Optical system and imaging apparatus

Abstract

To provide an optical system and an optical device capable of inhibiting a focal point from displacing due to temperature changes.SOLUTION: An optical system 4 comprises: a first lens 10 having positive refractive power; a second lens 20 having negative refractive power; a third lens 30 having positive refractive power; a diaphragm 90 in which an opening is formed; a fourth lens 40 having positive refractive power; a fifth lens 50 having positive refractive power; a sixth lens 60 having negative refractive power; and a seventh lens 70 including an aspherical front lens surface 70F and an aspherical rear lens surface 70R. A rear lens surface 50R of the fifth lens 50 and a front lens surface 60F of the sixth lens 60 are bonded to each other. Refractive index temperature coefficient of the fourth lens 40 to light of 587.6 nm wavelength at 20°C is 0.2×10-6 / °C or less. When focal distance of the entire optical system 4 is denoted by f, and focal distance of the fourth lens 40 is denoted by f4, f4 / f<2.8 is satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system and an imaging device.

Background Art

[0002] For example, the outside or inside of an automobile is photographed by a camera, and various controls and processes are performed based on the photographed image. In the optical system used in such a camera, high resolution is required in a wide temperature environment ranging from low temperature (for example, -40°C) to high temperature (for example, +85°C). However, if the focus of the optical system is shifted due to a change in the ambient temperature, the resolution will decrease. Therefore, in order to maintain high resolution in a wide temperature environment, an optical system with less focus shift due to ambient temperature changes is required.

[0003] As an optical system with less focus shift due to such temperature changes, a lens having a positive refractive power is arranged in front of the aperture, and glass is used as the material of this lens (see, for example, Patent Document 1). In the optical system proposed in this Patent Document 1, it is said that the focus shift can be suppressed from -15 μm to 20 μm (see FIGS. 2 and 3). However, in recent years, the high definition of imaging elements has been progressing, and even a focus shift of about -15 μm to 20 μm has a non-negligible effect on the resolution. Therefore, an optical system that can further suppress the focus shift due to temperature changes is required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an optical system capable of suppressing a shift in focus with respect to temperature changes and an imaging device including such an optical system.

Means for Solving the Problems

[0006] According to a first aspect of the present invention, there is provided an optical system capable of suppressing a shift in focus with respect to temperature changes. This optical system includes a front lens surface convex on the object side and a rear lens surface concave on the image plane side, which are arranged in order from the object side to the image plane side along the optical axis, and a first lens having a negative refractive power; a front lens surface concave on the object side and a rear lens surface convex on the image plane side, and a second lens having a negative refractive power; a front lens surface convex on the object side and a rear lens surface convex on the image plane side, and a third lens having a positive refractive power; a diaphragm provided with an aperture; a front lens surface convex on the object side and a rear lens surface convex on the image plane side, and a fourth lens having a positive refractive power; a front lens surface convex on the object side and a rear lens surface convex on the image plane side, and a fifth lens having a positive refractive power; a front lens surface concave on the object side and a rear lens surface convex on the image plane side, and a sixth lens having a negative refractive power; and a seventh lens including an aspherical front lens surface and an aspherical rear lens surface. The rear lens surface of the fifth lens and the front lens surface of the sixth lens are joined to each other. The refractive index temperature coefficient of the fourth lens with respect to light having a wavelength of 587.6 nm at 20°C is 0.2×10 -6 / °C or less. When the focal length of the entire optical system is f and the focal length of the fourth lens is f4, f4 / f < 2.8 is satisfied.

[0007] According to a second aspect of the present invention, there is provided an imaging device including an optical system capable of suppressing a shift in focus with respect to temperature changes and an imaging element arranged on the image plane.

Effects of the Invention

[0008] According to the present invention, an optical system with a small focus shift with respect to temperature changes can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 5A

Figure 5B

Figure 5C

Figure 6A

Figure 6B

Figure 6C

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the optical system and the imaging device according to the present invention will be described in detail with reference to FIGS. 1 to 6C. In FIGS. 1 to 6C, the same or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in FIGS. 1 to 6C, the scales and dimensions of each component may be exaggerated or some components may be omitted. In the following description, unless otherwise specified, terms such as "first" and "second" are used only to distinguish components from each other and do not represent a specific order or sequence.

[0011] FIG. 1 is a schematic diagram showing the configuration of the imaging device 1 in the first embodiment of the present invention. As shown in FIG. 1, the imaging device 1 includes a casing 2, a base plate 3, an optical system 4 housed between the casing 2 and the base plate 3, and an imaging element 5 disposed on the base plate 3. The imaging element 5 is disposed on the image plane S of the optical system 4.

[0012] The optical system 4 includes a first lens 10 having a negative refractive power, a second lens 20 having a negative refractive power, a third lens 30 having a positive refractive power, a diaphragm 90 with an aperture formed therein, a fourth lens 40 having a positive refractive power, an auxiliary diaphragm 95 with an aperture larger in diameter than the aperture of the diaphragm 90, a fifth lens 50 having a positive refractive power, a sixth lens 60 having a negative refractive power, a seventh lens 70, a filter 80 that cuts light in a predetermined frequency band (for example, infrared light), and a sensor protection glass 82 disposed between the filter 80 and the imaging element 5. The first lens 10, the second lens 20, the third lens 30, the diaphragm 90, the fourth lens 40, the auxiliary diaphragm 95, the fifth lens 50, the sixth lens 60, the seventh lens 70, the filter 80, and the sensor protection glass 82 are arranged in order from the object (subject) B side along the optical axis P toward the image plane S side. In this specification, the object B side along the optical axis P is defined as "front" and the image plane S side is defined as "rear".

[0013] The first lens 10 has a front lens surface 10F that is convex on the object B side and a rear lens surface 10R that is concave on the image plane S side. The first lens 10 is formed of glass.

[0014] The second lens 20 has a front lens surface 20F that is concave on the object B side and a rear lens surface 20R that is convex on the image plane S side. The second lens 20 is formed of resin (plastic), and the front lens surface 20F and the rear lens surface 20R of the second lens 20 are aspherical.

[0015] The third lens 30 has a front lens surface 30F that is convex on the object B side and a rear lens surface 30R that is convex on the image plane S side. The third lens 30 is formed of glass.

[0016] The combination of the first lens 10, the second lens 20, and the third lens 30 can guide light rays from a wide angle of view (for example, 119 degrees diagonal) to the diaphragm 90. In this embodiment, in order to satisfy the conditions of the focal length and the horizontal and diagonal angles of view described later, the front lens surface 20F and the rear lens surface 20R of the second lens 20 are aspherical.

[0017] The fourth lens 40 has a convex front lens surface 40F on the object B side and a convex rear lens surface 40R on the image plane S side. The fourth lens 40 is formed of glass. Since the fourth lens 40 is disposed behind the aperture 90, it plays a major role in converging the light rays that have passed through the aperture 90. For this reason, if the refractive index of the fourth lens 40 varies significantly with the ambient temperature, the amount of movement of the focal position of the optical system 4 will increase. Therefore, it is preferable that the refractive index temperature coefficient (dn / dt) of the fourth lens 40 be as small as possible. Specifically, the refractive index temperature coefficient of the fourth lens 40 with respect to light having a wavelength of 587.6 nm at 20°C is 0.2×10 -6 / °C or less, and the fourth lens 40 is configured accordingly.

[0018] Also, assuming that the focal length of the entire optical system 4 is f and the focal length of the fourth lens 40 is f4, the optical system 4 is configured such that f4 / f < 2.8 is satisfied.

[0019] Furthermore, when the change in the traveling direction of the light rays incident on the fourth lens 40 is equal to the change in the traveling direction of the light rays exiting the fourth lens 40, the occurrence of spherical aberration is suppressed. Therefore, if the radius of curvature of the front lens surface 40F of the fourth lens 40 is R 4F and the radius of curvature of the rear lens surface 40R is R 4R , then R 4F = -R 4R is preferably the case.

[0020] The fifth lens 50 has a convex front lens surface 50F on the object B side and a convex rear lens surface 50R on the image plane S side. The sixth lens 60 has a concave front lens surface 60F on the object B side and a convex rear lens surface 60R on the image plane S side. The rear lens surface 50R of the fifth lens 50 and the front lens surface 60F of the sixth lens 60 are joined to each other, and the fifth lens 50 and the sixth lens 60 form a single cemented lens.

[0021] Here, the fifth lens 50 is preferably formed of an ultra-low dispersion glass having an Abbe number of 80 or more, and the sixth lens 60 is preferably formed of a high dispersion glass having an Abbe number of less than 25. By using a cemented lens composed of a lens made of such ultra-low dispersion glass and a lens made of high dispersion glass, chromatic aberration in visible light (generally 430 nm - 650 nm) can be suppressed, and color fringing can be reduced.

[0022] The seventh lens 70 has a front lens surface 70F and a rear lens surface 70R. The seventh lens 70 is formed of resin (plastic), and the front lens surface 70F and the rear lens surface 70R of the seventh lens 70 are aspherical surfaces. By configuring the lens surfaces 70F and 70R of the seventh lens 70 as aspherical surfaces in this way, field curvature and spherical aberration at the focal plane can be suppressed, and a high-resolution image with little blur from the center to the diagonal can be obtained.

[0023] FIG. 2 is a schematic diagram showing the configuration of the imaging device 101 in the second embodiment of the present invention. In the optical system 104 in this embodiment, in addition to the auxiliary aperture 95 in the first embodiment described above, another auxiliary aperture 190 is disposed between the first lens 10 and the second lens 20. Further, in this embodiment, instead of the seventh lens 70 in the first embodiment, a seventh lens 170 having a front lens surface 170F and a rear lens surface 170R is used. The seventh lens 170 is formed of resin (plastic) in the same manner as the seventh lens 70, and the front lens surface 170F and the rear lens surface 170R of the seventh lens 170 are aspherical surfaces.

[0024] FIG. 3 is a schematic diagram showing the configuration of the imaging device 201 in the third embodiment of the present invention. In the optical system 204 in this embodiment, instead of the seventh lens 70 in the first embodiment, a seventh lens 270 having a front lens surface 270F and a rear lens surface 270R is used. The seventh lens 270 is formed of resin (plastic), like the seventh lens 70, and the front lens surface 270F and the rear lens surface 270R of the seventh lens 270 are aspherical. Also, in this embodiment, the second lens 20 is formed of glass, while the third lens 30 is formed of resin (plastic), and the front lens surface 30F and the rear lens surface 30R of the third lens 30 are aspherical.

[0025] In each of the above-described embodiments, each of the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, the sixth lens 60, and the seventh lenses 70, 170, 270 is composed of a single lens. However, each of the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, the sixth lens 60, and the seventh lenses 70, 170, 270 may be constituted by combining a plurality of lenses. Also, the positions of the auxiliary diaphragms 95, 190 are not limited to those shown in the figures.

[0026] When the lens surfaces of the second lens 20, the third lens 30, and the seventh lenses 70, 170, 270 described above are aspherical, the profile of this aspherical surface is represented by the following formula (1).

Equation

Example

[0027] As a first embodiment of the present invention, the imaging device 1 of the above-described embodiment was configured with an optical system having the following parameters, and its characteristics were analyzed. <Radius of curvature of the lens surface on the optical axis P> Front lens surface 10F of the first lens 10: 150.0000 mm Rear lens surface 10R of the first lens 10: 4.4211 mm Front lens surface 20F of the second lens 20: -5.0901 mm (aspherical) Rear lens surface 20R of the second lens 20: -15.2255 mm (aspherical) Front lens surface 30F of the third lens 30: 31.4264 mm Rear lens surface 30R of the third lens 30: -10.6612 mm Front lens surface 40F of the fourth lens 40: 11.9765 mm Rear lens surface 40R of the fourth lens 40: -11.9765 mm Front lens surface 50F of the fifth lens 50: 7.2993 mm Rear lens surface 50R of the fifth lens 50: -7.2993 mm Front lens surface 60F of the sixth lens 60: -7.2993 mm Rear lens surface 60R of the sixth lens 60: -45.0447 mm Front lens surface 70F of the seventh lens 70: 96.6350 mm (aspherical) Rear lens surface 70R of the seventh lens 70: -236.6065 mm (aspherical)

[0028] <Thickness or interval on the optical axis P> Thickness D1 of the first lens 10 = 1.2000 mm Interval D between the first lens 10 and the second lens 20 12 = 4.6071 mm Thickness D2 of the second lens 20 = 1.6879 mm Interval D between the second lens 20 and the third lens 30 23 = 0.1000 mm Thickness D3 of the third lens 30 = 2.5016 mm Interval D between the third lens 30 and the aperture 90 3P = 0.1000 mm The distance D between the aperture 90 and the fourth lens 40 P4 = 0.1034 mm The thickness D4 of the fourth lens 40 = 5.9976 mm The distance D between the fourth lens 40 and the auxiliary aperture 95 4Q = 0.1009 mm The distance D between the auxiliary aperture 95 and the fifth lens 50 Q5 = 0.0000 mm The thickness D5 of the fifth lens 50 = 4.9958 mm The thickness D6 of the sixth lens 60 = 0.8000 mm The distance D between the sixth lens 60 and the seventh lens 70 67 = 1.0021 mm The thickness D7 of the seventh lens 70 = 2.2217 mm The distance D between the seventh lens 70 and the filter 80 7F = 3.3589 mm The thickness D of the filter 80 F = 0.5000 mm The distance D between the filter 80 and the sensor protection glass 82 FG = 0.1000 mm The thickness D of the sensor protection glass 82 G = 0.3000 mm The distance D between the sensor protection glass 82 and the image plane S GS = 0.0400 mm

[0029] <Refractive index for d-line> The refractive index N of the first lens 10 d1 = 1.58 The refractive index N of the second lens 20 d2 = 1.69 The refractive index N of the third lens 30 d3 = 1.70 The refractive index N of the fourth lens 40 d4 = 1.47 The refractive index N of the fifth lens 50 d5 = 1.46 The refractive index N of the sixth lens 60 d6 = 1.92 The refractive index N of the seventh lens 70 d7 = 1.77 The refractive index N of the filter 80dF = 1.52 Refractive index N of the sensor protection glass 82 dG = 1.52

[0030] <Abbe number> Abbe number ν1 of the first lens 10 = 59.5 Abbe number ν2 of the second lens 20 = 31.1 Abbe number ν3 of the third lens 30 = 41.1 Abbe number ν4 of the fourth lens 40 = 66.9 Abbe number ν5 of the fifth lens 50 = 90.3 Abbe number ν6 of the sixth lens 60 = 20.9 Abbe number ν7 of the seventh lens 70 = 49.3 Abbe number ν of the filter 80 F = 64.1 Abbe number ν of the sensor protection glass 82 G = 64.1

[0031] <Focal length> Focal length f4 of the fourth lens 40 = 13.790 mm Focal length f of the entire optical system 4 = 5.011 mm Therefore, f4 / f = 2.752

[0032] <Aspherical data> Front lens surface 20F of the second lens 20: κ = 0 A4 = 7.8946×10 -4 A6 = 1.0955×10 -5 A8 = 4.3265×10 -7 A 10 = -5.4281×10 -9 A 12 = 0 A 14 = 0 A 16 = 0 Rear lens surface 20R of the second lens 20: κ = 0 A4 = 6.4009×10 -4 A6 = 3.2342×10 -6 A8 = 2.5346×10 -9 A 10 = 0 A 12 = 0 A 14 = 0 A 16 = 0 Front lens surface 70F of the 7th lens 70: κ = 0 A4 = -1.2939×10 -3 A6 = 1.2356×10 -5 A8 = -2.1250×10 -6 A 10 = 7.9174×10 -7 A 12 = -9.0566×10 -8 A 14 = 4.9520×10 -9 A 16 = -1.0512×10 -10 Rear lens surface 70R of the 7th lens 70: κ = 0 A4 = -8.3391×10 -4 A6 = 8.6116×10 -5 A8 = -1.6574×10 -5 A 10 = 2.5080×10 -6 A 12 = -2.0676×10 -7 A 14 = 8.8998×10 -9 A 16 = -1.5480×10 -10

[0033] <Refractive index temperature coefficient> Refractive index temperature coefficient of the fourth lens 40 with respect to light having a wavelength of 587.6 nm at 20°C: 0.2×10 -6 / °C

[0034] Regarding the optical system in this first embodiment, the results of obtaining the relationship between defocus and MTF (Modulation Transfer Function) at a plurality of different temperatures are shown in FIGS. 4A to 4C. Since it is assumed that the optical system is normally used at 20°C, the focus position at 20°C was used as a reference. FIG. 4A shows the calculation results at -40°C, FIG. 4B shows the results at +20°C, and FIG. 4C shows the results at +85°C. Note that FIGS. 4A to 4C are the results when the MTF frequency is 119 LP / mm.

[0035] As shown in FIGS. 4A to 4C, the defocus with respect to +20°C at -40°C is extremely small, about -0.007 mm (-7 μm), and the defocus with respect to +20°C at +85°C is also extremely small, about +0.007 mm (+7 μm). Thus, it can be seen that the optical system of the first embodiment is an optical system with little defocus due to temperature changes and little change in lens performance with respect to temperature changes.

Embodiment

[0036] As a second embodiment of the present invention, an imaging device 101 of the above-described second embodiment was configured with an optical system having the following parameters, and its characteristics were analyzed. <Radius of curvature of the lens surface on the optical axis P> Front lens surface 10F of the first lens 10: 150.0000 mm Rear lens surface 10R of the first lens 10: 4.5596 mm Front lens surface 20F of the second lens 20: -5.3037 mm (aspherical surface) Rear lens surface 20R of the second lens 20: -14.9847 mm (aspherical surface) Front lens surface 30F of the third lens 30: 27.4954 mm Rear lens surface 30R of the third lens 30: -11.5615 mm Front lens surface 40F of the fourth lens 40: 11.9757 mm Rear lens surface 40R of the 4th lens 40: -11.9757 mm Front lens surface 50F of the 5th lens 50: 7.2752 mm Rear lens surface 50R of the 5th lens 50: -7.2752 mm Front lens surface 60F of the 6th lens 60: -7.2752 mm Rear lens surface 60R of the 6th lens 60: -76.8028 mm Front lens surface 170F of the 7th lens 170: 16.9163 mm (aspherical) Rear lens surface 170R of the 7th lens 170: 21.6834 mm (aspherical)

[0037] <Thickness or interval on the optical axis P> Thickness D1 of the 1st lens 10 = 1.2000 mm Interval D between the 1st lens 10 and the auxiliary diaphragm 190 1R = 3.1639 mm Interval D between the auxiliary diaphragm 190 and the 2nd lens 20 R2 = 1.5000 mm Thickness D2 of the 2nd lens 20 = 1.6749 mm Interval D between the 2nd lens 20 and the 3rd lens 30 23 = 0.0996 mm Thickness D3 of the 3rd lens 30 = 2.4722 mm Interval D between the 3rd lens 30 and the diaphragm 90 3P = 0.9489 mm Interval D between the diaphragm 90 and the 4th lens 40 P4 = 0.1004 mm Thickness D4 of the 4th lens 40 = 5.5728 mm Interval D between the 4th lens 40 and the auxiliary diaphragm 95 4Q = 0.0999 mm Interval D between the auxiliary diaphragm 95 and the 5th lens 50 Q5 = 0.0000 mm Thickness D5 of the 5th lens 50 = 5.0036 mm Thickness D6 of the 6th lens 60 = 0.8000 mm Interval D between the 6th lens 60 and the 7th lens 170 67 = 0.9885 mm The thickness D7 of the seventh lens 170 = 2.1895 mm The distance D between the seventh lens 170 and the filter 80 7F = 3.0513 mm The thickness D of the filter 80 F = 0.5000 mm The distance D between the filter 80 and the sensor protection glass 82 FG = 0.1000 mm The thickness D of the sensor protection glass 82 G = 0.3000 mm The distance D between the sensor protection glass 82 and the image plane S GS = 0.0400 mm

[0038] <Refractive index for d-line> The refractive index N of the first lens 10 d1 = 1.58 The refractive index N of the second lens 20 d2 = 1.69 The refractive index N of the third lens 30 d3 = 1.70 The refractive index N of the fourth lens 40 d4 = 1.47 The refractive index N of the fifth lens 50 d5 = 1.46 The refractive index N of the sixth lens 60 d6 = 1.92 The refractive index N of the seventh lens 170 d7 = 1.77 The refractive index N of the filter 80 dF = 1.52 The refractive index N of the sensor protection glass 82 dG = 1.52

[0039] <Abbe number> The Abbe number ν1 of the first lens 10 = 59.5 The Abbe number ν2 of the second lens 20 = 31.1 The Abbe number ν3 of the third lens 30 = 41.1 The Abbe number ν4 of the fourth lens 40 = 66.9 The Abbe number ν5 of the fifth lens 50 = 90.3 The Abbe number ν6 of the sixth lens 60 = 20.9 The Abbe number ν7 of the seventh lens 170 = 49.3 Abbe number ν of the filter 80 F = 64.1 Abbe number ν of the sensor protection glass 82 G = 64.1

[0040] <Focal length> Focal length f4 of the fourth lens 40 = 13.705 mm Focal length f of the entire optical system 4 = 4.949 mm Therefore, f4 / f = 2.769

[0041] <Aspherical data> Front lens surface 20F of the second lens 20: κ = 0 A4 = 7.8599×10 -4 A6 = 4.0999×10 -5 A8 = -6.4493×10 -6 A 10 = 4.6613×10 -7 A 12 = 0 A 14 = 0 A 16 = 0 Rear lens surface 20R of the second lens 20: κ = 0 A4 = 7.4247×10 -4 A6 = -3.8046×10 -6 A8 = 3.0281×10 -7 A 10 = 0 A 12 = 0 A 14 = 0 A 16 = 0 Front lens surface 170F of the seventh lens 170: κ = 0 A4 = -9.5681×10 -4 A6 = 1.9180×10 -5 A8 = -7.6809×10 -6 A 10 = 1.4086×10 -6 A 12 = -1.2257×10 -7 A 14 = 5.7659×10 -9 A 16 = -1.2297×10 -10 Rear lens surface 170R of the seventh lens 170: κ = 0 A4 = -4.1194×10 -4 A6 = 6.0443×10 -5 A8 = -1.6186×10 -5 A 10 = 2.7405×10 -6 A 12 = -2.5294×10 -7 A 14 = 1.2923×10 -8 A 16 = -2.8404×10 -10

[0042] <Refractive index temperature coefficient> Refractive index temperature coefficient of the fourth lens 40 with respect to light of wavelength 587.6 nm at 20°C: 0.2×10 -6 / °C

[0043] Regarding the optical system in this second embodiment, the relationships between defocus and MTF obtained at a plurality of different temperatures are shown in FIGS. 5A to 5C. Similar to the first embodiment, based on the focal position at +20°C, the MTF frequency was set to 119 LP / mm. FIG. 5A shows the calculation results at -40°C, FIG. 5B shows the results at +20°C, and FIG. 5C shows the results at +85°C.

[0044] As shown in FIGS. 5A to 5C, the focus shift with respect to +20° C. at -40° C. is extremely small, about +0.004 mm (+4 μm), and the focus shift with respect to +20° C. at +85° C. is about -0.004 mm (-4 μm). Thus, it can be seen that the optical system of the second embodiment is an optical system with little focus shift due to temperature change and little change in lens performance with respect to temperature change.

Embodiment

[0045] As a third embodiment of the present invention, an imaging device 201 of the above-described third embodiment was configured by an optical system having the following parameters, and its characteristics were analyzed. <Radius of curvature of the lens surface on the optical axis P> Front lens surface 10F of the first lens 10: 150.0000 mm Rear lens surface 10R of the first lens 10: 4.4661 mm Front lens surface 20F of the second lens 20: -5.9012 mm Rear lens surface 20R of the second lens 20: -23.9519 mm Front lens surface 30F of the third lens 30: 35.3440 mm (aspherical surface) Rear lens surface 30R of the third lens 30: -11.2068 mm (aspherical surface) Front lens surface 40F of the fourth lens 40: 11.1417 mm Rear lens surface 40R of the fourth lens 40: -11.1417 mm Front lens surface 50F of the fifth lens 50: 7.2535 mm Rear lens surface 50R of the fifth lens 50: -7.2535 mm Front lens surface 60F of the sixth lens 60: -7.2535 mm Rear lens surface 60R of the sixth lens 60: -34.5301 mm Front lens surface 270F of the seventh lens 270: 169.5230 mm (aspherical surface) Rear lens surface 270R of the seventh lens 270: 3457.9627 mm (aspherical surface)

[0046] <Thickness or interval on the optical axis P> The thickness D1 of the first lens 10 = 1.2000 mm The distance D between the first lens 10 and the second lens 20 12 = 4.6013 mm The thickness D2 of the second lens 20 = 1.4835 mm The distance D between the second lens 20 and the third lens 30 23 = 0.1000 mm The thickness D3 of the third lens 30 = 2.7426 mm The distance D between the third lens 30 and the aperture 90 3P = 0.1108 mm The distance D between the aperture 90 and the fourth lens 40 P4 = 0.1016 mm The thickness D4 of the fourth lens 40 = 5.7258 mm The distance D between the fourth lens 40 and the auxiliary aperture 95 4Q = 0.7409 mm The distance D between the auxiliary aperture 95 and the fifth lens 50 Q5 = 0.0000 mm The thickness D5 of the fifth lens 50 = 5.0007 mm The thickness D6 of the sixth lens 60 = 0.8000 mm The distance D between the sixth lens 60 and the seventh lens 270 67 = 1.1075 mm The thickness D7 of the seventh lens 270 = 1.5006 mm The distance D between the seventh lens 270 and the filter 80 7F = 3.3305 mm The thickness D of the filter 80 F = 0.5000 mm The distance D between the filter 80 and the sensor protection glass 82 FG = 0.1000 mm The thickness D of the sensor protection glass 82 G = 0.3000 mm The distance D between the sensor protection glass 82 and the image plane S GS = 0.0400 mm

[0047] <Refractive index for d-line> The refractive index N of the first lens 10 d1 = 1.58 Refractive index N of the second lens 20 d2 = 1.80 Refractive index N of the third lens 30 d3 = 1.80 Refractive index N of the fourth lens 40 d4 = 1.47 Refractive index N of the fifth lens 50 d5 = 1.46 Refractive index N of the sixth lens 60 d6 = 1.92 Refractive index N of the seventh lens 270 d7 = 1.77 Refractive index N of the filter 80 dF = 1.52 Refractive index N of the sensor protection glass 82 dG = 1.52

[0048] <Abbe number> Abbe number ν1 of the first lens 10 = 59.5 Abbe number ν2 of the second lens 20 = 35.0 Abbe number ν3 of the third lens 30 = 45.5 Abbe number ν4 of the fourth lens 40 = 66.9 Abbe number ν5 of the fifth lens 50 = 90.3 Abbe number ν6 of the sixth lens 60 = 20.9 Abbe number ν7 of the seventh lens 270 = 49.3 Abbe number ν of the filter 80 F = 64.1 Abbe number ν of the sensor protection glass 82 G = 64.1

[0049] <Focal length> Focal length f4 of the fourth lens 40 = 12.859 mm Focal length f of the entire optical system 4 = 4.950 mm Therefore, f4 / f = 2.598

[0050] <Aspherical data> Front lens surface 30F of the third lens 30: κ = 0 A4 = -5.7184×10 -5 A6 = 7.5000×10-6 A8 = -1.4125×10 -8 A 10 = 0 A 12 = 0 A 14 = 0 A 16 = 0 Rear lens surface 30R of the 3rd lens 30: κ = 0 A4 = 1.6245×10 -4 A6 = 5.4537×10 -6 A8 = 1.6380×10 -7 A 10 = 0 A 12 = 0 A 14 = 0 A 16 = 0 Front lens surface 270F of the 7th lens 270: κ = 0 A4 = -1.5849×10 -3 A6 = -7.7767×10 -5 A8 = 2.0589×10 -5 A 10 = -2.0471×10 -6 A 12 = 1.1732×10 -7 A 14 = -3.2009×10 -9 A 16 = 2.7701×10 -11 Rear lens surface 270R of the 7th lens 270: κ = 0 A4 = -1.1587×10 -3 A6 = 1.5129×10 -5 A8 = 6.5525×10 -7 A 10=4.9813×10 -7 A 12 =-6.7678×10 -8 A 14 =3.6851×10 -9 A 16 =-7.3095×10 -11

[0051] <Refractive index temperature coefficient> Refractive index temperature coefficient of the fourth lens 40 with respect to light having a wavelength of 587.6 nm at 20°C: 0.2×10 -6 / °C

[0052] Regarding the optical system in this third embodiment, the results of obtaining the relationship between defocus and MTF at a plurality of different temperatures are shown in FIGS. 6A to 6C. Similar to the first embodiment, with the focal position at +20°C as a reference, the MTF frequency was set to 119 LP / mm. FIG. 6A shows the calculation results at -40°C, FIG. 6B shows the calculation results at +20°C, and FIG. 6C shows the calculation results at +85°C.

[0053] As shown in FIGS. 6A to 6C, the defocus with respect to +20°C at -40°C is extremely small, about -0.008 mm (-8 μm), and the defocus with respect to +20°C at +85°C is extremely small, about +0.008 mm (+8 μm). Thus, it can be seen that the optical system of the third embodiment is an optical system with little defocus due to temperature changes and little change in lens performance with respect to temperature changes.

[0054] As described above, the optical system according to the present invention can adopt the following configuration.

[0055] [Configuration 1] Arranged in order from the object side to the image side along the optical axis, A first lens having a convex front lens surface on the object side and a concave rear lens surface on the image side, and having a negative refractive power, A second lens having a concave front lens surface on the object side and a convex rear lens surface on the image side, and having a negative refractive power, A third lens including a front lens surface convex toward the object side and a rear lens surface convex toward the image side, and having a positive refractive power; A diaphragm provided with an aperture; A fourth lens including a front lens surface convex toward the object side and a rear lens surface convex toward the image side, and having a positive refractive power; A fifth lens including a front lens surface convex toward the object side and a rear lens surface convex toward the image side, and having a positive refractive power; A sixth lens including a front lens surface concave toward the object side and a rear lens surface convex toward the image side, and having a negative refractive power; A seventh lens including an aspherical front lens surface and an aspherical rear lens surface Comprising: The rear lens surface of the fifth lens and the front lens surface of the sixth lens are joined to each other; The refractive index temperature coefficient of the fourth lens with respect to light having a wavelength of 587.6 nm at 20°C is 0.2×10 -6 / °C or less; Assuming that the focal length of the entire optical system is f and the focal length of the fourth lens is f4, f4 / f < 2.8 An optical system satisfying the above conditions.

[0056] [Configuration 2] If the radius of curvature of the front lens surface of the fourth lens is R 4F and the radius of curvature of the rear lens surface is R 4R then R 4F = -R 4R The optical system according to Configuration 1, satisfying the above conditions.

[0057] [Configuration 3] The front lens surface and the rear lens surface of the second lens or the third lens are aspherical surfaces. The optical system according to Configuration 1 or 2.

[0058] [Configuration 4] The Abbe number of the fifth lens is 80 or more, and the Abbe number of the sixth lens is less than 25. The optical system according to any one of Configurations 1 to 3.

[0059] In addition, the imaging device according to the present invention can adopt the following configuration.

[0060] [Configuration 5] An optical system according to any one of Configurations 1 to 4, and an imaging element disposed on the image plane An imaging device comprising the same.

[0061] Although the preferred embodiments of the present invention have been described so far, it goes without saying that the present invention is not limited to the above-described embodiments and may be implemented in various different forms within the scope of its technical idea.

Explanation of Reference Numerals

[0062] 1,101,201 Imaging device 2 Casing 3 Base plate 4,104,204 Optical system 5 Imaging element 10 First lens 20 Second lens 30 Third lens 40 Fourth lens 50 Fifth lens 60 Sixth lens 70,170,270 Seventh lens 80 Filter 82 Sensor protection glass 90 Diaphragm 95,190 Auxiliary diaphragm B Object P Optical axis S Image plane

Claims

1. A first lens having a negative refractive power, including a front lens surface convex toward the object side and a rear lens surface concave toward the image plane side, arranged in order from the object side toward the image plane side along the optical axis; A second lens having a negative refractive power, including a front lens surface concave toward the object side and a rear lens surface convex toward the image plane side; A third lens having a positive refractive power, including a front lens surface convex toward the object side and a rear lens surface convex toward the image plane side; A diaphragm provided with an aperture; A fourth lens having a positive refractive power, including a front lens surface convex toward the object side and a rear lens surface convex toward the image plane side; A fifth lens having a positive refractive power, including a front lens surface convex toward the object side and a rear lens surface convex toward the image plane side; A sixth lens having a negative refractive power, including a front lens surface concave toward the object side and a rear lens surface convex toward the image plane side; A seventh lens including an aspherical front lens surface and an aspherical rear lens surface, wherein the rear lens surface of the fifth lens and the front lens surface of the sixth lens are joined to each other, satisfying the above conditions, an optical system.

2. The refractive index temperature coefficient of the fourth lens with respect to light having a wavelength of 587.6 nm at 20°C is 0.2×10 -6 / °C or less, Let the focal length of the entire optical system be f and the focal length of the fourth lens be f 4 Then f 4 / f < 2.8 The optical system according to Claim 1, satisfying the above conditions.

3. Let the radius of curvature of the front lens surface of the fourth lens be R 4F and the radius of curvature of the rear lens surface be R 4R Then R 4F = -R 4R The optical system according to Claim 1, wherein the front lens surface and the rear lens surface of the second lens or the third lens are aspherical surfaces.

4. The optical system according to Claim 1, wherein the Abbe number of the fifth lens is 80 or more and the Abbe number of the sixth lens is less than 25.

5. An imaging device comprising the optical system according to any one of Claims 1 to 4 and an imaging element disposed on the image plane. ​ ​ ​ ​

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