JP5712751B2 - OPTICAL SYSTEM, IMAGING DEVICE HAVING THE OPTICAL SYSTEM, AND OPTICAL SYSTEM MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to an optical system, an imaging apparatus having the optical system, and a method for manufacturing the optical system.

  Conventionally, many so-called Gaussian lenses have been proposed (see, for example, Patent Document 1).

JP 2010-014895 A

  However, the conventional Gaussian lens has insufficient correction of coma, and it is particularly difficult to improve sagittal coma. When using an aspherical surface in order to improve such aberrations, there are problems such as an increase in manufacturing difficulty and cost.

  The present invention has been made in view of such a problem, and is small, has a small number of components, has a high performance, particularly an optical system with little coma and spherical aberration, an image pickup apparatus having the optical system, and an optical system. An object of the present invention is to provide a manufacturing method of the system.

In order to solve the above-described problem, an optical system according to the present invention includes substantially two optical lenses, a first lens group and a second lens group having a positive refractive power, in order from the magnification side along the optical axis . enlargement consists lens, the first lens unit includes, in order from the magnification side along the optical axis, two positive lenses and one negative lens made from the second lens group along the optical axis The positive lens included in the first lens group and the second lens group includes , in order from the side, a cemented lens in which a negative lens on the enlargement side and a positive lens on the reduction side are cemented, and two positive lenses. An optical system characterized in that at least two lenses are specific positive lenses that satisfy the following conditional expression.
1.820 <nd
49.0 <νd
However,
nd: refractive index with respect to d-line of medium of specific positive lens νd: Abbe number of medium of specific positive lens

In such an optical system, it is preferable that at least one of the specific positive lenses satisfies the following conditional expression.
0.40 <f / f0 <7.0
However,
f: Focal length of the specific positive lens f0: Focal length of the entire system when focusing on infinity

  Such an optical system preferably has an aperture stop between the first lens group and the second lens group.

Such an optical system preferably satisfies the following conditional expression.
0.2 <f2 / f0 <3.0
However,
f2: focal length of the second lens group f0: focal length of the entire system when focusing on infinity

  Such an optical system preferably has at least one specific positive lens in each of the first lens group and the second lens group.

  In such an optical system, it is preferable that all positive lenses are specific positive lenses.

  In addition, an imaging apparatus according to the present invention includes any one of the above-described optical systems.

The method of manufacturing an optical system according to the present invention includes substantially two lens groups, a first lens group and a second lens group having a positive refractive power, in order from the magnification side along the optical axis. In this optical system manufacturing method, as the first lens group , two positive lenses and one negative lens are arranged in order from the magnification side along the optical axis, and as the second lens group, A cemented lens in which a negative lens on the magnification side and a positive lens on the reduction side are cemented in order from the magnification side along the optical axis, and two positive lenses are arranged, and the first lens group and the second lens group At least two of the included positive lenses are specific positive lenses that satisfy the following conditional expression:
1.820 <nd
49.0 <νd
However,
nd: refractive index with respect to d-line of medium of specific positive lens νd: Abbe number of medium of specific positive lens

  According to the present invention, it is possible to provide an optical system that is small in size, has a small number of components, has high performance, and has particularly low coma and spherical aberration, an imaging apparatus having the optical system, and a method for manufacturing the optical system. .

It is sectional drawing which shows the lens structure in the infinite point focusing state of the optical system which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 1 in an infinitely focused state. It is sectional drawing which shows the lens structure in the infinite point focusing state of the optical system which concerns on 2nd Example. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 2 in a focused state at infinity. It is sectional drawing which shows the lens structure in the infinite point focusing state of the optical system which concerns on 3rd Example. FIG. 11 is a diagram illustrating various aberrations of the optical system according to Example 3 in an infinitely focused state. A sectional view of a single-lens reflex camera with an optical system is shown. It is a flowchart for demonstrating the manufacturing method of an optical system.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the optical system OS according to the present embodiment includes a first lens group G1 and a second lens group G2 having a positive refractive power in order from the magnification side along the optical axis. Configured. The first lens group G1 includes at least one positive lens and at least one negative lens, and the second lens group includes at least one negative lens and at least one positive lens. Have. At least one of the positive lenses included in the first lens group G1 and the second lens group G2 satisfies the following conditional expression (1) and conditional expression (2) (hereinafter, this conditional expression (1 ) And conditional expression (2) are called “specific positive lenses”). In this optical system OS, the direction in which the enlarged image of the object is formed is referred to as “enlarged side”, and the direction in which the reduced image of the object is formed is referred to as “reduced side”.

1.790 <nd (1)
49.0 <νd (2)
However,
nd: refractive index with respect to d-line of medium of specific positive lens νd: Abbe number of medium of specific positive lens

  The optical system OS according to the present embodiment has a sagittal coma aberration, which is a defect of an optical system such as a Gaussian type or a Xenota type, which is basically composed of positive, negative, and positive partial lens groups. The present invention proposes a method for improving satisfactorily without deteriorating the point aberration and without using an aspherical surface or a diffraction grating. Further, the optical system OS according to the present embodiment is characterized in that an unprecedented high refractive index and low dispersion lens is used as the positive lens (specific positive lens) constituting the optical system OS. By using a lens material having a refractive index nd of 1.79 or more and an Abbe number of 49 or more in an optical system OS, the optimal Petzval is maintained while maintaining good longitudinal chromatic aberration and lateral chromatic aberration. It is possible to maintain the sum and keep the radius of curvature relatively large because of the high refractive index, and as a result, coma, particularly sagittal coma can be favorably corrected. Therefore, it is possible to perform good correction without using a special aspheric lens or diffraction grating.

Conditional expression (1) is a condition that defines the refractive index of the medium of at least one positive lens (specific positive lens) included in the optical system OS described above. If this condition is not met, the setting of the optimum value for the Petzval sum is impaired, and as a result, the field curvature deteriorates. Further, the radius of curvature of the specific positive lens is decreased, and coma aberration, particularly sagittal coma aberration is increased. Note that by setting the lower limit value of conditional expression (1) to 1.795, it is possible to correct coma and field curvature. Further, by setting the lower limit value of the conditional expression (1) to 1.800, it is possible to further improve coma aberration and field curvature. Further, by setting the lower limit value of conditional expression (1) to 1.810, it is possible to further correct coma aberration and field curvature. In addition, by setting the lower limit value of conditional expression (1) to 1.820, the effects of the present application can be maximized.

  In the optical system OS according to the present embodiment, the specific positive lens described above must satisfy the conditional expression (2) simultaneously with the conditional expression (1). Conditional expression (2) is a condition that defines the Abbe number of the medium of the specific positive lens set in the optical system OS. This condition is a condition set after satisfying conditional expression (1). If this conditional expression (2) is not satisfied, correction of axial chromatic aberration and lateral chromatic aberration becomes difficult, which is not preferable. If the lower limit value of conditional expression (2) is set to 49.3, the chromatic aberration can be corrected more favorably. Further, when the lower limit value of conditional expression (2) is set to 49.5, the correction of chromatic aberration becomes better. Further, when the lower limit value of conditional expression (2) is set to 50.0, the correction of chromatic aberration becomes better. Further, by setting the lower limit value of conditional expression (2) to 50.3, the effects of the present application can be maximized.

  In the optical system OS according to the present embodiment, it is desirable that at least one of the specific positive lenses satisfying the conditional expressions (1) and (2) satisfies the following conditional expression (3).

0.40 <f / f0 <7.0 (3)
However,
f: Focal length of the specific positive lens f0: Focal length of the entire system when focusing on infinity

  Conditional expression (3) is a condition that defines the focal length of at least one specific positive lens satisfying conditional expressions (1) and (2) among the positive lenses constituting the optical system OS. This conditional expression defines the optimum refractive power for aberration correction of the specific positive lens.

  If the upper limit of conditional expression (3) is exceeded, it means that the refractive power of the specific positive lens becomes weak. In this case, the Petzval sum is deteriorated from the optimum value, and as a result, the correction of the field curvature is deteriorated. Moreover, the correction capability of coma aberration also decreases, which is not preferable. When the upper limit value of conditional expression (3) is set to 5.0, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (3) is set to 4.0, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (3) is set to 3.5, the above-described correction of various aberrations becomes more advantageous. Further, by setting the upper limit value of conditional expression (3) to 3.0, the effect of the present application can be maximized.

  Further, when the lower limit of conditional expression (3) is not reached, it means that the refractive power of the specific positive lens becomes strong. In this case, the correction of spherical aberration and coma aberration deteriorates as a result, which is not preferable. Note that setting the lower limit of conditional expression (3) to 0.45 is advantageous for correcting various aberrations such as spherical aberration and coma. Setting the lower limit of conditional expression (3) to 0.50 is advantageous for correcting various aberrations such as spherical aberration and coma. Setting the lower limit of conditional expression (3) to 0.55 is advantageous for correcting various aberrations such as spherical aberration and coma. Further, by setting the lower limit value of conditional expression (3) to 0.60, the effect of the present application can be maximized.

  In the optical system OS according to the present embodiment, the first lens group G1 includes two positive lenses and one negative lens, so that spherical aberration and chromatic aberration can be corrected well, and includes a cemented lens. However, a single lens may be used. In that case, the cemented lens may be positive or negative.

  In addition, it is preferable that G2 in the second lens group includes a cemented lens formed by cementing a negative lens and a positive lens and at least one positive lens in order to correct coma, axial chromatic aberration, and lateral chromatic aberration. In that case, the cemented lens may be positive or negative.

  In addition, an aperture stop S is preferably provided between the first lens group G1 and the second lens group G2 in order to correct lateral chromatic aberration and distortion.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (4).

0.2 <f2 / f0 <3.0 (4)
However,
f2: focal length of the second lens group G2 f0: focal length of the entire system when focusing on infinity

  Conditional expression (4) is a condition that defines the focal length of the second lens group G2, in other words, the refractive power.

  When the upper limit value of the conditional expression (4) is exceeded, it means that the focal length of the second lens group G2 becomes large, in other words, the refractive power of the second lens group G2 becomes weak. In this case, the refractive power balance with the first lens group G1 is lost, and chromatic aberration of magnification and distortion are deteriorated in terms of aberration correction. If the upper limit value of conditional expression (4) is set to 2.0, correction of various aberrations is advantageous. If the upper limit value of conditional expression (4) is set to 1.50, correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (4) is set to 1.20, it becomes more advantageous to correct various aberrations. Further, by setting the upper limit value of conditional expression (4) to 0.90, the effects of the present application can be maximized.

  On the other hand, if the lower limit value of conditional expression (4) is not reached, it means that the focal length of the second lens group G2 becomes small, in other words, the refractive power of the second lens group G2 becomes strong. In this case, spherical chromatic aberration and coma are particularly deteriorated, which is not preferable. If the lower limit of conditional expression (4) is set to 0.30, various aberrations can be corrected more favorably. If the lower limit value of conditional expression (4) is set to 0.40, various aberrations can be corrected more favorably. If the lower limit value of conditional expression (4) is set to 0.50, various aberrations can be corrected more favorably. Moreover, by setting the lower limit value of conditional expression (4) to 0.55, the effect of the present application can be maximized.

  In addition, it is preferable that the optical system OS according to the present embodiment has at least two specific positive lenses that simultaneously satisfy the conditional expression (1) and the conditional expression (2) because it is effective in setting an optimal Petzval sum. Further, at least one specific positive lens is provided in each of the first lens group G1 and the second lens group G2, so that correction of field curvature and coma aberration is further preferable. In addition, when all the positive lenses constituting the optical system OS according to the present embodiment are specific positive lenses that simultaneously satisfy the conditional expression (1) and the conditional expression (2), the effects of the present application can be maximized. .

  FIG. 7 shows a schematic cross-sectional view of a single-lens reflex camera 1 (hereinafter simply referred to as a camera) as an imaging apparatus including the above-described optical system OS. In this camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 (optical system OS) and focused on the focusing screen 4 via the quick return mirror-3. The light imaged on the focusing screen 4 is reflected a plurality of times in the pentaprism 5 and guided to the eyepiece lens 6. Thus, the photographer can observe the object (subject) image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and the light of the object (subject) (not shown) condensed by the taking lens 2 is captured by the image sensor 7. A subject image is formed on the top. Thereby, the light from the object (subject) is captured by the image sensor 7 and recorded as an object (subject) image in a memory (not shown). In this way, the photographer can shoot an object (subject) with the camera 1. Note that the camera 1 shown in FIG. 7 may be one that holds the taking lens 2 in a detachable manner, or may be formed integrally with the taking lens 2. Further, the camera 1 may be a so-called single-lens reflex camera, or a compact camera without a quick return mirror or a mirrorless single-lens reflex camera.

  Here, by mounting the above-described optical system OS on the camera 1 as the photographing lens 2, a large-aperture lens with less spherical aberration, curvature of field, and coma is realized by its characteristic lens configuration. As a result, the camera 1 can realize an imaging apparatus that has a large aperture and is capable of wide-angle shooting with little spherical aberration, curvature of field, and coma.

  In addition, the contents described below can be employed as appropriate within a range that does not impair the optical performance.

  In the present embodiment, the optical system OS having the two-group configuration is shown, but the above-described configuration conditions and the like can be applied to other group configurations such as the third group, the fourth group, and the like. Further, a configuration in which a lens or a lens group is added on the most enlargement side, or a configuration in which a lens or a lens group is added on the most reduction side may be used. The lens group is a portion having at least one lens separated by the aperture stop S as described above, or at least one piece separated by an air interval that changes at the time of zooming or focusing. The part which has a lens is shown.

  In this embodiment, the entire (all groups) feed is used to focus on an object at a short distance from an object at infinity. A focusing lens group that performs focusing from an object to a short-distance object may be used. That is, a method using the first lens group G1 or a rear focus using the second lens group G2 may be used. In this case, the focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like).

  Also, by moving the lens group or partial lens group so that it has a component in the direction perpendicular to the optical axis, or rotating (swinging) in the in-plane direction including the optical axis, image blur caused by camera shake is corrected. An anti-vibration lens group may be used. In particular, it is preferable that at least one of the second lens group G2 is an anti-vibration lens group.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. It is preferable that the lens surface is a spherical surface or a flat surface because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembly adjustment is prevented. Further, even when the image plane is shifted in the optical axis direction, it is preferable because there is little deterioration in the drawing performance. When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin on the glass surface. Any of the aspherical surfaces may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  The aperture stop S is preferably arranged near the center of the optical system OS. However, the role of the aperture stop may be substituted by a lens frame without providing a member as an aperture stop.

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

  Hereinafter, an outline of a method for manufacturing the optical system OS according to the present embodiment will be described with reference to FIG. In the manufacturing method of the optical system OS, the first lens group G1 and the second lens group G2 having a positive refractive power are arranged in this order from the magnification side along the optical axis. Specifically, in the present embodiment, for example, as the first lens group G1, in order from the magnification side, a positive meniscus lens L1 having a convex surface on the magnification side, a positive meniscus lens L2 having a convex surface on the magnification side, and magnification A negative meniscus lens L3 with a convex surface facing the side is arranged (step S100), and as the second lens group G2, in order from the magnification side, a cemented lens CL in which a biconcave lens L4 and a biconvex lens L5 are cemented, and a convex surface on the reduction side And a positive meniscus lens L7 having a convex surface on the enlargement side are arranged (step S200). At this time, at least one of the positive lenses included in the first lens group G1 and the second lens group G2 satisfies the conditional expressions (1) and (2).

  As described above, according to the optical system OS according to the present embodiment, it is suitable for an imaging apparatus such as a camera, a printing lens, and a copying lens. It is possible to provide an optical system OS with less spherical aberration and an imaging device using the optical system OS.

  Hereinafter, embodiments of the optical system OS will be described with reference to the drawings. 1, 3 and 5 show the configuration of the optical system OS (OS1 to OS3) according to each embodiment.

[First embodiment]
FIG. 1 is a diagram illustrating a configuration of an optical system OS1 according to the first example. The optical system OS1 includes, in order from the magnification side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens group G2 having a positive refractive power. . The first lens group G1, in order from the magnifying side, is a positive meniscus lens L1 having a convex surface on the magnifying side, a positive meniscus lens L2 having a convex surface on the magnifying side and a stronger curvature, and a negative surface having a convex surface on the magnifying side. It is composed of a meniscus lens L3. The second lens group G2 is formed by cementing a biconcave lens L4 and a biconvex lens L5 in order from the magnification side, a cemented negative lens CL having a convex surface on the reduction side, and a positive meniscus lens L6 having a convex surface on the reduction side. And a positive meniscus lens L7 having a convex surface facing the enlargement side.

  Table 1 below lists values of specifications of the optical system OS1 according to the first example. In the overall specifications of Table 1, f is the focal length, FNO is the F number, ω is the half angle of view (unit: degree), Y is the image height, TL is the total length of the optical system OS1, and Σd is the most of the optical system OS1. A distance on the optical axis from the enlargement side lens surface (first surface) to the most reduction side lens surface (14th surface), and Bf represent back focus. The total length TL indicates the distance on the optical axis from the most magnified lens surface (first surface) of the optical system OS1 to the image plane, and the back focus Bf is the most demagnifying lens of the optical system OS1. It represents the distance on the optical axis from the surface (14th surface) to the image surface. In the lens data, the first column m indicates the order (surface number) of the optical surfaces from the magnifying side along the traveling direction of the light beam, the second column r indicates the curvature radius of each optical surface, The column d shows the distance (surface interval) on the optical axis from each optical surface to the next optical surface, and the fourth column νd and the fifth column nd show the Ab for the d-line (wavelength λ = 587.6 nm), respectively. Number and refractive index are shown. The surface numbers 1 to 14 shown in Table 1 correspond to the numbers 1 to 14 shown in FIG. A curvature radius of 0.0000 indicates a plane on the lens surface and an aperture on the aperture stop S. Further, the refractive index of air of 1.0000 is omitted. The lens group focal length indicates the surface number (starting surface) where each lens group starts and the focal length of each lens group.

  Here, the focal length f, the radius of curvature r, the surface interval d, and other length units listed in all the following specification values are generally “mm”, but the optical system is proportionally enlarged or proportional. Since the same optical performance can be obtained even if the image is reduced, the present invention is not limited to this. The description of these symbols and the description of the specification table are the same in the following embodiments.

(Table 1)
[Overall specifications]
f = 51.6
FNO = F1.21
ω = 23.25 °
Y = 21.6
TL = 92.60
Σd = 54.30
Bf = 38.30

[Lens data]
m rd νd nd
1 67.8449 5.5000 53.87 1.840160
2 776.2097 0.6000
3 29.9380 6.3000 53.87 1.840160
4 62.7808 2.0000
5 103.2918 1.3000 42.26 1.799520
6 21.1640 9.5000
7 0.0000 9.5000 Aperture stop S
8 -20.2169 1.3000 28.69 1.795040
9 686.2595 9.0000 50.55 1.854300
10 -31.3427 0.1000
11 -125.2254 5.3000 50.55 1.854300
12 -40.9197 0.1000
13 72.4810 3.8000 50.55 1.854300
14 530.8218 Bf

[Lens focal length]
Lens group Start surface Focal length First lens group 1 205.5192
Second lens group 8 40.1807

  Table 2 below shows values corresponding to the conditional expressions for the optical system OS1 according to the first example. In the first embodiment, the positive lens (specific positive lens) satisfying the conditional expressions (1) and (2) is the positive meniscus lens L1 included in the first lens group G1, and the second lens. These are a biconvex lens L5 and a positive meniscus lens L7 included in the group G2. In Table 2, nd is the refractive index of the medium of the specific positive lens with respect to the d-line, νd is the Abbe number of the medium of the specific positive lens, f is the focal length of the specific positive lens, and f0 is the optical at the time of focusing on infinity. The focal length of the entire system OS1, f2 represents the focal length of the second lens group G2. The description of these symbols is the same in the following embodiments.

(Table 2)
(1) nd
Nd of L1 = 1.84016
Nd of L5 = 1.85430
L7 nd = 1.85430

(2) νd
Νd of L1 = 53.87
Νd of L5 = 50.55
Νd of L7 = 50.55

(3) f / f0
F / f0 of L1 = 1.7088
F / f0 of L5 = 0.6839
F / f0 of L7 = 1.8970

(4) f2 / f0 = 0.7787

  Thus, the optical system OS1 according to the first example satisfies all the conditional expressions (1) to (4).

  FIG. 2 shows various aberration diagrams of spherical aberration, astigmatism, distortion aberration, lateral chromatic aberration, and coma aberration in the infinitely focused state of the optical system OS1 according to the first example. In each aberration diagram, FNO represents an F number, Y represents an image height, and ω represents a half angle of view [unit: degree]. In each aberration diagram, d represents the aberration with respect to the d-line (wavelength λ = 587.6 nm), and g represents the aberration with respect to the g-line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, at each half angle of view ω, the solid line represents the meridional coma aberration with respect to the d-line and the g-line, and the broken line on the left side from the origin represents the sagittal coma aberration generated in the meridional direction with respect to the d-line. The broken line represents the sagittal coma generated in the sagittal direction with respect to the d line. The description of this aberration diagram is the same in the following examples. As apparent from the respective aberration diagrams shown in FIG. 2, in the optical system OS1 according to the first example, various aberrations including spherical aberration, curvature of field, astigmatism, and coma are corrected well. It can be seen that the optical performance is high.

[Second Embodiment]
FIG. 3 is a diagram illustrating a configuration of the optical system OS2 according to the second embodiment. The optical system OS2 includes, in order from the magnification side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens group G2 having a positive refractive power. . The first lens group G1, in order from the magnifying side, is a positive meniscus lens L1 having a convex surface on the magnifying side, a positive meniscus lens L2 having a convex surface on the magnifying side and a stronger curvature, and a negative surface having a convex surface on the magnifying side. It is composed of a meniscus lens L3. The second lens group G2 is formed by cementing a biconcave lens L4 and a biconvex lens L5 in order from the magnification side, a cemented negative lens CL having a convex surface on the reduction side, and a positive meniscus lens L6 having a convex surface on the reduction side. And a positive meniscus lens L7 having a convex surface on the enlargement side.

  Table 3 below lists values of specifications of the optical system OS2 according to the second example. The surface numbers 1 to 14 shown in Table 3 correspond to the numbers 1 to 14 shown in FIG.

(Table 3)
[Overall specifications]
f = 51.6
FNO = F1.21
ω = 23.27 °
Y = 21.6
TL = 94.2965
Σd = 56.0000
Bf = 38.2965

[Lens data]
m rd νd nd
1 55.1887 6.5000 53.87 1.840160
2 351.5830 0.6000
3 29.5385 6.0000 53.87 1.840160
4 54.1748 1.6000
5 85.0733 1.3000 42.26 1.799520
6 20.0545 9.0000
7 0.0000 10.0000 Aperture stop S
8 -19.5111 1.3000 28.69 1.795040
9 617.0843 9.0000 50.55 1.854300
10 -31.0463 0.1000
11 -122.3433 6.0000 50.55 1.854300
12 -39.8141 0.1000
13 80.7453 4.5000 50.55 1.854300
14 6742.3794 Bf

[Lens focal length]
Lens group Start surface Focal length First lens group 1 210.04648
Second lens group 8 39.52651

  Table 4 below shows values corresponding to the conditional expressions for the optical system OS2 according to the second example. In the second embodiment, the positive lens (specific positive lens) that satisfies the conditional expressions (1) and (2) is the positive meniscus lens L1 included in the first lens group G1, and the second lens. These are a biconvex lens L5 and a positive meniscus lens L7 included in the group G2.

(Table 4)
(1) nd
Nd of L1 = 1.84016
Nd of L5 = 1.85430
L7 nd = 1.85430

(2) νd
Νd of L1 = 53.87
Νd of L5 = 50.55
Νd of L7 = 50.55

(3) f / f0
F / f0 of L1 = 1.4951
F / f0 of L5 = 0.6749
F / f0 of L7 = 1.8533

(4) f2 / f0 = 0.7660

  Thus, the optical system OS2 according to the second example satisfies all the conditional expressions (1) to (4).

  FIG. 4 shows various aberration diagrams of spherical aberration, astigmatism, distortion aberration, lateral chromatic aberration, and coma aberration in the infinitely focused state of the optical system OS2 according to the second example. As apparent from the respective aberration diagrams shown in FIG. 4, in the optical system OS2 according to the second example, various aberrations including spherical aberration, curvature of field, astigmatism, and coma are corrected well. It can be seen that the optical performance is high.

[Third embodiment]
FIG. 5 is a diagram illustrating a configuration of the optical system OS3 according to the third embodiment. This optical system OS3 includes, in order from the magnification side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens group G2 having a positive refractive power. . The first lens group G1, in order from the magnifying side, is a positive meniscus lens L1 having a convex surface on the magnifying side, a positive meniscus lens L2 having a convex surface on the magnifying side and a stronger curvature, and a negative surface having a convex surface on the magnifying side. It is composed of a meniscus lens L3. The second lens group G2 is formed by cementing a biconcave lens L4 and a biconvex lens L5 in order from the magnification side, a cemented negative lens CL having a convex surface on the reduction side, and a positive meniscus lens L6 having a convex surface on the reduction side. And a biconvex lens L7.

  Table 5 below lists values of specifications of the optical system OS3 according to the third example. The surface numbers 1 to 14 shown in Table 5 correspond to the numbers 1 to 14 shown in FIG.

(Table 5)
[Overall specifications]
f = 60.90
FNO = F1.21
ω = 19.81 °
Y = 21.6
TL = 92.0997
Σd = 53.8000
Bf = 38.2997

[Lens data]
m rd νd nd
1 51.8779 7.0000 53.87 1.840160
2 268.4277 0.6000
3 31.6257 7.0000 53.87 1.840160
4 50.4632 2.2000
5 85.9824 1.3000 31.59 1.756920
6 22.0110 9.0000
7 0.0000 8.0000 Aperture stop S
8 -24.6101 1.3000 33.27 1.806100
9 198.5789 7.7000 50.55 1.854300
10 -37.0077 0.1000
11 -50.0306 4.5000 50.55 1.854300
12 -36.6923 0.1000
13 79.4705 5.0000 50.55 1.854300
14 -275.4600 Bf

[Lens focal length]
Lens group Start surface Focal length First lens group 1 143.29418
Second lens group 8 50.88052

  Table 6 below shows values corresponding to the conditional expressions for the optical system OS3 according to the third example. In the third embodiment, the positive lens (specific positive lens) satisfying the conditional expressions (1) and (2) is the positive meniscus lens L1 included in the first lens group G1, and the second lens. These are a biconvex lens L5 and a positive meniscus lens L6 included in the group G2.

(Table 6)
(1) nd
Nd of L1 = 1.84016
Nd of L5 = 1.85430
Nd of L6 = 1.85430

(2) νd
Νd of L1 = 53.87
Νd of L5 = 50.55
Νd of L6 = 50.55

(3) f / f0
F / f0 of L1 = 1.2385
F / f0 of L5 = 0.6087
F / f0 of L6 = 2.2895

(4) f2 / f0 = 0.8355

  Thus, the optical system OS3 according to the third example satisfies all the conditional expressions (1) to (4).

  FIG. 6 shows various aberration diagrams of spherical aberration, astigmatism, distortion aberration, lateral chromatic aberration, and coma aberration in the infinite focus state of the optical system OS3 according to the third example. As is apparent from the aberration diagrams shown in FIG. 6, in the optical system OS3 according to the third example, various aberrations including spherical aberration, field curvature, astigmatism, and coma are corrected well. It can be seen that the optical performance is high.

  According to each of the above-described embodiments, it has a comprehensive angle of about 2ω = 39.62 to 46.5 °, and further has a large aperture F1.2, a relatively small size, high performance, spherical aberration, and image quality. An optical system OS in which surface curvature and coma aberration are corrected well can be realized.

  Needless to say, the above-described effects can be obtained by mounting the optical systems OS <b> 1 to OS <b> 3 shown in the above embodiments in the above-described camera 1. Moreover, each said Example has shown the specific example of this invention, and this invention is not limited to these.

OS (OS1 to OS3) Optical system G1 First lens group L1 First lens group positive lens L2 First lens group positive lens L3 First lens group negative lens G2 Second lens group L4 Second lens group negative lens L5 Positive lens in the second lens group L6 Positive lens in the second lens group L7 Positive lens in the second lens group CL Joint lens in the second lens group S Aperture stop 1 Single-lens reflex camera (imaging device)

Claims (8)

Along the optical axis from the magnification side,
A first lens group;
Substantially consisting of two lens groups with a second lens group having positive refractive power;
The first lens group includes two positive lenses and one negative lens in order from the magnification side along the optical axis .
The second lens group includes a cemented lens in which a negative lens on the magnification side and a positive lens on the reduction side are cemented in order from the magnification side along the optical axis, and two positive lenses .
An optical system, wherein at least two of the positive lenses included in the first lens group and the second lens group are specific positive lenses that satisfy the following conditional expression:
1.820 <nd
49.0 <νd
However,
nd: refractive index of the medium of the specific positive lens with respect to d-line νd: Abbe number of the medium of the specific positive lens The optical system according to claim 1, wherein at least one of the specific positive lenses satisfies the following conditional expression.
0.40 <f / f0 <7.0
However,
f: Focal length of the specific positive lens f0: Focal length of the entire system when focusing on infinity The optical system of claim 1 or 2, characterized in that an aperture stop between the first lens group and the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.2 <f2 / f0 <3.0
However,
f2: focal length of the second lens group f0: focal length of the entire system when focusing on infinity The specific positive lens, each of the first lens group and the second lens group, an optical system according to claim 1, characterized in that it comprises one by at least one. All the positive lenses are said specific positive lenses, The optical system as described in any one of Claims 1-5 characterized by the above-mentioned. Imaging apparatus characterized by having an optical system according to any one of claims 1 to 6. In order from the magnification side along the optical axis, a manufacturing method of an optical system consisting essentially of two lens groups, a first lens group and a second lens group having a positive refractive power,
As the first lens group , two positive lenses and one negative lens are arranged in order from the magnification side along the optical axis ,
As the second lens group, a cemented lens in which a negative lens on the magnification side and a positive lens on the reduction side are cemented in order from the magnification side along the optical axis, and two positive lenses are arranged,
An optical system manufacturing method, wherein at least two of the positive lenses included in the first lens group and the second lens group are specific positive lenses that satisfy the following conditional expression:
1.820 <nd
49.0 <νd
However,
nd: refractive index of the medium of the specific positive lens with respect to d-line νd: Abbe number of the medium of the specific positive lens

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