JP7490433B2 - Reduction optical system and imaging device - Google Patents

Description

The present invention relates to a reduction optical system and an imaging device.

Both Patent Document 1 and Patent Document 2 disclose a reduction optical system that is arranged on the image side of a main optical system (interchangeable lens), and the combined focal length of the main optical system and the reduction optical system is shorter than the focal length of the main optical system.

JP 2000-121932 A U.S. Pat. No. 8,903,232

For movies and photography, a small imaging device that emphasizes mobility and operability is desired, and a small reduction optical system is also required. In addition, a reduction optical system that has sufficient back focus and high optical performance is required. In the reduction optical system according to Numerical Example 3 of Patent Document 1, the object-side surface of the negative lens arranged closest to the object is flat, which is disadvantageous in correcting spherical aberration generated in the reduction optical system. In addition, in the reduction optical system of Patent Document 2, the refractive power of the negative lens arranged closest to the object is weak, so the back focus length is insufficient, which is disadvantageous in correcting field curvature. The present invention aims to provide a reduction optical system that is advantageous in terms of, for example, sufficient back focus, high optical performance, and small size.

One aspect of the present invention is a reduction optical system arranged on the image side of a main optical system and composed of five or six lenses, wherein a composite focal length of the main optical system and the reduction optical system is shorter than a focal length of the main optical system, the focal length of the reduction optical system being f, the focal length of a negative lens arranged closest to the object among the negative lenses included in the reduction optical system being fn, the radius of curvature of the object side lens surface of the negative lens arranged closest to the object being r1, and the lateral magnification of the reduction optical system arranged on the image side of the main optical system being β,
-2.000<fn/f<-0.150
-1.600<f/r1<-0.200
0.500<β<0.900
The reduction optical system is characterized in that it satisfies the following conditional expression:

The present invention can provide a reduction optical system that is advantageous in terms of, for example, sufficient back focus, high optical performance, and compact size.

FIG. 2 is a cross-sectional view of the reduction optical system according to the first embodiment. 4A and 4B are diagrams showing longitudinal aberration of an optical system in which the reduction optical system according to the first embodiment is attached to a main optical system focused at infinity. FIG. 11 is a cross-sectional view of a reduction optical system according to a second embodiment. 13A and 13B are diagrams showing longitudinal aberration of an optical system in which the reduction optical system according to Example 2 is attached to a main optical system focused at infinity. FIG. 11 is a cross-sectional view of a reduction optical system according to a third embodiment. 13A and 13B are diagrams showing longitudinal aberration of an optical system in which a reduction optical system according to Example 3 is attached to a main optical system focused at infinity. FIG. 11 is a cross-sectional view of a reduction optical system according to a fourth embodiment. 13A and 13B are diagrams showing longitudinal aberration of an optical system in which a reduction optical system according to Example 4 is attached to a main optical system focused at infinity. FIG. 13 is a cross-sectional view of a reduction optical system according to a fifth embodiment. 13A and 13B are diagrams showing longitudinal aberration of an optical system in which a reduction optical system according to Example 5 is attached to a main optical system focused at infinity. FIG. 13 is a cross-sectional view of a reduction optical system according to a sixth embodiment. 13A and 13B are diagrams showing longitudinal aberration of an optical system in which a reduction optical system according to Example 6 is attached to a main optical system focused at infinity. FIG. 13 is a cross-sectional view of a reduction optical system according to a seventh embodiment. 13 is a diagram showing longitudinal aberration of an optical system in which the reduction optical system according to Example 7 is attached to a main optical system focused at infinity. A cross-sectional view of the main optical system focused at infinity. FIG. 4 is a diagram showing longitudinal aberration of the main optical system focused at infinity. FIG. 1 is a diagram showing an example of the configuration of an imaging apparatus. FIG. 13 is a diagram showing another example of the configuration of an imaging apparatus.

Below, an embodiment of the present invention will be described with reference to the attached drawings. In principle (unless otherwise specified) throughout all the drawings used to explain the embodiment, the same components will be given the same reference numerals, and repeated explanations will be omitted.

[Embodiment]
A reduction optical system (rear wide converter) according to this embodiment will be described. The reduction optical system is arranged on the image side of the main optical system (interchangeable lens), and the combined focal length of the main optical system and the reduction optical system is shorter than the focal length of the main optical system, which is advantageous in terms of sufficient back focus, high optical performance, and compact size. The reduction optical system is composed of at least five lenses. The focal length of the reduction optical system is f, and the focal length of the negative lens arranged closest to the object among the negative lenses included in the at least five lenses is fn. In addition, the radius of curvature of the object-side surface of the negative lens arranged closest to the object is r1, and the lateral magnification of the reduction optical system arranged on the image side of the main optical system is β. Then, the reduction optical system is as follows:
−2.000<fn/f<−0.150 … (1)
−1.600<f/r1<−0.200 … (2)
0.500<β<0.900 ... (3)
The negative lens arranged closest to the object side is preferably arranged in the first half of the at least five lenses (if the number of lenses is N, the negative lens is M (≦N/2) from the object side; M and N are natural numbers). In the embodiment described later, the negative lens is arranged in the first two from the object side.

By satisfying conditional expression (1), a reduction optical system that is advantageous in terms of sufficient back focus, correction of curvature of field, and compactness can be realized. If conditional expression (1) is not satisfied with respect to the upper limit value, the refractive power of the negative lens arranged closest to the object becomes excessively strong, so that the diameter of the lens arranged closer to the image side than the negative lens increases, which is disadvantageous in terms of compactness of the reduction optical system. If conditional expression (1) is not satisfied with respect to the lower limit value, the refractive power of the negative lens becomes excessively weak, so that it is difficult to place the rear principal point of the reduction optical system sufficiently close to the image side, which is not advantageous in terms of having a sufficient back focus. In addition, if the refractive power of the negative lens is excessively weak, it is necessary to reduce the absolute value of the Petzval sum by a lens other than the negative lens, which is disadvantageous in terms of correction of curvature of field.

By satisfying conditional expression (2), the object-side surface of the negative lens arranged closest to the object becomes concave, realizing a reduction optical system that is advantageous in terms of correcting spherical aberration. If the upper limit of conditional expression (2) is not satisfied, the radius of curvature of the object-side surface of the negative lens becomes excessively large, which is detrimental to the correction of spherical aberration. If the lower limit of conditional expression (2) is not satisfied, the radius of curvature of the object-side surface of the negative lens becomes excessively small, which is detrimental to the correction of higher-order spherical aberration.

If conditional expression (3) is not satisfied with respect to the upper limit, the effect of making the composite focal length of the main optical system and the reduction optical system shorter than the focal length of the main optical system becomes excessively weak. If conditional expression (3) is not satisfied with respect to the lower limit, the refractive power of the reduction optical system becomes excessively strong, which is detrimental in terms of sufficient back focus and high optical performance.

The reduction optical system further preferably comprises:
−1.950<fn/f<−0.200 … (1a)
−1.500<f/r1<−0.250 … (2a)
0.600<β<0.850 (3a)
It is preferable to satisfy the following condition.

In addition, the reduction optical system has a focal length fp of the positive lens that is located closest to the object among the at least five lenses, and
0.100<|fp/fn|<4.000...(4)
By satisfying the conditional expression (4), a reduction optical system advantageous in terms of compactness and high optical performance can be realized. If the upper limit of the conditional expression (4) is not satisfied, the refractive power of the negative lens arranged closest to the object becomes excessively strong, so that the diameter of the lens arranged closer to the image side than the negative lens increases, which is disadvantageous in terms of compactness of the reduction optical system. If the lower limit of the conditional expression (4) is not satisfied, the refractive power of the positive lens arranged closest to the object becomes excessively strong, so that the curvature of each lens constituting the reduction optical system becomes large, which is disadvantageous in correcting high-order spherical aberration and high-order curvature of field.

The reduction optical system further preferably comprises:
0.120<|fp/fn|<3.000...(4a)
It is preferable to satisfy the following condition.

In addition, the reduction optical system is such that, among the negative lenses included in the at least five lenses, the focal length of the negative lens having the strongest refractive power excluding the negative lens arranged closest to the object side is fnmax, and
0.100<fnmax/fn<2.000...(5)
By satisfying conditional expression (5), a reduction optical system advantageous in terms of compactness and high optical performance can be realized. If the upper limit of conditional expression (5) is not satisfied, the refractive power of the negative lens arranged closest to the object becomes excessively strong, so that the diameter of the lens arranged closer to the image than the negative lens becomes excessively large, which is disadvantageous in terms of compactness of the reduction optical system. If the lower limit of conditional expression (5) is not satisfied, the reduction optical system includes a negative lens with an excessively strong refractive power, so that the curvature of the negative lens becomes large, which is disadvantageous in correcting high-order spherical aberration and high-order curvature of field.

The reduction optical system further preferably comprises:
0.120<fnmax/fn<1.800...(5a)
It is preferable to satisfy the following condition.

The reduction optical system further comprises at least five lenses each having a refractive index Nph and a focal length fph,
1.895<Nph... (6)
0.200<fph/f<1.500...(7)
The optical system has at least one positive lens that satisfies the following conditional expressions. By satisfying conditional expressions (6) and (7), a reduction optical system that is advantageous in correcting curvature of field can be realized. If conditional expression (6) is not satisfied, the refractive power of the positive lens constituting the reduction optical system having positive refractive power becomes excessively weak, which is disadvantageous in reducing the absolute value of the Petzval sum (correcting curvature of field). If conditional expression (7) is not satisfied with respect to the upper limit value, the refractive power of the positive lens that satisfies conditional expression (6) becomes excessively weak, which is disadvantageous in reducing the absolute value of the Petzval sum (correcting curvature of field). If conditional expression (7) is not satisfied with respect to the lower limit value, the refractive power of the positive lens that satisfies conditional expression (6) becomes excessively strong, which increases the curvature of each lens that constitutes the reduction optical system, which is disadvantageous in correcting high-order spherical aberration and high-order curvature of field.

The reduction optical system further preferably comprises:
1.920<Npn<2.150 ... (6a)
0.220<fph/f<1.350 (7a)
It is preferable to satisfy the following condition.

In addition, in the reduction optical system, the lens arranged adjacent to the image side of the negative lens arranged closest to the object among the at least five lenses is a positive lens. Also, the lens arranged adjacent to the object side of the positive lens arranged closest to the image among the positive lenses is a negative lens. This is advantageous for reducing the absolute value of the Petzval sum (correcting the field curvature).

In addition, the reduction optical system has at least five lenses, and the lens arranged closest to the image side is a biconvex lens. This is advantageous for providing a sufficient back focus, since the rear principal point of the reduction optical system can be arranged sufficiently close to the image side. This is also advantageous for correcting distortion caused by the negative lens arranged in front of the biconvex lens.

Furthermore, according to this embodiment, it is possible to configure an imaging device having the reduction optical system described above and an imaging element that captures an image formed via the reduction optical system. Alternatively, it is possible to configure an imaging device having an imaging device body that includes the reduction optical system described above. Therefore, according to this embodiment, it is possible to realize an imaging device that enjoys the advantages of the reduction optical system described above.

Below, we will explain examples 1 to 7 related to this embodiment.

Example 1
Fig. 1 is a cross-sectional view of a reduction optical system according to Example 1 (corresponding to Numerical Example 1). Fig. 15 is a cross-sectional view of a main optical system focused at infinity, which is attached to the reduction optical system of each Example. Fig. 16 is a diagram showing longitudinal aberration of the main optical system focused at infinity. Note that the unit of length is mm, including the numerical examples described later, unless otherwise specified.

In FIG. 1, CV indicates a reduction optical system, and F indicates a glass block such as a filter. In FIG. 15, ML indicates a main optical system (interchangeable lens), and SP indicates an aperture stop. In FIG. 1 and FIG. 15, I indicates an image plane, and I may be arranged with an imaging surface of an imaging element. In the diagrams showing longitudinal aberration, the straight line and two-dot chain line in spherical aberration correspond to the d-line and g-line, respectively. The dotted line and solid line in astigmatism correspond to the meridional image plane and sagittal image plane, respectively. The two-dot chain line in magnification chromatic aberration corresponds to the g-line. Also, ω indicates the half angle of view, and Fno indicates the F-number. The full scale of the horizontal axis in the diagrams showing longitudinal aberration is ±0.400 mm for spherical aberration, ±0.400 mm for astigmatism, ±5.000% for distortion, and ±0.100 mm for magnification chromatic aberration. The main optical system is compatible with an image size of 35 mm full size, and its image circle is 43.3 mm.

Figure 2 is a diagram showing the longitudinal aberration of an optical system in which the reduction optical system according to Example 1 is attached to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is located 2.638 mm from the 16th surface, which is the surface closest to the image side of the main optical system, to the image side. The reduction optical system according to this embodiment is composed of, in order from the object side, a meniscus convex lens G1 concave to the image side, a cemented lens formed by cementing a biconcave lens G2 and a meniscus convex lens G3 concave to the image side, a meniscus concave lens G4 convex to the object side, and a biconvex lens G5. In this embodiment, the negative lens arranged closest to the object side among the negative lenses is G2, and the positive lens arranged closest to the object side among the positive lenses is G1. Among the negative lenses, the negative lens with the strongest refractive power excluding the negative lens arranged closest to the object side is G4, and the positive lens arranged closest to the image side among the positive lenses is G5. In addition, the positive lenses that satisfy conditional expressions (6) and (7) are G1 and G3. By mounting the reduction optical system of this embodiment to the main optical system, an image circle with a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.710 is obtained.

The detailed numerical values for each numerical example are shown below. In each numerical example, r is the radius of curvature of each surface, d is the surface spacing, nd or Nd is the absolute refractive index at 1 atmosphere for the d-line of the Fraunhofer line, and νd is the Abbe number. BF is the back focus (air-equivalent length). The refractive indices for the g-line, F-line, d-line, and C-line of the Fraunhofer line are Ng, NF, Nd, and NC, respectively, and the Abbe number νd has the same definition as that generally used, that is, it is expressed as follows:

νd=(Nd−1)/(NF-NC)
The shape of an aspheric surface is expressed by taking the X-axis in the direction of the optical axis, the H-axis in the direction perpendicular to the direction of the optical axis, and the direction of light travelling as positive. The shape of an aspheric surface (deviation from a reference spherical surface) is expressed by the following formula, where R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10 and A12 are aspheric coefficients. Note that "e-Z" means "×10 ^-Z ".

本実施例における条件式（１）ないし条件式（７）に係る値を表１に示す。本実施例は、条件式（１）ないし条件式（７）をすべて満足し、十分なバックフォーカス、高い光学性能、小型の点で有利な縮小光学系を提供することができる。ここで、本実施例に係る縮小光学系は、条件式（１）ないし条件式（３）を満足すればよく、条件式（４）ないし条件式（７）は、必ずしも満足していなくてもよい。なお、条件式（１）ないし条件式（３）に加えて条件式（４）ないし条件式（７）のうちの少なくとも１つを満足している場合、そうしていない場合に比べ、より顕著な効果を奏することができる。

Table 1 shows values related to conditional expressions (1) to (7) in this embodiment. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Here, an imaging device including a reduction optical system CV according to the present embodiment will be described. FIG. 17 is a diagram showing an example of the configuration of an imaging device. In the figure, the imaging device 1 can be, for example, a so-called lens-interchangeable imaging device having an optical system including a main optical system 2 (ML) and a reduction optical system 5 (CV). The imaging device can be a so-called mirrorless camera. The optical system is configured such that a reduction optical system 5 is attached to the image side of the main optical system 2. In the imaging device 1, the optical system forms an image (subject image) on the imaging surface of an imaging element 3 arranged in an imaging device body 6 by light from an object (subject) not shown through an optical low-pass filter not shown. The imaging element 3 captures (captures or photoelectrically converts) the image and generates image data. The image data is displayed on a display unit 4 (image display unit, for example, an electronic viewfinder) included in the imaging device 1 (imaging device body 6). A user of the imaging device can observe the subject through the display unit 4. When a user operates an imaging start member (e.g., a release button), image data obtained via the imaging element 3 is stored, for example, in a storage unit (memory) within the imaging device body 6. In this way, the user can capture an image of a subject using the imaging device 1.

Figure 18 is a diagram showing another example of the configuration of an imaging device. In this figure, the imaging device 1 has an imaging device body 6 including a reduction optical system 5 (CV). The other configuration of the imaging device body 6 is the same as that in Figure 17. The main optical system 2 (ML) is attached to the imaging device body 6 without the reduction optical system 5.

According to this embodiment, it is possible to provide an imaging device 1 having a reduction optical system 5 that is advantageous in terms of sufficient back focus, high optical performance, and small size. The imaging device of this embodiment is not limited to a so-called mirrorless camera, but may be a single-lens reflex camera that has a quick-return mirror in the imaging device body 6 and allows the subject image to be observed through a viewfinder optical system. In addition, the imaging device of this embodiment may be a camera for video, cinema, or broadcast. As described above, according to this embodiment, it is possible to provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and small size, for example.

Example 2
FIG. 3 is a cross-sectional view of a reduction optical system according to Example 2 (corresponding to Numerical Example 2). FIG. 4 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 2 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 4.437 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of, in order from the object side, a biconcave lens G1, a meniscus convex lens G2 concave toward the image side, a cemented lens formed by cementing together a meniscus convex lens G3 concave toward the image side and a meniscus concave lens G4 convex toward the object side, and a biconvex lens G5. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G1, and the positive lens disposed closest to the object side among the positive lenses is G2. The negative lens with the strongest refractive power among the negative lenses, excluding the negative lens disposed closest to the object side, is G4, and the positive lens disposed closest to the image side among the positive lenses is G5. Moreover, the positive lenses that satisfy the conditional expressions (6) and (7) are G2 and G3. By mounting the reduction optical system according to this embodiment to the main optical system, an image circle having a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.714 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Example 3
FIG. 5 is a cross-sectional view of a reduction optical system according to Example 3 (corresponding to Numerical Example 3). FIG. 6 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 3 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 2.640 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of the following lenses, in order from the object side: a meniscus convex lens G1 concave toward the image side, a cemented lens formed by cementing a biconcave lens G2 and a meniscus convex lens G3 concave toward the image side, a meniscus concave lens G4 convex toward the object side, and a cemented lens formed by cementing a meniscus concave lens G5 convex toward the object side and a biconvex lens G6. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G2, and the positive lens disposed closest to the object side among the positive lenses is G1. Among the negative lenses, the negative lens with the strongest refractive power excluding the negative lens arranged closest to the object side is G4, and among the positive lenses, the positive lens arranged closest to the image side is G6. The positive lenses that satisfy conditional expressions (6) and (7) are G1 and G3. By mounting the reduction optical system according to this embodiment on the main optical system, an image circle with a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.780 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Example 4
FIG. 7 is a cross-sectional view of a reduction optical system according to Example 4 (corresponding to Numerical Example 4). FIG. 8 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 4 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 2.636 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of, in order from the object side, a biconvex lens G1, a cemented lens formed by cementing a biconcave lens G2 and a biconvex lens G3 together, a biconcave lens G4, and a biconvex lens G5. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G2, and the positive lens disposed closest to the object side among the positive lenses is G1. Among the negative lenses, the negative lens with the strongest refractive power except for the negative lens disposed closest to the object side is G4, and the positive lens disposed closest to the image side among the positive lenses is G5. The positive lenses that satisfy conditional expressions (6) and (7) are G1 and G3. By mounting the reduction optical system according to this embodiment on the main optical system, an image circle having a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.650 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Example 5
FIG. 9 is a cross-sectional view of a reduction optical system according to Example 5 (corresponding to Numerical Example 5). FIG. 10 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 5 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 5.240 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of, in order from the object side, a meniscus concave lens G1 concave toward the object side, a cemented lens formed by cementing a biconvex lens G2 and a meniscus concave lens G3 convex toward the image side, a biconcave lens G4, and a biconvex lens G5. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G1, and the positive lens disposed closest to the object side among the positive lenses is G2. The negative lens with the strongest refractive power among the negative lenses, excluding the negative lens disposed closest to the object side, is G4, and the positive lens disposed closest to the image side among the positive lenses is G5. Moreover, the positive lens that satisfies the conditional expressions (6) and (7) is G2. By mounting the reduction optical system according to this embodiment to the main optical system, an image circle having a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.714 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Example 6
FIG. 11 is a cross-sectional view of a reduction optical system according to Example 6 (corresponding to Numerical Example 6). FIG. 12 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 6 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 3.540 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of the following lenses, in order from the object side: a biconcave lens G1, a cemented lens formed by cementing together a meniscus convex lens G2 concave to the image side and a meniscus concave lens G3 convex to the object side, a meniscus concave lens G4 convex to the object side, and a cemented lens formed by cementing together a meniscus concave lens G5 convex to the object side and a biconvex lens G6. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G1, and the positive lens disposed closest to the object side among the positive lenses is G2. Among the negative lenses, the negative lens with the strongest refractive power excluding the negative lens arranged closest to the object side is G4, and among the positive lenses, the positive lens arranged closest to the image side is G6. The positive lens that satisfies conditional expressions (6) and (7) is G2. By mounting the reduction optical system according to this embodiment on the main optical system, an image circle with a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.714 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

Example 7
FIG. 13 is a cross-sectional view of a reduction optical system according to Example 7 (corresponding to Numerical Example 7). FIG. 14 is a diagram showing longitudinal aberration of an optical system formed by mounting the reduction optical system according to Example 7 to a main optical system focused at infinity. The surface closest to the object side of the reduction optical system of this embodiment is disposed at a position 2.000 mm toward the image side from the 16th surface, which is the surface closest to the image side of the main optical system. The reduction optical system according to this embodiment is composed of, in order from the object side, a meniscus convex lens G1 concave toward the image side, a cemented lens formed by cementing a biconcave lens G2 and a biconvex lens G3 together, a biconcave lens G4, and a biconvex lens G5. In this embodiment, the negative lens disposed closest to the object side among the negative lenses is G2, and the positive lens disposed closest to the object side among the positive lenses is G1. Among the negative lenses, the negative lens with the strongest refractive power except for the negative lens disposed closest to the object side is G4, and the positive lens disposed closest to the image side among the positive lenses is G5. In addition, the positive lens that satisfies conditional expressions (6) and (7) is G3. By mounting the reduction optical system according to this embodiment on the main optical system, an image circle having a diameter obtained by multiplying the diameter of the image circle of the main optical system by 0.783 is obtained.

The values related to conditional expressions (1) to (7) in this embodiment are shown in Table 1. This embodiment satisfies all of conditional expressions (1) to (7), and can provide a reduction optical system that is advantageous in terms of sufficient back focus, high optical performance, and compact size. Here, the reduction optical system according to this embodiment only needs to satisfy conditional expressions (1) to (3), and does not necessarily have to satisfy conditional expressions (4) to (7). Note that when at least one of conditional expressions (4) to (7) is satisfied in addition to conditional expressions (1) to (3), a more significant effect can be achieved compared to when this is not the case.

[Numerical Example]
<Main optical system>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
1 80.741 3.92 1.77250 49.6 35.49
2 -851.470 0.15 35.15
3 28.940 6.73 1.83481 42.7 33.03
4 53.453 1.56 30.04
5 81.904 3.28 1.72047 34.7 29.30
6 18.258 7.54 24.49
7(Aperture) ∞ 5.08 24.36
8 -27.317 1.39 1.73800 32.3 24.25
9 29.595 8.79 1.88100 40.1 27.13
10 -31.996 2.12 27.74
11 -21.263 2.52 1.72047 34.7 27.68
12 -82.521 0.15 30.73
13 723.827 7.10 1.59522 67.7 31.74
14 -28.930 0.15 32.40
15* 625.332 4.12 1.77250 49.5 31.05
16 -56.842 39.81 30.80
Image plane ∞

Aspheric data No. 15
K = 0.00000e+000 A4=-2.77448e-006 A6=-3.60131e-010 A8=-1.23803e-011
A10= 4.76619e-014 A12=-6.88926e-017

Various data Focal length 51.46
F-number 1.45
Half angle of view: 22.80
Image height 21.64
Lens length 94.41
BF 39.81

Entrance pupil position 27.09
Exit pupil position -56.91
Front principal point position 51.17
Rear principal point position -11.65

<Numerical Example 1>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 50.909 3.53 2.00100 29.1 31.73
18 206.169 1.96 31.42
19 -106.066 1.20 1.62004 36.3 31.38
20 26.641 7.00 2.00100 29.1 31.20
21 172.336 0.17 30.45
22 94.213 1.15 1.94594 18.0 30.18
23 25.510 3.53 28.62
24 80.745 4.59 1.69680 55.5 28.91
25 -63.832 7.08 29.24
26 ∞ 2.50 1.54430 69.9 50.00
27∞2.00 50.00
Image plane ∞

Various data

Focal length: 36.54
F-number 1.03
Half angle of view: 22.05
Image height 14.80
Lens length 91.95
BF 10.70

Entrance pupil position 27.09
Exit pupil position -276.12
Front principal point position 58.82
Rear principal point position -34.54

<Numerical Example 2>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 -98.929 1.20 1.51742 52.4 32.04
18 243.026 0.15 32.13
19 43.317 3.21 2.05090 26.9 33.72
20 84.506 0.20 33.43
21 29.194 5.52 1.95375 32.3 33.51
22 95.367 1.20 1.89286 20.4 32.47
23 20.565 5.20 28.79
24 84.375 3.37 1.80400 46.5 29.06
25 -177.375 7.61 29.20
26 ∞ 2.50 1.54430 69.9 50.00
27∞2.01 50.00
Image plane ∞

Various data

Focal length: 36.75
F-number 1.04
Half angle of view: 21.94
Image height 14.80
Lens length 91.20
BF 11.23

Entrance pupil position 27.09
Exit pupil position -219.05
Front principal point position 57.73
Rear principal point position -34.74

<Numerical Example 3>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 46.285 3.75 2.00100 29.1 32.91
18 168.332 1.34 32.44
19 -365.708 1.20 1.70154 41.2 32.36
20 27.525 5.46 1.91650 31.6 31.05
21 87.039 0.18 30.40
22 59.557 1.15 1.94594 18.0 30.16
23 27.818 3.83 28.84
24 176.644 1.20 1.85478 24.8 28.97
25 67.243 5.89 1.69680 55.5 29.21
26 -77.318 8.00 29.65
27 ∞ 2.50 1.51633 64.1 50.00
28∞2.16 50.00
Image plane ∞

Various data

Focal length 40.14
F-number 1.13
Half angle of view: 20.24
Image height 14.80
Lens length 93.90
BF 11.81

Entrance pupil position 27.09
Exit pupil position -122.63
Front principal point position 54.31
Rear principal point position -37.98

<Numerical Example 4>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 62.121 3.51 1.90043 37.4 31.27
18 -4465.572 2.00 31.16
19 -66.735 0.90 1.59270 35.3 31.13
20 24.721 8.32 2.05090 26.9 31.87
21 -7017.427 0.32 31.14
22 -793.922 0.90 1.94594 18.0 31.02
23 26.876 2.90 29.42
24 62.445 5.25 1.88300 40.8 29.66
25 -58.236 6.00 29.88
26 ∞ 2.50 1.51633 64.1 50.00
27∞2.08 50.00
Image plane ∞

Various data

Focal length 33.45
F-number: 0.94
Half angle of view: 22.42
Image height 13.80
Lens length 91.91
BF 9.73

Entrance pupil position 27.09
Exit pupil position 275.35
Front principal point position 64.63
Rear principal point position -31.37

<Numerical Example 5>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 -56.186 1.00 1.63980 34.5 31.20
18 -138.084 0.10 31.80
19 33.010 6.91 2.05090 26.9 34.00
20 -143.763 0.90 1.51742 52.4 34.00
21 -1299.097 1.21 32.20
22 -151.257 0.90 1.89286 20.4 31.20
23 24.745 3.43 29.40
24 60.714 4.40 1.80400 46.5 29.80
25 -86.475 8.93 29.80
26 ∞ 2.00 1.51742 52.4 50.00
27∞1.98 50.00
Image plane ∞

Various data

Focal length 36.76
F-number 1.04
Half angle of view: 20.58
Image height 13.80
Lens length 91.60
BF 12.22

Entrance pupil position 27.09
Exit pupil position -426.84
Front principal point position 60.69
Rear principal point position -34.78

<Numerical Example 6>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 -280.938 0.90 1.77250 49.6 32.08
18 179.829 0.10 31.25
19 27.619 6.74 2.00100 29.1 33.46
20 457.168 0.90 1.85896 22.7 32.78
21 104.798 1.22 31.82
22 288.333 0.90 1.85896 22.7 31.50
23 22.153 3.85 28.98
24 42.136 0.90 1.80518 25.4 29.98
25 37.395 4.50 1.81600 46.6 30.05
26 -206.057 8.93 30.09
27 ∞ 2.00 1.51742 52.4 50.00
28∞2.08 50.00
Image plane ∞

Various data

Focal length: 36.75
F-number 1.04
Half angle of view: 20.58
Image height 13.80
Lens length 91.15
BF 12.32

Entrance pupil position 27.09
Exit pupil position -267.64
Front principal point position 58.83
Rear principal point position -34.67

<Numerical Example 7>
Unit: mm

Surface data Surface number rd nd vd Effective diameter
17 58.301 2.83 1.88300 40.8 30.01
18 165.148 2.10 29.62
19 -119.174 1.45 1.51633 64.1 29.58
20 30.119 6.71 1.90043 37.4 29.75
21 -1223.055 0.92 29.20
22 -5261.247 1.15 1.85896 22.7 28.79
23 29.490 2.77 27.78
24 84.265 4.75 1.61772 49.8 28.05
25 -70.633 10.59 28.48
26 ∞ 2.50 1.54430 69.9 50.00
27∞1.00 50.00
Image plane ∞

Various data

Focal length 40.10
F-number 1.17
Half angle of view: 20.26
Image height 14.80
Lens length 93.36
BF 13.20

Entrance pupil position 27.09
Exit pupil position -134.05
Front principal point position 55.28
Rear principal point position -39.1

以上、本発明の好ましい実施形態について説明したが、本発明は、これらの実施形態に限定されず、その要旨の範囲内で種々の変形及び変更が可能である。

Although the 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 the gist of the present invention.

CV reduction optical system

Claims (9)

A reduction optical system arranged on the image side of a main optical system and composed of five or six lenses,
a composite focal length of the main optical system and the reduction optical system is shorter than a focal length of the main optical system,
The focal length of the reduction optical system is f, the focal length of the negative lens included in the reduction optical system and arranged closest to the object side is fn, the radius of curvature of the object-side lens surface of the negative lens arranged closest to the object side is r1, and the lateral magnification of the reduction optical system arranged on the image side of the main optical system is β,
-2.000<fn/f<-0.150
-1.600<f/r1<-0.200
0.500<β<0.900
A reduction optical system characterized by satisfying the following conditional expression: The focal length of the positive lens located closest to the object among the positive lenses included in the reduction optical system is defined as fp,
0.100<|fp/fn|<4.000
2. The reduction optical system according to claim 1, wherein the following condition is satisfied: Among the negative lenses included in the reduction optical system , the focal length of the negative lens having the strongest refractive power excluding the negative lens arranged closest to the object side is defined as fnmax,
0.100<fnmax/fn<2.000
3. The reduction optical system according to claim 1, wherein the following condition is satisfied: The reduction optical system has a refractive index and a focal length of Nph and fph, respectively,
1.895<Nph
0.200<fph/f<1.500
4. The reduction optical system according to claim 1, further comprising at least one positive lens which satisfies the following condition: ##EQU1## 5. The reduction optical system according to claim 1, wherein the lens arranged adjacent to the image side of the negative lens arranged closest to the object side is a positive lens, and the lens arranged adjacent to the object side of the positive lens arranged closest to the image side among the positive lenses included in the reduction optical system is a negative lens. 6. The reduction optical system according to claim 1, wherein the lens disposed closest to the image side among the lenses included in the reduction optical system is a biconvex lens. A reduction optical system according to any one of claims 1 to 6,
a main optical system disposed on the object side of the reduction optical system;
An optical system comprising: An optical system according to claim 7;
an image pickup element for capturing an image formed via the optical system;
1. An imaging device comprising: An imaging device to which a lens device having a main optical system can be attached, the imaging device including a reduction optical system according to any one of claims 1 to 6.

Images