JP6582535B2 - Optical system and imaging apparatus having this optical system - 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 inner focus lenses have been proposed (see, for example, Patent Document 1). However, the conventional inner focus lens is desired to have higher performance by further aberration correction.

JP 2011-170128 A

In the first invention,
In order from the object side along the optical axis,
A first lens group having a positive refractive power and fixed in the optical axis direction with respect to the image plane during focusing;
A second lens group having positive refractive power and moving along the optical axis for focusing;
Has a positive refractive power, upon focusing, substantially consists of three lens groups by a third lens group that is fixed in the optical axis direction with respect to the image plane,
The first lens group includes a partial lens group having at least two positive lenses and having a positive refractive power as a whole, and a negative lens.
The second lens group includes a positive lens, a negative lens, and a cemented lens having a positive refractive power from the object side,
The third lens group includes a cemented lens;
An optical system satisfying the following conditional expression was obtained.
−1.00 <(r2nb + r2na) / (r2nb−r2na) <0.00
However,
r2na: radius of curvature of the object side lens surface of the negative lens in the second lens group r2nb: radius of curvature of the image side lens surface of the negative lens in the second lens group

  In the second invention, an imaging apparatus having the optical system described above is provided.

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. It is sectional drawing which shows the lens structure in the infinite point focusing state of the optical system which concerns on 4th Example. FIG. 11 is a diagram illustrating various aberrations of the optical system according to Example 4 in the infinitely focused state. It is a figure which shows the structure of the single-lens reflex camera provided with the optical system of this application. It is a flowchart for demonstrating the manufacturing method of the optical system of this application.

  Hereinafter, embodiments will be described with reference to the drawings. As shown in FIG. 1, the optical system OS according to the present embodiment has a positive refractive power in order from the object side along the optical axis, and is fixed in the optical axis direction with respect to the image plane at the time of focusing. The first lens group G1, the second lens group G2 having a positive refractive power and moving along the optical axis for focusing, and the positive lens, and having a positive refractive power. And a third lens group G3 fixed in the optical axis direction. The first lens group G1 has at least two positive lenses L11 and L12 and has a positive refractive power as a whole. G2a includes a negative lens L1b, the second lens group G2 includes a positive lens L21, a negative lens L22, and a cemented lens L2a having a positive refractive power, and the third lens group G3 includes And a cemented lens L3a from the object side. The cemented lens L2a is formed by cementing at least the negative lens L23 and the positive lens L24.

  The optical system OS according to the present embodiment basically includes spherical aberration, coma aberration, sagittal coma aberration, chromatic aberration, which are disadvantageous in the front group and rear group fixed inner focus type optical systems, particularly large aperture lenses. This is an improvement without deteriorating the curvature of field and astigmatism. Hereinafter, conditions for configuring such an optical system OS will be described.

The optical system OS according to the present embodiment desirably satisfies the following conditional expression (1).
−1.00 <(r2nb + r2na) / (r2nb−r2na) <0.00 (1)
However,
r2na: radius of curvature of the object side lens surface of the negative lens L22 in the second lens group G2 r2nb: radius of curvature of the image side lens surface of the negative lens L22 in the second lens group G2

  Conditional expression (1) is a conditional expression that sets the value of the shape factor (q factor) of the negative lens L22 in the second lens group G2 to an optimum value. The main point of this embodiment is that the focusing lens group of the inner focus system is configured by a so-called Tesser type optical system. The Tesser type is a lens group with the minimum number of lenses applicable to a large aperture, and has optimum characteristics as a focusing lens group that satisfies the conditions of the autofocus system. In the Tesser type focusing lens group, the optimum shape factor of the central negative lens is important for obtaining good spherical aberration, astigmatism and coma.

  If the upper limit of the conditional expression (1) is exceeded, the shape of the negative lens L22 exceeds the biconcave shape in which the absolute values of the curvature radii of the object side lens surface and the image side lens surface are equal, and the object surface curvature is greater than the image side curvature. A shape in which the curvature on the object side is higher, that is, a shape in which the absolute value of the curvature radius of the object side lens surface is smaller than the absolute value of the curvature radius of the image side lens surface. If the positive number is larger, a flat concave shape with the concave surface facing the object side and a meniscus shape with the convex surface facing the image side are obtained. In this case, since spherical aberration and coma aberration deteriorate, it is not preferable. If the upper limit value of conditional expression (1) is set to -0.05, it becomes more advantageous for correcting the above-mentioned various aberrations. Setting the upper limit value of conditional expression (1) to -0.10 is more advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit value of conditional expression (1) to −0.20, the effect of the present embodiment can be maximized.

  If the lower limit of conditional expression (1) is not reached, the shape of the negative lens L22 becomes a meniscus shape that exceeds the plano-concave shape with the concave surface facing the image side and the convex surface toward the object side. In this case, correction of astigmatism, curvature of field, and coma becomes difficult, which is not preferable. If the lower limit value of conditional expression (1) is set to −0.90, it is more advantageous for correcting the above-mentioned various aberrations. Setting the lower limit of conditional expression (1) to −0.85 is further advantageous for correcting the above-mentioned various aberrations. Further, the effect of the present embodiment can be maximized by setting the lower limit value of conditional expression (1) to -0.83.

  According to the above configuration, it is possible to realize an optical system with a small number of components of the focusing lens group and high performance with few aberrations.

Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (2).
0.35 <f2 / f1 <1.00 (2)
However,
f2: focal length of the second lens group G2 f1: focal length of the first lens group G1

  Conditional expression (2) is a condition for setting the optimum value of the focal length of the second lens group G2, in other words, the optimum value of the refractive power of the second lens group G2.

  When the upper limit of conditional expression (2) is exceeded, the refractive power of the second lens group G2 is weakened, so that the optical system OS is enlarged and the amount of movement of the second lens group G2 for focusing is increased. Therefore, AF driving by the actuator becomes difficult. Further, it means that the refractive power of the first lens group G1 becomes relatively strong, and it is not preferable in terms of aberration correction because it becomes difficult to correct spherical aberration and axial chromatic aberration. If the upper limit value of conditional expression (2) is set to 0.90, it is more advantageous for correcting the above-mentioned various aberrations. Further, when the upper limit value of conditional expression (2) is set to 0.80, it is further advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit value of conditional expression (2) to 0.70, the effect of this embodiment can be maximized.

  On the other hand, if the lower limit of conditional expression (2) is not reached, the refractive power of the second lens group G2 will increase, which makes it particularly difficult to correct spherical aberration and coma aberration. If the lower limit of conditional expression (2) is set to 0.36, it is more advantageous for correcting various aberrations. Setting the lower limit value of conditional expression (2) to 0.37 is further advantageous for correcting various aberrations. Further, by setting the lower limit value of conditional expression (2) to 0.38, the effect of the present embodiment can be maximized.

In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (3).
0.00 <X2 / f2 <0.10 (3)
However,
X2: The amount of movement f2 of the second lens group G2 when focusing from the infinite focus state to the imaging magnification β = −1 / 30 times: the focal length of the second lens group G2

  Conditional expression (3) is a conditional expression that defines the relationship between the amount of movement of the second lens group G2, which is the focusing lens group, and the refractive power.

  If the upper limit of conditional expression (3) is exceeded, the amount of movement of the second lens group G2 for focusing increases, making AF driving by the actuator difficult. This also means that the focal length of the second lens group G2, which is the focusing lens group, is reduced and the refractive power is increased. As a result, it is difficult to correct spherical aberration and coma aberration. If the upper limit value of conditional expression (3) is set to 0.08, it is more advantageous for correcting the above-mentioned various aberrations. Further, when the upper limit value of conditional expression (3) is set to 0.07, it is further advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit value of conditional expression (3) to 0.06, the effect of the present embodiment can be maximized.

  If the lower limit of conditional expression (3) is exceeded, short-range fluctuations in spherical aberration and the like can be corrected satisfactorily. If the lower limit value of conditional expression (3) is set to 0.02, it is advantageous for correcting short-range fluctuations of spherical aberration. Setting the lower limit of conditional expression (3) to 0.03 is advantageous for correcting various aberrations. Further, by setting the lower limit value of conditional expression (3) to 0.04, the effect of the present embodiment can be maximized.

In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (4).
1.00 <f3 / f0 <20.00 (4)
However,
f3: focal length of the third lens group G3 f0: focal length of the entire system when focusing on infinity

  Conditional expression (4) is a condition for setting the optimum value of the focal length of the third lens group G3, in other words, the optimum value of the refractive power of the third lens group G3.

  If the upper limit of conditional expression (4) is exceeded, it means that the refractive power of the third lens group G3 fixed in the optical axis direction with respect to the image plane is significantly weakened during focusing. In this case, the aberration correction effect is also reduced, and as a result, it becomes difficult to correct off-axis aberrations such as coma aberration. If the upper limit value of conditional expression (4) is set to 19.00, it is more advantageous for correcting the above-mentioned various aberrations. Further, when the upper limit value of conditional expression (4) is set to 18.00, it is further advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit of conditional expression (4) to 17.50, the effect of the present embodiment can be maximized.

  If the lower limit of conditional expression (4) is not reached, the refractive power of the third lens group G3 becomes strong, the back focus becomes short, and the refractive power of each group is set so as to ensure sufficient back focus. In particular, it is difficult to correct spherical aberration and curvature of field, and fluctuations in short-range aberration become large, which is not preferable. If the lower limit value of conditional expression (4) is set to 1.30, it is advantageous for correcting the above-mentioned various aberrations. Setting the lower limit of conditional expression (4) to 1.50 is advantageous for correcting the above-mentioned various aberrations. Further, by setting the lower limit value of conditional expression (4) to 2.00, the effect of the present embodiment can be maximized.

In the optical system OS according to the present embodiment, the cemented lens L2a in the second lens group G2 is formed by cementing the negative lens L23 and the positive lens L24, and satisfies the following conditional expression (5). desirable.
0.10 <N24-N23 <0.50 (5)
However,
N23: Refractive index with respect to d line of the negative lens L23 constituting the cemented lens L2a in the second lens group G2 N24: Refractive index with respect to d line of the positive lens L24 constituting the cemented lens L2a in the second lens group G2.

  Conditional expression (5) is a condition in which the magnitude relationship between the refractive indexes of the positive lens L24 and the negative lens L23 constituting the cemented lens L2a in the second lens group G2 is set. This is an effective condition for setting the optimal Petzval sum and for good correction of field curvature and astigmatism.

  If the upper limit of the conditional expression (5) is exceeded, selecting a suitable glass material is not preferable because high-dispersion glass material is frequently used and it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. If the upper limit value of conditional expression (5) is set to 0.45, it is more advantageous for correcting the above-mentioned various aberrations. Further, when the upper limit value of conditional expression (5) is set to 0.40, it is further advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit value of conditional expression (5) to 0.30, the effect of the present embodiment can be maximized.

  On the other hand, if the lower limit of conditional expression (5) is not reached, it is difficult to set an optimal Petzval sum, and it becomes difficult to correct curvature of field and astigmatism, which is not preferable. If the lower limit value of conditional expression (5) is set to 0.15, it is more advantageous for correcting various aberrations. Setting the lower limit of conditional expression (5) to 0.19 is advantageous for correcting various aberrations. Further, by setting the lower limit value of conditional expression (5) to 0.21, the effect of the present embodiment can be maximized.

In the optical system OS according to the present embodiment, the cemented lens L3a in the third lens group G3 is cemented to the object side positive lens L31 disposed closest to the object side and the image side of the object side positive lens. And a negative lens L32, and it is preferable that the following conditional expression (6) is satisfied.
0.10 <N31-N32 <0.50 (6)
However,
N31: Refractive index with respect to d line of object side positive lens L31 N32: Refractive index with respect to d line of negative lens L32 cemented on the image side of object side positive lens L31

  Conditional expression (6) is a condition for setting the magnitude relationship between the refractive indexes of the object-side positive lens L31 and the negative lens L32 constituting the cemented lens L3a in the third lens group G3. This is an effective condition for optimal Petzvalsum setting, good curvature of field, and correction of astigmatism.

  If the upper limit of the conditional expression (6) is exceeded, selecting a suitable glass material is not preferable because high-dispersion glass material is frequently used, and it becomes difficult to correct longitudinal chromatic aberration and lateral chromatic aberration. If the upper limit value of conditional expression (6) is set to 0.45, it is more advantageous for correcting the above-mentioned various aberrations. Further, when the upper limit value of conditional expression (6) is set to 0.40, it is further advantageous for correcting the above-mentioned various aberrations. Further, by setting the upper limit value of conditional expression (6) to 0.30, the effect of the present embodiment can be maximized.

  On the other hand, if the lower limit of conditional expression (6) is not reached, it is difficult to set an optimal Petzval sum, and it becomes difficult to correct curvature of field and astigmatism. If the lower limit value of conditional expression (6) is set to 0.12, it will be more advantageous for correcting various aberrations. Setting the lower limit of conditional expression (6) to 0.13 is advantageous for correcting various aberrations. Further, by setting the lower limit value of conditional expression (6) to 0.15, the effect of the present embodiment can be maximized.

Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (7).
57.00 <νd1a (7)
However,
νd1a: average value of the Abbe number of at least two positive lenses (L11, L12) in the partial lens group G1a

  Conditional expression (7) is a condition for setting an average value of the Abbe numbers of all the positive lenses arranged in the partial lens group G1a having a plurality of positive lenses and having a positive refractive power. The partial lens group G1a located on the object side in the first lens group G1 and having a positive refractive power is greatly involved in good correction of axial chromatic aberration and lateral chromatic aberration. In the present embodiment, axial chromatic aberration is particularly corrected by using an abnormal partial dispersion glass or fluorite.

  If the condition of the conditional expression (7) is not satisfied, a glass material having so-called anomalous partial dispersion characteristics cannot be used. Therefore, good correction of longitudinal chromatic aberration and lateral chromatic aberration, particularly good correction of secondary dispersion. It becomes difficult. Note that setting the lower limit of conditional expression (7) to 60.00 is advantageous for correcting various aberrations such as chromatic aberration. Setting the lower limit of conditional expression (7) to 69.00 is advantageous for correcting various aberrations such as longitudinal chromatic aberration. Further, by setting the lower limit value of conditional expression (7) to 75.00, the effect of the present embodiment can be maximized.

  In addition, the optical system OS according to the present embodiment desirably has an aperture stop S that determines the F-number on the image side with respect to the first lens group G1. Further, it is more desirable that the optical system OS has an aperture stop S for determining the F number in the second lens group G2. The optical system OS also determines an aperture stop that determines an F-number between the positive lens L21 and the negative lens L22 in the second lens group G2 or between the negative lens L22 and the cemented lens L2a in the second lens group G2. It is further desirable to have As a result, it is possible to satisfactorily correct astigmatism and distortion.

  The optical system OS according to the present embodiment desirably has at least one aspheric surface. As a result, coma, particularly sagittal coma and spherical aberration can be favorably corrected.

  FIG. 9 is a schematic cross-sectional view of a single-lens reflex camera 1 (hereinafter simply referred to as camera 1) as an imaging apparatus including the optical system OS described above. In this camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 (optical system OS) and is imaged 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.

  Further, when a release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light of an object (subject) (not shown) condensed by the photographing lens 2 is captured on the image sensor 7. Form an image. As a result, light from the object (subject) is captured by the image sensor 7 and recorded in a memory (not shown) as an object (subject) image. In this way, the photographer can shoot an object (subject) with the camera 1. The camera 1 shown in FIG. 9 may be one that holds the photographing lens 2 so as to be detachable, or may be formed integrally with the photographing 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, the optical system OS described above as the photographic lens 2 of the camera 1 realizes an optical system having a small number of components of the focusing lens group, a high performance and less aberrations due to its characteristic lens configuration. . As a result, the camera 1 realizes high-speed focusing and high-performance shooting.

  In addition, the contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the present embodiment, the optical system OS having the three-group configuration is shown, but the above-described configuration conditions and the like can be applied to other group configurations such as the fourth group and the fifth group. Further, a configuration in which a lens or a lens group is added closest to the object side, a configuration in which a lens or a lens group is added closest to the image side, or a configuration in which a lens or a lens group is added between the lens groups may be used. The lens group refers to a portion having at least one lens separated by an air interval. The second lens group may have other lens components between the positive lens, the negative lens, and the object side, the image side, and each lens of the cemented lens having a positive refractive power.

  Further, the optical system of the present application uses a part of a lens group, an entire lens group, or a plurality of lens groups as a focusing lens group in order to perform focusing from an object at infinity to a near object in the optical axis direction. It is good also as a structure moved to. In particular, it is preferable that the second lens group is a focusing lens group as described above. Such a focusing lens group can also be applied to autofocus, and is also suitable for driving by an autofocus motor, such as an ultrasonic motor.

  Further, in the optical system of the present application, any lens group, partial lens group or part thereof is moved as a vibration-proof lens group so as to include a component in a direction perpendicular to the optical axis, or includes the optical axis. Image blur caused by camera shake or the like can be corrected by rotating (swinging) in the in-plane direction. In particular, in the optical system of the present application, it is preferable that the second lens group or a part of the second lens group is an anti-vibration lens group.

  The lens surface of the lens constituting the optical system of the present application may be a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, it is preferable because lens processing and assembly adjustment are easy, and deterioration of optical performance due to errors in lens processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is aspherical, any of aspherical surface by grinding, glass mold aspherical surface in which glass is molded into an aspherical shape, or composite aspherical surface in which resin provided on the glass surface is formed in an aspherical shape Good. 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.
The manufacturing method of the optical system OS includes a first lens group G1 having a positive refractive power in order from the object side along the optical axis and fixed in the optical axis direction with respect to the image plane at the time of focusing. Second lens group G2 having positive refractive power and moving along the optical axis for focusing; and positive refractive power, fixed in the optical axis direction with respect to the image plane during focusing And a third lens group G3, and includes the following steps S1 to S4.

  The first lens group G1 includes at least two positive lenses L11 and L12 and a partial lens group G1a having a positive refractive power as a whole and a negative lens L1b (step S1).

  The second lens group G2 includes a positive lens L21, a negative lens L22, and a cemented lens L2a having a positive refractive power from the object side (step S2).

  The third lens group G3 has a cemented lens L3a (step S3).

The following conditional expression (1) is satisfied (step S4).
−1.00 <(r2nb + r2na) / (r2nb−r2na) <0.00 (1)
However,
r2na: radius of curvature of the object side lens surface of the negative lens L22 in the second lens group r2nb: radius of curvature of the image side lens surface of the negative lens L22 in the second lens group

  According to the above manufacturing method, it is possible to manufacture an optical system with a small number of components of the focusing lens group, high performance, and low aberrations.

  Hereinafter, numerical examples of the optical system OS will be described with reference to the drawings. 1, 3, 5, and 7 illustrate the configuration of the optical system OS (OS1 to OS4) according to each embodiment.

In each embodiment, the height of the aspheric surface in the direction perpendicular to the optical axis is y, and the distance (sag amount) along the optical axis from the tangential plane of the apex of each aspheric surface to each aspheric surface at height y. Is S (y), r is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and An is the nth-order aspherical coefficient, and is expressed by the following equation (a). .
X (y) = (y ² / r) / [1+ [1-κ (y ² / r ² )] ^1/2 ]
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰ (a)

  In each example, the secondary aspheric coefficient A2 is zero. In the table of each example, an aspherical surface is marked with “*” on the right side of the surface number.

[First embodiment]
FIG. 1 is a diagram illustrating a configuration of an optical system OS1 according to the first example. The optical system OS1 has a positive refractive power in order from the object side along the optical axis, and a first lens group G1 fixed in the optical axis direction with respect to the image plane at the time of focusing, and a positive refraction. A second lens group G2 that moves toward the object side along the optical axis for focusing, and has a positive refractive power, and is fixed in the optical axis direction with respect to the image plane during focusing. And a third lens group G3.

  The first lens group G1 includes a partial lens group G1a having a positive refractive power and a negative meniscus lens L1b having a convex surface directed toward the object side. The partial lens group G1a includes a positive meniscus lens L11 having a convex surface directed toward the object side, and a positive meniscus lens L12 having a convex surface directed toward the object side.

  The second lens group G2, in order from the object side, has a positive meniscus lens L21 having a convex surface facing the object side, and both the object side and image side lens surfaces being aspherical, an aperture stop S, and a biconcave negative shape. The lens L22 includes a positive meniscus lens L23 having a convex surface facing the object side and a cemented positive lens L2a formed by cementing a biconvex positive lens L24.

  The third lens group G3 includes three lenses: a positive meniscus lens L31 having a convex surface facing the image side, a negative meniscus lens L32 having a convex surface facing the image side, and a positive meniscus lens L33 having a convex surface facing the image side. It consists of a cemented positive lens made by joining.

  Table 1 below lists values of specifications of the optical system OS1 according to the first example. In [Overall specifications] in Table 1, “f” is a focal length, “FNO” is an F number, “ω” is a half angle of view (unit is “°”), “Y” is an image height, and “TL”. Represents the total length of the optical system OS1, and "Bf" represents the back focus. Note that the total length TL indicates the distance on the optical axis from the most object side lens surface (first surface) of the optical system OS1 to the image plane.

  In [Surface Data], the first column shows the order (surface number) of the optical surfaces from the object side along the traveling direction of the light beam, the second column r shows the curvature radius of each optical surface, The third column d indicates the surface spacing (the spacing between the nth surface (n is an integer) and the n + 1th surface), the fourth column νd indicates the Abbe number with respect to the d-line (wavelength λ = 587.6 nm). Column 5 nd indicates the refractive index for the d-line. Note that the radius of curvature r = ∞ indicates a plane on the lens surface, and an aperture on the aperture stop S. In addition, the refractive index nd of air = 1.0000 is omitted. Further, the surface interval of the final surface (the 18th surface) is a distance on the optical axis to the image surface I. The surface numbers 1 to 18 correspond to the numbers 1 to 18 shown in FIG.

  In [Lens Group Focal Length], the surface number (starting surface) of the surface closest to the object among the lens groups and the focal length of each lens group are shown.

  In each interval data, “F” is the focal length of the entire system, “β” is the imaging magnification between the object and the image, and “Di” (where i is an integer) is the variable of the i-th surface. The surface spacing is shown. “Infinity” indicates an infinite focus state, “intermediate” indicates an intermediate distance focus state, and “short distance” indicates a short distance focus state. “D0” represents the distance from the object to the first surface.

  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 = 103.256
FNO = 1.45
ω = 11.68
Y = 21.6
TL = 130.513
Bf = 39.073

[Surface data]
Surface number rd νd nd
Object ∞ ∞
1 51.1279 16.3006 66.99 1.593490
2 755.5654 0.1000
3 41.4637 8.1027 95.25 1.433852
4 84.3725 4.5000
5 791.5941 1.4692 38.03 1.603420
6 33.8617 Variable
7 * 35.5717 7.4058 66.99 1.593490
8 * 48.2846 6.0000
9 (Aperture) 3.0000
10 -102.8594 1.5000 38.03 1.603420
11 42.6185 2.0000
12 102.8934 1.5000 40.98 1.581440
13 31.6297 8.0000 46.60 1.804000
14 -71.5505 Variable
15 -35.9311 2.5000 52.34 1.755000
16 -32.3912 1.5000 38.03 1.603420
17 -214.6029 3.5000 35.73 1.902650
18 -47.9685 39.07303
Image plane ∞

[Lens focal length]
Group Start surface Focal length
1 1 216.18736
2 7 105.33824
3 15 380.67323

[Each interval data]
Infinity middle short distance
F, β 103.25555 -0.03333 -0.13063
D0 ∞ 3107.7663 819.4870
d6 21.06494 16.43139 4.14418
D14 2.99667 7.63022 19.91743

In the optical system OS1 according to the first example, the lens surfaces of the seventh surface and the eighth surface are formed in an aspherical shape. Table 2 below shows the aspheric data, that is, the values of the conic constant κ and the aspheric constants A4 to A10. In the following examples, “E−n” indicates “× 10 ⁻ⁿ ”.

(Table 2)
[Aspherical data]
K A4 A 6 A 8 A10
7th surface 1.0000 2.14745E-06 4.07060E-09 -2.12514E-12 -7.96097E-16
8th surface 1.0000 5.98947E-06 6.10636E-09 2.89314E-12 -1.24745E-14

Table 3 below shows values corresponding to the conditional expressions for the optical system OS1 according to the first example.
Here, “r2na” indicates the radius of curvature of the object side lens surface of the negative lens L22 in the second lens group G2. “R2nb” indicates the radius of curvature of the image side lens surface of the negative lens L22 in the second lens group G2. “F2” indicates the focal length of the second lens group G2. “F1” indicates the focal length of the first lens group G1. “X2” indicates the amount of movement of the second lens group G2 when focusing from the infinitely focused state to the imaging magnification β = −1 / 30 times. “F3” indicates the focal length of the third lens group G3. “F0” indicates the focal length of the entire system when focused at infinity. “N23” indicates the refractive index with respect to the d-line of the negative lens L23 constituting the cemented lens L2a in the second lens group G2. “N24” indicates the refractive index with respect to the d-line of the positive lens L24 constituting the cemented lens L2a in the second lens group G2. “N31” indicates the refractive index with respect to the d-line of the object side positive lens L31. “N32” indicates the refractive index with respect to the d-line of the negative lens L32 cemented on the image side of the object side positive lens L31. “Νd1a” represents an average value of the Abbe numbers of at least two positive lenses (L11, L12) in the partial lens group G1a.

(Table 3)
(1) (r2nb + r2na) / (r2nb−r2na) = − 0.414
(2) f2 / f1 = 0.487
(3) X2 / f2 = 0.0440
(4) f3 / f0 = 3.69
(5) N24−N23 = 0.223
(6) N31-N32 = 0.152
(7) νd1a = 81.1

  Thus, the optical system OS1 according to the first example satisfies all the conditional expressions (1) to (7).

  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” indicates an F number, “Y” indicates an image height, and “ω” indicates a half angle of view [unit: “°”]. 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 is 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, sagittal coma, field curvature, astigmatism, and meridional coma are corrected well. It can be seen that it has high optical performance.

[Second Embodiment]
FIG. 3 is a diagram illustrating a configuration of the optical system OS2 according to the second embodiment. The optical system OS2 has a positive refractive power in order from the object side along the optical axis, and a first lens group G1 fixed in the optical axis direction with respect to the image plane during focusing, and a positive refraction. A second lens group G2 that moves toward the object side along the optical axis for focusing, and has a positive refractive power, and is fixed in the optical axis direction with respect to the image plane during focusing. And a third lens group G3.

  The first lens group G1 includes a partial lens group G1a having a positive refractive power and a negative meniscus lens L1b having a convex surface directed toward the object side. The partial lens group G1a includes a positive meniscus lens L11 having a convex surface directed toward the object side, and a positive meniscus lens L12 having a convex surface directed toward the object side.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, and both the object side and image side lens surfaces being aspherical, a biconcave negative lens L22, and an aperture. The aperture stop S includes a positive meniscus lens L23 having a convex surface facing the object side and a cemented positive lens L2a formed by cementing a biconvex positive lens L24.

  The third lens group G3 includes three lenses: a positive meniscus lens L31 having a convex surface facing the image side, a negative meniscus lens L32 having a convex surface facing the image side, and a positive meniscus lens L33 having a convex surface facing the image side. This is composed of a cemented positive lens L3a made of

  Table 4 below lists values of specifications of the optical system OS2 according to the second example. In addition, the surface numbers 1-18 shown in [surface data] respond | correspond to the numbers 1-18 shown in FIG.

(Table 4)
[Overall specifications]
f = 103.026
FNO = 1.45
ω = 11.76
Y = 21.6
TL = 131.154
Bf = 39.078

[Surface data]
Surface number rd νd nd
Object ∞ ∞
1 50.8264 18.0000 66.99 1.593490
2 574.4441 0.1000
3 41.5651 9.5000 95.25 1.433852
4 90.7854 4.5000
5 989.3195 2.0000 38.03 1.603420
6 31.8136 Variable
7 * 34.1685 6.3000 66.99 1.593490
8 * 65.5156 4.6142
9 -113.4743 1.5000 38.03 1.603420
10 42.6185 5.0000
11 (aperture) 1.5000
12 175.0933 1.5000 40.98 1.581440
13 41.8243 6.0000 46.60 1.804000
14 -68.3276 Variable
15 -32.0146 2.5000 52.34 1.755000
16 -26.3138 1.5000 38.03 1.603420
17 -109.0768 3.5000 35.73 1.902650
18 -42.6458 39.07848
Image plane ∞

[Lens focal length]
Group Start surface Focal length
1 1 219.63262
2 7 91.42405
3 15 397.58314

[Each interval data]
Infinity middle short distance
F, β 103.02606 -0.03333 -0.12814
D0 ∞ 3084.1355 818.8457
d6 21.06494 16.67023 5.33006
d14 2.99667 7.39138 18.73154

  In the optical system OS2 according to the second example, the seventh and eighth lens surfaces are formed in an aspherical shape. Table 5 below shows the aspheric data, that is, the values of the conic constant κ and the aspheric constants A4 to A10.

(Table 5)
KA 4 A 6 A 8 A10
7th surface 1.0000 2.44656E-06 4.38628E-09 4.85921E-12 0.00000
8th surface 1.0000 5.98947E-06 7.23342E-09 0.00000 0.00000

  Table 6 below shows values corresponding to the conditional expressions for the optical system OS2 according to the second example.

(Table 6)
(1) (r2nb + r2na) / (r2nb−r2na) = − 0.454
(2) f2 / f1 = 0.416
(3) X2 / f2 = 0.0481
(4) f3 / f0 = 3.86
(5) N24−N23 = 0.223
(6) N31-N32 = 0.152
(7) νd1a = 81.1

  Thus, the optical system OS2 according to the second example satisfies all the conditional expressions (1) to (7).

  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 is 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, sagittal coma, field curvature, astigmatism, and meridional coma are corrected well. It can be seen that it has high optical performance.

[Third embodiment]
FIG. 5 is a diagram illustrating a configuration of the optical system OS3 according to the third embodiment. The optical system OS3 has a positive refractive power in order from the object side along the optical axis, and a first lens group G1 fixed in the optical axis direction with respect to the image plane at the time of focusing, and a positive refraction. A second lens group G2 that moves toward the object side along the optical axis for focusing, and has a positive refractive power, and is fixed in the optical axis direction with respect to the image plane during focusing. And a third lens group G3.

  The first lens group G1 includes a partial lens group G1a having a positive refractive power and a negative meniscus lens L1b having a convex surface directed toward the object side. The partial lens group G1a includes a positive meniscus lens L11 having a convex surface directed toward the object side, and a positive meniscus lens L12 having a convex surface directed toward the object side.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, and both the object side and image side lens surfaces being aspherical, a biconcave negative lens L22, and an aperture. It comprises a stop S, and a cemented positive lens L2a formed by cementing a biconcave negative lens L23 and a biconvex positive lens L24.

  The third lens group G3 includes a cemented positive lens L3a formed by cementing three lenses: a positive meniscus lens L31 having a convex surface directed toward the image side, a biconcave negative lens L32, and a biconvex positive lens L33. Consists of.

  Table 7 below provides values of specifications of the optical system OS3 according to the third example. In addition, the surface numbers 1-18 shown in [surface data] respond | correspond to the numbers 1-18 shown in FIG.

(Table 7)
[Overall specifications]
f = 102.950
FNO = 1.45
ω = 11.76
Y = 21.6
TL = 129.128
Bf = 39.107

[Surface data]
Surface number rd νd nd
Object ∞ ∞
1 51.4246 15.0000 66.99 1.593490
2 475.3841 0.1000
3 40.6677 7.3441 95.25 1.433852
4 71.7978 5.7000
5 429.5958 2.0000 40.98 1.581440
6 32.9292 Variable
7 * 38.0361 8.5000 66.99 1.593490
8 * 426.5656 2.8267
9 -387.2993 1.5000 38.03 1.603420
10 36.3815 7.0000
11 (aperture) 2.5000
12 -172.8451 1.5000 40.98 1.581440
13 40.0035 8.0000 46.60 1.804000
14 -70.0997 Variable
15 -80.4245 2.5000 31.31 1.903660
16 -57.3390 1.6000 38.03 1.603420
17 117.5351 3.0000 35.73 1.902650
18 -238.3742 39.10698
Image plane ∞

[Lens focal length]
Group Start surface Focal length
1 1 245.07287
2 7 93.80859
3 15 1783.64648

[Each interval data]
Infinity middle short distance
F, β 102.94993 -0.03333 -0.12987
D0 ∞ 3099.4053 820.8718
d6 19.50557 15.46676 4.62396
d14 1.44483 5.48363 16.32644
BF 39.10698 39.10698 39.10698

  In the optical system OS3 according to the third example, the lens surfaces of the seventh surface and the eighth surface are formed in an aspherical shape. Table 8 below shows the aspheric data, that is, the values of the conic constant κ and the aspheric constants A4 to A10.

(Table 8)
KA 4 A 6 A 8 A10
7th surface 1.0000 1.53599E-07 5.63564E-10 0.00000 0.00000
8th surface 1.0000 2.89610E-06 1.42416E-10 0.00000 0.00000

  Table 9 below shows values corresponding to the conditional expressions for the optical system OS3 according to the third example.

(Table 9)
(1) (r2nb + r2na) / (r2nb−r2na) = − 0.828
(2) f2 / f1 = 0.383
(3) X2 / f2 = 0.0431
(4) f3 / f0 = 17.33
(5) N24−N23 = 0.223
(6) N31-N32 = 0.300
(7) νd1a = 81.1

  Thus, the optical system OS3 according to the third example satisfies all the conditional expressions (1) to (7).

  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 each aberration diagram shown in FIG. 6, in the optical system OS3 according to the third example, various aberrations including spherical aberration, sagittal coma, field curvature, astigmatism, and meridional coma are corrected well. It can be seen that it has high optical performance.

[Fourth embodiment]
FIG. 7 is a diagram illustrating a configuration of an optical system OS4 according to the fourth example. This optical system OS4 has a positive refractive power in order from the object side along the optical axis, and a first lens group G1 fixed in the optical axis direction with respect to the image plane during focusing, and a positive refraction. A second lens group G2 that moves toward the object side along the optical axis for focusing, and has a positive refractive power, and is fixed in the optical axis direction with respect to the image plane during focusing. And a third lens group G3.

  The first lens group G1 includes a partial lens group G1a having a positive refractive power and a negative meniscus lens L1b having a convex surface directed toward the object side. The partial lens group G1a includes a positive meniscus lens L11 having a convex surface directed toward the object side, and a positive meniscus lens L12 having a convex surface directed toward the object side.

  The second lens group G2, in order from the object side, has a positive meniscus lens L21 having a convex surface facing the object side, and both the object side and image side lens surfaces being aspherical, an aperture stop S, and a biconcave negative shape. The lens L22 includes a positive meniscus lens L23 having a convex surface facing the object side and a cemented positive lens L2a formed by cementing a biconvex positive lens L24.

  The third lens group G3 includes a cemented lens L3a having a negative refractive power and a positive meniscus lens L33 having a convex surface directed toward the image side. The cemented lens L3a is formed by cementing a positive meniscus lens L31 having a convex surface toward the image side and a negative meniscus lens L32 having a convex surface toward the image side.

  Table 10 below lists values of specifications of the optical system OS4 according to the fourth example. The surface numbers 1 to 19 shown in Table 10 correspond to the numbers 1 to 19 shown in FIG.

(Table 10)
[Overall specifications]
f = 103.323
FNO = 1.45
ω = 11.67
Y = 21.6
TL = 130.794
Bf = 38.989

[Surface data]
Surface number rd νd nd
Object ∞ ∞
1 51.1843 17.0852 66.99 1.593490
2 726.6420 0.1000
3 42.0230 8.3896 95.25 1.433852
4 88.5300 4.5000
5 988.8842 0.4859 38.03 1.603420
6 34.5201 Variable
7 * 34.5273 6.8835 66.99 1.593490
8 * 45.6828 6.0000
9 (Aperture) 3.0000
10 -118.3704 1.5000 38.03 1.603420
11 42.6185 2.3000
12 110.4518 1.5000 40.98 1.581440
13 32.2380 8.0000 46.60 1.804000
14 -75.9672 Variable
15 -34.8997 2.0000 52.34 1.755000
16 -30.5647 1.5000 38.03 1.603420
17 -136.3982 1.0000
18 -190.8904 3.5000 35.73 1.902650
19 -48.5142 38.98862
Image plane ∞

[Lens focal length]
Group Start surface Focal length
1 1 211.75620
2 7 111.18807
3 15 309.68514

[Each interval data]
Infinity middle short distance
F, β 103.32338 -0.03333 -0.13107
D0 ∞ 3111.0468 819.2056
d6 21.06494 16.13836 3.10018
d14 2.99667 7.92324 20.96143

  In the optical system OS4 according to the fourth example, the lens surfaces of the seventh surface and the eighth surface are formed in an aspherical shape. Table 11 below shows the aspheric data, that is, the values of the conic constant κ and the aspheric constants A4 to A10.

(Table 11)
KA 4 A 6 A 8 A10
7th surface 1.0000 2.22055E-06 4.81838E-09 -1.13690E-12 -1.12000E-15
8th surface 1.0000 5.98947E-06 7.00736E-09 6.63981E-12 -1.81185E-14

  Table 12 below shows values corresponding to the conditional expressions for the optical system OS4 according to the fourth example.

(Table 12)
(1) (r2nb + r2na) / (r2nb−r2na) = − 0.471
(2) f2 / f1 = 0.525
(3) X2 / f2 = 0.0443
(4) f3 / f0 = 2.997
(5) N24−N23 = 0.223
(6) N31-N32 = 0.152
(7) νd1a = 81.1

  As described above, the optical system OS4 according to the fourth example satisfies all the conditional expressions (1) to (7).

  FIG. 8 shows various aberration diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinitely focused state of the optical system OS4 according to the fourth example. As is apparent from the aberration diagrams shown in FIG. 8, in the optical system OS4 according to the fourth example, various aberrations including spherical aberration, sagittal coma, field curvature, astigmatism, and meridional coma are corrected well. It can be seen that it has high optical performance.

  According to each of the above-described embodiments, it has a comprehensive angle of about 2ω = 23 °, a large aperture of F1.4, and has high performance and excellent spherical aberration, astigmatism, field curvature, and coma. An optical system OS corrected to 1 can be realized.

  Needless to say, the above-described effects can be obtained by mounting the optical systems OS <b> 1 to OS <b> 4 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 OS4) Optical system G1 First lens group G2 Second lens group G3 Third lens group G1a Partial lens group L2a having positive refractive power in the first lens group L cemented positive lens L11 in the second lens group First positive lens L12 in the partial lens group G1a Second positive lens L1b in the partial lens group G1a Negative lens L21 in the first lens group Positive meniscus lens L22 in the second lens group Negative lens L23 in the second lens group Negative lens L24 in positive cemented lens L2a in second lens group Positive lens L31 in positive cemented lens L2a in second lens group Positive lens L32 in third lens group Negative lens L33 in third lens group Third Positive lens S in lens group Aperture stop 1 SLR camera (imaging device)

Claims (12)

In order from the object side along the optical axis,
A first lens group having a positive refractive power and fixed in the optical axis direction with respect to the image plane during focusing;
A second lens group having positive refractive power and moving along the optical axis for focusing;
Has a positive refractive power, upon focusing, substantially consists of three lens groups by a third lens group that is fixed in the optical axis direction with respect to the image plane,
The first lens group includes a partial lens group having at least two positive lenses and having a positive refractive power as a whole, and a negative lens.
The second lens group includes a positive lens, a negative lens, and a cemented lens having a positive refractive power from the object side,
The third lens group includes a cemented lens;
An optical system that satisfies the following conditional expression.
−1.00 <(r2nb + r2na) / (r2nb−r2na) <0.00
However,
r2na: radius of curvature of the object side lens surface of the negative lens in the second lens group r2nb: radius of curvature of the image side lens surface of the negative lens in the second lens group The optical system according to claim 1, which satisfies the following conditional expression.
0.35 <f2 / f1 <1.00
However,
f2: focal length of the second lens group f1: focal length of the first lens group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.00 <X2 / f2 <0.10
However,
X2: Amount of movement of the second lens group when focusing at an imaging magnification β = −1 / 30 times from an infinitely focused state f2: Focal length of the second lens group The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.00 <f3 / f0 <20.00
However,
f3: focal length of the third lens group f0: focal length of the entire system when focusing on infinity The cemented lens in the second lens group is formed by cementing a negative lens and a positive lens,
The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <N24-N23 <0.50
However,
N23: Refractive index with respect to d-line of the negative lens constituting the cemented lens in the second lens group N24: Refractive index with respect to d-line of the positive lens constituting the cemented lens in the second lens group The cemented lens in the third lens group includes an object-side positive lens disposed closest to the object side, and a negative lens cemented on the image side of the object-side positive lens,
The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <N31-N32 <0.50
However,
N31: Refractive index with respect to d line of the object side positive lens N32: Refractive index with respect to d line of the negative lens cemented on the image side of the object side positive lens The optical system according to claim 1, wherein the following conditional expression is satisfied.
57.00 <νd1a
However,
νd1a: average value of the Abbe number of the at least two positive lenses in the partial lens group   The optical system according to any one of claims 1 to 7, further comprising an aperture stop that determines an F-number on the image side of the first lens group.   The optical system according to claim 1, further comprising an aperture stop that determines an F number in the second lens group.   8. An aperture stop for determining an F-number between the positive lens and the negative lens in the second lens group or between the negative lens and the cemented lens in the second lens group. The optical system according to any one of the above.   The optical system according to claim 1, wherein the optical system has at least one aspherical surface.   An imaging apparatus comprising the optical system according to claim 1.

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