JP2014013296A - Optical system, imaging device including the same, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical system having a small number of lenses, reducing the generation of ghost and flare, achieving high performance, and having small aberrations, and an imaging device and a method of manufacturing the optical system.SOLUTION: An optical system OS includes a front group GF and a rear group GR with positive refractive power. At least one surface among optical surfaces in the above groups is provided with an antireflection film which includes at least one layer formed by using a wet process. The front group GF includes a first lens component LFP with positive refractive power, a second lens component LFN1 with negative refractive power in which a positive lens and a negative lens are cemented and whose convex surface is directed toward the object side, and a third lens component LFN2 with negative refractive power whose concave surface is directed toward the object side. The rear group GR includes a first lens component LRN in which a negative lens and a positive lens are cemented and whose concave surface is directed toward the object side, a second lens component LRP1 with positive refractive power whose concave surface is directed toward the image side, and a third lens component LRP2 with positive refractive power.

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 modified Gaussian lenses have been proposed (see, for example, Patent Document 1). In recent years, not only aberration performance but also ghost and flare requirements, which are one of the factors that impair optical performance, have become increasingly demanding for such optical systems. Higher performance is also required for the prevention film, and multilayer film design technology and multilayer film formation technology continue to advance to meet the demand (see, for example, Patent Document 2).

JP 2009-251398 A JP 2000-356704 A

  However, the conventional Gaussian lens has insufficient correction of coma, and it has been particularly difficult to improve sagittal coma. At the same time, the optical surface in such an optical system also has a problem that reflected light that becomes ghost or flare is easily generated.

  The present invention has been made in view of such problems, and is an optical system that is small in size, has a small number of components, has reduced ghosts and flares, has high performance, and has low coma, particularly sagittal coma and spherical aberration. An object of the present invention is to provide an imaging device having this optical system and a method for manufacturing the optical system.

In order to solve the above problems, an optical system according to the present invention includes, in order from the object side along the optical axis, a front group and a rear group having a positive refractive power. An antireflection film is provided on at least one of the optical surfaces, and the antireflection film is formed to include at least one layer formed by using a wet process. A first lens component having a power, a positive lens and a negative lens are cemented together, have a negative refractive power, have a second lens component having a convex surface facing the object side, and a concave surface facing the object side, and negative refraction A rear lens unit having a negative lens and a positive lens joined in order from the object side, and a first lens component having a concave surface facing the object side, and a positive refractive power. A second lens component having a concave surface facing the image side and a third lens component having a positive refractive power It has, and satisfies the following conditional expression.
0.0 <fR / | fF | <1.0
0.00 <(− fFN1) / f0 <10.00
However,
fF: Focal length of the front group fR: Focal length of the rear group fFN1: Focal length of the second lens component in the front group f0: Focal length of the entire system when focusing on infinity

  In such an optical system, the antireflection film is preferably a multilayer film, and the layer formed by the wet process is preferably the most surface layer among the layers constituting the multilayer film.

  Further, in such an optical system, when the refractive index of a layer formed by using a wet process is nd, the refractive index nd is preferably 1.30 or less.

  Such an optical system preferably has an aperture stop, and the optical surface provided with the antireflection film is preferably a concave lens surface when viewed from the aperture stop.

  In such an optical system, it is preferable that the concave lens surface viewed from the aperture stop is an object-side lens surface.

  In such an optical system, it is preferable that the concave lens surface as viewed from the aperture stop is a lens surface on the image plane side.

  In such an optical system, the optical surface provided with the antireflection film is preferably a concave lens surface as viewed from the object.

  In such an optical system, it is preferable that the concave lens surface as viewed from the object is the object side lens surface of the most image side lens in the front group.

  Further, in such an optical system, it is preferable that the concave lens surface as viewed from the object is an image surface side lens surface of the most image surface side lens in the front group.

  In such an optical system, the optical surface provided with the antireflection film is preferably a concave lens surface as viewed from the image plane.

  In such an optical system, it is preferable that the concave lens surface as viewed from the image plane is a rear lens surface.

Such an optical system preferably satisfies the following conditional expression.
0.20 <(-fFN2) / f0 <15.00
However,
fFN2: focal length of the third lens component in the front group

Such an optical system preferably satisfies the following conditional expression.
−2.00 <(rp2−rp1) / (rp2 + rp1) <− 0.00
However,
rp1: radius of curvature of the most object side surface of the second lens component in the rear group rp2: radius of curvature of the most image side surface of the second lens component in the rear group

Such an optical system preferably satisfies the following conditional expression.
0.00 <nRNP-nRNN <0.35
However,
nRNP: refractive index with respect to d-line of medium of positive lens in first lens component in rear group nRNN: refractive index with respect to d-line of medium of negative lens in first lens component in rear group

In such an optical system, the second lens component in the rear group is preferably a cemented lens in which a positive lens and a negative lens are cemented, and preferably satisfies the following conditional expression.
0.00 <nRPP-nRPN <0.35
However,
nRPP: refractive index of the second lens component in the rear group with respect to the d-line of the medium of the positive lens nRPN: refractive index of the second lens component in the rear group with respect to the d-line of the medium of the negative lens

Such an optical system preferably satisfies the following conditional expression.
1.00 <fRP / f0 <12.00
However,
fRP: focal length of the second lens component in the rear group

Such an optical system preferably satisfies the following conditional expression.
0.1 <fRP2 / f0 <3.0
However,
fRP2: focal length of the third lens component in the rear group

  In such an optical system, the front group preferably has at least one aspheric surface.

  In such an optical system, the rear group preferably has at least one aspheric surface.

  In such an optical system, the third lens component in the rear group is preferably a positive lens having a convex surface facing the object side.

  Such an optical system preferably has an aperture stop between the front group and the rear group.

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

The optical system manufacturing method according to the present invention includes, in order from the object side along the optical axis, a front group and a rear group having a positive refractive power, and the optical surfaces of the front group and the rear group Of these, an antireflection film is provided on at least one surface, and this antireflection film is a method of manufacturing an optical system including at least one layer formed using a wet process. In order, a first lens component having a positive refractive power, a positive lens and a negative lens are cemented, a second lens component having a negative refractive power and having a convex surface facing the object side, and a concave surface facing the object side. And a third lens component having negative refractive power, and as a rear group, a negative lens and a positive lens are sequentially joined from the object side, and a first lens component having a concave surface facing the object side; A second lens component having a positive refractive power and having a concave surface facing the image side, and positive refraction A third lens component, a place with, and satisfies the following conditional expression.
0.0 <fR / | fF | <1.0
0.00 <(− fFN1) / f0 <10.00
However,
fF: Focal length of the front group fR: Focal length of the rear group fFN1: Focal length of the second lens component in the front group f0: Focal length of the entire system when focusing on infinity

  According to the present invention, an optical system that is small in size, has a small number of components, has reduced ghosts and flares, has high performance, has high performance, and has low coma, particularly sagittal coma and spherical aberration, an image pickup apparatus having the optical system, and An optical system manufacturing method can be 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 of the optical system which concerns on 1st Example, Comprising: The figure explaining an example of a mode that the incident light ray reflects in the 1st reflected light generation surface and the 2nd reflected light generation surface It is. 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 equipped with an optical system is shown. It is a flowchart for demonstrating the manufacturing method of an optical system. It is explanatory drawing which shows an example of the layer structure of an antireflection film. It is a graph which shows the spectral characteristic of an antireflection film. It is a graph which shows the spectral characteristics of the antireflection film concerning a modification. It is a graph which shows the incident angle dependence of the spectral characteristic of the antireflection film concerning a modification. It is a graph which shows the spectral characteristic of the anti-reflective film produced with the prior art. It is a graph which shows the incident angle dependence of the spectral characteristic of the anti-reflective film produced with the prior art.

  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 front group GF and a rear group GR having a positive refractive power in order from the object side along the optical axis. . Further, in the front group GF, in order from the object side, a first lens component LFP having a positive refractive power, a positive lens L12, and a negative lens L13 are cemented, and a negative refractive power with a convex surface facing the object side is provided. A second lens component LFN1 having a concave surface facing the object side and a third lens component LFN2 having a negative refractive power. The rear group GR includes a negative lens L21 and a positive lens L22 in order from the object side. A first lens component LRN having a concave surface facing the object side, a second lens component LRP1 having a positive refractive power and a concave surface facing the image side, and a third lens component having a positive refractive power And LRP2. In the following description, “lens component” refers to a single lens (lens element) or a cemented lens in which two or more single lenses (lens elements) are cemented.

  The optical system OS according to the present embodiment has coma aberration, particularly sagittal coma aberration, which is a defect of so-called Gaussian type and xenota type optical systems, which are basically represented by positive, negative, positive, negative, chromatic aberration, curvature of field and non-existence. This is an improvement without deteriorating the point aberration. 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).

0.0 <fR / | fF | <1.0 (1)
However,
fF: focal length of front group GF fR: focal length of rear group GR

  Conditional expression (1) is a condition that defines an optimum value for the ratio of the focal lengths of the front group GF and the rear group GR, in other words, the ratio of refractive power. The feature of the present invention is based on the refractive power arrangement in which the front group GF has a relatively weak refractive power and the rear group GR has a relatively strong refractive power. In particular, the optimum refractive power balance between the front group GF and the rear group GR is necessary to achieve good aberration correction including coma.

  When the upper limit value of the conditional expression (1) is exceeded, it indicates that the focal length of the front group GF is significantly smaller than the focal length of the rear group GR, that is, the refractive power of the front group GF is significantly increased. Means. In this case, the optimum refractive power balance is lost, and correction of spherical aberration, lateral chromatic aberration, and distortion is deteriorated. If the upper limit value of conditional expression (1) is set to 0.7, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (1) is set to 0.5, the above-mentioned correction of various aberrations becomes more advantageous. Further, when the upper limit value of conditional expression (1) is set to 0.2, the above-described correction of various aberrations becomes more advantageous. In addition, the effect of the present application can be maximized by setting the upper limit value of conditional expression (1) to 0.1.

  Moreover, when it falls below the lower limit value of the conditional expression (1), the sign is inverted, and the rear group GR has a negative refractive power. In this case, the refractive power balance is greatly lost, and correction of spherical aberration, coma, astigmatism, and distortion is deteriorated, which is not preferable. In addition, the back focus is shortened, which makes it difficult to use for a single-lens reflex camera.

  Further, in the optical system OS according to this embodiment, an antireflection film is provided on at least one of the optical surfaces in the front group GF and the rear group GR, and this antireflection film is a layer formed by using a wet process. Contains at least one layer. With this configuration, the optical system according to the present embodiment can further reduce ghosts and flares caused by reflection of light from an object on an optical surface, and can achieve high imaging performance. .

  In the optical system OS according to this embodiment, the antireflection film is preferably a multilayer film, and the layer formed by the wet process is preferably the outermost layer among the layers constituting the multilayer film. In this way, since the difference in refractive index with air can be reduced, the reflection of light can be further reduced, and ghosts and flares can be further reduced.

  In the optical system OS according to this embodiment, the refractive index nd is preferably 1.30 or less, where nd is the refractive index of the layer formed using the wet process. In this way, since the difference in refractive index with air can be reduced, the reflection of light can be further reduced, and ghosts and flares can be further reduced.

  In addition, the optical system OS according to the present embodiment has an aperture stop S, and an optical surface provided with an antireflection film among the optical surfaces in the front group GF and the rear group GR has a concave shape as viewed from the aperture stop S. It is preferable that it is a lens surface. Of the optical surfaces in the front group GF and the rear group GR, reflected light is likely to be generated on a concave lens surface when viewed from the aperture stop S. Thus, ghosts and flares can be effectively reduced. .

  In addition, the concave lens surface viewed from the aperture stop S and provided with the antireflection film in the front group GF and the rear group GR of the optical system OS according to the present embodiment is preferably a lens surface on the object side. . Of the optical surfaces in the front group GF and the rear group GR, reflected light is likely to be generated on a concave lens surface as viewed from the aperture stop S. Therefore, by forming an antireflection film on such an optical surface, ghosts and flares are generated. It can be effectively reduced.

  In addition, the concave lens surface as viewed from the aperture stop in which the antireflection film is provided in the front group GF and the rear group GR of the optical system OS according to the present embodiment is preferably a lens surface on the image plane side. . Of the optical surfaces in the front group GF and rear group GR, reflected light is likely to be generated on the concave lens surface when viewed from the aperture stop. Therefore, an anti-reflection film is formed on such an optical surface, so that ghost and flare are effective. Can be reduced.

  Of the optical surfaces in the front group GF of the optical system OS according to the present embodiment, the optical surface provided with the antireflection film is preferably a concave lens surface as viewed from the object. Since reflected light is likely to be generated on a concave lens surface as viewed from the object among the optical surfaces in the front group GF, ghosts and flares can be effectively reduced in this way.

  Further, the concave lens surface viewed from the object provided with the antireflection film among the optical surfaces in the front group GF of the optical system OS according to the present embodiment is the lens closest to the image plane of the front group GF. An object side lens surface is preferable. Of the optical surfaces in the front group GF, reflected light is likely to be generated by a concave lens surface when viewed from the object, so that an antireflection film is formed on such an optical surface to effectively reduce ghosts and flares. Can do.

  Further, the concave lens surface viewed from the object provided with the antireflection film among the optical surfaces in the front group GF of the optical system OS according to the present embodiment is the lens closest to the image plane of the front group GF. An image side lens surface is preferable. Of the optical surfaces in the front group GF, reflected light is likely to be generated by a concave lens surface when viewed from the object, so that an antireflection film is formed on such an optical surface to effectively reduce ghosts and flares. Can do.

  Of the optical surfaces in the rear group GR of the optical system OS according to the present embodiment, the optical surface provided with the antireflection film is preferably a concave lens surface as viewed from the image plane. Since reflected light is likely to be generated on a concave lens surface as viewed from the image plane among the optical surfaces in the rear group GR, in this way, ghosts and flares can be effectively reduced.

  In the optical system OS according to the present embodiment, the antireflection film is not limited to a wet process, and may be formed by a dry process or the like. At this time, it is preferable that the antireflection film includes at least one layer having a refractive index of 1.30 or less. By making the antireflection film include at least one layer having a refractive index of 1.30 or less, even if the antireflection film is formed by a dry process or the like, the same effect as that obtained by using a wet process can be obtained. Can be obtained. At this time, the layer having a refractive index of 1.30 or less is preferably the most surface layer among the layers constituting the multilayer film.

  Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (2).

0.00 <(− fFN1) / f0 <10.00 (2)
However,
fFN1: focal length of the second lens component LFN1 in the front group GF f0: focal length of the entire system when focusing on infinity

  Conditional expression (2) is a condition that defines the combined focal length of the negative lens component (second lens component LFN1) with the convex surface facing the object side of the front group GF. The front group GF of the optical system OS according to the present embodiment has a positive and negative configuration, and defines the optimum refractive power of the negative lens component (second lens component LFN1) at the intermediate portion.

  When the upper limit value of the conditional expression (2) is exceeded, it means that the negative refractive power of the negative lens component (second lens component LFN1) becomes weak. In this case, correction of field curvature and astigmatism deteriorates, which is not preferable. When the upper limit value of conditional expression (2) is set to 8.00, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (2) is set to 5.00, the above-described correction of various aberrations becomes more advantageous. Further, by setting the upper limit of conditional expression (2) to 1.80, the effect of the present application can be maximized.

  Further, when the lower limit value of conditional expression (2) is not reached, it means that the negative refractive power of the negative lens component (second lens component LFN1) becomes strong. In that case, correction of coma aberration, spherical aberration, and distortion is deteriorated as a result, which is not preferable. If the lower limit value of conditional expression (2) is set to 0.01, it is advantageous for correction of various aberrations such as spherical aberration. Setting the lower limit value of conditional expression (2) to 0.016 is advantageous for correcting various aberrations such as spherical aberration. Further, by setting the lower limit value of conditional expression (2) to 0.02, the effect of the present application can be maximized.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (3).

0.2 <(− fFN2) / f0 <15.0 (3)
However,
fFN2: focal length of the third lens component LFN2 in the front group GF f0: focal length of the entire system when focusing on infinity

  Conditional expression (3) is a condition that defines the magnitude of the focal length of the negative lens component (third lens component LFN2) on the image side of the front group GF, in other words, the magnitude of the negative refractive power.

  When the upper limit value of the conditional expression (3) is exceeded, it means that the negative refractive power of the negative lens component (third lens component LFN2) on the image side of the front group GF is reduced. In this case, the balance of correction for spherical aberration and coma is lost, which is not preferable. When the upper limit value of conditional expression (3) is set to 10.0, the above-described correction of various aberrations is advantageous. If the upper limit value of conditional expression (3) is set to 8.00, the above-described correction of various aberrations is advantageous. Further, by setting the upper limit of conditional expression (3) to 7.00, the effect of the present application can be maximized.

  Further, when the lower limit value of conditional expression (3) is not reached, it means that the negative refractive power of the negative lens component (third lens component LFN2) on the image side of the front group GF is increased. This is not preferable because sagittal coma and distortion are particularly deteriorated. When the lower limit value of conditional expression (3) is set to 0.80, the above-mentioned various aberrations can be corrected more favorably. If the lower limit value of conditional expression (3) is set to 0.86, the above-mentioned various aberrations can be corrected more favorably. If the lower limit value of conditional expression (3) is set to 1.20, the above-mentioned various aberrations can be corrected more favorably. Further, by setting the lower limit value of conditional expression (3) to 2.80, the effect of the present application can be maximized.

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

−2.00 <(rp2−rp1) / (rp2 + rp1) <− 0.00 (4)
However,
rp1: radius of curvature of the most object side surface of the second lens component LRP1 in the rear group GR rp2: radius of curvature of the most image side surface of the second lens component LRP1 in the rear group GR

  Conditional expression (4) is a condition that defines the reciprocal of the form factor of the entire second lens component LRP1 having a positive refractive power with the concave surface facing the image side in the rear group GR. This condition is greatly related to correction of spherical aberration and sagittal coma. The fact that the value set in the conditional expression (4) is negative means that the entire shape of the second lens component LRP1 with the concave surface facing the image side in the rear group GR is a positive lens component. However, it shows a negative meniscus shape. The presence of an air lens formed between this shape and the positive lens component (third lens component LRP2) located on the image side enables satisfactory correction of sagittal coma, meridional coma, and spherical aberration.

  When the upper limit value of conditional expression (4) is exceeded, the second lens component LRP1 changes its shape greatly from the negative meniscus shape and is a positive meniscus shape with a convex surface facing the object side, or a negative meniscus with a concave surface facing the object side Become a shape. Regardless of which shape is reached, the correction of sagittal coma and meridional coma is deteriorated, and correction of spherical aberration is also undesirably deteriorated when trying to correct it satisfactorily. If the upper limit value of conditional expression (4) is set to -0.01, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (4) is set to -0.03, the above-mentioned correction of various aberrations becomes more advantageous. In addition, the effect of the present application can be maximized by setting the upper limit value of conditional expression (4) to -0.05.

  When the lower limit value of conditional expression (4) is not reached, the second lens component LRP1 changes greatly from the negative meniscus shape to a biconvex shape or a biconcave shape. For this reason, the air lens described above does not exist, and the characteristics from the negative meniscus shape are not maintained, so that sagittal coma aberration, meridional coma aberration correction, and spherical aberration correction are deteriorated, which is not preferable. If the lower limit value of conditional expression (4) is set to -1.00, it is advantageous for correcting the above-mentioned various aberrations. Setting the lower limit of conditional expression (4) to −0.60 is advantageous for correcting the above-mentioned various aberrations. In addition, the effect of the present application can be maximized by setting the lower limit value of conditional expression (4) to −0.40.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (5).

0.00 <nRNP-nRNN <0.35 (5)
However,
nRNP: refractive index with respect to the d-line of the medium of the positive lens L22 in the first lens component LRN in the rear group GR nRNN: refractive index with respect to the d-line of the medium of the negative lens L21 in the first lens component LRN in the rear group GR

  Conditional expression (5) is a condition that regulates the difference in refractive index between the medium of the positive lens L22 and the negative lens L21 constituting the first lens component LRN in the rear group GR and the d-line (wavelength λ = 587.6 nm). is there. If this condition is not met, the Petzval sum will lose the optimal value setting, resulting in a worse field curvature.

  If the upper limit value of this conditional expression (5) is exceeded, it means that the difference in refractive index is remarkably increased. Even in this case, the Petzval sum is deteriorated from the optimum value, and as a result, the correction of the field curvature is deteriorated. In addition, the ability to correct spherical aberration also decreases, which makes it impossible to select a glass material for optimal chromatic aberration. If the upper limit value of conditional expression (5) is set to 0.30, the above-described correction of various aberrations becomes more advantageous. Further, when the upper limit value of conditional expression (5) is set to 0.20, the above-described correction of various aberrations becomes more advantageous. Further, by setting the upper limit of conditional expression (5) to 0.13, the effect of the present application can be maximized.

  If the lower limit of conditional expression (5) is not reached, the difference in refractive index becomes extremely small, and finally the refractive index of the negative lens L21 becomes larger than the refractive index of the positive lens L22. In this case, the positive and negative refractive indexes are reversed, and it is difficult to keep the Petzval sum small. Accordingly, the Petzval sum deviates greatly from the optimum value, and as a result, correction of curvature of field and correction of astigmatism are deteriorated, which is not preferable. Note that setting the lower limit of conditional expression (5) to 0.02 is advantageous for correcting various aberrations such as field curvature and astigmatism. Setting the lower limit of conditional expression (5) to 0.03 is advantageous for correcting various aberrations such as field curvature and astigmatism. Further, by setting the lower limit value of conditional expression (5) to 0.05, the effects of the present application can be maximized.

  In the optical system OS according to the present embodiment, the second lens component LRP1 of the rear group GR is a cemented lens in which the positive lens L23 and the negative lens L24 are cemented, and the following conditional expression (6) is satisfied. It is desirable to be satisfied.

0.00 <nRPP-nRPN <0.35 (6)
However,
nRPP: refractive index of the second lens component LRP1 in the rear group GR with respect to the d-line of the medium of the positive lens L23 nRPN: refractive index of the medium of the negative lens L24 of the second lens component LRP1 in the rear group GR with respect to the d-line

  Conditional expression (6) is a condition that defines the relationship between the refractive indices of the positive lens L23 and the negative lens L24 in the positive lens component (second lens component LRP1) in the rear group GR. Basically, the positive lens L23 has a higher refractive index than the negative lens L24, and the Petzval sum is suppressed to a small value.

  If the upper limit value of the conditional expression (6) is exceeded, the difference in refractive index between the positive lens L23 and the negative lens L24 becomes remarkably large, so that a dispersion difference cannot be secured with the currently existing glass material, and the correction of chromatic aberration deteriorates. When the upper limit value of conditional expression (6) is set to 0.40, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (6) is set to 0.30, the above-mentioned correction of various aberrations becomes more advantageous. Moreover, by setting the upper limit value of conditional expression (6) to 0.25, the effect of the present application can be maximized.

  If the lower limit value of conditional expression (6) is not reached, the difference in refractive index between the positive lens L23 and the negative lens L24 becomes smaller, and the height is finally reversed. Since the refractive index of the negative lens L24 is higher than that of the positive lens L23, it becomes difficult to set an optimal value for the Petzval sum, and as a result, field curvature and astigmatism are deteriorated. Note that setting the lower limit of conditional expression (6) to 0.10 is advantageous for correcting the above-mentioned various aberrations. Setting the lower limit of conditional expression (6) to 0.13 is advantageous for correcting the above-mentioned various aberrations. Further, by setting the lower limit value of conditional expression (6) to 0.16, the effects of the present application can be maximized.

  Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (7).

1.00 <fRP / f0 <12.00 (7)
However,
fRP: focal length of the second lens component LRP1 in the rear group GR f0: focal length of the entire system when focusing on infinity

  Conditional expression (7) is a condition that defines the combined focal length of the positive lens component (second lens component LRP1) with the concave surface facing the image side in the rear group GR. In the optical system OS according to the present embodiment, the rear group GR has a negative positive or positive configuration, and a positive lens component (second lens) disposed at the intermediate portion and having a concave surface facing the image side. It defines the optimum refractive power of the component LRP1).

  When exceeding the upper limit value of the conditional expression (7), it means that the focal length of the positive lens component (second lens component LRP1) becomes extremely long and the positive refractive power becomes weak. In this case, the correction of sagittal coma, meridional coma, field curvature, and astigmatism deteriorates, which is not preferable. If the upper limit value of conditional expression (7) is set to 10.00, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (7) is set to 9.00, the above-described correction of various aberrations becomes more advantageous. Further, by setting the upper limit value of conditional expression (7) to 8.00, the effect of the present application can be maximized.

  On the other hand, if the lower limit value of conditional expression (7) is not reached, it means that the focal length of the positive lens component (second lens component LRP1) is remarkably shortened and the positive refractive power is remarkably increased. In this case, the correction of spherical aberration, sagittal coma aberration, and meridional coma aberration deteriorates as a result, which is not preferable. Also, the sensitivity to eccentricity increases, which is not preferable. Note that setting the lower limit of conditional expression (7) to 1.50 is advantageous for correcting various aberrations such as spherical aberration. Setting the lower limit of conditional expression (7) to 1.92 is advantageous for correcting various aberrations such as spherical aberration. Further, by setting the lower limit value of conditional expression (7) to 2.40, the effects of the present application can be maximized.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (8).

0.1 <fRP2 / f0 <3.0 (8)
However,
fRP2: focal length of the third lens component LRP2 in the rear group GR f0: focal length of the entire system when focusing on infinity

  Conditional expression (8) is a condition that defines the focal length of the positive lens component (third lens component LRP2) located on the image side in the rear group GR. In the optical system OS according to the present embodiment, the rear group GR has a negative positive or positive configuration, and an optimum refractive power of the positive lens component (third lens component LRP2) disposed on the image side. It prescribes.

  When the upper limit value of the conditional expression (8) is exceeded, it means that the focal length of the positive lens component (third lens component LRP2) is remarkably increased and the positive refractive power is weakened. In this case, the correction capability of spherical aberration and coma aberration is lowered, which is not preferable. If the upper limit value of conditional expression (8) is set to 2.5, the above-described correction of various aberrations becomes more advantageous. If the upper limit value of conditional expression (8) is set to 2.0, the above-described correction of various aberrations becomes more advantageous. Further, by setting the upper limit value of conditional expression (8) to 1.5, the effect of the present application can be maximized.

  On the other hand, if the lower limit value of conditional expression (8) is not reached, it means that the focal length of the positive lens component (third lens component LRP2) is remarkably shortened and the positive refractive power is remarkably increased. In this case, the correction of spherical aberration, sagittal coma aberration, and meridional coma aberration deteriorates as a result, which is not preferable. Also, the sensitivity to eccentricity increases, which is not preferable. If the lower limit value of conditional expression (8) is set to 0.2, it is advantageous for correction of various aberrations such as spherical aberration. Setting the lower limit of conditional expression (8) to 0.4 is advantageous for correcting various aberrations such as spherical aberration. Further, by setting the lower limit of conditional expression (8) to 0.6, the effect of the present application can be maximized.

  In the optical system OS according to the present embodiment, it is desirable that the front group GF has at least one aspheric surface, which is advantageous for correcting spherical aberration and coma corresponding to a large aperture. In addition, it is desirable that the rear group GR described above also has at least one aspheric surface. Similarly, the rear group GR is advantageous for correcting spherical aberration and coma corresponding to a large aperture. It should be noted that having one aspherical surface before and after the aperture stop S is effective in correcting aberrations caused by a large aperture such as spherical aberration, sagittal coma aberration, meridional coma aberration.

  The positive lens component (third lens component LRP2) disposed on the image side in the rear group GR is preferably a positive lens having a convex surface directed toward the object side. Combined with the positive lens component (second lens component LRP1) with the concave surface facing the image side in the rear group GR just before, a convex air lens can be made, which is advantageous for correcting spherical aberration and sagittal coma aberration. .

  In addition, an aperture stop S between the front group GF and the rear group GR is preferable for correcting lateral chromatic aberration and distortion.

  In the optical system OS according to the present embodiment, the first lens component LFP and the third lens component LFN2 constituting the front group GF and the third lens component LRP2 constituting the rear group GR are simply shown in FIG. Although it is configured by a lens, it may be configured by a cemented lens in which two or more single lenses are cemented.

  FIG. 8 is 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 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 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. The camera 1 shown in FIG. 8 may be one that holds the photographic lens 2 in a detachable manner or may be molded integrally with the photographic 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 photographic lens 2, the ghost and flare are further reduced by the characteristic lens configuration, and spherical aberration, sagittal coma flare, field curvature, coma A large aperture lens with little aberration is realized. Accordingly, the camera 1 can realize an imaging apparatus that can reduce ghosts and flares, has less spherical aberration, sagittal coma aberration, field curvature, and meridional coma aberration, has a large aperture, and can perform wide-angle shooting.

  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 object side, a configuration in which a lens or a lens group is added between the front group GF and the rear group GR on the most image side, or a lens group between the lens groups. An added configuration may be used. The lens group in the present invention is a portion having at least one lens separated by the aperture stop S as described above, or at least separated by an air interval that changes at the time of zooming or focusing. A portion having one 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. However, by moving a single lens group, a plurality of lens groups, or a partial lens group in the optical axis direction, the object is infinite A focusing lens group that performs focusing from an object to a short-distance object may be used. That is, a method using the front group GF or a rear focus using the rear group GR 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 rear group GR 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 this method of manufacturing the optical system OS, the front group GF and the rear group GR having a positive refractive power are arranged in this order from the object side along the optical axis. An antireflection film is provided on at least one of the optical surfaces in the front group and the rear group, and the antireflection film includes at least one layer formed by using a wet process.

  Specifically, in the present embodiment, for example, as the front group GF, an aspherical positive meniscus lens L11 (first positive lens component LFP) having a convex surface facing the object side in order from the object side, a biconvex positive lens A cemented negative meniscus lens (second lens component LFN1) having a negative refractive power and having a convex surface directed toward the object side, and a negative refractive power. A negative meniscus lens L14 (third lens component LFN2) having a concave surface facing the object side (step S100), and as a rear group GR, in order from the object side, a biconcave negative lens L21 and a biconvex shape The positive lens L22 is cemented, the first lens component LRN having a concave surface facing the object side, the biconvex positive lens L23 and the biconcave negative lens L24 are cemented, and has a positive refractive power as a whole. , Concave on the image side Digit second lens component LRPl, and to place the aspherical positive lens of biconvex shape having a positive refractive power L25 (third lens component LRP2) (step S200). At this time, each group satisfies the above-described conditional expression (1) and conditional expression (2).

  As described above, according to the optical system OS according to the present embodiment, a small and high-performance lens suitable for an imaging device such as a camera, a printing lens, and a copying lens, and an imaging device using the same. Can be provided.

Hereinafter, embodiments of the optical system OS will be described with reference to the drawings. 1, 4, and 6 illustrate the configuration of the optical system OS (OS1 to OS3) 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). . In the following examples, “E−n” indicates “× 10 ⁻ⁿ ”.

S (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 embodiment, the secondary aspheric coefficient A2 is zero. In the table of each example, an aspherical surface is marked with * on the left side of the surface number.

[First embodiment]
FIG. 1 is a cross-sectional view illustrating a lens configuration of an optical system OS1 according to the first example.

  The optical system OS1 includes, in order from the object side, a front group GF having a positive refractive power, an aperture stop S, and a rear group GR having a positive refractive power.

  The front group GF includes, in order from the object side, an aspherical positive meniscus lens L11 having a convex surface facing the object side. The first lens component LFP having a positive refractive power, a biconvex positive lens L12, and a biconcave shape. It consists of a cemented negative meniscus lens that is cemented with the negative lens L13, and has a negative refractive power, a second lens component LFN1 with a convex surface facing the object side, and a negative meniscus lens L14 with a concave surface facing the object side The third lens component LFN2 has a negative refractive power.

  In the rear group GR, in order from the object side, a biconcave negative lens L21 and a biconvex positive lens L22 are cemented, and have a negative refractive power as a whole, with the concave surface facing the object side. 1 lens component LRN, a biconvex positive lens L23 and a biconcave negative lens L24 are cemented together, a second lens component LRP1 having a positive refractive power as a whole and having a concave surface facing the image side, and It is composed of a biconvex aspherical positive lens L25 and is composed of a third lens component LRP2 having a positive refractive power.

  The optical system OS1 according to the first example includes the image side lens surface (surface number 5) of the biconcave negative lens L13 of the front group GF and the object side lens surface (surface number 5) of the negative meniscus lens L14 of the front group GF. An antireflection film described later is formed on the surface number 6).

  A dummy glass FL corresponding to an optical low-pass filter is disposed between the rear group GR of the optical system OS1 and the image plane.

  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 Bf is the back focus. Represents each. 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, and the air conversion back focus Bf is obtained when the dummy glass FL is removed. This represents the distance on the optical axis from the lens surface (16th surface) closest to the image side to the image surface of the optical system OS1. In the lens data, the first column m indicates the order (surface number) of the optical surfaces from the object 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. In addition, the surface numbers 1-18 shown in this Table 1 respond | correspond to the numbers 1-18 shown in FIG. Further, the curvature radius “∞” and the curvature radius 0.0000 of the object plane and the image plane indicate a plane. Further, the refractive index of air of 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. 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) First Example [Overall Specifications]
f = 58.0216
FNO = F1.229
ω = 20.82 °
Y = 21.6
TL = 122.05004
Air conversion Bf = 38.01861

[Lens data]
m rd νd nd
(Surface) ∞
* 1 41.8098 11.0500 49.53 1.744430
* 2 2652.8412 1.0000
3 117.6517 5.4000 82.57 1.497820
4 -257.3631 1.5000 48.78 1.531720
5 22.4645 11.0000
6 -55.6445 2.0000 70.31 1.487490
7 -96.0152 3.0000
8 0.0000 10.0000 Aperture stop S
9 -29.5135 1.7000 28.38 1.728250
10 109.6394 11.0000 46.59 1.816000
11 -40.5171 0.1000
12 44.9154 14.5000 49.62 1.772500
13 -50.7224 1.6000 41.51 1.575010
14 33.7818 2.5000
15 54.2656 7.0000 49.53 1.744430
* 16 -233.5493 36.0000
17 0.0000 2.0000 63.88 1.516800
18 0.0000 0.7000
(Image plane) ∞

[Lens focal length]
Lens group Start surface Focal length Front group 1 6928.27452
Rear group 9 43.40473

  In the optical system OS1 according to the first example, the lens surfaces of the first surface, the second surface, and the sixteenth 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.

(Table 2)
κ A4 A6 A8 A10
First side -1.3241 3.10229E-06 -7.79759E-10 3.01550E-13 -7.29996E-16
2nd surface -0.1653E + 05 -7.21606E-08 7.08003E-11 -3.55610E-13 1.07080E-17
16th surface -16.7337 1.90857E-06 4.23655E-09 -1.20892E-11 2.56021E-14

  Table 3 below shows values corresponding to the conditional expressions for the optical system OS1 according to the first example. In Table 3, fF is the focal length of the front group GF, fR is the focal length of the rear group GR, fFN1 is the focal length of the second lens component LFN1 in the front group GF, and fFN2 is the third focal length in the front group GF. The focal length of the lens component LFN2, fRP is the focal length of the second lens component LRP1 in the rear group GR, fRP2 is the focal length of the third lens component LRP2 in the rear group GR, and f0 is the total system at the time of focusing on infinity. Focal length, rp1 is the radius of curvature of the most object side surface of the second lens component LRP1 in the rear group GR, rp2 is the radius of curvature of the most image side surface of the second lens component LRP1 in the rear group GR, and nRNP is the rear Refractive index with respect to d-line of medium of positive lens L22 in first lens component LRN in group GR, nRNN is refractive index with respect to d-line of medium of negative lens L21 in first lens component LRN in rear group GR, nRPP Is the rear group GR Refractive index at the d-line of the medium of the positive lens L23 of the second lens component LRP1 of, NRPN: represents the refractive index at the d-line of the medium of the negative lens L24 of the second lens component LRP1 in the group GR, respectively. The description of these symbols is the same in the following embodiments.

(Table 3)
(1) fR / | fF | = 0.006265
(2) (−fFN1) /f0=0.9018
(3) (−fFN2) /f0=4.7562
(4) (rp2-rp1) / (rp2 + rp1) = − 0.1415
(5) nRNP-nRNN = 0.08775
(6) nRPP-nRPN = 0.1975
(7) fRP / f0 = 2.7473
(8) fRP2 / f0 = 1.0302

  Thus, the optical system OS1 according to the first example satisfies all the conditional expressions (1) to (8).

  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 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.

  In FIG. 3, when a light beam BM from the object side is incident on the optical system as shown in the drawing, the negative meniscus lens L14 is reflected by the object-side lens surface (the first reflected light generating surface whose surface number is 6). Then, the reflected light is reflected again by the lens surface on the image plane side (the second reflected light generation surface, whose surface number is 5) in the biconcave negative lens L13, and reaches the image surface I to cause the ghost. And flare. The first reflected light generating surface 6 is a concave lens surface when viewed from the object, and the second reflected light generating surface 5 is a concave lens surface when viewed from the aperture stop. By forming an antireflection film corresponding to a wide incident angle in a wider wavelength range on such a surface, ghosts and flares can be effectively reduced.

[Second Embodiment]
FIG. 4 is a cross-sectional view showing the lens configuration of the optical system OS2 according to the second example.

  The optical system OS2 includes, in order from the object side, a front group GF having a positive refractive power, an aperture stop S, and a rear group GR having a positive refractive power.

  The front group GF includes, in order from the object side, an aspherical positive meniscus lens L11 having a convex surface facing the object side. The first lens component LFP having a positive refractive power, a biconvex positive lens L12, and a biconcave shape. It consists of a cemented negative meniscus lens that is cemented with the negative lens L13, and has a negative refractive power, a second lens component LFN1 with a convex surface facing the object side, and a negative meniscus lens L14 with a concave surface facing the object side The third lens component LFN2 has a negative refractive power.

  In the rear group GR, in order from the object side, a biconcave negative lens L21 and a biconvex positive lens L22 are cemented, and have a negative refractive power as a whole, with the concave surface facing the object side. 1 lens component LRN, a biconvex positive lens L23 and a biconcave negative lens L24 are cemented together, a second lens component LRP1 having a positive refractive power as a whole and having a concave surface facing the image side, and It is composed of a biconvex aspherical positive lens L25 and is composed of a third lens component LRP2 having a positive refractive power.

  The optical system OS2 according to the second example includes an image side lens surface (surface number 7) of the negative meniscus lens L14 of the front group GF and an object side lens surface of the biconcave negative lens L21 of the rear group GR (surface number 7). An antireflection film described later is formed on the surface number 9).

  A dummy glass FL corresponding to an optical low-pass filter is disposed between the rear group GR of the optical system OS2 and the image plane.

  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 this Table 4 respond | correspond to the numbers 1-18 shown in FIG.

(Table 4) Second Example [Overall Specifications]
f = 58.0216
FNO = F1.2300
ω = 20.83 °
Y = 21.6
TL = 121.55017
Air conversion Bf = 38.01873

[Lens data]
m rd νd nd
(Surface) ∞
* 1 42.3882 11.0500 49.53 1.744430
* 2 2167.3376 1.0000
3 113.8826 5.4000 82.57 1.497820
4 -622.3931 1.5000 48.78 1.531720
5 22.7071 11.0000
6 -60.3750 2.0000 52.20 1.517420
7 -96.0594 3.0000
8 0.0000 10.0000 Aperture stop S
9 -28.9264 1.7000 28.38 1.728250
10 129.6692 11.0000 46.59 1.816000
11 -39.3334 0.1000
12 46.0594 14.0000 49.62 1.772500
13 -50.2692 1.6000 41.51 1.575010
14 34.3180 2.5000
15 55.6965 7.0000 49.53 1.744430
* 16 -232.9169 36.0000
17 0.0000 2.0000 63.88 1.516800
18 0.0000 0.7002
(Image plane) ∞

[Lens focal length]
Lens group Start surface Focal length Front group 1 1869.98022
Rear group 9 43.86208

  In the optical system OS2 according to the second example, the first, second, and sixteenth 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)
κ A4 A6 A8 A10
1st surface -1.3412 2.99857E-06 -8.24891E-10 2.35245E-13 -4.91290E-16
2nd surface -0.3444E + 04 -8.68033E-08 4.62357E-11 -2.08722E-13 -2.01437E-17
16th surface -8.6128 1.92924E-06 2.40259E-09 -6.72709E-12 1.77887E-14

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

(Table 6)
(1) fR / | fF | = 0.02346
(2) (−fFN1) /f0=0.9251
(3) (−fFN2) /f0=5.5192
(4) (rp2-rp1) / (rp2 + rp1) =-0.1461
(5) nRNP-nRNN = 0.08775
(6) nRPP-nRPN = 0.1975
(7) fRP / f0 = 2.8784
(8) fRP2 / f0 = 1.0515

  As described above, the optical system OS2 according to the second example satisfies all the conditional expressions (1) to (8).

  FIG. 5 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 aberration diagrams shown in FIG. 5, 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. 6 is a cross-sectional view showing the lens configuration of the optical system OS3 according to the third example.

  The optical system OS3 includes, in order from the object side, a front group GF having a positive refractive power, an aperture stop S, and a rear group GR having a positive refractive power.

  The front group GF includes, in order from the object side, an aspherical positive meniscus lens L11 having a convex surface facing the object side. The first lens component LFP having a positive refractive power, a biconvex positive lens L12, and a biconcave shape. It consists of a cemented negative meniscus lens that is cemented with the negative lens L13, and has a negative refractive power, a second lens component LFN1 with a convex surface facing the object side, and a negative meniscus lens L14 with a concave surface facing the object side The third lens component LFN2 has a negative refractive power.

  In the rear group GR, in order from the object side, a biconcave negative lens L21 and a biconvex positive lens L22 are cemented, and have a positive refractive power as a whole, with the concave surface facing the object side. 1 lens component LRN, a biconvex positive lens L23 and a biconcave negative lens L24 are cemented together, a second lens component LRP1 having a positive refractive power as a whole and having a concave surface facing the image side, and It is composed of a biconvex aspherical positive lens L25 and is composed of a third lens component LRP2 having a positive refractive power.

  The optical system OS3 according to the third example includes an image surface side lens surface (surface number 14) of the biconcave negative lens L24 of the rear group GR and an aspheric positive lens L25 of the biconvex lens shape of the rear group GR. An antireflection film described later is formed on the object side lens surface (surface number 15).

  A dummy glass FL corresponding to an optical low-pass filter is disposed between the rear group GR of the optical system OS3 and the image plane.

  Table 7 below provides values of specifications of the optical system OS3 according to the third example. The surface numbers 1 to 18 shown in Table 7 correspond to the numbers 1 to 18 shown in FIG.

(Table 7) Third Example [Overall Specifications]
f = 58.0216
FNO = F1.2300
ω = 20.82 °
Y = 21.6
TL = 118.89463
Air equivalent Bf = 38.01320

[Lens data]
m rd νd nd
(Surface) ∞
* 1 39.7073 11.0000 49.53 1.744430
* 2 2526.2002 0.1000
3 102.0678 6.5000 82.57 1.497820
4 -84.0848 1.5000 52.20 1.517420
5 21.4694 11.0000
6 -62.0246 2.0000 31.16 1.688930
7 -97.3881 3.0000
8 0.0000 10.0000 Aperture stop S
9 -26.3978 1.7000 29.57 1.717360
10 72.7424 12.0000 46.59 1.816000
11 -37.7187 0.1000
12 45.2189 10.0000 49.62 1.772500
13 -117.8426 1.3000 41.51 1.575010
14 33.4623 3.0000
15 56.4087 7.0000 49.53 1.744430
* 16 -132.4054 36.0000
17 0.0000 2.0000 63.88 1.516800
18 0.0000 0.6946
(Image plane) ∞

[Lens focal length]
Lens group Start surface Focal length Front group 1 678.80939
Rear group 9 42.58204

  In the optical system OS3 according to the third example, the lens surfaces of the first surface, the second surface, and the sixteenth 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)
κ A4 A6 A8 A10
First side -0.8567 3.05299E-06 -6.59016E-10 6.97421E-13 -4.05702E-16
2nd surface 0.5931E + 04 6.03268E-08 7.20986E-11 -2.17040E-13 8.89735E-17
16th surface 1.4374 1.57765E-06 -1.04169E-09 1.88087E-12 -4.58581E-16

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

(Table 9)
(1) fR / | fF | = 0.06273
(2) (−fFN1) /f0=0.9153
(3) (−fFN2) /f0=4.3742
(4) (rp2-rp1) / (rp2 + rp1) = − 0.1494
(5) nRNP-nRNN = 0.09864
(6) nRPP-nRPN = 0.1975
(7) fRP / f0 = 5.1695
(8) fRP2 / f0 = 0.9306

  As described above, the optical system OS3 according to the third example satisfies all the conditional expressions (1) to (8).

  FIG. 7 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 OS3 according to the third example. As is apparent from the aberration diagrams shown in FIG. 7, 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.

  Here, an antireflection film (also referred to as a multilayer broadband antireflection film) used in the optical system OS of the present application will be described. FIG. 10 is a diagram illustrating an example of the film configuration of the antireflection film. The antireflection film 101 is composed of seven layers and is formed on the optical surface of the optical member 102 such as a lens. The first layer 101a is formed of aluminum oxide deposited by a vacuum deposition method. Further, a second layer 101b made of a mixture of titanium oxide and zirconium oxide deposited by a vacuum deposition method is further formed on the first layer 101a. Further, a third layer 101c made of aluminum oxide deposited by a vacuum deposition method is formed on the second layer 101b, and titanium oxide and zirconium oxide deposited by a vacuum deposition method are formed on the third layer 101c. A fourth layer 101d made of the mixture is formed. Furthermore, a fifth layer 101e made of aluminum oxide deposited by vacuum deposition is formed on the fourth layer 101d, and titanium oxide and zirconium oxide deposited by vacuum deposition on the fifth layer 101e. A sixth layer 101f made of the mixture is formed.

  Then, a seventh layer 101g made of a mixture of magnesium fluoride and silica is formed on the sixth layer 101f formed in this way by a wet process, and the antireflection film 101 of this embodiment is formed. For the formation of the seventh layer 101g, a sol-gel method which is a kind of wet process is used. The sol-gel method is a method in which a sol obtained by mixing raw materials is made into a non-flowable gel by hydrolysis / polycondensation reaction, etc., and this gel is heated and decomposed to obtain a product, In the production of an optical thin film, a film can be formed by applying an optical thin film material sol on the optical surface of an optical member and forming a gel film by drying and solidifying. The wet process is not limited to the sol-gel method, and a method of obtaining a solid film without going through a gel state may be used.

  Thus, the first layer 101a to the sixth layer 101f of the antireflection film 101 are formed by electron beam evaporation which is a dry process, and the seventh layer 101g which is the uppermost layer is prepared by a hydrofluoric acid / magnesium acetate method. It is formed by the following procedure by a wet process using the prepared sol solution. First, an aluminum oxide layer to be the first layer 101a, a titanium oxide-zirconium oxide mixed layer to be the second layer 101b, a third layer on the lens film formation surface (the optical surface of the optical member 102 described above) in advance using a vacuum deposition apparatus, An aluminum oxide layer to be the layer 101c, a titanium oxide-zirconium oxide mixed layer to be the fourth layer 101d, an aluminum oxide layer to be the fifth layer 101e, and a titanium oxide-zirconium oxide mixed layer to be the sixth layer 101f are formed in this order. And after taking out the optical member 102 from a vapor deposition apparatus, the thing which added the silicon alkoxide to the sol liquid prepared by the hydrofluoric acid / magnesium acetate method is apply | coated by the spin coat method, The magnesium fluoride used as the 7th layer 101g A layer made of a mixture of silica and silica is formed. The reaction formula when prepared by the hydrofluoric acid / magnesium acetate method is shown in the following formula (b).

2HF + Mg (CH3COO) 2 → MgF2 + 2CH3COOH (b)

  The sol solution used for the film formation is used for film formation after mixing raw materials and subjecting to an autoclave at 140 ° C. for 24 hours at a high temperature and pressure. The optical member 102 is completed by heat treatment at 160 ° C. for 1 hour in the air after the seventh layer 101g is formed. By using such a sol-gel method, the seventh layer 101g is formed by depositing particles having a size of several nm to several tens of nm leaving a void.

  The optical performance of the optical member having the antireflection film 101 formed in this way will be described using the spectral characteristics shown in FIG.

  The optical member (lens) having the antireflection film according to this embodiment is formed under the conditions shown in Table 10 below. Here, in Table 10, the reference wavelength is λ, and the layers 101a (first layer) to 101g (seventh layer) of the antireflection film 101 when the refractive index of the substrate (optical member) is 1.62, 1.74, and 1.85. The optical film thickness of each layer is determined. In Table 10, aluminum oxide is represented by Al2O3, a mixture of titanium oxide and zirconium oxide is represented by ZrO2 + TiO2, and a mixture of magnesium fluoride and silica is represented by MgF2 + SiO2.

(Table 10)
Material Refractive index Optical film thickness Optical film thickness Optical film thickness Medium Air 1.00
7th layer MgF2 + SiO2 1.26 0.268λ 0.271λ 0.269λ
6th layer ZrO2 + TiO2 2.12 0.057λ 0.054λ 0.059λ
5th layer Al2O3 1.65 0.171λ 0.178λ 0.162λ
4th layer ZrO2 + TiO2 2.12 0.127λ 0.13λ 0.158λ
3rd layer Al2O3 1.65 0.122λ 0.107λ 0.08λ
Second layer ZrO2 + TiO2 2.12 0.059λ 0.075λ 0.105λ
1st layer Al2O3 1.65 0.257λ 0.03λ 0.03λ
Refractive index of substrate 1.62 1.74 1.85

  FIG. 11 shows the spectral characteristics when light rays are perpendicularly incident on an optical member whose optical thickness of each layer of the antireflection film 101 is designed with the reference wavelength λ of 550 nm in Table 10.

  From FIG. 11, it can be seen that the optical member having the antireflection film 101 designed with the reference wavelength λ of 550 nm can suppress the reflectance to 0.2% or less over the entire range of the wavelength of light rays from 420 nm to 720 nm. Further, even in the optical member having the antireflection film 101 in which each optical film thickness is designed with the reference wavelength λ as d-line (wavelength 587.6 nm) in Table 10, the spectral characteristics are hardly affected, and the reference shown in FIG. Spectral characteristics substantially equivalent to those when the wavelength λ is 550 nm.

  Next, a modified example of the antireflection film will be described. This antireflection film consists of five layers, and similarly to Table 10, the optical film thickness of each layer with respect to the reference wavelength λ is designed under the conditions shown in Table 11 below. In this modification, the above-described sol-gel method is used for forming the fifth layer.

(Table 11)
Material Refractive index Optical film thickness Optical film thickness Medium Air 1.00
5th layer MgF2 + SiO2 1.26 0.275λ 0.269λ
4th layer ZrO2 + TiO2 2.12 0.045λ 0.043λ
3rd layer Al2O3 1.65 0.212λ 0.217λ
Second layer ZrO2 + TiO2 2.12 0.077λ 0.066λ
1st layer Al2O3 1.65 0.288λ 0.290λ
Refractive index of substrate 1.46 1.52

  FIG. 12 shows spectral characteristics when light rays are perpendicularly incident on an optical member having an antireflection film in which the optical film thickness is designed with the refractive index of the substrate being 1.52 and the reference wavelength λ being 550 nm in Table 11. Yes. From FIG. 12, it can be seen that the antireflection film of this modification has a reflectance of 0.2% or less over the entire wavelength range of 420 nm to 720 nm. In Table 11, even an optical member having an antireflection film in which each optical film thickness is designed with the reference wavelength λ as d-line (wavelength 587.6 nm) hardly affects the spectral characteristics, and the spectral characteristics shown in FIG. Has almost the same characteristics.

  FIG. 13 shows the spectral characteristics in the case where the incident angle of the light beam to the optical member having the spectral characteristics shown in FIG. 12 is 30 degrees, 45 degrees, and 60 degrees. 13 and 12 do not show the spectral characteristics of the optical member having the antireflection film whose refractive index is 1.46 shown in Table 11, but the refractive index of the substrate is almost equal to 1.52. Needless to say, it has the following spectral characteristics.

  For comparison, FIG. 14 shows an example of an antireflection film formed only by a dry process such as a conventional vacuum deposition method. FIG. 14 shows the spectral characteristics when a light beam is perpendicularly incident on an optical member designed with an antireflection film configured under the conditions shown in Table 12 below at a refractive index of 1.52 of the same substrate as in Table 11. FIG. 15 shows the spectral characteristics when the incident angles of the light rays to the optical member having the spectral characteristics shown in FIG. 14 are 30, 45, and 60 degrees, respectively.

(Table 12)
Material Refractive index Optical film thickness Medium Air 1.00
7th layer MgF2 1.39 0.243λ
6th layer ZrO2 + TiO2 2.12 0.119λ
5th layer Al2O3 1.65 0.057λ
4th layer ZrO2 + TiO2 2.12 0.220λ
3rd layer Al2O3 1.65 0.064λ
Second layer ZrO2 + TiO2 2.12 0.057λ
1st layer Al2O3 1.65 0.193λ
Refractive index of substrate 1.52

  When comparing the spectral characteristics of the optical member having the antireflection film according to this embodiment shown in FIGS. 11 to 13 with the spectral characteristics of the conventional example shown in FIGS. 14 and 15, the antireflection film according to this embodiment is shown. It can be seen that has a lower reflectivity at any angle of incidence and a lower reflectivity over a wider band.

  The antireflection film can be provided on a parallel plane optical surface and used as an optical element, or can be provided on an optical surface of a lens formed in a curved surface.

  Next, an example in which the antireflection film shown in Table 10 and Table 11 is applied to the first to third examples of the present application will be described.

In the optical system of the first example, the refractive index of the biconcave negative lens L13 of the front group GF is
As shown in Table 1, since nd = 1.531720 and the refractive index of the negative meniscus lens L14 of the front group GF is nd = 1.487490, the lens on the image plane side in the biconcave negative lens L13 An antireflection film 101 (see Table 11) corresponding to a refractive index of the substrate corresponding to 1.52 is used as the surface, and an antireflection film corresponding to a refractive index of the substrate corresponding to 1.46 is applied to the object side lens surface of the negative meniscus lens L14. By using a film (see Table 11), the reflected light from each lens surface can be reduced, and ghost and flare can be reduced.

  In the optical system of the second example, the refractive index of the negative meniscus lens L14 of the front group GF is nd = 1.517420 as shown in Table 4, and the refractive index of the biconcave negative lens L21 of the rear group GR is Since the refractive index is nd = 1.728250, the antireflective film 101 (see Table 11) corresponding to the refractive index of the substrate of 1.52 is used on the image surface side lens surface of the negative meniscus lens L14. By using an antireflection film (see Table 10) corresponding to a refractive index of the substrate of 1.74 on the object-side lens surface of the negative lens L21 having a shape, reflected light from each lens surface can be reduced, and ghost and flare Can be reduced.

  In the optical system of the third example, the refractive index of the biconcave negative lens L24 of the rear group GR is nd = 1.575010 as shown in Table 7, and the non-convex shape of the biconvex lens shape of the rear group GR is shown. Since the refractive index of the spherical positive lens L25 is nd = 1.744430, the antireflective film 101 corresponding to the refractive index of the substrate of 1.52 on the image surface side lens surface of the biconcave negative lens L24 (table) 11) and an antireflection film (see Table 10) corresponding to a refractive index of the substrate of 1.74 is used on the object-side lens surface of the aspherical positive lens L25 having a biconvex lens shape. The reflected light can be reduced, and ghost and flare can be reduced.

  According to each of the above-described embodiments, it has a comprehensive angle of about 2ω = 41.6 °, further has a large aperture of F1.2, further reduces ghosts and flares, and has high performance with spherical aberration and sagittal coma. An optical system OS in which aberrations, field curvature, and meridional coma 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 GF Front group LFP First lens component in front group LFN1 Second lens component in front group LFN2 Third lens component in front group GR Rear group LRN First lens component in rear group L21 Negative lens L22 Positive lens LRP1 Rear lens second lens component L23 Positive lens L24 Negative lens LRP2 Rear lens third lens component S Aperture stop 1 Single-lens reflex camera (imaging device) I Image surface 101 Antireflection film 101a First layer 101b Second layer 101c 3rd layer 101d 4th layer 101e 5th layer 101f 6th layer 101g 7th layer 102 Optical member

Claims (23)

In order from the object side along the optical axis,
The front group,
A rear group having a positive refractive power,
An antireflection film is provided on at least one of the optical surfaces in the front group and the rear group, and the antireflection film includes at least one layer formed by using a wet process,
The front group is in order from the object side,
A first lens component having a positive refractive power;
A second lens component in which a positive lens and a negative lens are cemented, has a negative refractive power, and has a convex surface facing the object side;
A third lens component having a negative refractive power with a concave surface facing the object side,
The rear group is in order from the object side,
A first lens component in which a negative lens and a positive lens are cemented and a concave surface is directed to the object side;
A second lens component having a positive refractive power and having a concave surface facing the image side;
A third lens component having a positive refractive power,
An optical system satisfying the following conditional expression:
0.0 <fR / | fF | <1.0
0.00 <(− fFN1) / f0 <10.00
However,
fF: focal length of the front group fR: focal length of the rear group fFN1: focal length of the second lens component in the front group f0: focal length of the entire system when focusing on infinity The antireflection film is a multilayer film,
The optical system according to claim 1, wherein the layer formed by the wet process is a layer on a most surface side among layers constituting the multilayer film.   The optical system according to claim 1, wherein the refractive index nd is 1.30 or less, where nd is a refractive index of a layer formed using the wet process. Having an aperture stop,
The optical system according to claim 1, wherein the optical surface provided with the antireflection film is a concave lens surface when viewed from the aperture stop. The optical system according to claim 4, wherein the concave lens surface when viewed from the aperture stop is an object-side lens surface. 5. The optical system according to claim 4, wherein the concave lens surface as viewed from the aperture stop is a lens surface on the image plane side. The optical system according to claim 1, wherein the optical surface provided with the antireflection film is a concave lens surface when viewed from an object.   8. The optical system according to claim 7, wherein the concave lens surface as viewed from the object is an object side lens surface of a lens closest to the image plane in the front group.   The optical system according to claim 7, wherein a concave lens surface when viewed from the object is an image surface side lens surface of the most image surface side lens of the front group. The optical system according to claim 1, wherein the optical surface provided with the antireflection film is a concave lens surface when viewed from the image plane.   The optical system according to claim 10, wherein a lens surface that is concave when viewed from the image plane is the lens surface of the rear group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.20 <(-fFN2) / f0 <15.00
However,
fFN2: focal length of the third lens component in the front group The optical system according to claim 1, wherein the following conditional expression is satisfied.
−2.00 <(rp2−rp1) / (rp2 + rp1) <− 0.00
However,
rp1: radius of curvature of the surface closest to the object side of the second lens component in the rear group rp2: radius of curvature of the surface closest to the image side of the second lens component in the rear group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.00 <nRNP-nRNN <0.35
However,
nRNP: Refractive index for the d-line of the medium of the positive lens in the first lens component in the rear group nRNN: Refractive index for the d-line of the medium of the negative lens in the first lens component in the rear group The second lens component in the rear group is a cemented lens in which a positive lens and a negative lens are cemented, and satisfies the following conditional expression. The optical system described in 1.
0.00 <nRPP-nRPN <0.35
However,
nRPP: refractive index of the second lens component in the rear group with respect to the d-line of the medium of the positive lens nRPN: refractive index of the second lens component in the rear group with respect to the d-line of the medium of the negative lens The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.00 <fRP / f0 <12.00
However,
fRP: focal length of the second lens component in the rear group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.1 <fRP2 / f0 <3.0
However,
fRP2: focal length of the third lens component in the rear group   The optical system according to claim 1, wherein the front group has at least one aspheric surface.   The optical system according to claim 1, wherein the rear group has at least one aspheric surface.   The optical system according to claim 1, wherein the third lens component in the rear group is a positive lens having a convex surface directed toward the object side.   21. The optical system according to claim 1, further comprising an aperture stop between the front group and the rear group.   An imaging apparatus comprising the optical system according to any one of claims 1 to 21. In order from the object side along the optical axis, a manufacturing method of an optical system having a front group and a rear group having a positive refractive power,
An antireflection film is provided on at least one of the optical surfaces in the front group and the rear group, and the antireflection film includes at least one layer formed using a wet process,
As the front group, in order from the object side, a first lens component having a positive refractive power, a positive lens and a negative lens are cemented, a negative lens having a negative refractive power, and a convex surface facing the object side. A component, and a third lens component having a negative refractive power with a concave surface facing the object side,
As the rear group, in order from the object side, a negative lens and a positive lens are cemented, a first lens component having a concave surface facing the object side, a second lens having a positive refractive power and a concave surface facing the image side. A lens component and a third lens component having a positive refractive power,
An optical system manufacturing method satisfying the following conditional expression:
0.0 <fR / | fF | <1.0
0.00 <(− fFN1) / f0 <10.00
However,
fF: focal length of the front group fR: focal length of the rear group fFN1: focal length of the second lens component in the front group f0: focal length of the entire system when focusing on infinity

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