JP6331362B2 - Close-up lens - Google Patents

Description

  The present invention relates to a close-up lens used in water, an imaging apparatus having the close-up lens, and a method for manufacturing the close-up lens.

  Conventionally, underwater photography has used amphibious lenses, for example (see, for example, Patent Document 1).

JP-A-6-242369

  However, conventional amphibious lenses do not have sufficient optical performance in water and do not sufficiently correct aberrations that occur in water.

  The present invention has been made in view of such a situation, and provides a close-up lens having high optical performance in water, an imaging device including the close-up lens, and a method for manufacturing the close-up lens. For the purpose.

In order to achieve the above object, the close-up lens according to the present invention is used by being attached to the object side of the master lens, and is a detachable close-up lens, which is negative in order from the object side along the optical axis. And a second lens having a positive refractive power and satisfying the following conditions.
0.00 <fCw
40.08 ≦ ν2−ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens

  In addition, an imaging apparatus according to the present invention includes the above close-up lens.

The method for manufacturing a close-up lens according to the present invention is a method for manufacturing a detachable close-up lens that is used by being attached to the object side of a master lens, and is negative in order from the object side along the optical axis. A first lens having a refractive power of 2 and a second lens having a positive refractive power are arranged so as to satisfy the following conditions.
0.00 <fCw
40.08 ≦ ν2−ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens

  ADVANTAGE OF THE INVENTION According to this invention, the close-up lens provided with the high optical performance in water, the imaging device provided with this close-up lens, and the manufacturing method of the said close-up lens can be provided.

It is sectional drawing which shows the lens structure of the master lens with which the close-up lens which concerns on 1st-3rd Example is mounted | worn. It is sectional drawing which shows the lens structure of the state which mounted | wore with the close-up lens which concerns on 1st Example on the master lens in water. 2A and 2B are diagrams showing various aberrations of the master lens in FIG. 1, where (a) shows a land use and (b) shows an underwater use. FIG. 3 is a diagram illustrating various aberrations of the optical system in FIG. 2. It is sectional drawing which shows the lens structure of the state which mounted | wore with the close-up lens which concerns on 2nd Example on the master lens in water. FIG. 6 is a diagram illustrating various aberrations of the optical system in FIG. 5. It is sectional drawing which shows the lens structure of the state which mounted | wore with the close-up lens which concerns on 3rd Example on the master lens in water. FIG. 8 is a diagram illustrating various aberrations of the optical system in FIG. 7. It is a figure which shows the structure of the imaging device equipped with the close-up lens which concerns on this invention. It is a flowchart which shows the outline of the manufacturing method of the close-up lens based on this invention.

  Hereinafter, a close-up lens, an imaging device, and a method for manufacturing the close-up lens according to the present invention will be described. In the present specification, the “close-up lens” refers to an optical system that is attached to the object side of the master lens and functions to increase the photographing magnification of the master lens. “Land” means in the air.

  First, the close-up lens according to the present invention will be described. The close-up lens according to the present invention is a detachable close-up lens that is used on the object side of a master lens that has been satisfactorily corrected on land, and has a negative refractive power in order from the object side. It is comprised from the 1st lens and the 2nd lens which has positive refractive power.

  In this way, by disposing a lens having a negative refractive power on the object side of a lens having a positive refractive power, distortion can be corrected better than when a lens having a positive refractive power is disposed alone. can do. In particular, when the close-up lens according to the present invention is used in water, distortion occurring in water can be corrected well.

Further, under such a configuration, the close-up lens according to the present invention can realize high optical performance in water by satisfying the following conditional expression (1).
(1) 0.00 <fCw
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0

  Conditional expression (1) is a conditional expression for defining that the focal length of the close-up lens is positive. By satisfying conditional expression (1), the close-up lens acts on the master lens to which the close-up lens is attached in the same manner as a so-called magnifying glass. That is, the shooting magnification of the master lens can be increased simply by attaching the close-up lens. As a result, the shooting scene can be easily expanded.

  If the corresponding value of conditional expression (1) is less than the lower limit, the focal length of the close-up lens becomes negative, and it is not preferable because the photographing magnification of the master lens cannot be increased.

Further, under such a configuration, the close-up lens according to the present invention can realize high optical performance in water by satisfying the following conditional expression (2).
(2) 29.00 ≦ ν2-ν1
However,
ν1: Dispersion value of the glass material of the first lens ν2: Dispersion value of the glass material of the second lens

  Conditional expression (2) is a conditional expression that defines the difference between the dispersion value of the glass material of the first lens that is a negative lens and the dispersion value of the glass material of the second lens that is a positive lens, and satisfies the conditional expression (2). By doing so, it is possible to satisfactorily correct chromatic aberration caused by dispersion in water.

  If the corresponding value of conditional expression (2) is less than the lower limit, it becomes difficult to correct chromatic aberration, which is not preferable. In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (2) to 32.00.

  In the close-up lens according to the present invention, it is preferable that the medium is water, and that the lens surface closest to the object and the lens surface closest to the image are both in contact with water. By using in such a state, high optical performance can be exhibited.

  An imaging apparatus according to the present invention includes the close-up lens having the above-described configuration. Thereby, an imaging device having high optical performance even in water can be realized.

A close-up lens manufacturing method according to the present invention is a method for manufacturing a detachable close-up lens that is used by being attached to the object side of a master lens that has been satisfactorily corrected on land. A first lens having a negative refractive power and a second lens having a positive refractive power are arranged in order, and are configured to satisfy the following conditional expressions (1) and (2).
(1) 0.00 <fCw
(2) 29.00 ≦ ν2-ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens

  By such a close-up lens manufacturing method, a close-up lens having high optical performance in water can be manufactured.

(Numerical example)
Hereinafter, numerical examples of close-up lenses according to the present invention will be described with reference to the accompanying drawings. The second embodiment is a reference example.

(First embodiment)
FIG. 1 is a sectional view showing a lens configuration of a master lens ML to which a close-up lens CL1 according to the first embodiment of the present invention is attached.

  As shown in FIG. 1, the master lens ML to which the close-up lens CL1 is attached includes a parallel plate PF, a biconvex lens L1, and a negative meniscus lens having a convex surface facing the object side in order from the object side along the optical axis. L2, a positive meniscus lens L3 having a convex surface facing the object side, a flare cut stop FS, an aperture stop S, a flare cut stop FS, a cemented lens of a biconcave lens L4 and a biconvex lens L5, and a biconvex lens L6 And a filter group FL disposed in the vicinity of the image plane I. The parallel plate PF arranged on the most object side is attached to a lens barrel (not shown) of the master lens ML when the master lens ML is used in water, and is for protecting the master lens ML from water pressure. Do not install when using on land.

  In the master lens ML, the image side surface of the negative meniscus lens L2 and the image side surface of the biconvex lens L6 are aspherical. Further, the negative meniscus lens L2, the positive meniscus lens L3, the flare cut stop FS, the aperture stop S, the flare cut stop FS, the cemented lens of the biconcave lens L4 and the biconvex lens L5, and the biconvex lens L6 are integrated. By moving in the optical axis direction, an object at infinity is focused on an object at a short distance. In addition, since the same master lens ML as the present embodiment is used in other embodiments described later, the description of the configuration of the master lens ML is omitted in the other embodiments.

  FIG. 2 is a cross-sectional view showing the lens configuration of the entire optical system in a state where the close-up lens CL1 according to the first example is attached to the master lens ML in water.

  As shown in FIG. 2, the close-up lens CL1 according to the present embodiment is composed of a cemented lens of a negative meniscus lens G1 having a convex surface facing the object side and a biconvex lens G2. The negative meniscus lens G1 is disposed on the object side, and the biconvex lens G2 is disposed on the image plane I side.

  Further, as shown in FIG. 2, the close-up lens CL1 according to the present embodiment has an object-side surface of the negative meniscus lens G1 and an image-side surface of the biconvex lens G2 both in the surrounding medium when used underwater. Is in contact with water. That is, when used underwater, water is interposed between the image side surface of the biconvex lens G2 and the object side surface of the parallel plate PF of the master lens ML.

  The close-up lens CL1 according to the present embodiment can be attached to and detached from the master lens ML on land or in water. When the close-up lens CL1 is mounted on the master lens ML on land and the master lens ML with the close-up lens CL1 mounted is put in water, water enters between the biconvex lens G2 and the parallel plate PF. .

  Table 1-1 below shows the specification values of the master lens ML, and Table 1-2 shows the specification values of the entire optical system with the close-up lens CL1 according to this embodiment attached to the master lens ML. Raise.

In [Surface data] in Table 1-1 and Table 1-2, the surface number is the order of the lens surfaces counted from the object side, r is the radius of curvature of the lens surfaces, d is the distance between the lens surfaces, and nd is the d-line ( The refractive index for the wavelength λ = 587.6 nm and νd indicate the Abbe number for the d-line (wavelength λ = 587.6 nm), respectively. The object plane is the object plane, (S) is the aperture stop S, (FS) is the flare cut stop FS, and the image plane is the image plane I. Furthermore, the curvature radius r = ∞ is shows the plane. When the lens surface is an aspheric surface, the surface number is marked with * and the paraxial radius of curvature is shown in the column of the radius of curvature r.

[Aspherical data] shows paraxial curvature radius r, conic constant κ, and aspherical coefficients A4 to A10 when the shape of the aspherical surface shown in [Surface data] is expressed by the following equation.
x = (h ² / r) / [1+ {1-κ (h / r) ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8y ⁸ + A10h ¹⁰
Here, x is the displacement in the optical axis direction at the position of the height h from the optical axis when the vertex of the surface is used as a reference. In addition, “E−n” indicates “× 10 ⁻ⁿ ”, for example, “1.234E-05” indicates “1.234 × 10 ⁻⁵ ”.

  In [various data], f (ML) is the focal length of the master lens ML, FNO (ML) is the F number of the master lens ML, f is the entire optical system in water with the close-up lens CL1 attached to the master lens ML. The combined focal length of the system, FNO is the F number of the entire optical system in water with the close-up lens CL1 attached to the master lens ML, air-converted BF is the air-converted back focus, and fCw is the focus of the close-up lens CL1 in water The distance, ν1 represents the dispersion value of the glass material of the first lens having the negative refractive power of the close-up lens CL1, and ν2 represents the dispersion value of the glass material of the second lens having the positive refractive power of the close-up lens CL1.

  In [variable interval data], the focal length f (ML) of the master lens ML in the infinite object focusing state, the shooting magnification β (ML) of the master lens ML in the near object focusing state, and the close-up lens CL1 are mastered. The focal length f of an object focused at infinity in water when attached to the lens ML, the imaging magnification β, the distance between surfaces, and the focal distance f of an object focused at close distance in water when the close-up lens CL1 is attached to the master lens ML. The value of air equivalent BF is shown. di (i is an integer) indicates the distance between the i-th surfaces, and d0 indicates the distance from the object to the lens surface closest to the object.

  [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

  Here, “mm” is generally used as a unit of the focal length f, the radius of curvature r, and other lengths described in Table 1-1 and Table 1-2. However, the optical system is not limited to this because an equivalent optical performance can be obtained even when proportionally enlarged or proportionally reduced.

  In addition, the code | symbol of Table 1-1 mentioned above and Table 1-2 shall be similarly used also in the table | surface of each Example mentioned later.

(Table 1-1) Master lens ML
[Surface data]
Object ∞
1) ∞ 2.0000 1.522160 58.80
2) ∞ 1.1910
3) 345.8009 1.2000 1.603000 65.47
4) −345.8009 d4
5) 24.2548 1.2000 1.583126 59.38
* 6) 4.6949 3.7000
7) 9.3610 2.9000 1.749500 35.27
8) 307.8348 0.3000
9) (FS) ∞ 1.7000
10) (S) ∞ 1.4000
11) (FS) ∞ 0.9000
12) −9.2376 1.0000 1.808090 22.79
13) 70.0310 2.7000 1.755000 52.29
14) −10.9860 0.4000
15) 25.6611 2.9500 1.592010 67.05
* 16) -12.9991 d16
17) ∞ 0.5000 1.516330 64.14
18) ∞ 1.1100
19) ∞ 1.5900 1.516330 64.14
20) ∞ 0.3000
21) ∞ 0.7000 1.516330 64.14
22) ∞ 0.7000
Image plane ∞

[Aspherical data]
Surface number: 6
κ = 0.1122
A4 = 5.52910E−04
A6 = 3.73730E-06
A8 = 3.27460E-07
A10 = −7.20750E−10

Surface number: 16
κ = −10.5680
A4 = −3.93180E−04
A6 = 1.42680E−05
A8 = −2.39470E−07
A10 = 1.98280E−09

[Various data]
f (ML) = 10.31108
FNO (ML) = 2.91985

[Variable interval data]
Infinite focus state Short range focus state
f (ML) or β (ML) 10.31108 −0.06220
d0 ∞ 158.1027
d4 2.45900 1.81825
d16 10.56327 11.20402
BF converted air 13.79476 14.43551

(Table 1-2) First Example [Surface Data]
Surface number r d nd νd
Object ∞ 1.333060 53.98
1) 32.0000 2.0000 1.846660 23.80
2) 22.9000 11.0000 1.516800 63.88
3) −63.8129 3.0000 1.333060 53.98
4) ∞ 2.0000 1.522160 58.80
5) ∞ 1.1910
6) 345.8009 1.2000 1.603000 65.47
7) −345.8009 d7
8) 24.2548 1.2000 1.583126 59.38
* 9) 4.6949 3.7000
10) 9.3610 2.9000 1.749500 35.27
11) 307.8348 0.3000
12) (FS) ∞ 1.7000
13) (S) ∞ 1.4000
14) (FS) ∞ 0.9000
15) -9.2376 1.0000 1.808090 22.79
16) 70.0310 2.7000 1.755000 52.29
17) −10.9860 0.4000
18) 25.6611 2.9500 1.592010 67.05
* 19) -12.9991 d19
20) ∞ 0.5000 1.516330 64.14
21) ∞ 1.1100
22) ∞ 1.5900 1.516330 64.14
23) ∞ 0.3000
24) ∞ 0.7000 1.516330 64.14
25) ∞ 0.7000
Image plane ∞

[Aspherical data]
Surface number: 9
κ = 0.1122
A4 = 5.52910E−04
A6 = 3.73730E-06
A8 = 3.27460E-07
A10 = −7.20750E−10

Surface number: 19
κ = −10.5680
A4 = −3.93180E−04
A6 = 1.42680E−05
A8 = −2.39470E−07
A10 = 1.98280E−09

[Various data]
f = 11.19461
FNO = 2.93086
fCw = 213.41378
ν1 = 23.80
ν2 = 63.88

[Variable interval data]
Infinite focus state Short range focus state
f or β 11.19461 −0.10569
d0 232.5860 115.2534
d7 2.45900 1.81825
d19 10.56327 11.20402
BF converted air 13.79476 14.43551

[Values for each conditional expression]
(1) fCw = 213.41378
(2) ν2−ν1 = 40.08

   3A and 3B are graphs showing various aberrations of the master lens ML shown in FIG. 1. FIG. 3A shows various aberrations when used on land, and FIG. 3B shows various aberrations when used underwater. FIG. 4 is a diagram showing various aberrations when the optical system shown in FIG. 2, that is, the entire optical system in a state where the close-up lens CL1 is attached to the master lens ML, is used in water.

  In each aberration diagram, FNO represents an F number, A represents a half angle of view (unit: degree), NA represents a numerical aperture, and HO represents an object height. In the figure, d indicates an aberration curve at the d-line (wavelength λ = 587.6 nm), g indicates an aberration curve at the g-line (wavelength λ = 435.8 nm), and those not described are d-line The aberration curve at is shown. In the aberration diagram showing astigmatism, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The aberration diagram showing the coma aberration shows the meridional coma aberration with respect to the d-line and the g-line at each half angle of view for the master lens ML, and the entire optical system with the close-up lens CL1 attached to the master lens ML. Regarding the system, the meridional coma aberration with respect to the d-line and the g-line is shown at each object height. In addition, in the various aberration diagrams of the following examples, the same reference numerals as those of the present example are used.

  As shown in FIG. 3A, the master lens ML has excellent imaging performance with various aberrations corrected well on land. However, in water, as shown in FIG. 3B, it can be seen that various aberrations fluctuate greatly and deteriorate.

  Furthermore, as shown in FIG. 4, by attaching the close-up lens CL1 to the master lens ML, the entire optical system in a state where the close-up lens CL1 is attached to the master lens ML has various aberrations in water. It can be seen that it has been corrected and has excellent imaging performance.

(Second embodiment)
Next, a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view showing the lens configuration of the entire optical system in a state where the close-up lens CL2 according to the second example is attached to the master lens ML in water.

  As shown in FIG. 5, the close-up lens CL2 according to the present embodiment includes a negative meniscus lens G1 having a convex surface facing the object side and a positive meniscus having a convex surface facing the object side in order from the object side along the optical axis. It consists of a lens G2.

  Further, as shown in FIG. 5, in the close-up lens CL2 according to the present embodiment, when used underwater, the object side surface of the negative meniscus lens G1 and the image side surface of the positive meniscus lens G2 are both peripheral. It is in contact with water, the medium. That is, when used underwater, water is interposed between the image side surface of the positive meniscus lens G2 and the object side surface of the parallel plate PF of the master lens ML.

  The close-up lens CL2 according to the present embodiment can be attached to and detached from the master lens ML both on land and in water as in the first embodiment. When the close-up lens CL2 is mounted on the master lens ML on land, and the master lens ML with the close-up lens CL2 is put in water, water enters between the positive meniscus lens G2 and the parallel plate PF. Yes. Note that water does not enter between the image side surface of the negative meniscus lens G1 and the object side surface of the positive meniscus lens G2, and air is interposed.

  Table 2 below lists specifications of the entire optical system in a state where the close-up lens CL2 according to the present example is attached to the master lens ML.

(Table 2) Second Example [Surface Data]
Surface number r d nd νd
Object ∞ 1.333060 53.98
1) 41.0000 3.0000 1.805180 25.45
2) 24.0000 1.0000
3) 22.9000 9.0000 1.622990 58.12
4) 103.6014 4.0000 1.333060 53.98
5) ∞ 2.0000 1.522160 58.80
6) ∞ 1.1910
7) 345.8009 1.2000 1.603000 65.47
8) −345.8009 d8
9) 24.2548 1.2000 1.583126 59.38
* 10) 4.6949 3.7000
11) 9.3610 2.9000 1.749500 35.27
12) 307.8348 0.3000
13) (FS) ∞ 1.7000
14) (S) ∞ 1.4000
15) (FS) ∞ 0.9000
16) -9.2376 1.0000 1.808090 22.79
17) 70.0310 2.7000 1.755000 52.29
18) −10.9860 0.4000
19) 25.6611 2.9500 1.592010 67.05
* 20) -12.9991 d20
21) ∞ 0.5000 1.516330 64.14
22) ∞ 1.1100
23) ∞ 1.5900 1.516330 64.14
24) ∞ 0.3000
25) ∞ 0.7000 1.516330 64.14
26) ∞ 0.7000
Image plane ∞

[Aspherical data]
Surface number: 10
κ = 0.1122
A4 = 5.52910E−04
A6 = 3.73730E-06
A8 = 3.27460E-07
A10 = −7.20750E−10

Surface number: 20
κ = −10.5680
A4 = −3.93180E−04
A6 = 1.42680E−05
A8 = −2.39470E−07
A10 = 1.98280E−09

[Various data]
f = 11.25066
FNO = 2.91914
fCw = 232.92579
ν1 = 25.45
ν2 = 58.12

[Variable interval data]
Infinite focus state Short range focus state
f or β 11.25066 −0.10135
d0 310.9972 121.1678
d8 2.45900 1.81825
d20 10.56327 11.20402
BF converted air 13.79476 14.43551

[Values for each conditional expression]
(1) fCw = 232.92579
(2) ν2−ν1 = 32.67

  FIG. 6 is a diagram showing various aberrations of the optical system shown in FIG. 5, that is, the entire optical system in the state where the close-up lens CL2 is attached to the master lens ML, when used in water. As shown in FIG. 6, when the close-up lens CL2 is attached to the master lens ML, the entire optical system in which the close-up lens CL2 is attached to the master lens ML is well corrected for various aberrations in water. It can be seen that the imaging performance is excellent.

(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 7 is a cross-sectional view showing the lens configuration of the entire optical system in a state where the close-up lens CL3 according to the third example is attached to the master lens ML in water.

  As shown in FIG. 7, the close-up lens CL3 according to the present embodiment includes a negative meniscus lens G1 having a convex surface directed toward the object side and a positive meniscus having a convex surface directed toward the object side in order from the object side along the optical axis. It consists of a lens G2.

  Further, as shown in FIG. 7, in the close-up lens CL3 according to the present embodiment, when used underwater, the object side surface of the negative meniscus lens G1 and the image side surface of the positive meniscus lens G2 are both peripheral. It is in contact with water, the medium. That is, when used underwater, water is interposed between the image side surface of the positive meniscus lens G2 and the object side surface of the parallel plate PF of the master lens ML.

  The close-up lens CL3 according to the present embodiment can be attached to and detached from the master lens ML both on land and in water as in the first embodiment. When the close-up lens CL3 is mounted on the master lens ML on land, and the master lens ML with the close-up lens CL3 is mounted in water, water enters between the positive meniscus lens G2 and the parallel plate PF. Yes. Note that water does not enter between the image side surface of the negative meniscus lens G1 and the object side surface of the positive meniscus lens G2, and air is interposed.

  Table 3 below lists specifications of the entire optical system in a state where the close-up lens CL3 according to the present example is attached to the master lens ML.

(Table 3) Third Example [Surface Data]
Surface number r d nd νd
Object ∞ 1.333060 53.98
1) 41.0000 3.0000 1.808090 22.74
2) 26.5000 1.0000
3) 23.0000 9.0000 1.603000 65.44
4) 71.9789 4.0000 1.333060 53.98
5) ∞ 2.0000 1.522160 58.80
6) ∞ 1.1910
7) 345.8009 1.2000 1.603000 65.47
8) −345.8009 d8
9) 24.2548 1.2000 1.583126 59.38
* 10) 4.6949 3.7000
11) 9.3610 2.9000 1.749500 35.27
12) 307.8348 0.3000
13) (FS) ∞ 1.7000
14) (S) ∞ 1.4000
15) (FS) ∞ 0.9000
16) -9.2376 1.0000 1.808090 22.79
17) 70.0310 2.7000 1.755000 52.29
18) −10.9860 0.4000
19) 25.6611 2.9500 1.592010 67.05
* 20) -12.9991 d20
21) ∞ 0.5000 1.516330 64.14
22) ∞ 1.1100
23) ∞ 1.5900 1.516330 64.14
24) ∞ 0.3000
25) ∞ 0.7000 1.516330 64.14
26) ∞ 0.7000
Image plane ∞

[Aspherical data]
Surface number: 10
κ = 0.1122
A4 = 5.52910E−04
A6 = 3.73730E-06
A8 = 3.27460E-07
A10 = −7.20750E−10

Surface number: 20
κ = −10.5680
A4 = −3.93180E−04
A6 = 1.42680E−05
A8 = −2.39470E−07
A10 = 1.98280E−09

[Various data]
f = 11.35687
FNO = 2.91908
fCw = 233.04833
ν1 = 22.74
ν2 = 65.44

[Variable interval data]
Infinite focus state Short range focus state
f or β 11.35687 −0.1008
d0 313.8750 122.9035
d8 2.45900 1.81825
d20 10.56327 11.20402
BF converted air 13.79476 14.43551

[Values for each conditional expression]
(1) fCw = 233.04833
(2) ν2−ν1 = 42.70

  FIG. 8 is a diagram showing various aberrations of the optical system shown in FIG. 7, that is, the entire optical system in a state where the close-up lens CL3 is attached to the master lens ML, when used in water. As shown in FIG. 8, when the close-up lens CL3 is attached to the master lens ML, the entire optical system in which the close-up lens CL3 is attached to the master lens ML has various aberrations corrected well in water. It can be seen that the imaging performance is excellent.

  As described above, according to each of the above embodiments, a close-up lens having high optical performance in water can be realized.

  In addition, although each said Example has shown the example which attached the close-up lens based on this invention to the same master lens ML, it can also be attached to another master lens. In addition, the contents described below can be appropriately adopted as long as the optical performance is not impaired.

  The lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface.

  When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance.

  When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  Further, each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength region in order to reduce flare and ghost and achieve high optical performance with high contrast.

  Next, an optical device provided with the close-up lens CL of the present invention will be described.

  FIG. 9 is a diagram illustrating a configuration of a camera including the close-up lens CL according to the present invention. As shown in FIG. 9, the camera 1 is a so-called mirrorless camera with an interchangeable lens provided with a photographing lens 2. The taking lens 2 is a master lens ML to which any one of the above close-up lenses CL1 to CL3 is attached. In the camera 1, light from an underwater object (subject) (not shown) is collected by the photographing lens 2 to form a subject image on the imaging surface of the imaging unit 3 via an optical low-pass filter (not shown). Then, the subject image is photoelectrically converted by the photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed on the electronic viewfinder 4 provided in the camera 1. Thus, the photographer can observe the subject through the electronic viewfinder 4.

  When a release button (not shown) is pressed by the photographer, an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

  With the above configuration, the camera 1 including the close-up lens CL according to the present invention can realize high optical performance in water. In this embodiment, an example of a mirrorless camera has been described. However, the close-up lens CL according to the present invention is attached to a single-lens reflex type camera having a quick return mirror in the camera body and observing a subject with a finder optical system. Even in this case, the same effect as the camera 1 can be obtained.

  Next, a method for manufacturing the close-up lens CL of the present invention will be described.

FIG. 10 is a diagram showing an outline of the manufacturing method of the close-up lens CL of the present invention. The close-up lens CL manufacturing method of the present invention is a close-up lens manufacturing method that is detachably mounted on the object side of a lens system that has been satisfactorily corrected on land, as shown in FIG. These steps S1 to S2 are included.
Step S1: A first lens having a negative refractive power and a second lens having a positive refractive power are disposed in order from the object side along the optical axis.
Step S2: Configure so as to satisfy the following conditional expressions (1) and (2).
(1) 0.00 <fCw
(2) 29.00 ≦ ν2-ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens

  According to the method for manufacturing a close-up lens of the present invention, a close-up lens having high optical performance in water can be manufactured.

ML Master lens CL Close-up lens G1 First lens G2 Second lens FS Flare cut stop S Aperture stop I Image surface 1 Camera 2 Shooting lens 3 Imaging unit 4 Electronic viewfinder

Claims (4)

A close-up lens that is attached to and used on the object side of the master lens and is detachable.
A first lens having a negative refractive power and a second lens having a positive refractive power in order from the object side along the optical axis,
A close-up lens that satisfies the following conditions.
0.00 <fCw
40.08 ≦ ν2−ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens 2. The close-up lens according to claim 1, wherein the medium is water and is used in a state where a lens surface closest to the object side and a lens surface closest to the image side are in contact with water.   An imaging apparatus comprising the close-up lens according to claim 1. A method for manufacturing a detachable close-up lens that is used by being attached to the object side of a master lens,
A first lens having a negative refractive power and a second lens having a positive refractive power are disposed in order from the object side along the optical axis,
A close-up lens configured to satisfy the following conditions.
0.00 <fCw
40.08 ≦ ν2−ν1
However,
fCw: focal length of the close-up lens in a medium having a refractive index substantially larger than 1.0 ν1: dispersion value of the glass material of the first lens ν2: dispersion value of the glass material of the second lens

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