Converter lens, interchangeable lens, and image capturing device

Abstract

To provide a converter lens which is designed to be placed on the image side of a master lens to allow an entire system to provide superior optical performance.SOLUTION: A converter lens RCL of the present invention comprises three negative lenses and is designed to increase a focal length of an entire system. An average refractive index Ndave of materials of the three negative lenses of the converter lens RCL for the d-ray (587.56 nm wavelength) is appropriately set.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a converter lens, an interchangeable lens, and an imaging device. [Background technology]

[0002] 2. Description of the Related Art A rear converter lens (hereinafter referred to as a converter lens) is known that is capable of expanding (lengthening) the focal length of the entire system by being disposed between an interchangeable lens and an imaging device.

[0003] Patent Document 1 discloses a converter lens having five negative lenses and a focal length magnification of 2.0 times. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-173692 A Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, a converter lens has a negative refractive power, and the negative refractive power tends to become stronger as the focal length magnification increases. It is also known that if the curvature of the negative lens in the converter lens is increased in order to strengthen the negative refractive power, various aberrations such as coma aberration caused by off-axis light beams are likely to occur.

[0006] Furthermore, because a converter lens does not have an aperture stop, the chief ray of an off-axis light beam that passes through the master lens in an interchangeable lens is incident on the image plane without intersecting with the optical axis of the converter lens, which makes it difficult to perform aberration correction using lenses placed before and after the aperture stop, as is the case with interchangeable lenses.

[0007] In view of the above problems, an object of the present invention is to provide a converter lens that is capable of obtaining high optical characteristics in the entire system when it is disposed on the image side of a master lens. [Means for solving the problem]

[0008] A converter lens is disposed on the image side of a master lens, has a negative refractive power as a whole, and lengthens the focal length of the entire system, the converter lens having three positive lenses and three negative lenses, the lens disposed closest to the image side in the converter lens has a positive refractive power, and the lens disposed second closest from the image side has a negative refractive power, and the average refractive index at the d-line of the material of the three negative lenses is Ndave, 1.92 <Ndave<2.10 The present invention is characterized in that the following condition is satisfied: Effect of the Invention

[0009] According to the converter lens of the present invention, even when it is disposed on the image side of the master lens, high optical characteristics can be obtained in the entire system. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of the converter lens of Example 1. [Diagram 2] FIG. 11 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 1 disposed on the image side of the master lens. [Diagram 3] FIG. 11 is a lateral aberration diagram when focusing on an object at infinity with the converter lens of Example 1 disposed on the image side of the master lens. [Figure 4] FIG. 11 is a cross-sectional view of a converter lens according to a second embodiment. [Diagram 5] FIG. 11 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 2 disposed on the image side of the master lens. [Figure 6]FIG. 11 is a lateral aberration diagram when focusing on an object at infinity with the converter lens of Example 2 disposed on the image side of the master lens. [Figure 7] FIG. 11 is a cross-sectional view of a converter lens according to a third embodiment. [Figure 8] FIG. 11 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 3 disposed on the image side of the master lens. [Figure 9] FIG. 11 is a lateral aberration diagram when focusing on an object at infinity with the converter lens of Example 3 disposed on the image side of the master lens. [Figure 10] FIG. 11 is a cross-sectional view of a converter lens according to a fourth embodiment. [Figure 11] FIG. 11 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 4 disposed on the image side of the master lens. [Figure 12] FIG. 11 is a lateral aberration diagram when focusing on an object at infinity with the converter lens of Example 4 disposed on the image side of the master lens. [Figure 13] FIG. 11 is a cross-sectional view of a converter lens according to a fifth embodiment. [Figure 14] FIG. 13 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 5 disposed on the image side of the master lens. [Figure 15] FIG. 13 is a lateral aberration diagram when focusing on an object at infinity with the converter lens of Example 5 disposed on the image side of the master lens. [Figure 16] FIG. 13 is a cross-sectional view of a converter lens according to a sixth embodiment. [Figure 17] FIG. 13 is a longitudinal aberration diagram when focusing on an object at infinity with the converter lens of Example 6 disposed on the image side of the master lens. [Figure 18] FIG. 13 is a lateral aberration diagram when focusing on an object at infinity when the converter lens of Example 6 is disposed on the image side of the master lens. [Figure 19] FIG. 2 is a cross-sectional view of a master lens. [Figure 20] 4 is a longitudinal aberration diagram of a master lens when focused on an object at infinity. [Figure 21] 4A to 4C are diagrams showing lateral aberration of a master lens when focused on an object at infinity. [Figure 22] FIG. 1 is a diagram illustrating a configuration of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a converter lens and an imaging device according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0012] The Abbe number νd of a material is given by Nd, NF, NC, and Ng, which are the refractive indices at the Fraunhofer d line (587.56 nm), F line (486.13 nm), C line (656.27 nm), and g line (wavelength 435.84 nm). νd=(Nd-1) / (NF-NC) It is expressed as:

[0013] The converter lens of each embodiment is disposed, for example, between an imaging device and an interchangeable lens that is detachable from the imaging device. The converter lens of each embodiment can make the focal length of a photographic optical system (whole system) consisting of the optical system of the interchangeable lens and the converter lens longer than the focal length of a photographic optical system consisting of only the interchangeable lens.

[0014] In the cross-sectional views of the converter lens shown in Figures 1, 4, 7, 10, 13, and 16, and the cross-sectional view of the master lens shown in Figure 19, the left side is the object side (front) and the right side is the image side (rear). In each cross-sectional view, if i is the order of the lens groups from the object side to the image side, Li indicates the i-th lens group. The aperture diaphragm SP determines (limits) the light flux at the maximum F-number (Fno). FP is a flare-cutting diaphragm that cuts out unnecessary light.

[0015] When the imaging device is a digital video camera or a digital camera, the image plane IP corresponds to an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor. When the imaging device is a silver halide film camera, the image plane IP corresponds to the film surface.

[0016] Figures 2, 5, 8, 11, 14, and 17 are longitudinal aberration diagrams of the converter lens of each embodiment described below, and Figure 20 is a longitudinal aberration diagram of the master lens. In the spherical aberration diagrams, the solid line indicates the d-line and the two-dot chain line indicates the g-line. In the astigmatism diagrams, the dashed line M indicates the meridional image plane and the solid line S indicates the sagittal image plane. Distortion aberration is shown for the d-line. Magnification chromatic aberration is shown for the g-line. ω is the half angle of view (degrees) and Fno is the F-number.

[0017] 3, 6, 9, 12, 15, and 18 are diagrams showing lateral aberration of the converter lens of each embodiment described later, and Fig. 21 is a diagram showing lateral aberration of the master lens. In the lateral aberration diagrams, the dashed line M is the meridional image plane, and the solid line S is the sagittal image plane.

[0018] As described above, in a converter lens having a negative refractive power as a whole, various aberrations such as coma due to off-axis light beams tend to occur, and correction of these aberrations tends to be difficult.

[0019] Therefore, the converter lens according to the embodiment has a negative refractive power as a whole and includes three or more negative lenses.The average refractive index of the negative lens material included in the converter lens is made relatively large to reduce the curvature of the lens surface, thereby reducing the occurrence of various aberrations such as coma caused by off-axis light beams.

[0020] Specifically, when the average refractive index of the material of the three negative lenses included in the converter lens at the d line (wavelength 587.56 nm) is Ndave, 1.92 <Ndave<2.10 ···(1) The conditional expression is satisfied.

[0021] If the average refractive index of the lens material decreases below the lower limit of condition (1), it becomes easier to reduce the Petzval sum and to correct the curvature of field, etc. However, this is not preferable because the curvature of the lens surface increases and it becomes difficult to correct various aberrations such as coma.

[0022] Generally, the dispersion of the glass material increases as the average refractive index of the material increases, so if the average refractive index of the material of the negative lens increases beyond the upper limit of condition (1), it becomes difficult to correct lateral chromatic aberration, which is not desirable.

[0023] In this way, the converter lens of the embodiment, by having the above-mentioned lens configuration and satisfying conditional formula (1), makes it possible to effectively correct aberrations caused by off-axis light beams, such as coma aberration, and to obtain high optical performance even when attached to a master lens.

[0024] Furthermore, by using the converter lens of the present invention, a user can use a master lens for an imaging device having an imaging element with a low maximum image height without feeling any discomfort in terms of aberration, even when using the master lens in an imaging device having an imaging element with a high maximum image height.

[0025] It is preferable that the numerical range of conditional expression (1) is as follows: 1.95 <Ndave<2.08 ···(1a)

[0026] Furthermore, it is preferable that the numerical range of conditional expression (1) is as follows: 1.98 <Ndave<2.05 ···(1b)

[0027] It is also preferable that the converter lens has three or more negative lenses, and more preferably four or more negative lenses, in the second lens group.

[0028] Furthermore, it is preferable that the converter lens satisfies one or more of the following conditional expressions: 1.30<(R1+R2) / (R1-R2)<2.50 (2) 0.10 <sk / TD<0.50 ···(3) -2.30 <f1 / f2<-0.95 ···(4) -1.40 <f1 / f<-0.30 ···(5)

[0029] Here, the radius of curvature of the object side surface of the lens arranged closest to the image side is R1, and the radius of curvature of the image side surface of said lens is R2. The air-equivalent length from the surface of the converter lens closest to the image side to the image plane is sk, and the distance on the optical axis from the surface of the converter lens closest to the object side to the surface closest to the image side is TD. The focal length of the first lens group is f1, the focal length of the second lens group is f2, and the focal length of the converter lens is f. Here, the first lens group is composed of a cemented lens formed by cementing a negative lens and a positive lens together.

[0030] Conditional formula (2) specifies the shape of the positive lens of the converter lens that is located closest to the image side. In order to largely refract off-axis light beams while suppressing the occurrence of aberrations, it is preferable to make the radius of curvature of one surface larger than that of the other surface. This makes it possible to refract off-axis light beams more than on-axis light beams while suppressing the occurrence of aberrations, making it easier to correct aberrations caused by off-axis light beams.

[0031] Conditional expression (2) was established in consideration of this. If the difference between the curvature of the image-side surface and the curvature of the object-side surface becomes large below the lower limit of conditional expression (2), the field curvature will be under, which is undesirable. If the difference between the curvature of the image-side surface and the curvature of the object-side surface becomes small above the upper limit of conditional expression (2), the field curvature will be over, which is undesirable.

[0032] Conditional formula (3) specifies the ratio of the back focal length of the converter lens to the distance from the object side surface of the lens closest to the object to the image side surface of the lens closest to the image (lens construction length). If the ratio falls below conditional formula (3), the lens construction length becomes long, which is undesirable. If the lens construction length exceeds conditional formula (3) and becomes short, the refractive power of each lens becomes high, making it difficult to correct spherical aberration, which is undesirable.

[0033] Conditional formula (4) defines the ratio of the focal length of the first lens group to the focal length of the second lens group. If the lower limit of conditional formula (4) is exceeded, spherical aberration occurs significantly on the over side, which is undesirable as it becomes difficult to correct. If the upper limit of conditional formula (4) is exceeded, spherical aberration occurs significantly on the under side, which is undesirable as it becomes difficult to correct.

[0034] Conditional formula (5) prescribes the ratio of the focal length of the first lens group to the focal length of the converter lens. If the lower limit of conditional formula (5) is exceeded and the absolute value of the focal length of the first lens group becomes large and the refractive power becomes weak, spherical aberration occurs on the over side, which is not preferable. If the upper limit of conditional formula (5) is exceeded and the absolute value of the focal length of the first lens group becomes small and the refractive power becomes strong, spherical aberration occurs on the under side, which is not preferable.

[0035] Furthermore, it is preferable that the numerical ranges of the conditional expressions (2) to (5) are as follows: 1.40<(R1+R2) / (R1-R2)<2.30 (2a) 0.15 <sk / TD<0.40 ···(3a) -2.10 <f1 / f2<-1.00 ···(4a) -1.20 <f1 / f<-0.32 ···(5a)

[0036] Furthermore, it is preferable that the numerical ranges of the conditional expressions (2) to (5) are as follows: 1.50<(R1+R2) / (R1-R2)<2.10 (2b) 0.25 <sk / TD<0.35 ···(3b) -1.90 <f1 / f2<-1.10 ···(4b) -1.10 <f1 / f<-0.34 ···(5b)

[0037] By satisfying at least one of the above conditional expressions, it is possible to obtain higher optical characteristics in the entire system even when the lens is disposed on the image side of the master lens.

[0038] Next, the master lens of the examples and the converter lens of each example will be described.

[0039] [Converter lens] Next, the converter lenses of Examples 1 to 6 will be described.

[0040] [Example 1] Fig. 1(a) is a cross-sectional view of the converter lens RCL of Example 1. Fig. 1(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 1 arranged on the image side of the master lens ML. Figs. 2 and 3 are longitudinal and lateral aberration diagrams when the converter lens RCL of Example 1 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 1.61 times.

[0041] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0042] The second lens group is made up of a cemented lens composed of a negative lens, a positive lens and a negative lens, and a positive lens arranged on the image side of the cemented lens. That is, the converter lens RCL has three negative lenses.

[0043] [Example 2] Fig. 4(a) is a cross-sectional view of the converter lens RCL of Example 2. Fig. 4(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 2 arranged on the image side of the master lens ML. Figs. 5 and 6 are longitudinal and lateral aberration diagrams when the converter lens RCL of Example 2 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 1.60 times.

[0044] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0045] The second lens group includes, arranged in order from the object side to the image side, a cemented lens including a negative lens and a positive lens, a negative lens, a positive lens, a negative lens, and a positive lens. That is, the converter lens RCL has four negative lenses.

[0046] [Example 3] Fig. 7(a) is a cross-sectional view of the converter lens RCL of Example 3. Fig. 7(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 3 arranged on the image side of the master lens ML. Figs. 8 and 9 are longitudinal and lateral aberration diagrams when the converter lens RCL of Example 3 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 2.01 times.

[0047] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0048] The second lens group includes, arranged in order from the object side to the image side, a cemented lens including a negative lens and a positive lens, a negative lens, a positive lens, a negative lens, and a positive lens. That is, the converter lens RCL has four negative lenses.

[0049] [Example 4] Fig. 10(a) is a cross-sectional view of the converter lens RCL of Example 4. Fig. 10(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 4 arranged on the image side of the master lens ML. Figs. 11 and 12 are longitudinal and lateral aberration diagrams when the converter lens RCL of Example 4 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 2.02 times.

[0050] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0051] The second lens group includes, arranged in order from the object side to the image side, a cemented lens including a negative lens and a positive lens, a negative lens, a negative lens, a positive lens, a negative lens, and a positive lens. That is, the converter lens RCL has five negative lenses.

[0052] [Example 5] Fig. 13(a) is a cross-sectional view of the converter lens RCL of Example 5. Fig. 13(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 5 arranged on the image side of the master lens ML. Figs. 14 and 15 are longitudinal and lateral aberration diagrams when the converter lens of Example 5 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 1.61 times.

[0053] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0054] The second lens group is made up of a cemented lens composed of a negative lens, a positive lens and a negative lens, and a positive lens arranged on the image side of the cemented lens. That is, the converter lens RCL has three negative lenses.

[0055] [Example 6] Fig. 16(a) is a cross-sectional view of the converter lens RCL of Example 6. Fig. 16(b) is a cross-sectional view of the master lens ML and the converter lens RCL of Example 6 arranged on the image side of the master lens ML. Figs. 17 and 18 are longitudinal and lateral aberration diagrams when the converter lens RCL of Example 6 is arranged on the image side of the master lens ML and focused on an object at infinity. The magnification of the converter lens RCL is 1.59 times.

[0056] The first lens group is composed of a cemented lens of a negative lens G1 and a positive lens G2.

[0057] The second lens group is made up of a cemented lens composed of a negative lens, a positive lens and a negative lens, and a positive lens arranged on the image side of the cemented lens. That is, the converter lens RCL has three negative lenses.

[0058] [Master lens] Fig. 19 is a cross-sectional view of the master lens ML when focused on an object at infinity, Fig. 20 is a longitudinal aberration diagram of the master lens ML when focused on an object at infinity, and Fig. 21 is a lateral aberration diagram of the master lens ML when focused on an object at infinity.

[0059] The master lens ML is a single focal length lens consisting of an aperture stop SP, a front group Lf arranged on the object side of the aperture stop SP, and a rear group Lr arranged on the image side of the aperture stop SP. The F-number of the master lens ML is 2.88, and the half angle of view is 29 degrees. Note that the master lens ML given above is just an example, and any other optical system that can form an image on the image plane may be used.

[0060] [Numerical Example] Numerical examples of the master lens ML described above and Numerical Examples 1 to 6 corresponding to the converter lens RCL of Examples 1 to 6, respectively, are shown below.

[0061] In each numerical example, the surface number indicates the order of the optical surface from the object side, r is the radius of curvature of the optical surface (mm), d for surface number i is the distance (mm) between the i-th optical surface and the (i+1)-th optical surface, nd is the refractive index of the material of the optical member at the d-line, and νd is the Abbe number of the material of the optical member based on the d-line, as defined above.

[0062] BF indicates the back focus, which is the distance on the optical axis from the surface closest to the image side to the paraxial image plane expressed in terms of the air equivalent length.

[0063] The total lens length of the master lens ML is the distance on the optical axis from the surface of the master lens ML closest to the object (first lens surface) to the surface of the master lens ML closest to the image (last lens surface) plus the back focus. The total lens length when the converter lens RCL is disposed on the image side of the master lens ML is the distance on the optical axis from the surface of the master lens ML closest to the object to the surface of the converter lens RCL closest to the image plus the back focus of the converter lens RCL.

[0064] The lens spacing between the master lens and the converter is the distance on the optical axis from the surface of the master lens closest to the image to the surface of the converter lens closest to the object. The spacing between the master lens and the converter lens is expressed in terms of air equivalent length. The magnification is the ratio of the focal length of the entire system when the master lens and converter are used to the focal length of the master lens.

[0065] The lens construction length of the converter lens is the distance on the optical axis from the surface of the converter lens closest to the object side to the surface of the converter lens closest to the image side.

[0066] The effective diameter is the diameter of the range through which on-axis light beams and off-axis light beams pass. The entrance pupil position is the distance from the surface closest to the object to the entrance pupil, and the exit pupil position is the distance from the surface closest to the image to the exit pupil. The front principal point position is the distance from the surface closest to the object to the front principal point, and the rear principal point position is the distance from the surface closest to the image to the rear principal point. Note that the numerical values ​​for the front principal point position and the rear principal point position are paraxial amounts, and the signs are positive in the direction from the object side to the image side.

[0067] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where x is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4×h4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In addition, "e±XX" in each aspheric coefficient is "×10± XX The physical quantities used in the above-mentioned conditional expressions in each of Numerical Examples 1 to 6 are shown in [Table 1], and the values ​​corresponding to the above-mentioned conditional expressions are shown in [Table 2].

[0068] In the numerical examples shown below, the unit of length is mm and the unit of angle is degrees, but since the optical system can be used with proportional enlargement or reduction, other units of length can also be used.

[0069] [Master lens] -Converter lens numerical examples 1 to 6 common- Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 23.706 2.83 1.91082 35.3 16.13 2 63.184 0.25 14.42 3 22.266 0.90 1.48749 70.2 12.89 4 7.213 4.00 10.11 5 ∞ 3.26 8.13 (Flare cut aperture) 6 (Aperture) ∞ 3.24 8.78 7 -16.321 4.82 1.69680 55.5 9.30 8 -8.400 0.80 1.80610 33.3 11.37 9 -36.438 0.20 13.67 10 227.537 4.39 1.59522 67.7 15.23 11 -15.547 0.90 16.72 12* -34.842 3.55 1.58313 59.4 17.76 13 -15.035 35.68 18.94 Image plane ∞ Aspheric Data Side 12 K = 0.00000e+000 A 4=-5.24174e-005 A 6= 5.25723e-008 A 8=-3.53661e-009 A10= 3.36031e-011 A12=-1.48386e-013 Master lens data Focal length 24.50 F-number: 2.88 Half angle of view (degrees) 29.14 Image height 13.66 Lens length 64.83 BF 35.68 Entrance pupil position 10.34 Exit pupil position -35.77 Front principal point position 26.44 Back principal point position 11.18 Master lens single lens data Lens starting surface focal length 1 1 40.28 2 3 -22.32 3 7 19.87 4 8 -13.72 5 10 24.62 6 12 42.54

[0070] [Converter lens]

[0071] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 141.314 1.20 1.95375 32.3 25.80 2 20.811 8.90 1.80518 25.4 25.40 3 -50.545 4.45 25.60 4 -36.637 1.20 2.00100 29.1 24.10 5 62.836 8.70 1.62588 35.7 25.00 6 -19.857 1.30 2.00100 29.1 25.80 7 -424.225 7.20 29.00 8 -74.271 9.35 1.59551 39.2 35.20 9 -25.409 13.96 37.90 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 39.54 F-number: 4.65 Half angle of view (degrees) 28.68 Image height 21.64 Lens length 89.59 BF 13.96 Converter lens data Focal length -148.00 Lens length: 42.30 Front principal point position -24.78 Back principal point position -76.86 Magnification 1.61 Converter lens single lens data Lens starting surface focal length 1 1 -25.71 2 2 19.39 3 4 -22.98 4 5 25.13 5 6 -20.84 6 8 60.53

[0072] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 108.446 1.20 2.00100 29.1 25.90 2 18.934 8.60 1.85478 24.8 25.40 3 -62.820 4.00 25.40 4 -49.683 1.20 2.05090 26.9 24.30 5 27.755 6.00 1.80810 22.8 24.90 6 -109.942 1.30 25.50 7 -45.352 1.20 2.05090 26.9 25.60 8 144.322 0.10 27.30 9 49.805 5.00 1.53172 48.8 29.50 10 -100.714 1.30 30.30 11 -52.534 1.60 2.00100 29.1 30.40 12 -149.361 2.90 32.10 13 -86.192 8.00 1.54072 47.2 34.30 14 -27.523 13.08 36.50 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 39.21 F-number: 4.61 Half angle of view (degrees) 28.89 Image height 21.64 Lens length 88.80 BF 13.08 Converter lens data Focal length -83.09 Lens length: 42.40 Front principal point position 0.34 Back principal point position -36.78 Magnification 1.60 Converter lens single lens data Lens starting surface focal length 1 1 -23.07 2 2 17.89 3 4 -16.81 4 5 27.97 5 7 -32.73 6 9 63.41 7 11 -81.63 8 13 71.36

[0073] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 71.603 1.20 2.05090 26.9 25.50 2 17.334 9.10 1.85478 24.8 24.20 3 -55.856 0.45 24.00 4 -83.837 1.20 2.00100 29.1 23.40 5 15.257 8.15 1.80810 22.8 22.50 6 -109.942 3.45 22.80 7 -36.477 1.20 2.05090 26.9 22.80 8 53.517 0.20 24.30 9 38.586 4.70 1.53172 48.8 26.20 10 -174.517 6.95 27.20 11 -127.684 1.60 2.00100 29.1 32.50 12 424.763 4.65 33.50 13 -73.668 10.00 1.51742 52.4 35.20 14 -24.017 11.00 37.90 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 49.27 F-number: 5.79 Half angle of view (degrees) 23.71 Image height 21.64 Lens length 97.18 BF 11.00 Converter lens data Focal length -81.18 Lens length: 52.85 Front principal point position -9.30 Back principal point position -71.02 Magnification 2.01 Converter lens single lens data Lens starting surface focal length 1 1 -22.01 2 2 16.42 3 4 -12.82 4 5 17.08 5 7 -20.50 6 9 59.89 7 11 -97.93 8 13 64.44

[0074] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 81.547 1.20 2.05090 26.9 25.60 2 17.175 8.90 1.85478 24.8 24.40 3 -74.877 0.40 24.10 4 -800.041 1.20 2.00100 29.1 23.60 5 15.215 8.10 1.80810 22.8 22.40 6 -109.942 1.35 22.50 7 -59.136 1.20 2.00100 29.1 22.40 8 800.004 3.95 22.80 9 -35.142 1.20 2.05090 26.9 23.40 10 309.433 0.15 25.30 11 50.320 5.10 1.53172 48.8 28.20 12 -77.229 0.60 29.10 13 -79.630 1.60 2.00100 29.1 29.20 14 387.478 6.50 30.70 15 -116.685 10.00 1.51742 52.4 35.50 16 -25.328 13.96 37.90 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 49.40 F-number: 5.81 Half angle of view (degrees) 23.65 Image height 21.64 Lens length 98.73 BF 13.96 Converter lens data Focal length -75.46 Lens length: 51.45 Front principal point position -6.52 Back principal point position -62.68 Magnification 2.02 Converter lens single lens data Lens starting surface focal length 1 1 -20.90 2 2 17.11 3 4 -14.91 4 5 17.03 5 7 -54.97 6 9 -29.98 7 11 58.11 8 13 -65.88 9 15 60.27

[0075] [Numerical Example 5] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 105.372 1.10 1.90525 35.0 25.80 2 20.274 9.30 1.74077 27.8 25.40 3 -43.036 3.30 25.50 4 -34.856 1.20 1.85150 40.8 24.20 5 50.808 9.00 1.54072 47.2 24.90 6 -19.532 1.30 2.00330 28.3 25.60 7 -612.486 7.20 28.90 8 -70.239 9.60 1.61293 37.0 35.20 9 -24.676 13.95 37.90 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 39.45 F-number: 4.64 Half angle of view (degrees) 28.74 Image height 21.64 Lens length 89.28 BF 13.95 Converter lens data Focal length -162.19 Lens length 42.00 Front principal point position -29.93 Back principal point position -84.93 Magnification 1.61 Converter lens single lens data Lens starting surface focal length 1 1 -27.90 2 2 19.84 3 4 -24.12 4 5 27.32 5 6 -20.13 6 8 57.46

[0076] [Numerical Example 6] Unit: mm Surface Data Surface number rd nd vd Effective diameter 1 258.268 1.00 2.00100 29.1 25.80 2 23.518 7.70 1.85478 24.8 25.70 3 -54.781 6.10 25.90 4 -30.390 1.00 2.05090 26.9 24.40 5 31.048 7.40 1.89286 20.4 26.30 6 -48.829 1.00 2.24163 16.9 27.30 7 -1396.349 8.60 28.70 8 -130.600 9.80 1.51742 52.4 36.30 9 -26.447 13.65 38.60 Image plane ∞ Master lens to converter lens distance 4.19 Various data when the converter lens is placed on the image side of the master lens Focal length 39.02 F-number: 4.59 Half angle of view (degrees) 29.00 Image height 21.64 Lens length 89.58 BF 13.65 Converter lens data Focal length -194.07 Lens length: 42.60 Front principal point position -40.70 Back principal point position -101.32 Magnification 1.59 Converter lens single lens data Lens starting surface focal length 1 1 -25.90 2 2 20.16 3 4 -14.49 4 5 22.23 5 6 -40.77 6 8 62.10

[0077] [Table 1]

[0078] [Table 2]

[0079] [Example of imaging device] FIG. 22 is a diagram showing the configuration of an imaging device (digital camera) 10. FIG. 22(a) is a perspective view, and FIG. 22(b) is a side view. The imaging device 10 includes a camera body 13, a master lens ML, a converter lens RCL similar to any one of the above-mentioned embodiments 1 to 6, and a light receiving element (imaging element) 12 that photoelectrically converts an image formed by the master lens ML and the converter lens RCL. An imaging element such as a CCD sensor or a CMOS sensor can be used as the light receiving element 12. The master lens ML and the converter lens RCL may be integral with the camera body 13, or each may be detachably attached to the camera body 13.

[0080] When the master lens ML and the converter lens RCL are constructed integrally with the camera body 13, the converter lens RCL is constructed so as to be insertable and detachable onto the optical axis.

[0081] [Example of interchangeable lenses] The present invention can also be applied to an interchangeable lens in which a master lens ML and a converter lens RCL are configured in the same lens barrel and are detachable from an imaging device. The interchangeable lens may be a fixed focal length lens or a zoom lens with a variable focal length. In this case, the converter lens RCL is configured to be removable from the optical axis. The converter lens RCL is positioned on or off the optical axis in response to an instruction from a user via an operating member or a user interface.

[0082] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications and alterations are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0083] RCL Converter Lens ML Master Lens

Claims

1. A converter lens is disposed on the image side of the master lens, has a negative refractive power as a whole, and lengthens the focal length of the entire system, The converter lens has three positive lenses, the converter lens has three negative lenses, In the converter lens, a lens disposed closest to the image side has a positive refractive power, and a lens disposed second closest to the image side has a negative refractive power, When the average refractive index of the material of the three negative lenses at the d line is Ndave, 1.92<Ndave<2.10 A converter lens characterized by satisfying the following conditional expressions:

2. When the radius of curvature of the object side surface of the converter lens arranged closest to the image side is R1 and the radius of curvature of the image side surface is R2, 1.30<(R1+R2) / (R1-R2)<2.50 2. The converter lens according to claim 1, which satisfies the following condition:

3. Let sk be the air-equivalent length from the surface of the converter lens closest to the image side to the image plane, and TD be the distance on the optical axis from the surface of the converter lens closest to the object side to the surface closest to the image side, 0.10<sk / TD<0.50 3. The converter lens according to claim 1, wherein the following condition is satisfied:

4. 4. The converter lens according to claim 1, wherein the converter lens has four or more positive lenses.

5. An interchangeable lens comprising: a master lens; and a converter lens according to any one of claims 1 to 4.

6. 6. An imaging device comprising: a master lens; the converter lens according to claim 1; and an imaging element that receives an image formed by the master lens and the converter lens.

Images