Rear converter lens, lens device, and imaging device

Abstract

This invention provides a rear converter lens with excellent optical performance capable of correcting chromatic aberration of near-infrared light from the main lens. [Solution] A rear converter lens positioned on the image side of the main lens, comprising a first positive lens, a second positive lens, and a first negative lens, wherein the materials of the first positive lens, the second positive lens, and the first negative lens are appropriately set to define the anomalous dispersion of the C-line and t-line based on the partial dispersion ratio of the C-line and t-line and the Abbe number in the d-line.

Description

Technical Field

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

Background Art

[0002] Conventionally, a rear converter lens has been proposed which is disposed on the image side of a main lens and adds various functions. (Patent Documents 1, 2)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, a zoom lens optimized for visible light has had a problem that correction of chromatic aberration in the near-infrared region other than visible light is insufficient. In response to such a problem, it is conceivable to correct the chromatic aberration of the near-infrared region of the main lens with a rear converter lens. The rear converter lenses of Patent Documents 1 and 2 are sufficient for correcting chromatic aberration from visible light to near-infrared light generated by the rear converter lens itself, but insufficient in terms of the effect of correcting chromatic aberration of near-infrared light of the main lens. The present invention has been made in view of such problems, and an object thereof is to provide a rear converter lens that sufficiently corrects chromatic aberration of near-infrared light of a main lens.

Means for Solving the Problems

[0005] To solve the above problems, a rear converter lens according to one aspect of the present invention is a rear converter lens arranged on the image side of a main lens, having a first positive lens, a second positive lens, and a first negative lens, wherein when the partial dispersion ratio of the material with respect to the C line and t line is θct and the Abbe number at the d line is νd, the anomalous dispersion Δθct with respect to the C line and t line is, Δθct=θct-(0.0046925×νd+0.5466489) As defined, and when the anomalous dispersion of the C-line and t-line of the materials of the first positive lens, the second positive lens, and the first negative lens are Δθct_p1, Δθct_p2, and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 -0.20 ≤ Δθct_p2 ≤ -0.02 0.017≦Δθct_n1≦0.05 It is characterized by satisfying the following conditions.

[0006] Furthermore, another embodiment of the present invention is a rear converter lens disposed on the image side of a main lens, comprising a positive lens and a negative lens, wherein the partial dispersion ratio of the material with respect to the C line and t line is θct, the Abbe number at the d line is νd, and the anomalous dispersion of the C line and t line is Δθct, Δθct=θct-(0.0046925×νd+0.5466489) As defined, and when the anomalous dispersion properties of the C-line and t-line of the materials of the positive lens and the negative lens are Δθct_p1 and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 0.017≦Δθct_n1≦0.05 It is characterized by satisfying the following conditions. [Effects of the Invention]

[0007] According to the present invention, a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens can be provided. [Brief explanation of the drawing]

[0008] [Figure 1]This is a cross-sectional view at the wide-angle end when the rear converter lens of Example 1 is attached to the main lens, with infinity focus. [Figure 2] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 1 is attached to the main lens and the focus is at infinity. [Figure 3] This is a cross-sectional view of the lens at the wide-angle end when the rear converter lens of Example 2 is attached to the main lens, with infinity focus. [Figure 4] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 2 is attached to the main lens, at infinity focus. [Figure 5] This is a cross-sectional view of the lens at the wide-angle end when the rear converter lens of Example 3 is attached to the main lens, with infinity focus. [Figure 6] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 3 is attached to the main lens, with infinity focus. [Figure 7] This is a cross-sectional view of the lens at the wide-angle end when the rear converter lens of Example 4 is attached to the main lens, with infinity focus. [Figure 8] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 4 is attached to the main lens, with infinity focus. [Figure 9] This is a cross-sectional view of the lens at the wide-angle end when the rear converter lens of Example 5 is attached to the main lens, with infinity focus. [Figure 10] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 5 is attached to the main lens, with infinity focus. [Figure 11] This is a cross-sectional view of the lens at the wide-angle end when the rear converter lens of Example 6 is attached to the main lens, with infinity focus. [Figure 12] This is a vertical aberration diagram at the wide-angle end when the rear converter lens of Example 6 is attached to the main lens, with infinity focus. [Figure 13] This is a schematic diagram of the main components of the imaging device of the present invention.

Best Mode for Carrying Out the Invention

[0009] The preferred embodiments of the present invention will be described below. The rear converter lens Gr according to this embodiment is disposed on the image side of the main lens Gm and is configured to include a first positive lens Lp1, a second positive lens Lp2, and a first negative lens Ln1. When the anomalous dispersions of the materials of the first positive lens Lp1, the second positive lens Lp2, and the first negative lens Ln1 with respect to the C-line and the t-line are Δθct_p1, Δθct_p2, and Δθct_n1, respectively, -0.20 ≦ Δθct_p1 ≦ -0.02 ···(1) -0.20 ≦ Δθct_p2 ≦ -0.02 ···(2) 0.017 ≦ Δθct_n1 ≦ 0.05 ···(3) the following conditions are satisfied.

[0010] However, the anomalous dispersion Δθct of the material with respect to the C-line and the t-line is given by: Δθct = θct - (0.0046925 × νd + 0.5466489) where θct is the partial dispersion ratio of the material with respect to the C-line and the t-line, and νd is the Abbe number with respect to the d-line. Here, when the refractive indices of the optical material with respect to the d-line, C-line, F-line, and t-line are Nd, NC, NF, and Nt, respectively, the Abbe number νd and the partial dispersion ratio θct are given by: νd = (Nd - 1) / (NF - NC) θct = (NC - Nt) / (NF - NC) respectively.

[0011] Thus, the rear converter lens Gr according to this embodiment is configured with a first positive lens Lp1, a second positive lens Lp2, and a first negative lens Ln1 made of materials having appropriate anomalous dispersions with respect to the C-line and the t-line. As a result, a rear converter lens Gr capable of correcting the chromatic aberration of near-infrared light of the main lens Gm is realized.

[0012] Generally, the main lens Gm, which is specialized for correcting chromatic aberration of visible light, retains axial chromatic aberration of near-infrared light in the over-direction (away from the object) relative to the reference wavelength (d line). In this invention, the over-axis chromatic aberration of the main lens Gm is corrected by applying materials with a refractive index for near-infrared light that is relatively higher than that for visible light to at least two positive lenses (first positive lens Lp1, second positive lens Lp2) of the rear converter lens Gr. Specifically, materials with large negative anomalous dispersion of C-line and t-line are applied to the first positive lens Lp1 and the second positive lens Lp2.

[0013] Furthermore, in this invention, at least one negative lens (first negative lens Ln1) of the rear converter lens Gr is made of a material whose refractive index for near-infrared light is relatively lower than that for visible light. This suppresses the occurrence of axial chromatic aberration in the over-direction for near-infrared light that remains after the visible light color correction of the rear converter lens Gr. Specifically, the first negative lens Ln1 is made of a material in which the anomalous dispersion of C-line and t-line is large in the positive direction.

[0014] If the upper limit of condition (1) or condition (2) is exceeded, the anomalous dispersion of the materials of the first positive lens Lp1 and the second positive lens Lp2 becomes too large in the positive direction, and the effect of correcting axial chromatic aberration of near-infrared light becomes too small. If the lower limit of condition (1) or condition (2) is exceeded, materials with too low a refractive index at the reference wavelength (d line) are selected for the first positive lens Lp1 and the second positive lens Lp2, making it difficult to adequately correct spherical aberration.

[0015] If the upper limit of condition (3) is exceeded, the Abbe number of the first negative lens Ln1 will be too low, resulting in the selection of a material with excessively low dispersion, making it difficult to achieve first-order achromatic aberration of visible light. If the lower limit of condition (3) is exceeded, the anomalous dispersion of the first negative lens Ln1 will become too large in the negative direction, making it difficult to suppress axial chromatic aberration in the over-direction for near-infrared light. More preferably, the conditional expressions (1) to (3) should be set as follows. -0.18≦Δθct_p1≦-0.03 (1a) -0.18≦Δθct_p2≦-0.03 (2a) 0.018≦Δθct_n≦0.04 (3a)

[0016] More preferably, the conditional expressions (1a) to (3a) should be set as follows. -0.17≦Δθct_p1≦-0.04 (1b) -0.17≦Δθct_p2≦-0.04 (2b) 0.0182≦Δθct_n≦0.036 (3b)

[0017] In a more desirable aspect of the present invention, when the Abbe numbers for the d-line of the first positive lens Lp1 and the second positive lens Lp2 are νp1 and νp2, respectively, 50 ≤ νp1 ≤ 100 ···(4) 50 ≤ νp² ≤ 100 ···(5) It is characterized by satisfying the following conditions.

[0018] If the upper limit of condition (4) or condition (5) is not met, the materials for the first positive lens Lp1 and the second positive lens Lp2 will have excessively high dispersion, making it difficult to correct axial chromatic aberration in visible light. If the lower limit of condition (4) or condition (5) is not met, materials with too low a refractive index at the reference wavelength (d line) will be selected for the first positive lens Lp1 and the second positive lens Lp2, making it difficult to adequately correct spherical aberration.

[0019] In a more desirable aspect of the present invention, when the Abbe number of the first negative lens Ln1 with respect to the d line is νn1, 30 ≤ νn1 ≤ 80 ···(6) It is characterized by satisfying the following conditions. If the upper limit of condition (6) is not met, the Abbe number of the first negative lens Ln1 becomes too low-dispersion, making it difficult to correct the first-order achromaticity of visible light. If the lower limit of condition (6) is not met, the Abbe number of the first negative lens Ln1 becomes too high-dispersion, making it difficult to correct the second-order spectrum of visible light.

[0020] In a more desirable aspect of the present invention, a second negative lens Ln2 is provided in addition to the first negative lens Ln1, and when the anomalous dispersion Δθct_n2 of the C line and t line of the second negative lens Ln2 is defined as follows: 0.017 ≤ Δθct_n² ≤ 0.05 ···(7) It is characterized by satisfying the following conditions. If the upper limit of condition (7) is not met, the Abbe number of the second negative lens Ln2 will be too low, resulting in the selection of a material with excessively low dispersion, making it difficult to achieve first-order achromatic aberration of visible light. If the lower limit of condition (7) is not met, the anomalous dispersion of the second negative lens Ln2 will become too large in the negative direction, making it difficult to suppress axial chromatic aberration in the over-direction for near-infrared light.

[0021] In a more desirable embodiment of the present invention, when the focal length of the first positive lens Lp1 is fp1 and the focal length of the rear converter lens Gr is f, 0.02≦fp1 / |f|≦0.8 ···(8) It is characterized by satisfying the following conditions. If the upper limit of condition (8) is not met, the refractive power of the first positive lens Lp1 becomes too weak, resulting in insufficient correction of axial chromatic aberration in near-infrared light. If the lower limit of condition (8) is not met, the refractive power of the first positive lens Lp1 becomes too weak, making it difficult to adequately correct spherical aberration.

[0022] In a more desirable embodiment of the present invention, when the focal length of the second positive lens Lp2 is fp2 and the focal length of the rear converter lens Gr is f, 0.05≦fp2 / |f|≦1.2 ···(9) It is characterized by satisfying the following conditions. If the upper limit of condition (9) is not met, the refractive power of the second positive lens Lp2 becomes too weak, resulting in insufficient correction of axial chromatic aberration in near-infrared light. If the lower limit of condition (9) is not met, the refractive power of the second positive lens Lp2 becomes too weak, making it difficult to adequately correct spherical aberration.

[0023] In a more desirable aspect of the present invention, when the focal length of the first negative lens Ln1 is fn1 and the focal length of the rear converter lens Gr is f, -0.9≦fn1 / |f|≦-0.02 ···(10) It is characterized by satisfying the following conditions. If the upper limit of condition (10) is not met, the refractive power of the first negative lens Ln1 becomes too strong, making it difficult to suppress axial chromatic aberration in the over-direction for near-infrared light. If the lower limit of condition (10) is not met, the refractive power of the first negative lens Ln1 becomes too weak, making it difficult to perform first-order achromatic aberration for visible light.

[0024] In a more desirable embodiment of the present invention, the rear converter lens Gr has a third positive lens Lp3, and when the anomalous dispersion of the C-line and t-line of the material of the third positive lens Lp3 is Δθct_p3 and the refractive index with respect to the d-line is Np3, -0.20 ≤ Δθct_p3 ≤ -0.02 ···(11) 1.6 ≤ Np3 ≤ 1.8 ···(12) It is characterized by satisfying the following conditions. If the upper limit of condition (11) is not met, the anomalous dispersion of the material of the third positive lens Lp3 becomes too large in the positive direction, and the effect of correcting axial chromatic aberration of near-infrared light becomes too small. If the lower limit of condition (11) is not met, a material with a low refractive index at the reference wavelength (d line) must be selected for the third positive lens Lp3, making it difficult to adequately correct spherical aberration.

[0025] If the upper limit of condition (12) is not met, the material of the third positive lens Lp3 will have too much dispersion, making it difficult to correct axial chromatic aberration of visible light. If the lower limit of condition (12) is not met, a material with a low refractive index at the reference wavelength (d line) will have to be selected for the third positive lens Lp3, making it difficult to adequately correct spherical aberration.

[0026] In a more desirable aspect of the present invention, when the ratio of the combined focal length of the main lens Gm and the rear converter lens Gr to the focal length of the main lens Gm is β (β = (combined focal length of the main lens Gm and the rear converter lens Gr) / (focal length of the main lens Gm)), 0.6 ≤ β ≤ 2.2 ···(13) It is characterized by satisfying the following conditions. If the upper limit of condition (13) is not met, the magnification of the rear converter lens Gr becomes too large, making it difficult to correct the chromatic aberration of near-infrared light from the main lens Gm. If the lower limit of condition (13) is not met, the positive refractive power of the rear converter lens Gr becomes too strong, making it difficult to adequately correct spherical aberration.

[0027] In a more desirable aspect of the present invention, it is preferable to set the numerical ranges of conditional expressions (4) to (13) as follows. 60 ≤ νp1 ≤ 98 ···(4a) 60 ≤ νp² ≤ 98 ···(5a) 32 ≤ νn1 ≤ 70 ···(6a) 0.018≦Δθct_n2≦0.04 (7a) 0.03≦fp1 / |f|≦0.75 (8a) 0.06≦fp2 / |f|≦1.15 (9a) -0.88≦fn1 / |f|≦-0.03 ···(10a) -0.1≦Δθct_p3≦-0.025 (11a) 1.67 ≤ Nd3 ≤ 1.78 ···(12a) 0.67 ≤ β ≤ 2.1 ···(13a)

[0028] The following describes each embodiment according to the embodiments with reference to the drawings. First, we will describe the main lens Gm, which has a common configuration to which the rear converter lens Gr of each embodiment described later is applied.

[0029] (Main lens Gm) The main lens Gm is composed of four lens groups, arranged from the object side to the image side: the first lens group L1 with positive refractive power, the second lens group L2 with negative refractive power, the third lens group L3 with negative refractive power, the fourth lens group L4 with positive refractive power, and the fifth lens group L5 with positive refractive power. The spacing between adjacent lens groups changes during zooming.

[0030] During zooming from the wide-angle end to the telephoto end, the second lens group L2 moves toward the image, while the third lens group L3 and the fourth lens group L4 move toward the object along different convex trajectories. The first lens group L1 and the fifth lens group L5 do not move for zooming.

[0031] The first lens group L1 consists of the 1st to 11th surfaces from the object side, and the 5th and 6th lenses, corresponding to the 8th to 11th surfaces, move along the optical axis during focusing. The second lens group L2 consists of the 12th to 18th surfaces from the object side. The third lens group L3 consists of the 19th to 23rd surfaces from the object side. The fourth lens group L4 consists of the 24th to 27th surfaces from the object side. The 28th surface is the aperture diaphragm and does not move for zooming. The fifth lens group L5 consists of the 29th to 41st surfaces from the object side.

[0032] I is the image plane, and when used as an imaging optical system for surveillance cameras and video cameras, it corresponds to the imaging surface of a solid-state image sensor (photoelectric conversion element) that receives the image formed by the main lens Gm and the rear converter lens Gr and converts it into photoelectric light. Next, the characteristics of the rear converter lens Gr in each embodiment will be described. [Examples]

[0033] Figure 1 shows the overall configuration of the optical system when the rear converter lens Gr according to Example 1 is placed on the main lens Gm at the wide-angle end when focusing at infinity. Figure 2 shows a longitudinal aberration diagram with the rear converter lens Gr according to Example 1 positioned on the main lens Gm at the wide-angle end when focused at infinity. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F-number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.34 mm, astigmatism on a scale of 0.34 mm, distortion on a scale of 5%, and chromatic aberration on a scale of 0.065 mm.

[0034] The rear converter lens Gr according to Embodiment 1 is positioned on the image side of the main lens Gm, thereby increasing the focal length of the main lens Gm by 1.3 times. The rear converter lens Gr according to Embodiment 1 consists of six lenses arranged in order from the object side to the image side along the optical axis: a negative lens, a cemented lens formed by joining a second positive lens Lp2 and a second negative lens Ln2, a cemented lens formed by joining a first positive lens Lp1 and a first negative lens Ln1, and a third positive lens Lp3.

[0035] The rear converter lens Gr is composed of three positive lenses and three negative lenses, providing a configuration advantageous for correcting spherical aberration and field curvature of visible light. Furthermore, by including lenses made of materials with anomalous dispersion properties regarding the partial dispersion ratio of the C-line and t-line, the effect of correcting the near-infrared chromatic aberration of the main lens Gm with the rear converter lens Gr is achieved.

[0036] As shown in the aberration diagram in Figure 2, the rear converter lens Gr of Example 1 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 1 satisfy equations (1) to (13), and the rear converter lens Gr of Example 1 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens. [Examples]

[0037] Figure 3 shows the overall configuration of the optical system with the rear converter lens Gr according to Example 2 placed on the main lens Gm in the wide-angle end state. Figure 4 shows the longitudinal aberration diagram at the wide-angle end when an object at infinity is in focus, with the rear converter lens Gr according to Example 2 positioned on the main lens Gm. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.34 mm, astigmatism on a scale of 0.34 mm, distortion on a scale of 5%, and chromatic aberration on a scale of 0.065 mm.

[0038] The rear converter lens Gr according to Embodiment 2 is a converter lens that, when placed on the image side of the main lens Gm, expands the focal length of the main lens Gm by 1.3 times. The rear converter lens Gr consists of four lenses arranged in order from the object side along the optical axis: a second negative lens Ln2, a cemented lens formed by joining the first positive lens Lp1 and the first negative lens Ln1, and a second positive lens Lp2.

[0039] By configuring the rear converter lens Gr with two positive lenses and two negative lenses, a configuration advantageous for correcting spherical aberration and field curvature of visible light is achieved. Furthermore, by applying materials to these lenses that exhibit anomalous dispersion in the partial dispersion ratio of the C-line and t-line, the effect of correcting the chromatic aberration of near-infrared light from the main lens Gm with the rear converter lens Gr is achieved.

[0040] As shown in the aberration diagram in Figure 4, the rear converter lens Gr of Example 2 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 2 satisfy equations (1) to (13), and the rear converter lens Gr of Example 2 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens. [Examples]

[0041] Figure 5 shows the overall configuration of the optical system with the rear converter lens Gr according to Example 3 placed on the main lens Gm in the wide-angle end state. Figure 6 shows the longitudinal aberration diagram at the wide-angle end when an object at infinity is in focus, with the rear converter lens Gr according to Example 3 positioned on the main lens Gm. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F-number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.2 mm, astigmatism on 0.2 mm, distortion on 5%, and chromatic aberration on 0.050 mm.

[0042] The rear converter lens Gr according to Embodiment 3 is a converter lens that corrects the chromatic aberration of near-infrared light of the main lens Gm without increasing the focal length of the main lens Gm, by being positioned on the image side of the main lens Gm. The rear converter lens Gr consists of six lenses arranged in order from the object side along the optical axis: a negative lens, a cemented lens formed by joining the second positive lens Lp2 and the second negative lens Ln2, a cemented lens formed by joining the first positive lens Lp1 and the first negative lens Ln1, and the third positive lens Lp3.

[0043] By composing the rear converter lens Gr with three positive lenses and three negative lenses, a configuration advantageous for correcting spherical aberration and field curvature of visible light is achieved. Furthermore, by applying materials with anomalous dispersion in the partial dispersion ratio of the C-line and t-line to these lenses, the effect of correcting the chromatic aberration of near-infrared light from the main lens Gm with the rear converter lens Gr is achieved.

[0044] As shown in the aberration diagram in Figure 6, the rear converter lens Gr of Example 3 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 3 satisfy equations (1) to (13), and the rear converter lens Gr of Example 3 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens. [Examples]

[0045] Figure 7 shows the overall configuration of the optical system with the rear converter lens Gr according to Example 4 placed on the main lens Gm in the wide-angle end state. Figure 8 shows the longitudinal aberration diagram at the wide-angle end when an object at infinity is in focus, with the rear converter lens Gr according to Example 4 positioned on the main lens Gm. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F-number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.1 mm, astigmatism on 0.1 mm, distortion on 5%, and chromatic aberration on 0.035 mm.

[0046] The rear converter lens Gr according to Embodiment 4 is a converter lens that reduces the focal length of the main lens to 0.7 times by being placed on the image side of the main lens Gm. The rear converter lens Gr consists of five lenses arranged in order from the object side along the optical axis: the second negative lens Ln2, the first positive lens Lp1, the cemented lens formed by joining the second positive lens Lp2 and the first negative lens Ln1, and the third positive lens Lp3.

[0047] By configuring the rear converter lens Gr with three positive lenses and two negative lenses, a configuration advantageous for correcting spherical aberration and field curvature of visible light is achieved. Furthermore, by applying materials with anomalous dispersion in the partial dispersion ratio of the C-line and t-line to these lenses, the effect of correcting the chromatic aberration of near-infrared light from the main lens Gm with the rear converter lens Gr is achieved.

[0048] As shown in the aberration diagram in Figure 8, the rear converter lens Gr of Example 4 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 4 satisfy equations (1) to (13), and the rear converter lens Gr of Example 4 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens. [Examples]

[0049] Figure 9 shows the overall configuration of the optical system with the rear converter lens Gr according to Example 5 placed on the main lens Gm in the wide-angle end state. Figure 10 shows the longitudinal aberration diagram at the wide-angle end when an object at infinity is in focus, with the rear converter lens Gr according to Example 5 positioned on the main lens Gm. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F-number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.45 mm, astigmatism on a scale of 0.45 mm, distortion on a scale of 5%, and chromatic aberration on a scale of 0.075 mm.

[0050] The rear converter lens Gr according to Example 5 is a converter lens that, when placed on the image side of the main lens Gm, expands the focal length of the main lens Gm by 1.5 times. The rear converter lens Gr consists of seven lenses arranged in order from the object side along the optical axis: a positive lens, a negative lens, a cemented lens formed by joining the second positive lens Lp2 and the second negative lens Ln2, a cemented lens formed by joining the first positive lens Lp1 and the first negative lens Ln1, and a third positive lens Lp3.

[0051] By composing the rear converter lens Gr with four positive lenses and three negative lenses, a configuration advantageous for correcting spherical aberration and field curvature of visible light is achieved. Furthermore, by applying materials with anomalous dispersion in the partial dispersion ratio of the C-line and t-line to these lenses, the effect of correcting the chromatic aberration of near-infrared light from the main lens Gm with the rear converter lens Gr is achieved.

[0052] As shown in the aberration diagram in Figure 10, the rear converter lens Gr of Example 5 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 5 satisfy equations (1) to (13), and the rear converter lens Gr of Example 5 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens. [Examples]

[0053] Figure 11 shows the overall configuration of the optical system with the rear converter lens Gr according to Example 6 placed on the main lens Gm in the wide-angle end state. Figure 12 shows the longitudinal aberration diagram at the wide-angle end when an object at infinity is in focus, with the rear converter lens Gr according to Example 6 positioned on the main lens Gm. In the longitudinal aberration diagram, the straight line and dashed line in spherical aberration are the d line and t line, respectively. The dashed line and solid line in astigmatism are the meridional image plane and sagittal image plane, respectively, and the dashed line in chromatic aberration is the t line. ω is the half-angle of view, and Fno is the F-number. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.72 mm, astigmatism on a scale of 0.72 mm, distortion on a scale of 5%, and chromatic aberration on a scale of 0.095 mm.

[0054] The rear converter lens Gr according to Example 6 is a converter lens that doubles the focal length of the main lens Gm by being positioned on the image side of the main lens Gm. The rear converter lens Gr consists of eight lenses arranged in order from the object side along the optical axis: a positive lens, a negative lens, another positive lens, a cemented lens formed by joining the second positive lens Lp2 and the second negative lens Ln2, and a cemented lens formed by joining the first positive lens Lp1, the first negative lens Ln1, and the third positive lens Lp3.

[0055] By composing the rear converter lens Gr with five positive lenses and three negative lenses, a configuration advantageous for correcting spherical aberration and field curvature of visible light is achieved. Furthermore, by applying materials with anomalous dispersion in the partial dispersion ratio of the C-line and t-line to these lenses, the effect of correcting the chromatic aberration of near-infrared light from the main lens Gm with the rear converter lens Gr is achieved.

[0056] As shown in the aberration diagram in Figure 12, the rear converter lens Gr of Example 6 effectively corrects each aberration. Furthermore, as shown in Table 1, the numerical values ​​corresponding to each conditional equation of Example 6 satisfy equations (1) to (13), and the rear converter lens Gr of Example 6 realizes a rear converter lens that sufficiently corrects the chromatic aberration of near-infrared light from the main lens.

[0057] Next, numerical examples 1 to 6 corresponding to Examples 1 to 6 of the present invention are shown. In each numerical example, i indicates the order of the surfaces from the object side, ri is the radius of curvature of the i-th surface counted from the object side, di is the distance between the i-th surface and the (i+1)-th surface from the object side, and ndi and νdi are the refractive index and Abbe number of the optical element between the i-th surface and the (i+1)-th surface, respectively. The focal length, F-number, and angle of view represent the values ​​when focused on an object at infinity. BF is the distance from the final surface of the lens to the image plane converted to air equivalent. The main lens Gm is common to all embodiments, with surfaces 1 through 41 corresponding to the main lens Gm, and the surfaces closer to the image plane corresponding to the rear converter lens Gr.

[0058] <Main lens Gm> Unit: mm Surface data Face number rd nd vd 1 -185.439 2.30 1.80100 35.0 2 486.543 2.84 3 -98329.224 2.30 1.80100 35.0 4 91.150 16.10 1.49700 81.5 5 -129.965 0.40 6 165.185 7.38 1.43387 95.1 7 -347.780 6.90 8 109.329 10.97 1.61800 63.3 9 -264.615 0.15 10 63.587 5.74 1.77250 49.6 11 114.104 (variable) 12 65.758 0.90 1.88300 40.8 13 14.444 6.74 14 -76.887 7.75 1.80810 22.8 15 -13.515 0.70 1.88300 40.8 16 56.355 0.20 17 25.182 2.72 1.67270 32.1 18 53.836 (variable) 19 290.152 0.75 1.77250 49.6 20 24.237 2.69 1.84666 23.8 21 51.848 4.44 22 -21.958 0.75 1.77250 49.6 23 -41.575 (variable) 24 -97.365 3.75 1.63854 55.4 25 -28.574 0.15 26 108.068 3.39 1.51633 64.1 27 -100.494 (variable) 28 (aperture) ∞ 1.30 29 39.067 7.36 1.51742 52.4 30 -38.220 0.90 1.83481 42.7 31 214.266 32.40 32 78.982 4.90 1.49700 81.5 33 -51.551 3.48 34 156.842 1.40 1.83400 37.2 35 19.962 5.80 1.48749 70.2 36 127.749 0.20 37 52.200 5.90 1.51823 58.9 38 -32.007 1.40 1.83481 42.7 39 -361.712 7.50 40 44.409 5.35 1.50127 56.5 41 -58.231 38.40 Image plane ∞ Various data Zoom ratio 21.98 Wide-angle, Medium, Telephoto Focal length 7.70 36.06 169.16 F-number 1.90 1.90 2.80 0.00 0.00 0.00 Image height 0.00 0.00 0.00 Lens length: 268.34 268.31 268.13 BF 38.40 38.40 38.40 d11 0.89 36.86 51.88 d18 54.99 6.83 7.98 d23 5.30 10.60 1.15 d27 0.81 7.71 1.00 Zoom lens group data Group starting plane focal length 1 1 67.38 2 12 -13.71 3 19 -36.63 4 24 38.57 5 28 54.53

[0059] <Numerical Example 1> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 -826.194 0.90 1.64000 60.1 0.8645 43 25.634 4.68 44 -58.642 4.10 1.55200 70.7 0.8096 45 -25.244 0.90 1.64000 60.1 0.8645 46 -316.776 0.60 47 46.317 8.95 1.55200 70.7 0.8096 48 -21.563 0.90 1.64000 60.1 0.8645 49 -122.170 0.20 50 85.954 4.48 1.69930 51.1 0.7593 51 -76.002 38.07 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 5.90 Focal length 10.07 F-number 2.49 Half-angle 32.84 Image height 6.50 Lens length: 299.58 BF 38.07 Focal length of rear converter lens Gr 289.09 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 -38.83 2 44 76.94 3 45 -42.91 4 47 27.97 5 48 -41.06 6 50 58.35

[0060] <Numerical Example 2> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 -110.280 1.20 1.51633 64.1 0.8687 43 23.839 6.55 44 -348.990 9.66 1.55200 70.7 0.8096 45 -17.068 1.20 1.51633 64.1 0.8687 46 147.386 0.20 47 36.548 8.35 1.59522 67.7 0.7953 48 -79.221 40.91 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 2.89 Focal length 10.03 F-number 2.48 Field of view 32.96 Image height 6.50 Lens length: 300.85 BF 40.91 Focal length of rear converter lens Gr 349.59 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 -37.85 2 44 32.18 3 45 -29.55 4 47 43.18

[0061] <Numerical Example 3> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 -87.388 0.90 1.64000 60.1 0.8645 43 25.967 1.79 44 40.967 7.07 1.55200 70.7 0.8096 45 -25.128 0.90 1.64000 60.1 0.8645 46 48.408 0.60 47 32.116 9.72 1.59522 67.7 0.7953 48 -18.627 0.90 1.64000 60.1 0.8645 49 -41.436 0.20 50 118.430 6.17 1.75106 43.1 0.7100 51 ∞ 23.24 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 6.60 Focal length 7.87 F-number 1.94 Field of view 32.44 Image height 5.00 Lens length: 287.99 BF 23.24 Focal length of rear converter lens Gr 104.16 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 -31.18 2 44 29.33 3 45 -25.72 4 47 21.33 5 48 -53.70 6 50 157.69

[0062] <Numerical Example 4> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 -30.282 0.90 1.65160 58.5 0.8525 43 32.057 2.10 44 36.476 6.79 1.43875 94.9 0.8373 45 -24.088 0.00 46 31.892 4.99 1.43875 94.9 0.8373 47 -82.254 0.90 1.61340 44.3 0.7825 48 36.951 0.20 49 29.488 6.20 1.75106 43.1 0.7100 50 -381.032 20.09 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 1.98 Focal length 5.45 F-number 1.35 Field of view 32.70 Image height 3.50 Lens length: 274.05 BF 20.09 Focal length of rear converter lens Gr 47.59 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 -23.76 2 44 34.24 3 46 53.09 4 47 -41.45 5 49 36.68

[0063] <Numerical Example 5> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 100.000 3.00 1.59522 67.7 0.7953 43 -100.000 1.00 44 -79.769 0.90 1.64000 60.1 0.8645 45 23.972 4.33 46 -43.116 4.50 1.59522 67.7 0.7953 47 -16.402 0.90 1.64000 60.1 0.8645 48 4049.304 0.60 49 49.907 8.75 1.59522 67.7 0.7953 50 -16.750 0.90 1.65160 58.5 0.8525 51 1583.415 0.20 52 143.930 4.28 1.75106 43.1 0.7100 53 -48.946 34.81 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 6.62 Focal length 11.48 F-number 2.83 Field of view 33.16 Image height 7.50 Lens length: 300.69 BF 34.81 Focal length of rear converter lens Gr -687.30 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 84.48 2 44 -28.70 3 46 41.84 4 47 -25.52 5 49 22.15 6 50 -25.43 7 52 49.10

[0064] <Numerical Example 6> Unit: mm Surface data Face number rd nd vd θct (1-41 Main lens Gm) 42 -145.230 3.00 1.59522 67.7 0.7953 43 -41.743 1.00 44 -56.676 0.90 1.64000 60.1 0.8645 45 32.090 2.28 46 200.000 3.00 1.59522 67.7 0.7953 47 -200.000 2.00 48 -38.006 2.72 1.52841 76.5 0.8175 49 -46.587 0.90 1.64000 60.1 0.8645 50 173.871 0.60 51 50.616 9.01 1.55200 70.7 0.8096 52 -15.435 0.90 1.65160 58.5 0.8525 53 27.522 6.61 1.75106 43.1 0.7100 54 -64.240 50.76 Image plane ∞ Various data Distance between the final surface of the main lens Gm d41 4.20 Focal length 15.41 F-number 3.81 Field of view 32.97 Image height 10.00 Lens length: 317.76 BF 50.76 Focal length of rear converter lens Gr -94.08 Rear converter lens Gr individual lens data Lens starting plane, focal length 1 42 97.37 2 44 -31.89 3 46 168.48 4 48 -438.55 5 49 -57.32 6 51 22.52 7 52 -15.05 8 53 26.47

[0065] Table 1 shows the corresponding values ​​for each conditional expression in this embodiment. This embodiment satisfies equations (1) to (13), and realizes a rear converter lens Gr with good correction of various aberrations. [Table 1]

[0066] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its essence.

[0067] The lens surface of the lens constituting the rear converter lens Gr of the present invention may be flat or aspherical. If the lens surface is aspherical, it may be an aspherical surface produced by grinding, a glass molded aspherical surface formed by molding glass into an aspherical shape, or a composite aspherical surface formed by forming an aspherical shape from resin provided on the glass surface. The lens surface may also be a diffractive surface, and the lens may be a refractive index distribution lens (GRIN lens) or a plastic lens.

[0068] Furthermore, an anti-reflective coating having high transmittance over a wide wavelength range may be applied to the lens surface of the lens constituting the rear converter lens Gr of the present invention. This reduces flare and ghosting and achieves high-contrast optical performance.

[0069] (Imaging device) Next, an imaging device equipped with the rear converter lens Gr of the present invention will be described. Figure 13 is a diagram showing the configuration of a camera equipped with the rear converter lens Gr according to the present invention. Camera 1 is a lens-interchangeable camera equipped with a photographic lens 2 as shown in Figure 13. The photographic lens 2 is configured as an optical system in which the rear converter lens Gr is arranged on the image side of the main lens Gm. For example, the photographic lens 2 is configured in which the rear converter lens Gr is detachably attached to the image side of the main lens Gm.

[0070] In camera 1, light from an object (subject) is focused by the photographic lens 2 and, via an optical low-pass filter (not shown), forms an image of the subject on the imaging surface of the imaging unit 3. Then, the subject image is photoelectrically converted by a photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed in the electronic viewfinder 4 provided in camera 1.

[0071] This allows the photographer to observe the subject through the electronic viewfinder 4, and when the photographer presses a release button (not shown), the image converted photoelectrically by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph the subject with the camera 1. With the above configuration, the camera 1 equipped with the rear converter lens Gr according to the present invention can capture images with sufficient correction of chromatic aberration of near-infrared light from the main lens Gm.

[0072] This embodiment includes the following configuration. (Composition 1) A rear converter lens positioned on the image side of the main lens, It has a first positive lens, a second positive lens, and a first negative lens. When the partial dispersion ratio of the material with respect to the C-line and t-line is θct and the Abbe number at the d-line is νd, the anomalous dispersion Δθct with respect to the C-line and t-line is, Δθct=θct-(0.0046925×νd+0.5466489) As defined, and when the anomalous dispersion of the C-line and t-line of the materials of the first positive lens, the second positive lens, and the first negative lens are Δθct_p1, Δθct_p2, and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 -0.20 ≤ Δθct_p2 ≤ -0.02 0.017≦Δθct_n1≦0.05 A rear converter lens characterized by satisfying the following conditions. (Configuration 2) When the Abbe number of the first positive lens is νp1 and the Abbe number of the second positive lens is νp2, 50 ≤ νp1 ≤ 100 50 ≤ νp² ≤ 100 A rear converter lens according to configuration 1, characterized by satisfying the following conditions. (Composition 3) When the Abbe number of the first negative lens is denoted as νn1, 30 ≤ νn1 ≤ 80 A rear converter lens according to configuration 1 or 2, characterized by satisfying the following conditions. (Composition 4) It has a second negative lens, When the anomalous dispersion of the C line and t line of the second negative lens is Δθct_n2, 0.017 ≤ Δθct_n2 ≤ 0.05 A rear converter lens according to any one of configurations 1 to 3, characterized by satisfying the following conditions. (Composition 5) When the focal length of the first positive lens is fp1 and the focal length of the rear converter lens is f, 0.02 ≤ fp1 / |f| ≤ 0.8 A rear converter lens according to any one of configurations 1 to 4, characterized by satisfying the following conditions. (Composition 6) When the focal length of the second positive lens is fp2 and the focal length of the rear converter lens is f, 0.05 ≤ fp² / |f| ≤ 1.2 The rear converter lens according to configuration 4, characterized by satisfying the following conditions. (Composition 7) When the focal length of the first negative lens is fn1 and the focal length of the rear converter lens is f, -0.9 ≤ fn1 / |f| ≤ -0.02 A rear converter lens according to any one of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) It has a third positive lens Lp3, When the anomalous dispersion of the C-line and t-line of the third positive lens is Δθct_p3 and the refractive index with respect to the d-line is Nd3, -0.05 ≤ Δθct_p3 ≤ -0.02 1.6 ≤ Np3 ≤ 1.8 A rear converter lens according to any one of the configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) The rear converter lens according to any one of configurations 1 to 8, characterized in that the first negative lens forms a cemented lens with at least one of the first positive lens or the second positive lens. (Composition 10) A rear converter lens positioned on the image side of the main lens, including a positive lens and a negative lens, Let θct be the partial dispersion ratio of the material for the C-line and t-line, and νd be the Abbe number at the d-line. Let Δθct be the anomalous dispersion of the C-line and t-line. Δθct=θct-(0.0046925×νd+0.5466489) As defined, and when the anomalous dispersion properties of the C-line and t-line of the materials of the positive lens and the negative lens are Δθct_p1 and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 0.017≦Δθct_n1≦0.05 A rear converter lens characterized by satisfying the following conditions. (Composition 11) The device comprises a main lens and a rear converter lens described in any of configurations 1 to 10, which is detachably attached to the image side of the main lens. When β is the ratio of the combined focal length of the main lens and the rear converter lens to the focal length of the main lens, 0.6 ≤ β ≤ 2.2 A lens device characterized by satisfying the following conditions. (Composition 12) An imaging device equipped with a rear converter lens as described in any of configurations 1 to 10. [Explanation of symbols]

[0073] Gm main lens Gr Rear Converter Lens Lp1 First positive lens Lp2 Second positive lens Ln1 First Negative Lens

Claims

1. A rear converter lens positioned on the image side of the main lens, It has a first positive lens, a second positive lens, and a first negative lens. When the partial dispersion ratio of the material with respect to the C-line and t-line is θct, and the Abbe number at the d-line is νd, the anomalous dispersion Δθct with respect to the C-line and t-line is, Δθct=θct-(0.0046925×νd+0.5466489) As defined, when the anomalous dispersion properties of the C-line and t-line of the materials of the first positive lens, the second positive lens, and the first negative lens are Δθct_p1, Δθct_p2, and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 -0.20 ≤ Δθct_p2 ≤ -0.02 0.017 ≤ Δθct_n1 ≤ 0.05 A rear converter lens characterized by satisfying the following conditions.

2. When the Abbe number of the first positive lens is νp1 and the Abbe number of the second positive lens is νp2, 50 ≤ νp1 ≤ 100 50 ≤ νp² ≤ 100 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

3. When the Abbe number of the first negative lens is denoted as νn1, 30 ≤ νn1 ≤ 80 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

4. It has a second negative lens, When the anomalous dispersion of the C line and t line of the second negative lens is denoted as Δθct_n2, 0.017 ≤ Δθct_n2 ≤ 0.05 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

5. When the focal length of the first positive lens is fp1 and the focal length of the rear converter lens is f, 0.02≦fp1 / |f|≦0.8 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

6. When the focal length of the second positive lens is fp2 and the focal length of the rear converter lens is f, 0.05≦fp2 / |f|≦1.2 The rear converter lens according to feature 4, which satisfies the following conditions.

7. When the focal length of the first negative lens is fn1 and the focal length of the rear converter lens is f, -0.9≦fn1 / |f|≦-0.02 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

8. It has a third positive lens Lp3, When the anomalous dispersion of the C-line and t-line of the third positive lens is Δθct_p3 and the refractive index with respect to the d-line is Nd3, -0.05 ≤ Δθct_p3 ≤ -0.02 1.6 ≤ Np3 ≤ 1.8 The rear converter lens according to claim 1, characterized in that it satisfies the following conditions.

9. The rear converter lens according to claim 1, characterized in that the first negative lens constitutes a cemented lens with at least one of the first positive lens or the second positive lens.

10. A rear converter lens positioned on the image side of the main lens, including a positive lens and a negative lens, Let θct be the partial dispersion ratio of the material for the C and t lines, and νd be the Abbe number for the d line. Let Δθct be the anomalous dispersion of the C and t lines. Δθct=θct-(0.0046925×νd+0.5466489) As defined, and when the anomalous dispersion of the C-line and t-line of the materials of the positive lens and the negative lens are Δθct_p1 and Δθct_n1, respectively, -0.20 ≤ Δθct_p1 ≤ -0.02 0.017 ≤ Δθct_n1 ≤ 0.05 A rear converter lens characterized by satisfying the following conditions.

11. The device comprises a main lens and a rear converter lens according to any one of claims 1 to 10, which is detachably attached to the image side of the main lens. When β is the ratio of the combined focal length of the main lens and the rear converter lens to the focal length of the main lens, ０．６≦β≦２．２ A lens device characterized by satisfying the following conditions.

12. An imaging device comprising a rear converter lens according to any one of claims 1 to 10.

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