JP2013235078A - Optical system, optical instrument with optical system, and manufacturing method for optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system having a satisfactory optical performance, an optical instrument with the optical system, and a manufacturing method for the optical system.SOLUTION: An optical system OS used in a camera 1 or the like includes, in order from an object side: a first lens group G1 of positive refractive power; a second lens group G2 of positive refractive power; and a third lens group G3 of positive refractive power. A reflection preventing film is provided on at least one of optical faces of the first to third lens groups. The reflection preventing film comprises at least one layer formed using a wet process. When focusing takes place, the first lens group G1 and the third lens group G3 are fixed with respect to an image face, and the second lens group G2 is moved along an optical axis.

Description

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

  2. Description of the Related Art Conventionally, an inner focus type optical system suitable for shortening the autofocus speed of a photographic camera, an electronic still camera, a video camera, or the like has been proposed (for example, see 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 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).

Japanese Patent Laid-Open No. 7-199066 JP 2000-356704 A

  However, the conventional optical system has a problem that the power arrangement between the in-focus group and the other groups is not optimized, and good optical performance cannot be achieved from infinity to the closest distance. 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 the above problems, and provides an optical system that further reduces ghosts and flares and has good optical performance, an optical apparatus having the optical system, and a method for manufacturing the optical system. The purpose is to do.

In order to solve the above problems, an optical system according to the present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a positive refractive power. A third lens group, and an antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film is a layer formed using a wet process. At the time of focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group moves along the optical axis, satisfying the following conditional expression: It is characterized by doing.
0.20 <f3 / f2 <7.80
However,
f2: focal length of the second lens group f3: focal length of the third lens group

  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 as viewed from the aperture stop is an object side lens surface of the lens in the first lens group or the second lens group.

  In such an optical system, the concave lens surface as viewed from the aperture stop is preferably a lens surface on the image plane side of the lens in the first lens group or the second lens 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, the concave lens surface provided with the antireflection film is preferably the lens surface of the lens closest to the image plane in the third lens group.

Such an optical system preferably satisfies the following conditional expression.
0.30 <f3 / f <6.00
However,
f: focal length of the entire system when focusing on infinity f3: focal length of the third lens unit

Such an optical system preferably satisfies the following conditional expression.
0.50 <f2 / f <2.00
However,
f2: Focal length of the second lens group f: Focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
1.90 <f1 / f <50.00
However,
f1: Focal length of the first lens unit f: Focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
0.40 <f1 / f3 <20.00
However,
f1: Focal length of the first lens group f3: Focal length of the third lens group

  In such an optical system, it is preferable that the second lens group has a positive lens closest to the object side.

Such an optical system preferably satisfies the following conditional expression.
0.30 <r1 / f2 <15.00
However,
r1: radius of curvature of the object side surface of the positive lens included in the second lens group f2: focal length of the second lens group

  In such an optical system, it is preferable that the first lens group has two positive lenses in order from the object side.

  In such an optical system, it is preferable that the most image side lens of the second lens group has a biconvex shape.

  In such an optical system, it is preferable that all lens surfaces be spherical or flat.

  An optical apparatus according to the present invention includes any one of the above optical systems.

The optical system manufacturing method according to the present invention includes a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens having a positive refractive power in order from the object side. A lens group, and an antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film is a layer formed using a wet process. A method of manufacturing an optical system including at least one layer, wherein the first lens group, the second lens group, and the third lens group satisfying the following conditional expressions are focused on the first lens group and the first lens group. The three lens groups are fixed with respect to the image plane, and the second lens group is disposed so as to move along the optical axis.
0.20 <f3 / f2 <7.80
However,
f2: focal length of the second lens group f3: focal length of the third lens group

  ADVANTAGE OF THE INVENTION According to this invention, a ghost and flare can be reduced more and the optical system which has favorable optical performance, the optical apparatus which has this optical system, and the manufacturing method of an optical system can be provided.

It is sectional drawing which shows the lens structure of the optical system which concerns on 1st Example. FIG. 5A is a diagram illustrating various aberrations of the optical system according to Example 1, where (a) shows an infinite focus state and (b) shows a short distance focus state (D0 = 700 mm). 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 of the optical system which concerns on 2nd Example. FIG. 5A is a diagram illustrating various aberrations of the optical system according to Example 2, wherein (a) shows an infinite focus state and (b) shows a short distance focus state (D0 = 700 mm). It is sectional drawing which shows the lens structure of the optical system which concerns on 3rd Example. FIG. 6A is a diagram illustrating various aberrations of the optical system according to Example 3, wherein (a) shows an infinitely focused state, and (b) shows a short-range focused state (D0 = 700 mm). It is sectional drawing which shows the lens structure of the optical system which concerns on 4th Example. FIG. 7A is a diagram illustrating various aberrations of the optical system according to Example 4, where (a) shows an infinitely focused state, and (b) shows a short-range focused state (D0 = 700 mm). 1 is a cross-sectional view of a camera equipped with an optical system according to the present embodiment. It is a flowchart for demonstrating the manufacturing method of the optical system which concerns on this embodiment. 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 this embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a positive And a third lens group G3 having refractive power. With such a configuration, it is possible to satisfactorily correct the downsizing of the lens barrel and each aberration. In the optical system OS, when focusing on an object at a short distance from infinity, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is along the optical axis. Move. With such a configuration, it is possible to satisfactorily correct the aberration variation of the lens barrel and focusing.

  Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (1).

0.20 <f3 / f2 <7.80 (1)
However,
f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3

  Conditional expression (1) defines the ratio between the focal length f3 of the third lens group G3 and the focal length f2 of the second lens group G2. This optical system OS can realize good optical performance by satisfying conditional expression (1).

  If the upper limit value of the conditional expression (1) is exceeded, the refractive power of the second lens group G2 becomes strong, and when focusing on an object at a close distance, the spherical aberration is overcorrected and the field curvature is undercorrected. It becomes difficult to correct the curvature of field at the same time. The effect of the present application can be ensured by setting the upper limit of conditional expression (1) to 7.10. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (1) to 6.40.

  If the lower limit of conditional expression (1) is not reached, the refractive power of the third lens group G3 becomes strong, and when focusing on an object at a close distance, the spherical aberration is insufficiently corrected and the field curvature becomes excessively corrected. It becomes difficult to correct aberration and curvature of field simultaneously. In addition, the refractive power of the second lens group G2 is weakened, and the amount of focusing movement is increased, which increases the total length of the optical system OS, which is not preferable. The effect of the present application can be ensured by setting the lower limit value of conditional expression (1) to 0.60. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (1) to 1.00.

  In the optical system OS according to the present embodiment, an antireflection film is provided on at least one of the optical surfaces in the first lens group G1 to the third lens group G3, and the antireflection film is formed using a wet process. At least one layer formed. With this configuration, the optical system OS according to the present embodiment can further reduce ghosts and flares caused by reflection of light from an object on an optical surface, and achieve high imaging performance. it can.

  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 the present embodiment, when the refractive index of a layer formed using a wet process is nd, the refractive index nd is preferably 1.30 or less. 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 first lens group G1 and the second lens group G2 is formed from the aperture stop S. A concave lens surface is preferable. Of the optical surfaces in the first lens group G1 and the second lens group G2, reflected light is likely to be generated on a concave lens surface as viewed from the aperture stop S. Therefore, an antireflection film is formed on such an optical surface. Ghosts and flares can be effectively reduced.

  In addition, the concave lens surface viewed from the aperture stop S provided with the antireflection film in the first lens group G1 and the second lens group G2 of the optical system OS according to the present embodiment is a lens surface on the object side. Preferably there is. Of the optical surfaces in the first lens group G1 and the second lens group G2, reflected light is likely to be generated on a concave lens surface as viewed from the aperture stop S. Therefore, an antireflection film is formed on such an optical surface. Ghost and flare can be effectively reduced.

  In addition, the concave lens surface viewed from the aperture stop S provided with the antireflection film in the first lens group G1 and the second lens group G2 of the optical system OS according to the present embodiment is a lens surface on the image plane side. It is preferable that Of the optical surfaces in the first lens group G1 and the second lens group G2, reflected light is likely to be generated on a concave lens surface as viewed from the aperture stop S. Therefore, an antireflection film is formed on such an optical surface. Ghost and flare can be effectively reduced.

  Of the optical surfaces in the third lens group G3 of the optical system OS according to this embodiment, the optical surface provided with the antireflection film is preferably a concave lens surface when viewed from the image plane side. In this way, ghost light is likely to be generated on the concave lens surface when viewed from the image plane side among the optical surfaces in the third lens group G3. Therefore, an antireflection film is formed on such an optical surface. Ghosts and flares can be effectively reduced.

  In addition, among the optical surfaces in the third lens group G3 of the optical system OS according to the present embodiment, the concave lens surface provided with the antireflection film as viewed from the image surface side is the most image of the third lens group G3. The lens surface of the surface side lens is preferable. Of the optical surfaces in the third lens group G3, reflected light is likely to be generated on a concave lens surface when viewed from the object. Therefore, ghosts and flares are effectively reduced by forming an antireflection film on such an optical surface. Can be made.

  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).

0.30 <f3 / f <6.00 (2)
However,
f3: focal length of the third lens group G3 f: focal length of the entire system when focusing on infinity

  Conditional expression (2) defines the ratio between the focal length f3 of the third lens group G3 and the focal length f of the entire system in the infinitely focused state. The present optical system OS can realize good optical performance from infinity to the closest distance by satisfying conditional expression (2).

  If the lower limit value of the conditional expression (2) is not reached, the refractive power of the third lens group G3 becomes strong, and when focusing on an object at a close distance, the spherical aberration is insufficiently corrected and the field curvature becomes excessively corrected. It becomes difficult to correct the curvature of field at the same time. The effect of the present application can be ensured by setting the lower limit of conditional expression (2) to 0.80. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (2) to 1.30.

  If the upper limit value of conditional expression (2) is exceeded, the refractive power of the third lens group G3 becomes weak, and when focusing on a close object, the spherical aberration is overcorrected and the curvature of field becomes undercorrected. It becomes difficult to correct aberration and curvature of field simultaneously. In addition, the effect of this application can be ensured by making the upper limit of conditional expression (2) 5.50. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (2) to 5.00.

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

0.50 <f2 / f <2.00 (3)
However,
f2: focal length of the second lens group G2 f: focal length of the entire system when focusing on infinity

  Conditional expression (3) defines the ratio between the focal length f2 of the second lens group G2 and the focal length f of the entire system in the infinitely focused state. This optical system OS can realize good optical performance from infinity to a close range by satisfying conditional expression (3).

  If the lower limit value of conditional expression (3) is not reached, the refractive power of the second lens group G2 becomes strong, and it becomes difficult to correct the variation in spherical aberration during focusing. The effect of the present application can be ensured by setting the lower limit of conditional expression (3) to 0.60. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (3) to 0.70.

  If the upper limit of conditional expression (3) is exceeded, the refractive power of the second lens group G2 becomes weak, the amount of focusing movement increases, and the overall length of the optical system OS increases. In addition, it becomes difficult to correct spherical aberration and curvature of field. The effect of the present application can be ensured by setting the upper limit value of conditional expression (3) to 1.70. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (3) to 1.50.

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

1.90 <f1 / f <50.00 (4)
However,
f1: Focal length of the first lens group G1 f: Focal length of the entire system when focusing on infinity

  Conditional expression (4) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f of the entire system in the infinitely focused state. This optical system OS can realize good optical performance by satisfying conditional expression (4).

  If the upper limit value of the conditional expression (4) is exceeded, the refractive power of the first lens group G1 becomes weak, and it becomes difficult to correct the focusing variation of spherical aberration and field curvature. The effect of the present application can be ensured by setting the upper limit of conditional expression (4) to 20.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (4) to 10.00.

  On the other hand, if the lower limit of conditional expression (4) is not reached, the refractive power of the first lens group G1 becomes strong and it becomes difficult to correct spherical aberration. In addition, the effect of this application can be made reliable by making the lower limit of conditional expression (4) into 2.00. More preferably, the effect of this application can be made more reliable by setting the lower limit value of conditional expression (4) to 2.10.

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

0.40 <f1 / f3 <20.00 (5)
However,
f1: Focal length of the first lens group G1 f3: Focal length of the third lens group G3

  Conditional expression (5) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f3 of the third lens group G3. This optical system OS can realize good optical performance by satisfying conditional expression (5).

  If the upper limit of conditional expression (5) is exceeded, the refractive power of the third lens group G3 becomes strong, and when focusing on an object at a close distance, the spherical aberration is insufficiently corrected and the curvature of field becomes excessively corrected. It becomes difficult to correct the curvature of field at the same time. The effect of the present application can be ensured by setting the upper limit value of conditional expression (5) to 12.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (5) to 5.00.

  On the other hand, if the lower limit of conditional expression (5) is not reached, the refractive power of the first lens group G1 becomes strong and it becomes difficult to correct spherical aberration. Note that the effect of the present application can be ensured by setting the lower limit of conditional expression (5) to 0.45. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (5) to 0.50.

  In the optical system OS according to the present embodiment, it is desirable that the second lens group G2 has a positive lens closest to the object side (for example, a positive meniscus lens L21 in FIG. 1). With such a configuration, it is possible to satisfactorily correct spherical aberration fluctuations accompanying focusing.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (6).

0.30 <r1 / f2 <15.00 (6)
However,
r1: radius of curvature of the object side surface of the positive lens arranged closest to the object side in the second lens group G2 f2: focal length of the second lens group G2

  Conditional expression (6) defines the ratio between the radius of curvature r1 of the object side surface of the positive lens disposed closest to the object side of the second lens group G2 and the focal length f2 of the second lens group G2. This optical system OS can realize good optical performance by satisfying conditional expression (6).

  If the upper limit of conditional expression (6) is exceeded, it will be difficult to correct fluctuations in spherical aberration and coma due to focusing. In addition, the effect of this application can be made reliable by making upper limit of conditional expression (6) into 10.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (6) to 5.00.

  If the lower limit of conditional expression (6) is not reached, it will be difficult to correct variations in spherical aberration and coma due to focusing. The effect of the present application can be ensured by setting the lower limit value of conditional expression (6) to 0.40. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (6) to 0.50.

  Further, it is desirable that the first lens group G1 of the optical system OS according to the present embodiment has two positive lenses in order from the object side (for example, a positive meniscus lens L11 and a positive meniscus lens L12 in FIG. 1). With such a configuration, it is possible to satisfactorily correct spherical aberration, field curvature, and coma.

  In addition, it is desirable that the most image side lens of the second lens group G2 of the optical system OS according to the present embodiment has a biconvex shape (for example, a biconvex lens L24 in FIG. 1). With such a configuration, spherical aberration and coma can be favorably corrected.

  In addition, it is desirable that all lens surfaces of the optical system OS according to the present embodiment be spherical or flat. With such a configuration, lens processing is facilitated, and aberration fluctuations due to processing errors can be reduced.

  Next, a camera including the optical system OS of the present application will be described with reference to FIG. FIG. 10 is a diagram illustrating a configuration of a camera including the optical system OS of the present application. As shown in FIG. 10, the camera 1 is a so-called mirrorless camera of an interchangeable lens provided with the above-described optical system OS as a photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and is on the imaging surface of the imaging unit 3 via an OLPF (Optical low pass filter) (not shown). A subject image is formed on the screen. Then, the subject image is photoelectrically converted by the photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic view finder) 4 provided in the camera 1. Thus, the photographer can observe the subject via the EVF 4.

  Further, when a release button (not shown) is pressed by the photographer, an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1. In this embodiment, an example of a mirrorless camera has been described. However, an optical system OS according to this embodiment is mounted on a single-lens reflex camera that has a quick return mirror in the camera body and observes a subject using a finder optical system. Even in this case, the same effect as the camera 1 can be obtained.

  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 to the most object side, or a configuration in which a lens or a lens group is added to the most image side may be used. The lens group refers to a portion having at least one lens separated by an air interval that changes during focusing.

  The second lens group G2, which is the focusing lens group described above, can also 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 a part of the two lenses on the image side from the aperture stop S of the second lens group G2 is an anti-vibration lens group.

  The lens surface may be formed as an aspheric surface. 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 with an aspheric shape on the glass surface. Any aspherical surface 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.

  Further, each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength region 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 of the present embodiment will be described with reference to FIG. First, each lens is arranged and a lens group is prepared (step S100). The lens group is provided with an antireflection film on at least one of the optical surfaces, and the antireflection film includes at least one layer formed by using a wet process. Includes a lens. In this embodiment, for example, as shown in FIG. 1, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a convex surface facing the object side. A positive meniscus lens L13 and a negative meniscus lens L14 having a convex surface facing the object side are arranged as a first lens group G1, and in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, a biconcave shape. A negative lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex positive lens L24 are arranged as a second lens group G2, and a positive meniscus lens L31 having a convex surface facing the object side and the object side A negative meniscus lens L31 with a negative meniscus lens L32 having a convex surface facing the lens, and a positive meniscus lens L33 with a convex surface facing the object side. That. The aperture stop S is disposed between the positive meniscus lens L21 of the second lens group G2 and the negative biconcave lens L22. The lens groups prepared in this way are arranged to manufacture the optical system OS.

  At this time, in focusing, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is arranged to move along the optical axis (step S200). In addition, the first lens group G1, the second lens group G2, and the third lens group G3 are arranged so as to satisfy the above-described conditional expression (1) (step S300).

  Hereinafter, each example of the present application will be described with reference to the drawings. 1, 4, 6, and 8 show the configuration of the optical system OS (OS1 to OS4) according to each embodiment and the movement of each lens group in the change of the in-focus state from infinity to a close object. It is sectional drawing which shows a mode.

[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 first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised.

  The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface directed toward the object side, a positive meniscus lens L12 having a convex surface directed toward the object side, a positive meniscus lens L13 having a convex surface directed toward the object side, and It is composed of a negative meniscus lens L14 having a convex surface facing the object side.

  The second lens group G2, in order from the object side, includes a positive meniscus lens L21 having a convex surface facing the object side, a biconcave negative lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex shape. Consists of a positive lens L24.

  The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 including a positive meniscus lens L31 having a convex surface facing the object side and a negative meniscus lens L32 having a convex surface facing the object side, and a convex surface facing the object side. And a positive meniscus lens L33.

  Thus, in the optical system OS1 according to the first example, the first lens group G1 includes two positive lenses (a positive meniscus lens L11 and a positive meniscus lens L12) arranged in order from the object side. In the second lens group G2, the most positive lens (positive meniscus lens L21) is disposed on the object side, and the most image-side lens has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS1 are constituted by spherical surfaces or flat surfaces.

  The aperture stop S is disposed between the positive meniscus lens L21 and the biconcave negative lens L22 of the second lens group G2. A filter group FL is disposed between the optical system OS1 and the image plane I.

  In the optical system OS1 according to the first example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G3 is fixed at the time of focusing from infinity to a close object. The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  The optical system OS1 according to the first example includes an image surface side lens surface (surface number 15) of the positive meniscus lens L23 of the second lens group G2 and an object side of the positive meniscus lens L33 of the third lens group G3. An antireflection film described later is formed on the lens surface (surface number 21).

  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 of the entire system, FNO is the F number, ω is the half field angle, Y is the image height, TL is the full length, and Bf is 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) to the image plane I when focusing on infinity, and the back focus is the most image side lens surface (22nd lens surface). The distance on the optical axis from the surface) to the image plane I is shown. In the lens data, the first column m indicates the order (surface number) of the lens surfaces from the object side along the light traveling direction, the second column r indicates the curvature radius of each optical surface, and the third column d. Indicates the distance (surface distance) on the optical axis from each optical surface to the next optical surface, and the fourth column nd and the fifth column νd indicate the refractive index and Abbe number for the d-line (λ = 587.6 nm), respectively. ing. The surface numbers 1 to 24 shown in Table 1 correspond to the numbers 1 to 24 shown in FIG. Further, the curvature radius “∞” and the curvature radius 0.0000 of the object plane and the image plane represent a plane. Further, the refractive index of air of 1.0000 is omitted. The lens group focal length indicates the surface number and focal length of the start surface of each of the first to third lens groups G1 to G3. Here, “mm” is generally used for the focal length, the radius of curvature, the surface interval, and other length units listed in all the following specifications, but the optical system is proportionally enlarged or reduced. However, the same optical performance can be obtained, and 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 = 32.30
FNO = 1.23
ω = 13.97
Y = 8.00
TL = 61.93
Bf = 14.10

[Lens data]
m r d nd νd
Object ∞ ∞
1 58.9509 2.7624 1.81600 46.63
2 296.6226 0.1000
3 30.8042 2.7169 1.83481 42.72
4 68.4943 0.1000
5 20.8894 2.8130 1.83400 37.17
6 21.5342 2.5000
7 56.1565 1.7000 1.78472 25.68
8 16.3967 d1
9 99.9914 1.3939 1.72916 54.66
10 961.1485 1.6042
11 0.0000 3.6310 Aperture stop S
12 -15.7157 1.2000 1.69895 30.13
13 40.0528 1.4252
14 -307.9409 2.5406 1.88300 40.77
15 -39.7561 0.1000
16 61.5510 4.0998 1.81600 46.63
17 -24.1299 d2
18 18.9404 3.4997 1.83481 42.72
19 78.3470 1.5000 1.74077 27.79
20 14.0997 2.2371
21 33.6753 2.2809 1.90265 35.71
22 215.9000 10.8099
23 0.0000 2.7900 1.51680 64.12
24 0.0000 0.5000
Image plane ∞

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 126.08
Second lens group 9 42.03
Third lens group 18 59.00

  In the first example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 2 below shows variable intervals when focusing on infinity and focusing on a short-distance object. In Table 2, D0 represents the distance from the lens surface (first surface) closest to the object of the optical system OS1 to the object. The description of this variable interval is the same in the following embodiments.

(Table 2)
Infinity Short distance D0 ∞ 700.0000
d1 8.5270 4.3965
d2 1.1000 5.2305

  Table 3 below shows values corresponding to the respective conditions of the optical system OS1 according to the first example. In Table 3, f is the focal length of the entire system, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, and f3 is the focal length of the third lens group G3. R1 represents the radius of curvature of the object side surface of the positive lens arranged closest to the object side in the second lens group G2. The description of the above symbols is the same in the following embodiments.

(Table 3)
(1) f3 / f2 = 1.40
(2) f3 / f = 1.83
(3) f2 / f = 1.30
(4) f1 / f = 3.90
(5) f1 / f3 = 2.14
(6) r1 / f2 = 2.38

  Note that r1 in the conditional expression (6) corresponds to the radius of curvature of the ninth surface. Thus, the optical system OS1 according to the first example satisfies all the conditional expressions (1) to (6).

  FIG. 2 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS1 according to the first embodiment. The aberration diagrams of are shown. In each aberration diagram, FNO is the F number, NA is the numerical aperture, Y is the image height with respect to the half field angle, d is the d-line (λ = 587.6 nm), and g is the g-line (λ = 435.8 nm). ) Respectively. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, the coma aberration diagram shows the aberration with respect to the image height Y. The explanation of these aberration diagrams is the same in the following examples. As apparent from the respective aberration diagrams shown in FIG. 2, in the optical system OS1 according to the first example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

  FIG. 3 shows an optical system having the same configuration as that of the first embodiment, and incident light rays are reflected by the first reflecting surface and the second reflecting surface to form ghosts and flares on the image plane I. It is a figure which shows an example of a mode to do.

  In FIG. 3, when a light beam BM from the object side enters the optical system as shown in the figure, the object side lens surface of the positive meniscus lens L33 (the first reflected light generation surface, whose surface number is 21). The reflected light is reflected again by the lens surface on the image plane side of the positive meniscus lens L23 (the second reflected light generation surface and its surface number is 15) to reach the image surface I, and the ghost and Flares will be generated. The first reflected light generation surface 21 is a concave lens surface when viewed from the image plane I, and the second reflected light generation surface 15 is a concave lens surface when viewed from the aperture stop S. . 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. That is, the image side lens surface of the positive meniscus lens L23 in the second lens group G2 (the lens surface concave on the image plane side when viewed from the aperture stop S) and the object side of the positive meniscus lens L33 in the third lens group G3. Ghosting and flare reduction is achieved by forming an antireflection film, which will be described later, on the lens surface (lens surface that is concave when viewed from the image surface I on the most image surface side). In addition, the effect | action and effect of an anti-reflective film are the same also in a subsequent example, and a detailed description is abbreviate | omitted.

[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 first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconcave negative lens L22, a biconcave negative lens L23, and a biconvex positive lens L24. The lens includes a positive lens CL21 and a biconvex positive lens L25.

  The third lens group G3 is composed of, in order from the object side, a cemented negative lens CL31 of a positive meniscus lens L31 having a convex surface directed toward the image side and a biconcave negative lens L32, and a biconvex positive lens L33. The

  Thus, in the optical system OS2 according to the second example, the first lens group G1 includes two positive lenses (biconvex positive lens L11 and positive meniscus lens L12) arranged in order from the object side. Yes. In the second lens group G2, the positive lens (positive meniscus lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L25). Further, all lens surfaces of the optical system OS2 are constituted by spherical surfaces or flat surfaces.

  The aperture stop S is disposed between the biconcave negative lens L22 and the biconcave negative lens L23 of the second lens group G2. A filter group FL is disposed between the optical system OS2 and the image plane I.

  In the optical system OS2 according to the second example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a close object, and the second The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  The optical system OS2 according to the second example includes an image side lens surface (surface number 6) of the negative meniscus lens L13 of the first lens group G1 and an object side of the positive meniscus lens L21 of the second lens group G2. An antireflection film described later is formed on the lens surface (surface number 7).

  Table 4 below lists values of specifications of the optical system OS2 according to the second example. The surface numbers 1 to 24 shown in Table 4 correspond to the numbers 1 to 24 shown in FIG.

(Table 4) Second Example [Overall Specifications]
f = 31.50
FNO = 1.23
ω = 14.33
Y = 8.00
TL = 54.30
Bf = 13.70

[Lens data]
m r d nd νd
Object ∞ ∞
1 36.5576 4.5395 1.51680 64.10
2 -179.0694 0.1000
3 15.9667 4.5519 1.83480 42.72
4 30.4447 0.6098
5 37.6030 1.8631 1.67270 32.11
6 10.5289 d1
7 29.2292 1.6293 1.80400 46.58
8 74.2437 1.6887
9 -24.1013 1.0000 1.64768 33.80
10 23.7658 2.0921
11 0.0000 1.1570 Aperture stop S
12 -173.1509 1.1997 1.67270 32.11
13 23.8072 2.9707 1.83480 42.72
14 -41.4088 0.1000
15 32.6245 3.0534 1.77249 49.61
16 -41.4025 d2
17 -55.0447 1.9311 1.90366 31.27
18 -19.3923 1.5000 1.67270 32.11
19 16.7526 1.2805
20 21.3864 3.1896 1.83480 42.72
21 -85.7704 10.4124
22 0.0000 2.7900 1.51680 64.12
23 0.0000 0.5000
Image plane ∞

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 69.77
Second lens group 7 25.22
Third lens group 17 135.82

  In the second embodiment, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 5 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 5)
Infinity Short distance D0 ∞ 700.0000
d1 6.0410 4.3247
d2 0.1000 1.8162

  Table 6 below shows values corresponding to the respective conditions of the optical system OS2 according to the second example.

(Table 6)
(1) f3 / f2 = 5.38
(2) f3 / f = 4.31
(3) f2 / f = 0.80
(4) f1 / f = 2.21
(5) f1 / f3 = 0.51
(6) r1 / f2 = 1.16

  Note that r1 in the conditional expression (6) corresponds to the radius of curvature of the seventh surface. As described above, the optical system OS2 according to the second example satisfies all the conditional expressions (1) to (6).

  FIG. 5 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS2 according to the second embodiment. The aberration diagrams of are shown. As apparent from the respective aberration diagrams shown in FIG. 5, in the optical system OS2 according to the second example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

[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 first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised.

  The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Composed.

  The second lens group G2, in order from the object side, includes a biconvex positive lens L21, a biconcave negative lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex positive lens L24. Composed.

  The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 of a biconvex positive lens L31 and a biconcave negative lens L32, and a positive meniscus lens L33 with a convex surface facing the object side. The

  Thus, in the optical system OS3 according to the third example, the first lens group G1 includes two positive lenses (a positive meniscus lens L11 and a positive meniscus lens L12) arranged in order from the object side. In the second lens group G2, a positive lens (biconvex lens L21) is disposed closest to the object side, and a lens closest to the image side has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS3 are constituted by spherical surfaces or flat surfaces.

  The aperture stop S is disposed between the biconvex positive lens L21 and the biconcave negative lens L22 of the second lens group G2. A filter group FL is disposed between the optical system OS3 and the image plane I.

  In the optical system OS3 according to the third example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a short distance object, and the second The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  The optical system OS3 according to the third example includes an image surface side lens surface (surface number 15) of the biconvex lens L24 of the second lens group G2, and an object side lens of the positive meniscus lens L33 of the third lens group G3. An antireflection film described later is formed on the surface (surface number 19).

  Table 7 below provides values of specifications of the optical system OS3 according to the third example. The surface numbers 1 to 22 shown in Table 7 correspond to the numbers 1 to 22 shown in FIG.

(Table 7) Third Example [Overall Specifications]
f = 31.99
FNO = 1.23
ω = 14.11
Y = 8.00
TL = 64.25
Bf = 14.30

[Lens data]
m r d nd νd
Object ∞ ∞
1 31.5954 4.3000 1.83481 42.73
2 221.2096 0.1000
3 28.0000 3.2000 1.83400 37.18
4 39.0000 2.7000
5 182.5453 1.2000 1.75520 27.57
6 17.8832 d1
7 54.5012 2.2000 1.77250 49.62
8 -121.1911 1.4000
9 0.0000 3.5000 Aperture stop S
10 -17.5587 1.2000 1.68893 31.16
11 32.6949 1.5000
12 -123.2970 2.3000 1.88300 40.66
13 -53.0000 1.7000
14 75.1287 4.8000 1.81600 46.59
15 -23.0269 d2
16 21.5035 3.9500 1.95400 33.46
17 -714.3048 1.3000 1.80518 25.45
18 14.8026 1.2000
19 24.9460 2.5000 1.88300 40.66
20 55.6297 11.0102
21 0.0000 2.7900 1.51680 64.12
22 0.0000 0.5000
Image plane ∞

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 210.36
Second lens group 7 39.09
Third lens group 16 68.51

  In the third example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 8 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 8)
Infinity Short distance D0 ∞ 700.0000
d1 9.3000 5.7083
d2 1.6000 5.1916

  Table 9 below shows values corresponding to the respective conditions of the optical system OS3 according to the third example.

(Table 9)
(1) f3 / f2 = 1.75
(2) f3 / f = 2.14
(3) f2 / f = 1.22
(4) f1 / f = 6.57
(5) f1 / f3 = 3.07
(6) r1 / f2 = 1.39

  Note that r1 in the conditional expression (6) corresponds to the radius of curvature of the seventh surface. Thus, the optical system OS3 according to the third example satisfies all the conditional expressions (1) to (6).

  FIG. 7 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS3 according to the third embodiment. The aberration diagrams of are shown. As is apparent from the respective aberration diagrams shown in FIG. 7, in the optical system OS3 according to the third example, various aberrations are satisfactorily corrected in each state from the infinity in-focus state to the short-distance object in-focus state, It can be seen that the imaging performance is excellent.

[Fourth embodiment]
FIG. 8 is a cross-sectional view showing the lens configuration of the optical system OS4 according to the fourth example. The optical system OS4 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power, It is comprised.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 having a convex surface facing the object side, a positive meniscus lens L13 having a convex surface facing the object side, and a convex surface facing the object side Is composed of a negative meniscus lens L14.

  The second lens group G2, in order from the object side, includes a positive meniscus lens L21 having a convex surface facing the object side, a biconcave negative lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex shape. Consists of a positive lens L24.

  The third lens group G3 includes, in order from the object side, a biconvex positive lens L31, and a cemented negative lens CL31 including a biconcave negative lens L32 and a positive meniscus lens L33 having a convex surface facing the object side. The

  Thus, in the optical system OS4 according to the fourth example, the first lens group G1 includes two positive lenses (a biconvex positive lens L11 and a positive meniscus lens L12) arranged in order from the object side. Yes. In the second lens group G2, the most positive lens (positive meniscus lens L21) is disposed on the object side, and the most image-side lens has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS4 are constituted by spherical surfaces or flat surfaces.

  The aperture stop S is disposed between the positive meniscus lens L21 and the biconcave negative lens L22 of the second lens group G2. A filter group FL is disposed between the optical system OS4 and the image plane I.

  In the optical system OS4 according to the fourth example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a close object, and the second lens group G3 is fixed to the image plane. The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  The optical system according to the fourth example includes the image surface side lens surface (surface number 15) of the positive meniscus lens L23 of the second lens group G2 and the biconvex positive lens L31 of the third lens group G3. An antireflection film described later is formed on the object side lens surface (surface number 18).

  Table 10 below lists values of specifications of the optical system OS4 according to the fourth example. The surface numbers 1 to 24 shown in Table 10 correspond to the numbers 1 to 24 shown in FIG.

(Table 10) Fourth Example [Overall Specifications]
f = 31.50
FNO = 1.23
ω = 14.24
Y = 8.00
TL = 55.00
Bf = 13.70

[Lens data]
m r d nd νd
Object ∞ ∞
1 57.7937 3.8669 1.60311 60.67
2 -152.7504 0.1000
3 21.6543 3.7584 1.60311 60.67
4 41.5111 0.1000
5 30.0061 2.7318 1.83480 42.72
6 49.8338 0.8669
7 127.2755 1.4984 1.67270 32.11
8 16.5082 d1
9 20.0297 1.1782 1.83480 42.72
10 20.7248 2.4693
11 0.0000 2.9702 Aperture stop S
12 -14.3410 1.0000 1.64768 33.80
13 40.2723 1.4672
14 -56.8420 2.1002 1.83480 42.72
15 -23.2653 0.1000
16 42.7022 3.8131 1.77249 49.61
17 -24.2988 d2
18 59.8262 2.5837 1.83480 42.72
19 -31.8636 0.5731
20 -27.0382 1.3000 1.68893 31.07
21 20.7059 2.5815 1.83480 42.72
22 63.7424 10.4100
23 0.0000 2.7900 1.51680 64.12
24 0.0000 0.5000
Image plane ∞

[Lens focal length]
Lens group Start surface Focal length First lens group 1 70.00
Second lens group 9 36.83
Third lens group 18 100.83

  In the fourth example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 11 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 11)
Infinity Short distance D0 ∞ 700.0000
d1 6.1423 3.0681
d2 0.1000 3.1741

  Table 12 below shows values corresponding to the respective conditions of the optical system OS4 according to the fourth example.

(Table 12)
(1) f3 / f2 = 2.74
(2) f3 / f = 3.20
(3) f2 / f = 1.17
(4) f1 / f = 2.22
(5) f1 / f3 = 0.75
(6) r1 / f2 = 0.54

  Note that r1 in the conditional expression (6) corresponds to the radius of curvature of the ninth surface. As described above, the optical system OS4 according to the fourth example satisfies all the conditional expressions (1) to (6).

  FIG. 9 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS4 according to the fourth example. The aberration diagrams of are shown. As is apparent from the respective aberration diagrams shown in FIG. 9, in the optical system OS4 according to the fourth example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

  Here, an antireflection film (also referred to as a multilayer broadband antireflection film) used in the optical system according to the embodiment of the present application will be described. FIG. 12 is a diagram illustrating an example of a 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 (a).

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

  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 13 below. Here, in Table 13, the reference wavelength is λ, and the layers 101a (first layer) to 101g (seventh layer) of the antireflection film 101 with respect to the refractive index of the substrate (optical member) of 1.62, 1.74, and 1.85. The optical film thickness of each layer is determined. In Table 13, 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 13)
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. 13 shows the spectral characteristics when light rays are perpendicularly incident on an optical member in which the reference wavelength λ is 550 nm and the optical film thickness of each layer of the antireflection film 101 is designed in Table 13.

  From FIG. 13, 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 wavelength range of 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 13, 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 13, the optical film thickness of each layer with respect to the reference wavelength λ is designed under the conditions shown in Table 14 below. In this modification, the above-described sol-gel method is used for forming the fifth layer.

(Table 14)
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. 14 shows spectral characteristics when light rays are vertically 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 14. Yes. From FIG. 14, it can be seen that the antireflection film of this modification has a reflectivity of 0.2% or less over the entire wavelength range of 420 nm to 720 nm. In Table 14, even an optical member having an antireflection film whose optical film thickness is designed with the reference wavelength λ as the d-line (wavelength 587.6 nm) hardly affects the spectral characteristics, and the spectral characteristics shown in FIG. Has almost the same characteristics.

  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. 14 and 15 do not show the spectral characteristics of the optical member having the antireflection film with the refractive index of 1.46 shown in Table 14, 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. 16 shows an example of an antireflection film formed only by a dry process such as a conventional vacuum deposition method. FIG. 16 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 15 below with a refractive index of 1.52 of the same substrate as Table 14. FIG. 17 shows the spectral characteristics when the incident angles of the light rays to the optical member having the spectral characteristics shown in FIG. 16 are 30, 45, and 60 degrees, respectively.

(Table 15)
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 the spectral characteristics of the optical member having the antireflection film according to this embodiment shown in FIGS. 13 to 15 are compared with the spectral characteristics of the conventional example shown in FIGS. 16 and 17, the antireflection film according to this embodiment is compared. 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 13 and Table 14 is applied to the first to fourth embodiments of the present application will be described.

  In the optical system OS1 of the first example, the refractive index of the positive meniscus lens L23 in the second lens group G2 is nd = 1.88300 as shown in Table 1, and the positive meniscus lens in the third lens group G3. Since the refractive index of L33 is nd = 1.90265, an antireflection film 101 (see Table 13) having a refractive index of the substrate corresponding to 1.85 is used for the image side lens surface of the positive meniscus lens L23. By using an antireflection film 101 (see Table 13) whose refractive index of the substrate corresponds to 1.85 on the object-side lens surface of the positive meniscus lens L33, reflected light from each lens surface can be reduced, and ghost and flare Can be reduced.

  In the optical system OS2 of the second example, the refractive index of the negative meniscus lens L13 in the first lens group G1 is nd = 1.67270 as shown in Table 4, and the positive meniscus lens in the second lens group G2. Since the refractive index of L21 is nd = 1.80400, an antireflection film 101 (see Table 13) having a refractive index of the substrate corresponding to 1.62 is used for the lens surface on the image plane side of the negative meniscus lens L13. By using an antireflection film 101 (see Table 13) having a refractive index of the substrate corresponding to 1.85 on the object side lens surface of the positive meniscus lens L21, reflected light from each lens surface can be reduced, and ghost and flare Can be reduced.

  In the optical system OS3 of the third example, the refractive index of the biconvex positive lens L24 of the second lens group G2 is nd = 1.81600 as shown in Table 7, and the refractive index of the third lens group G3 Since the refractive index of the positive meniscus lens L33 is nd = 1.88300, the antireflective film 101 corresponding to the refractive index of the substrate corresponding to 1.85 on the image surface side lens surface of the biconvex positive lens L24 (table) 13) and the antireflection film 101 (see Table 13) having a refractive index of the substrate corresponding to 1.85 is used on the object-side lens surface of the positive meniscus lens L33, so that the reflected light from each lens surface is reflected. It can be reduced, and ghost and flare can be reduced.

  In the optical system OS4 of the fourth example, the refractive index of the positive meniscus lens L23 of the second lens group G2 is nd = 1.83480 as shown in Table 10, and the biconvex shape of the third lens group G3. Since the refractive index of the positive lens L31 is nd = 1.83480, the antireflective film 101 corresponding to the refractive index of the substrate of 1.85 on the image side lens surface of the positive meniscus lens L23 (see Table 13). , And the antireflection film 101 (see Table 13) having a refractive index of the substrate corresponding to 1.85 is used on the object-side lens surface of the biconvex positive lens L31, so that the reflected light from each lens surface is reflected. It can be reduced, and ghost and flare can be reduced.

OS (OS1 to OS4) Optical system G1 First lens group G2 Second lens group G3 Third lens group S Aperture stop 1 Camera (optical device) 2 Imaging lens 3 Imaging unit 4 EVF I Image surface 101 Antireflection film 101a First Layer 101b second layer 101c third layer 101d fourth layer 101e fifth layer 101f sixth layer 101g seventh layer 102 optical member

Claims (19)

From the object side,
A first lens group having a positive refractive power;
A second lens group having a positive refractive power;
A third lens group having a positive refractive power,
An antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film includes at least one layer formed by using a wet process,
Upon focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group moves along the optical axis,
An optical system satisfying the following conditional expression:
0.20 <f3 / f2 <7.80
However,
f2: Focal length of the second lens group f3: Focal length of the third lens group 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.   5. The optical system according to claim 4, wherein the concave lens surface when viewed from the aperture stop is an object-side lens surface of the lens in the first lens group or the second lens group.   5. The optical system according to claim 4, wherein the lens surface having a concave shape when viewed from the aperture stop is a lens surface on an image surface side of a lens in the first lens group or the second lens 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 7, wherein the concave lens surface provided with the antireflection film is a lens surface of a lens closest to the image plane of the third lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.30 <f3 / f <6.00
However,
f: Focal length of the entire system when focusing on infinity f3: Focal length of the third lens group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.50 <f2 / f <2.00
However,
f2: Focal length of the second lens group f: Focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.90 <f1 / f <50.00
However,
f1: Focal length of the first lens group f: Focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.40 <f1 / f3 <20.00
However,
f1: Focal length of the first lens group f3: Focal length of the third lens group   The optical system according to claim 1, wherein the second lens group includes a positive lens closest to the object side. The optical system according to claim 13, wherein the following conditional expression is satisfied:
0.30 <r1 / f2 <15.00
However,
r1: radius of curvature of the object side surface of the positive lens included in the second lens group f2: focal length of the second lens group   The optical system according to claim 1, wherein the first lens group includes two positive lenses in order from the object side.   The optical system according to any one of claims 1 to 15, wherein the most image-side lens of the second lens group has a biconvex shape.   The optical system according to claim 1, wherein all lens surfaces are spherical surfaces or flat surfaces.   An optical apparatus comprising the optical system according to claim 1. In order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power,
An antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film includes at least one layer formed by a wet process. An optical system manufacturing method comprising:
When focusing the first lens group, the second lens group, and the third lens group that satisfy the following conditional expression, the first lens group and the third lens group are fixed with respect to the image plane, A method of manufacturing an optical system, wherein the second lens group is arranged so as to move along an optical axis.
0.20 <f3 / f2 <7.80
However,
f2: Focal length of the second lens group f3: Focal length of the third lens group

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