberration, (B) shows astigmatism, and (C) shows distortion. ing. Here, the spherical aberration corresponds to the characteristic of the d-line (wavelength 587.6 nm) in FIG. 11A, and the axial chromatic aberration is the characteristic of the F-line (wavelength 486.1 nm) in FIG. And the difference between the characteristics of C-line (wavelength 656.3 nm). In the astigmatism shown in FIG. 11B, R represents radial characteristics and T represents tangential characteristics.

  FIG. 12 is a characteristic diagram showing the MTF of the endoscope camera lens as the optical characteristic of Comparative Example 2, with an image height of 0% (effective image height ratio 0.0, on the optical axis) and 40% ( 0.4), 80% (0.8), and 10% (1.0). In the MTF of FIG. 12, the image height of 0% (on the optical axis) corresponds to the center characteristic (center MTF), and the image height of 80% (0.8) corresponds to the peripheral characteristic (peripheral MTF). Represents radial characteristics, and T represents tangential characteristics in each direction.

  As shown in FIGS. 11 and 12, the optical camera lens of Comparative Example 2 is partially degraded in optical characteristics as compared with Example 1. The spherical aberration is +0.012 mm or less, the axial chromatic aberration is −0.017 mm or less, the lateral chromatic aberration is −0.005 mm or less (not shown), and a color shift of 1 pixel (4 μm) or more occurs. The distortion is equal to or less than that of Example 1 at 30% or less. The MTF has a center MTF of 70% at the spatial frequency 100 (cycles / mm), which is the same as that of the first embodiment, but the peripheral MTF is greatly deteriorated to 7%, and the image height is 40% (0.4) and 21%. However, there is a problem in practical use.

  Table 2 shows a list of optical characteristics of each of the examples 1, 2 and comparative example 2 described above.

  As in Example 1 and Example 2, the thickness of a single lens is 0.3 mm or less, and the Abbe number νd obtained from the F line, d line, and C line is 55 or more, preferably 58 or more. Thus, spherical aberration, chromatic aberration, and distortion are reduced, and practically sufficient optical characteristics can be obtained. As in Comparative Example 2, when the Abbe number νd is as small as about 30, even if the lens configuration is the same, the chromatic aberration is particularly deteriorated to cause a color shift, and the peripheral MTF is also deteriorated, which hinders practical use.

  As described above, the endoscope camera lens according to the present embodiment has a single lens configuration, the object-side first surface is a plane, the image-side second surface is an aspheric surface, and the outer periphery is cylindrical. The shape has a frame shape. The front side of the lens is bonded to the waterproof glass, and the rear side is bonded to the cover glass of the image sensor. According to this configuration, a low-cost ultra-thin camera lens can be provided even when the angle of view is a wide angle of 100 degrees or more. Also, a high-performance ultra-thin camera lens having a smaller diameter and a shorter optical total length than conventional ones, for example, having a spherical aberration, a chromatic aberration, and a distortion aberration can be provided even when the diameter is about 1 mm. In addition, since there is one lens and the number of curved surfaces is one, there is little variation in focal length, and back focus adjustment during assembly is unnecessary.

  Further, the thickness of a single lens is 0.3 mm or less (≦ 0.3 mm), the refractive index nd of d line is 1.6 or less (nd ≦ 1.6), F line, d line and C line. The Abbe number νd obtained from the equation (1) is 55 or more (νd ≧ 55). As a lens material that satisfies this condition, for example, a plastic material such as a heat-resistant acrylic resin is used. By setting the lens thickness thin, resolution degradation can be reduced, and spherical aberration and distortion can be reduced. Further, by setting the refractive index of the lens low, the lens material can be formed of plastic and can be manufactured at low cost. Also, chromatic aberration can be reduced by setting the Abbe number of the lens high. According to this configuration, it is possible to provide an ultra-thin camera lens with small aberration and low cost even when the angle of view is 100 degrees or more.

  In the present embodiment, the diaphragm is formed on one surface of the waterproof glass, and the waterproof glass is adhered to the lens by adjusting the position of the diaphragm while performing imaging. According to this configuration, it is not necessary to form a diaphragm with high accuracy in accordance with the optical axis of the lens, and a low-cost ultra-thin camera lens can be provided.

  In the present embodiment, the diaphragm thickness is 20 ± 10 μm. According to this configuration, the peripheral MTF can be increased without significantly reducing the peripheral light amount, and a low-cost ultra-thin camera lens can be provided.

  As described above, according to the present embodiment, it is possible to realize an endoscope camera lens having a small diameter and an inexpensive diameter. In addition, since the number of lenses for the endoscope camera lens can be configured by one and the lens material can be formed of plastic, the manufacturing cost can be drastically reduced. This embodiment is particularly suitable for a wide-angle lens of a surgical ultra-thin diameter camera that can be disposable.

  When the endoscope camera lens and the endoscope camera of the present embodiment are applied to an ultra-thin camera for surgery, an endoscope with a small diameter formed in a slender cable shape (soft) or a rod shape (hardness). An endoscope camera lens and an endoscope camera are provided at the distal end of the insertion portion toward the front of the distal end surface. In the case where the endoscope camera is configured to include an illumination unit, for example, at the distal end portion of the endoscope, a light guide formed of an optical fiber or the like is provided around the outer periphery of the lens for the endoscope camera along the outer periphery of the lens. Arranged so that the object can be illuminated.

  Hereinafter, the configuration, operation, and effects of the above-described endoscope camera lens and endoscope camera according to the present invention will be described.

The lens for an endoscope camera according to one embodiment of the present invention has a flat surface on the first surface on the object side and an aspheric convex surface on the second surface on the image side, and a cylindrical frame portion on the outer peripheral portion. Are integrally formed, a waterproof glass is provided on the first surface of the lens, and an imaging element is provided on the image side end surface of the frame portion of the lens.
According to this configuration, an inexpensive and small-diameter endoscope camera lens can be provided.

In the endoscope camera lens of one embodiment of the present invention, the lens has a thickness of 0.3 mm or less.
According to this configuration, the spherical aberration and distortion can be reduced by setting the lens thickness thin.

In the endoscope camera lens of one embodiment of the present invention, the d-line refractive index nd is 1.6 or less, and the Abbe number νd obtained from the F-line, d-line, and C-line is 55 or more. is there.
According to this configuration, since the refractive index of the lens is set low, the lens material can be formed of, for example, plastic, and a small-diameter lens can be manufactured at low cost. Further, the chromatic aberration can be reduced by setting the Abbe number of the lens high. Therefore, it is possible to provide an endoscope camera lens with a small diameter and a small aberration.

In the endoscope camera lens of one embodiment of the present invention, the lens has an angle of view of 100 degrees or more.
According to this configuration, even for a wide-angle lens, an endoscope camera lens with a small diameter and a small aberration can be provided.

In the endoscope camera lens of one embodiment of the present invention, waterproof glass is bonded and fixed to the first surface of the lens, and the waterproof glass has a diaphragm disposed on the lens side surface.
According to this configuration, it is not necessary to form a diaphragm with high accuracy in accordance with the optical axis of the lens, and it is possible to provide an endoscope camera lens with good assembling workability and low cost.

In the endoscope camera lens of one embodiment of the present invention, the diaphragm has a thickness of 20 ± 10 μm.
According to this configuration, the peripheral MTF can be increased without significantly reducing the peripheral light amount, and the influence of the diaphragm thickness can be minimized. Therefore, it is possible to provide an endoscope camera lens with a small diameter and a small aberration.

An endoscope camera according to an aspect of the present invention includes any one of the above-described endoscope camera lenses and an image sensor, and a cover glass of the image sensor on an image side end surface of a frame portion of the lens. Is fixed by bonding.
According to this configuration, an inexpensive endoscope camera having a small diameter can be provided.

  While various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood. In addition, the constituent elements in the above-described embodiment may be arbitrarily combined without departing from the spirit of the invention.

  INDUSTRIAL APPLICABILITY The present invention has an effect that a desired optical performance can be sufficiently obtained even at a small diameter at a low cost, and is useful as, for example, a lens for a small-diameter endoscope camera and an endoscope camera used for surgery. is there.

DESCRIPTION OF SYMBOLS 10 Endoscope camera lens 11 Lens 12 Waterproof glass 13 Aperture 14 Frame part 15 Convex lens part 20 Imaging element 21 Imaging chip 22 Cover glass

Claims (7)

  It has a single lens with a flat surface on the first surface on the object side, an aspherical convex surface on the second surface on the image side, and a cylindrical frame portion integrally formed on the outer periphery. An endoscope camera lens configured such that a waterproof glass can be bonded to the first surface of the lens and an image sensor can be bonded to an image side end surface of the frame portion of the lens.   The lens for an endoscope camera according to claim 1, wherein the lens has a thickness of 0.3 mm or less.   The lens for an endoscope camera according to claim 2, wherein the lens has a refractive index nd of d line of 1.6 or less, and an Abbe number νd obtained from F line, d line, and C line of 55 or more.   The endoscope lens according to claim 2 or 3, wherein the lens has an angle of view of 100 degrees or more.   5. The endoscope camera according to claim 1, wherein a waterproof glass is bonded and fixed to a first surface of the lens, and a diaphragm is disposed on the lens-side surface of the waterproof glass. lens.   The lens for an endoscope camera according to claim 5, wherein the diaphragm has a thickness of 20 ± 10 μm. An endoscope camera lens according to any one of claims 1 to 6 and an imaging device, wherein a cover glass of the imaging device is bonded and fixed to an image side end surface of the frame portion of the lens. An endoscopic camera.

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