JP2013083782A - Optical system, optical device, and method for manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system in which ghosts and flares are further reduced and excellent optical performance is obtained.SOLUTION: An optical system WL comprises, in order from an object side along the optical axis, a first lens group G1 having a negative refractive power, and a second lens group G2 having a positive refractive power. In the optical system WL, when focusing from an infinite distance object to a finite distance object, the first lens group G1 is fixed, and the second lens group G2 moves. The second lens group G2 comprises a front group G2a closer to the object side than a diaphragm S arranged in the second lens group G2, and a rear group G2b closer to the image side than the diaphragm S. An antireflection film is provided on at least one of the optical surfaces in the first lens group G1 and the second lens group G2. The antireflection film is configured to include at least one layer formed by using wet process.

Description

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

  Conventionally, various wide-angle lenses suitable for photographic cameras, electronic still cameras, video cameras, and the like have been proposed (see, for example, Patent Document 1). Further, in recent years, for such a wide-angle lens, not only aberration performance but also ghost and flare, which are one of the factors that impair optical performance, are becoming more severe. Therefore, higher performance is also required for the antireflection film applied to the lens surface, and multilayer film design technology and multilayer film formation technology continue to advance to meet the demand (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 11-211978 JP 2000-356704 A

  However, the conventional wide-angle lens has a problem that good optical performance cannot be achieved. In addition, there is a problem that reflected light that becomes ghost or flare is easily generated from the optical surface of such a wide-angle lens.

  The present invention has been made in view of such problems, and provides an optical system, an optical device, and a method of manufacturing an optical system that have good optical performance by further reducing ghosts and flares. Objective.

In order to achieve such an object, the optical system according to the present invention includes a first lens group having a negative refractive power and a second lens group having a positive refractive power, which are arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a finite distance, the first lens group is fixed, the second lens group is moved, and the second lens group is An optical surface of the first lens group and the second lens group includes a front group located on the object side with respect to the stop disposed in the second lens group and a rear group located on the image side with respect to the stop. Of these, an antireflection film is provided on at least one surface, and the antireflection film includes at least one layer formed using a wet process, and satisfies the following conditional expression.
0.10 <f2a / f <1.70
However,
f2a: focal length of the front group of the second lens group,
f: Focal length of the optical system in an infinitely focused state.

  In the above optical system, it is preferable that the antireflection film is a multilayer film, and the layer formed by using the wet process is a layer on the most surface side among the layers constituting the multilayer film.

  In the above optical system, it is preferable that the refractive index of the layer formed by using the wet process is 1.30 or less.

  In the above optical system, it is preferable that the antireflection film is provided on the concave optical surface when viewed from the diaphragm.

  In the optical system described above, it is preferable that the concave optical surface viewed from the diaphragm is an object side lens surface in the lenses in the first lens group and the second lens group.

  In the optical system described above, it is preferable that the concave optical surface viewed from the diaphragm is a lens surface on the image plane side in the lenses in the first lens group and the second lens group.

  In the above optical system, it is preferable that the antireflection film is provided on the concave optical surface as viewed from the image plane.

  In the optical system described above, it is preferable that the concave optical surface as viewed from the image plane is an object side lens surface of the lens in the second lens group.

  In the above-described optical system, it is preferable that the concave optical surface as viewed from the image surface is a lens surface on the image surface side of the lens in the second lens group.

In the above-described optical system, when the focal length of the rear group of the second lens group is f2b, the following expression 0.10 <f2a / f2b <1.00
It is preferable to satisfy the following conditions.

In the optical system described above, when the focal length of the first lens group is f1 and the focal length of the second lens group is f2, the following expression 0.10 <(− f1) / f2 <2.50
It is preferable to satisfy the following conditions.

In the above optical system, when the focal length of the second lens group is f2, the following expression 0.20 <f2 / f <1.55
It is preferable to satisfy the following conditions.

  In the optical system described above, it is preferable that the rear group of the second lens group has at least one aspheric lens.

  In the above optical system, it is preferable that the rear group of the second lens group includes two positive lenses arranged in order from the image side along the optical axis.

In the above optical system, when the focal length of the first lens group is f1, the following formula (−f1) / f <5.0
It is preferable to satisfy the following conditions.

  In the above optical system, it is preferable that the first lens group has two negative lenses arranged in order from the object side along the optical axis.

  In the above optical system, it is preferable that the first lens group has at least one aspheric lens.

In the above optical system, the first lens group includes a positive lens, and when the average value of the refractive index of the positive lens is n1p and the average value of the Abbe number of the positive lens is ν1p, n1p> 1.800
ν1p> 28.00
It is preferable to satisfy each of the conditions.

  In the above optical system, it is preferable that the front group and the rear group of the second lens group move together along the optical axis when focusing from an object at infinity to an object at a finite distance.

  An optical apparatus according to the present invention is an optical apparatus that includes an optical system that forms an image of an object on a predetermined surface, and uses the optical system according to the present invention as the optical system.

In the optical system manufacturing method according to the present invention, the first lens group having negative refracting power and the second lens group having positive refracting power are arranged in order from the object side along the optical axis. In the manufacturing method of the system, when focusing from an object at infinity to an object at finite distance, the first lens group is fixed, the second lens group is moved, and the second lens group is moved to the first lens group. An optical surface of the first lens group and the second lens group, which includes a front group located on the object side of the diaphragm disposed in the two lens groups and a rear group located on the image side of the diaphragm. An antireflection film is provided on at least one surface, and the antireflection film includes at least one layer formed by using a wet process so as to satisfy the following conditional expression.
0.10 <f2a / f <1.70
However,
f2a: focal length of the front group of the second lens group,
f: Focal length of the optical system in an infinitely focused state.

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

It is sectional drawing which shows the lens structure of the optical system which concerns on 1st Example. (A) is an aberration diagram when focusing on infinity of the optical system according to the first example, and (b) is an aberration diagram when focusing on a short distance (D0 = 200 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. (A) is an aberration diagram when focusing on infinity of the optical system according to Example 2, and (b) is an aberration diagram when focusing on a short distance (D0 = 200 mm). It is sectional drawing which shows the lens structure of the optical system which concerns on 3rd Example. (A) is an aberration diagram of the optical system according to the third example when focusing on infinity, and (b) is an aberration diagram of focusing on a short distance (D0 = 200 mm). It is sectional drawing which shows the lens structure of the optical system which concerns on 4th Example. (A) is various aberration diagrams at the time of focusing on infinity of the optical system according to Example 4, and (b) is various aberration diagrams at the time of focusing on short distance (D0 = 200 mm). It is sectional drawing of a digital single-lens reflex camera. It is a flowchart which shows 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 in the spectral characteristics 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 in the spectral characteristics of the anti-reflective film produced with the prior art.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. A digital single lens reflex camera CAM provided with the optical system according to the present application is shown in FIG. In the digital single-lens reflex camera CAM shown in FIG. 10, light from an object (subject) (not shown) is collected by a photographing lens (optical system WL) and imaged on a focusing screen F via a quick return mirror M. Is done. The light imaged on the focusing screen F is reflected a plurality of times in the pentaprism P and guided to the eyepiece lens E. Thus, the photographer can observe the image of the object (subject) as an erect image through the eyepiece lens E.

  When a release button (not shown) is pressed by the photographer, the quick return mirror M is retracted out of the optical path, and the light from the object (subject) collected by the photographing lens (optical system WL) is captured by the image sensor C. The image is formed on the object to form an image of the subject. As a result, light from the object (subject) is imaged on the image sensor C, picked up by the image sensor C, and recorded in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph an object (subject) with the digital single-lens reflex camera CAM. Even a mirrorless camera that does not have the quick return mirror M can achieve the same effects as the camera CAM. The digital single-lens reflex camera CAM shown in FIG. 10 may be configured to hold the photographic lens (optical system WL) in a detachable manner, and is configured integrally with the photographic lens (optical system WL). Also good.

  The photographing lens includes the optical system WL according to this embodiment. For example, as shown in FIG. 1, the optical system WL according to the present embodiment includes a first lens group G1 having negative refractive power arranged in order from the object side along the optical axis, and a first lens group having positive refractive power. 2 lens group G2. With such a configuration, the lens barrel can be reduced in size and each aberration can be corrected well. The second lens group G2 includes a front group G2a located on the object side of the diaphragm S disposed in the second lens group G2, and a rear group G2b located on the image side of the diaphragm S. Further, when focusing from an infinitely distant object to a short distance (finite distance) object, the first lens group G1 is fixed and the second lens group G2 is moved. With such a configuration, the lens barrel can be reduced in size, and aberration variations due to focusing can be corrected well.

  In the optical system WL having such a configuration, when the focal length of the front group G2a of the second lens group G2 is f2a and the focal length of the optical system WL in the infinitely focused state is f, the following conditional expression ( It is preferable to satisfy the condition represented by 1).

  0.10 <f2a / f <1.70 (1)

Conditional expression (1) defines the ratio between the focal length f2a of the front group G2a of the second lens group G2 and the focal length f of the entire optical system WL in an infinitely focused state. The optical system WL of the present embodiment can realize good optical performance by satisfying the conditional expression (1). When the condition is lower than the lower limit value of the conditional expression (1), the refractive power of the front group G2a of the second lens group G2 becomes strong, and it becomes difficult to correct spherical aberration and to secure the back focus. On the other hand, when the condition exceeds the upper limit value of the conditional expression (1), the refractive power of the front group G2a becomes weak and it becomes difficult to correct sagittal coma. Further, the refractive power of the rear group G2b of the second lens group G2 becomes strong, and it becomes difficult to correct spherical aberration and coma aberration.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 1.65. In order to make the effect of the present embodiment more certain, it is preferable to set the upper limit of conditional expression (1) to 1.60. On the other hand, in order to ensure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.50. In order to make the effect of the present embodiment more reliable, it is preferable to set the lower limit of conditional expression (1) to 1.00.

  In the optical system WL according to the present embodiment, an antireflection film is provided on at least one of the optical surfaces in the first lens group G1 and the second lens group G2, and the antireflection film is formed using a wet process. At least one layer formed. With this configuration, it is possible to further reduce ghosts and flares caused by reflection of light from an object on an optical surface, and achieve high imaging performance.

  In such an optical system WL, 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 such an optical system WL, it is preferable that the refractive index nd (relative to the d-line) of the layer formed using the wet process is 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 such an optical system WL, it is preferable that an antireflection film is provided on the concave optical surface as viewed from the stop S. In this way, reflected light is likely to be generated on a concave optical surface as viewed from the diaphragm S among the optical surfaces in the first lens group G1 and the second lens group G2, and thus an antireflection film is formed on such an optical surface. By forming the ghost and flare can be effectively reduced.

  In such an optical system WL, it is preferable that the concave optical surface viewed from the diaphragm S is an object side lens surface in the lenses in the first lens group G1 and the second lens group G2. In this case, reflected light is likely to be generated on the concave lens surface when viewed from the diaphragm S among the optical surfaces in the first lens group G1 and the second lens group G2, and thus an antireflection film is formed on such a lens surface. By forming the ghost and flare can be effectively reduced.

  In such an optical system WL, it is preferable that the concave optical surface viewed from the stop S is a lens surface on the image plane side in the lenses in the first lens group G1 and the second lens group G2. In this case, reflected light is likely to be generated on the concave lens surface when viewed from the diaphragm S among the optical surfaces in the first lens group G1 and the second lens group G2, and thus an antireflection film is formed on such a lens surface. By forming the ghost and flare can be effectively reduced.

  In such an optical system WL, it is preferable that an antireflection film is provided on an optical surface that is concave when viewed from the image plane. In this way, reflected light is likely to be generated on a concave optical surface as viewed from the image plane among the optical surfaces in the second lens group G2, and thus by forming an antireflection film on such an optical surface, Ghost and flare can be effectively reduced.

In such an optical system WL, it is preferable that the concave optical surface as viewed from the image plane is an object side lens surface in the lens in the second lens group G2. In this way, reflected light is likely to be generated on the concave lens surface as viewed from the image plane among the optical surfaces in the second lens group G2, and thus by forming an antireflection film on such a lens surface, Ghost and flare can be effectively reduced.

  In such an optical system WL, it is preferable that the concave optical surface as viewed from the image surface is a lens surface on the image surface side of the lens in the second lens group G2. In this way, reflected light is likely to be generated on the concave lens surface as viewed from the image plane among the optical surfaces in the second lens group G2, and thus by forming an antireflection film on such a lens surface, Ghost and flare can be effectively reduced.

  Note that the antireflection film is not limited to a wet process, and may be formed by a dry process or the like. In this case, the antireflection film preferably includes at least one layer having a refractive index of 1.30 or less. By including at least one layer having a refractive index of 1.30 or less, even when 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. 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.

  In such an optical system WL, it is preferable that the condition expressed by the following conditional expression (2) is satisfied when the focal length of the rear group G2b of the second lens group G2 is f2b.

  0.10 <f2a / f2b <1.00 (2)

  Conditional expression (2) defines the ratio of the focal length f2a of the front group G2a and the focal length f2b of the rear group G2b in the second lens group G2. The optical system WL of the present embodiment can satisfactorily correct sagittal coma flare by satisfying this conditional expression (2). When the condition exceeds the upper limit value of the conditional expression (2), the refractive power of the front group G2a becomes weak, and it becomes difficult to correct sagittal coma. Further, the refractive power of the rear group G2b becomes strong, and it becomes difficult to correct spherical aberration and coma aberration. On the other hand, when the condition is lower than the lower limit value of the conditional expression (2), the refractive power of the front group G2a becomes strong, and it becomes difficult to correct spherical aberration and to secure the back focus.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 0.95. In order to make the effect of the present embodiment more certain, it is preferable to set the upper limit of conditional expression (2) to 0.90. On the other hand, in order to ensure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.20. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.30.

  In such an optical system WL, when the focal length of the first lens group G1 is f1, and the focal length of the second lens group G2 is f2, the condition represented by the following conditional expression (3) is satisfied. It is preferable to do.

  0.10 <(− f1) / f2 <2.50 (3)

  Conditional expression (3) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f2 of the second lens group G2. The optical system WL of the present embodiment can realize good optical performance by satisfying this conditional expression (3). When the condition exceeds the upper limit value of conditional expression (3), the refractive power of the second lens group G2 becomes strong, and it becomes difficult to correct spherical aberration and coma aberration. On the other hand, when the condition is less than the lower limit value of the conditional expression (3), the refractive power of the first lens group G1 becomes strong, and it becomes difficult to correct field curvature and distortion.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 2.30. In order to make the effect of the present embodiment more certain, it is preferable to set the upper limit of conditional expression (3) to 2.10. On the other hand, in order to ensure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.70. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 1.20.

  In such an optical system WL, it is preferable that the condition expressed by the following conditional expression (4) is satisfied when the focal length of the second lens group G2 is f2.

  0.20 <f2 / f <1.55 (4)

  Conditional expression (4) defines the ratio between the focal length f2 of the second lens group G2 and the focal length f of the entire optical system WL in an infinitely focused state. The optical system WL of the present embodiment can realize good optical performance by satisfying the conditional expression (4). When the condition is less than the lower limit value of the conditional expression (4), the refractive power of the second lens group G2 becomes strong, and it becomes difficult not only to secure the back focus but also to correct spherical aberration and coma aberration. . On the other hand, when the condition exceeds the upper limit value of the conditional expression (4), the refractive power of the second lens group G2 becomes weak, and the total length of the optical system WL increases. In addition, it becomes difficult to correct spherical aberration and coma.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 1.45. In order to make the effect of the present embodiment more certain, it is preferable to set the upper limit value of conditional expression (4) to 1.35. On the other hand, in order to ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.35. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.65. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 1.00.

  In such an optical system WL, it is preferable that the rear group G2b of the second lens group G2 has at least one aspheric lens. With this configuration, spherical aberration and sagittal coma can be favorably corrected.

  In such an optical system WL, it is preferable that the rear group G2b of the second lens group G2 has two positive lenses arranged in order from the image side along the optical axis. With this configuration, spherical aberration and coma can be favorably corrected.

  In such an optical system WL, it is preferable that the condition expressed by the following conditional expression (5) is satisfied when the focal length of the first lens group G1 is f1.

  (−f1) / f <5.0 (5)

  Conditional expression (5) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f of the entire optical system WL in an infinitely focused state. The optical system WL of the present embodiment can realize good optical performance by satisfying this conditional expression (5). When the condition exceeds the upper limit value of the conditional expression (5), the refractive power of the first lens group G1 becomes weak, the refractive power of the second lens group G2 becomes strong to obtain a predetermined angle of view, and spherical aberration and It becomes difficult to correct coma.

In addition, the effect of this embodiment can be made more reliable by setting the upper limit of conditional expression (5) to 4.0. Preferably, by setting the upper limit of conditional expression (5) to 3.0, the effect of the present embodiment can be made more reliable.

  In such an optical system WL, it is preferable that the first lens group G1 has two negative lenses arranged in order from the object side along the optical axis. With this configuration, coma, curvature of field, and distortion can be favorably corrected.

  In such an optical system WL, it is preferable that the first lens group G1 has at least one aspheric lens. With this configuration, field curvature and distortion can be favorably corrected.

  Further, in such an optical system WL, the first lens group G1 has a positive lens, and when the average value of the refractive index of the positive lens is n1p and the average value of the Abbe number of the positive lens is ν1p, It is preferable that the following conditional expressions (6) and (7) are satisfied.

n1p> 1.800 (6)
ν1p> 28.00 (7)

  Conditional expression (6) and conditional expression (7) define the characteristics of the positive lens glass material of the first lens group G1. The optical system WL of the present embodiment can satisfactorily correct the lateral chromatic aberration, distortion, and field curvature that occur in the negative lens of the first lens group G1 by satisfying this condition. When the condition is less than the lower limit value of the conditional expression (6), it becomes difficult to correct distortion aberration, field curvature, and coma aberration generated in the negative lens. Further, when the condition is less than the lower limit value of the conditional expression (7), the secondary dispersion becomes large, so that it is difficult to sufficiently correct the lateral chromatic aberration.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (6) to 1.840. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (7) to 30.00.

  In such an optical system WL, when focusing from an object at infinity to an object at a short distance (finite distance), the front group G2a and the rear group G2b of the second lens group G2 are integrated into light. It is preferable to move along the axis. With such a configuration, it is possible to reduce a variation in focusing aberration caused by a manufacturing error. As described above, according to the present embodiment, it is possible to further reduce ghosts and flares and obtain an optical system WL having good optical performance and an optical device (digital single-lens reflex camera CAM) including the optical system WL. Become.

  Here, a method of manufacturing the optical system WL having the above-described configuration will be described with reference to FIG. First, the first lens group G1 and the second lens group G2 of this embodiment are assembled in a cylindrical lens barrel (step S1). At this time, the lenses of the first to second lens groups G1 to G2 are arranged so as to satisfy the conditional expression (1) described above. When each lens is incorporated into the lens barrel, the lens groups may be incorporated into the lens barrel one by one in the order along the optical axis, and a part or all of the lens groups are integrally held by the holding member and then the lens barrel. You may assemble with a member.

  After assembling each lens group in the lens barrel, it is confirmed whether an object image is formed in a state where each lens group is incorporated in the lens barrel, that is, whether the centers of the lens groups are aligned (step S2). ). In this embodiment, an antireflection film is provided on at least one of the optical surfaces in the first lens group G1 and the second lens group G2, and this antireflection film is a layer formed by using a wet process. It is configured to include at least one layer to reduce ghosts and flares.

Then, after confirming whether an image is formed, various operations of the optical system WL are confirmed (step S).
3). Examples of various operations include a focusing operation in which a lens group that performs focusing from a long-distance object to a short-distance object moves along the optical axis direction, and at least some lenses have a component perpendicular to the optical axis. An image stabilization operation that moves like this can be cited. In the present embodiment, the first lens group G1 is fixed and the second lens group G2 is moved when focusing from a long distance object (infinite object) to a short distance object (finite distance object). It is like that. In addition, the confirmation order of various operations is arbitrary. According to such a manufacturing method, it is possible to manufacture an optical system WL having good optical performance by suppressing aberration fluctuations and further reducing ghosts and flares.

(First embodiment)
Embodiments of the present application will be described below with reference to the accompanying drawings. First, a first embodiment of the present application will be described with reference to FIGS. FIG. 1 is a cross-sectional view illustrating a lens configuration of an optical system WL (WL1) according to the first example. The optical system WL1 according to the first example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. The second lens group G2 includes a front group G2a having a positive refractive power, an aperture stop S, and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The

  The first lens group G1 is arranged in order from the object side along the optical axis, and includes a first negative meniscus lens L11 having a convex surface facing the object side, and a first positive meniscus lens L12 having a convex surface facing the object side. It consists of a cemented negative lens formed by cementing with a second negative meniscus lens L13 having a convex surface facing the object side, and a cemented first bilens positive lens L14 and biconcave first negative lens L15. It consists of a cemented positive lens. In the first lens group G1, the lens surface on the image plane I side of the second negative meniscus lens L13 is aspheric.

  The front group G2a of the second lens group G2 includes a biconvex second positive lens L21. The rear group G2b of the second lens group G2 is arranged in order from the object side along the optical axis, and includes a third negative meniscus lens L22 having a convex surface directed toward the object side, and a biconcave second negative lens L23. From a cemented negative lens formed by cementing with a biconvex third positive lens L24, a biconvex fourth positive lens L25, and a second positive meniscus lens L26 having a convex surface facing the image plane I side Composed. In the rear group G2b of the second lens group G2, the lens surface on the image plane I side of the fourth positive lens L25 is aspheric. Further, an antireflection film, which will be described later, is formed on the image surface I side lens surface (surface number 14) of the third negative meniscus lens L22 and the image surface I side lens surface (surface number 19) of the fourth positive lens L25. Is formed.

  The first lens group G1 is fixed and the second lens group G2 is moved during focusing from an object at infinity to an object at a short distance (finite distance). At this time, the front group G2a, the stop S, and the rear group G2b of the second lens group G2 are moved integrally.

Tables 1 to 4 are shown below, and these are tables listing the values of the specifications of the optical systems according to the first to fourth examples. In [Overall specifications] in each table, f is a focal length, FNO is an F number, ω is a half angle of view (maximum incident angle: unit is “°”), Y is an image height, and TL is a total lens length. (Air conversion length) and Bf indicate back focus (air conversion length), respectively. In [Lens Specifications], the first column N is the lens surface number counted from the object side, the second column R is the radius of curvature of the lens surface, the third column D is the lens surface interval, and the fourth column. nd represents the refractive index with respect to the d line (wavelength λ = 587.6 nm), and the fifth column νd represents the Abbe number with respect to the d line (wavelength λ = 587.6 nm). Note that * attached to the right of the surface number indicates that the lens surface is an aspherical surface. The curvature radius “0.0000” indicates a plane, and the refractive index nd = 1.0000 of air is omitted from the description.

Also, the aspheric coefficient shown in [Aspherical data] is x, the displacement in the optical axis direction at the position of the height h from the optical axis with respect to the vertex of the surface, and κ, the conic constant. When the next aspherical coefficient (n = 4, 6, 8, 10) is An, and the paraxial radius of curvature shown in [Lens Specifications] is r, it is expressed by the following equation (8). In each example, the secondary aspherical coefficient A2 is 0, and the description is omitted. In [Aspherical data], “En” indicates “× 10 ⁻ⁿ ”.

x = (h ² / r) / [1+ {1-κ × (h / r) ² } ^1/2 }]
+ A4 × h ⁴ + A6 × h ⁶ + A8 × h ⁸ + A10 × h ¹⁰ (8)

  In [variable interval data], the distance from the object to the lens surface closest to the object is D0, and each variable interval at the time of focusing at infinity (D0 = ∞) and at the time of focusing at a short distance (D0 = 200 mm). Indicates the value of. The focal length f, curvature radius R, surface distance D, and other length units listed in all the following specifications are generally “mm”, 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. In addition, the same reference numerals as in the present embodiment are used in the specification values of the second to fourth embodiments described later.

  Table 1 below shows specifications in the first embodiment. In addition, the curvature radius R of the 1st surface-the 21st surface in Table 1 respond | corresponds to code | symbol R1-R21 attached | subjected to the 1st surface-the 21st surface in FIG. In the first embodiment, the sixth and nineteenth lens surfaces are aspherical.

(Table 1)
[Overall specifications]
f = 28.70
FNO = 1.85
ω = 37.65
Y = 21.60
TL = 115.14
Bf = 38.90
[Lens specifications]
N R D nd νd
Object ∞ ∞
1 49.1524 1.5000 1.77250 49.61
2 22.6487 6.3000
3 64.7809 3.5000 1.83481 42.73
4 150.0000 1.7000 1.51680 63.88
5 32.5000 0.1000 1.55389 38.23
6 * 28.4668 15.0000
7 41.4076 4.5000 1.83481 42.73
8 -157.2545 1.4000 1.51742 52.32
9 39.7009 (d1)
10 31.9258 5.8146 1.69680 55.52
11 -152.5356 3.9000
12 0.0000 0.9989 (Aperture)
13 89.3478 1.3000 1.51742 52.20
14 39.6652 5.0000
15 -26.3069 1.4000 1.78472 25.64
16 50.5684 3.5000 1.59319 67.87
17 -98.4501 0.5000
18 151.4501 3.0000 1.77250 49.62
19 * -89.8749 1.1000
20 -169.6497 4.5000 1.80400 46.60
21 -29.4540 (Bf)
Image plane ∞
[Aspherical data]
6th surface κ = 1.0000, A4 = -4.67675E-06, A6 = -7.54681E-09, A8 = -1.54602E-11, A10 = -1.83890E-14
19th surface κ = 1.0000, A4 = 1.47607E-05, A6 = -2.02245E-10, A8 = 0.00000E + 00, A10 = 0.00000E + 00
[Variable interval data]
Infinity short distance D0 = ∞ 200.0000
d1 = 11.2300 6.3103

  FIGS. 2A to 2B are graphs showing various aberrations of the optical system WL1 according to the first example. Here, FIG. 2A is a diagram showing various aberrations when focusing on infinity, and FIG. 2B is a diagram showing various aberrations when focusing on short distance (D0 = 200 mm). In each aberration diagram, FNO represents an F number, and Y represents an image height. In each aberration diagram, d indicates the aberration at the d-line (λ = 587.6 nm), and g indicates the aberration at the g-line (λ = 435.8 nm). In the aberration diagrams showing astigmatism, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane. The description of the aberration diagrams is the same in the other examples.

  From the respective aberration diagrams, it can be seen that in the first example, various aberrations are corrected well and the imaging performance is excellent. As a result, by mounting the optical system WL1 of the first embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  FIG. 3 shows an optical system WL1 having the same configuration as that of the first embodiment, in which incident light rays are reflected by the first reflecting surface and the second reflecting surface, and a ghost or flare is reflected on the image surface I. It is a figure which shows an example of a mode that forms. In FIG. 3, when a light beam BM from the object side enters the optical system WL1 as shown in the drawing, the lens surface on the image plane I side of the fourth positive lens L25 (the first reflected light generation surface, The surface number is reflected by 19), and the reflected light is reflected again by the lens surface on the image plane I side of the third negative meniscus lens L22 (the second reflected light generation surface, the surface number is 14). As a result, it reaches the image plane I, and ghost and flare are generated. The 19th surface, which is the first reflected light generation surface, is a concave lens surface as viewed from the aperture stop S, and the 14th surface, which is the second reflected light generation surface, is the image plane. It is a concave lens surface as viewed from I. 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)
Next, a second embodiment of the present application will be described with reference to FIGS. 4 to 5 and Table 2. FIG. FIG. 4 is a cross-sectional view illustrating a lens configuration of an optical system WL (WL2) according to the second example. The optical system WL2 according to the second example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. The second lens group G2 includes a front group G2a having a positive refractive power, an aperture stop S, and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The

The first lens group G1 is arranged in order from the object side along the optical axis, and includes a first negative meniscus lens L11 having a convex surface facing the object side, and a second negative meniscus lens L12 having a convex surface facing the object side.
And a cemented positive lens formed by cementing a first positive meniscus lens L13 having a convex surface toward the object side and a third negative meniscus lens L14 having a convex surface toward the object side. In the first lens group G1, the lens surface on the image plane I side of the second negative meniscus lens L12 is aspheric. In addition, an antireflection film, which will be described later, is provided on the image surface I side lens surface (surface number 2) of the first negative meniscus lens L11 and the object side lens surface (surface number 3) of the second negative meniscus lens L12. Is formed.

  The front group G2a of the second lens group G2 includes a biconvex first positive lens L21 and a biconcave first negative lens L22 that are arranged in order from the object side along the optical axis. . The rear group G2b of the second lens group G2 is a joint formed by joining a biconcave second negative lens L23 and a biconvex second positive lens L24 arranged in order from the object side along the optical axis. The lens includes a negative lens, a second positive meniscus lens L25 having a convex surface facing the image surface I, and a third positive meniscus lens L26 having a convex surface facing the image surface I. In the rear group G2b of the second lens group G2, the lens surface on the image plane I side of the second positive lens L24 is aspheric.

  The first lens group G1 is fixed and the second lens group G2 is moved during focusing from an object at infinity to an object at a short distance (finite distance). At this time, in the second lens group G2, the front group G2a and the stop S move integrally so that the distance between the front group G2a and the rear group G2b is reduced, and the front group G2a and the stop S move differently. The rear group G2b moves by the amount.

  Table 2 below shows specifications in the second embodiment. In addition, the curvature radius R of the 1st surface-the 20th surface in Table 2 respond | corresponds to code | symbol R1-R20 attached | subjected to the 1st surface-the 20th surface in FIG. In the second embodiment, the lens surfaces of the fifth surface and the sixteenth surface are aspherical.

(Table 2)
[Overall specifications]
f = 31.02
FNO = 1.85
ω = 35.53
Y = 21.60
TL = 112.35
Bf = 41.12
[Lens specifications]
N R D nd νd
Object ∞ ∞
1 51.3500 1.5000 1.69679 55.52
2 25.2423 4.9661
3 68.6565 1.5000 1.51680 64.11
4 28.1354 0.1000 1.52050 50.97
5 * 26.2816 11.5436
6 40.1060 3.7730 1.83480 42.72
7 245.2122 1.3000 1.51822 58.94
8 55.0388 (d1)
9 35.8474 5.4498 1.75499 52.31
10 -90.5185 0.2911
11 -1293.1200 1.3203 1.51742 52.31
12 59.5863 2.7402
13 0.0000 (d2) (Aperture)
14 -21.2472 1.4020 1.78472 25.68
15 62.9942 3.1710 1.72915 54.66
16 * -81.0024 2.1794
17 -55.3719 3.3993 1.59319 67.90
18 -29.4567 0.1000
19 -608.4131 5.2751 1.80400 46.58
20 -29.8770 (Bf)
Image plane ∞
[Aspherical data]
5th surface κ = 1.0000, A4 = -3.12860E-06, A6 = -6.82480E-09, A8 = 9.01370E-12, A10 = -1.54600E-14
16th surface κ = 1.0000, A4 = 1.80620E-05, A6 = -5.80110E-09, A8 = 0.00000E + 00, A10 = 0.00000E + 00
[Variable interval data]
Infinity short distance D0 = ∞ 200.0000
d1 = 10.2521 4.3259
d2 = 10.9700 10.7329

  FIGS. 5A to 5B are graphs showing various aberrations of the optical system WL2 according to the second example. Here, FIG. 5A is a diagram of various aberrations when focusing on infinity, and FIG. 5B is a diagram of various aberrations when focusing on short distance (D0 = 200 mm). From the respective aberration diagrams, it can be seen that in the second example, various aberrations are satisfactorily corrected and the imaging performance is excellent. As a result, by mounting the optical system WL2 of the second embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

(Third embodiment)
Next, a third embodiment of the present application will be described with reference to FIGS. FIG. 6 is a cross-sectional view showing a lens configuration of an optical system WL (WL3) according to the third example. The optical system WL3 according to the third example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. The second lens group G2 includes a front group G2a having a positive refractive power, an aperture stop S, and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The

  The first lens group G1 is arranged in order from the object side along the optical axis, and includes a first negative meniscus lens L11 having a convex surface facing the object side, and a second negative meniscus lens L12 having a convex surface facing the object side. And a positive cemented lens formed by cementing a positive meniscus lens L13 having a convex surface facing the object side and a third negative meniscus lens L14 having a convex surface facing the object side. In the first lens group G1, the lens surface on the image plane I side of the second negative meniscus lens L12 is aspheric.

  The front group G2a of the second lens group G2 includes a biconvex first positive lens L21. The rear group G2b of the second lens group G2 is arranged in order from the object side along the optical axis, and includes a fourth negative meniscus lens L22 having a convex surface facing the object side, a biconcave negative lens L23, and a biconvex shape This is composed of a cemented negative lens formed by cementing with the second positive lens L24 and a biconvex third positive lens L25. In the rear group G2b of the second lens group G2, the lens surface on the image plane I side of the second positive lens L24 is aspheric. An antireflection film described later is formed on the object side lens surface (surface number 12) of the fourth negative meniscus lens L22.

The first lens group G1 is fixed and the second lens group G2 is moved during focusing from an object at infinity to an object at a short distance (finite distance). At this time, the front group G2a, the stop S, and the rear group G2b of the second lens group G2 are moved integrally.

  Table 3 below shows specifications in the third embodiment. In addition, the curvature radius R of the 1st surface-18th surface in Table 3 respond | corresponds to code | symbol R1-R18 attached | subjected to the 1st surface-18th surface in FIG. In the third embodiment, the lens surfaces of the fifth surface and the sixteenth surface are formed in an aspheric shape.

(Table 3)
[Overall specifications]
f = 28.70
FNO = 1.85
ω = 37.68
Y = 21.60
TL = 115.35
Bf = 38.90
[Lens specifications]
N R D nd νd
Object ∞ ∞
1 47.3292 1.5000 1.72915 54.66
2 22.8109 5.5771
3 35.4413 1.5000 1.51680 64.11
4 23.4810 0.2000 1.52050 50.97
5 * 21.5311 17.0000
6 37.4414 3.3161 1.81600 46.62
7 104.2195 1.3000 1.51822 58.94
8 40.6864 (d1)
9 35.8877 5.2516 1.69679 55.52
10 -232.6661 5.9928
11 0.0000 5.0287 (Aperture)
12 31.9060 1.3000 1.75519 27.51
13 27.2893 5.6256
14 -25.1103 1.4000 1.78472 25.68
15 30.2467 5.0249 1.80332 41.71
16 * -69.5995 0.1000
17 160.9651 5.4531 1.80610 40.94
18 -31.3476 (Bf)
Image plane ∞
[Aspherical data]
5th surface κ = 1.0000, A4 = -5.69480E-06, A6 = -3.25880E-08, A8 = 6.98270E-11, A10 = -2.50300E-13
16th surface κ = 1.0000, A4 = 1.27800E-05, A6 = 8.55920E-09, A8 = 0.00000E + 00, A10 = 0.00000E + 00
[Variable interval data]
Infinity short distance D0 = ∞ 200.0000
d1 = 10.8827 4.8932

FIGS. 7A to 7B are graphs showing various aberrations of the optical system WL3 according to the third example. Here, FIG. 7A is a diagram of various aberrations when focusing on infinity, and FIG. 7B is a diagram of various aberrations when focusing on short distance (D0 = 200 mm). From the respective aberration diagrams, it can be seen that in the third example, various aberrations are satisfactorily corrected and the imaging performance is excellent. As a result, by mounting the optical system WL3 of the third embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

(Fourth embodiment)
Next, a fourth embodiment of the present application will be described with reference to FIGS. FIG. 8 is a cross-sectional view illustrating a lens configuration of an optical system WL (WL4) according to the fourth example. The optical system WL4 according to the fourth example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. The second lens group G2 includes a front group G2a having a positive refractive power, an aperture stop S, and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The

  The first lens group G1 is arranged in order from the object side along the optical axis, and includes a first negative meniscus lens L11 having a convex surface facing the object side, and a second negative meniscus lens L12 having a convex surface facing the object side. The first positive meniscus lens L13 having a convex surface facing the object side and the cemented positive lens formed by cementing a third negative meniscus lens L14 having a convex surface facing the object side. In the first lens group G1, the lens surface on the image plane I side of the second negative meniscus lens L12 is aspheric.

  The front group G2a of the second lens group G2 includes a biconvex first positive lens L21. The rear group G2b of the second lens group G2 is arranged in order from the object side along the optical axis, and includes a fourth negative meniscus lens L22 having a convex surface facing the object side, a biconcave negative lens L23, and a biconvex shape A negative lens formed by cementing with the second positive lens L24, a biconvex third positive lens L25, and a second positive meniscus lens L26 having a convex surface facing the image plane I side. . In the rear group G2b of the second lens group G2, the lens surface on the image plane I side of the third positive lens L25 is aspheric. Further, an antireflection film, which will be described later, is provided on the image surface I side lens surface (surface number 13) of the fourth negative meniscus lens L22 and the object side lens surface (surface number 19) of the second positive meniscus lens L26. Is formed.

  The first lens group G1 is fixed and the second lens group G2 is moved during focusing from an object at infinity to an object at a short distance (finite distance). At this time, the front group G2a, the stop S, and the rear group G2b of the second lens group G2 are moved integrally.

  Table 4 below shows specifications in the fourth embodiment. In addition, the curvature radius R of the 1st surface-20th surface in Table 4 respond | corresponds to code | symbol R1-R20 attached | subjected to the 1st surface-20th surface in FIG. In the fourth embodiment, the lens surfaces of the fifth surface and the eighteenth surface are formed in an aspherical shape.

(Table 4)
[Overall specifications]
f = 31.00
FNO = 1.84
ω = 35.45
Y = 21.60
TL = 111.05
Bf = 40.08
[Lens specifications]
N R D nd νd
Object ∞ ∞
1 54.8755 1.5000 1.77250 49.61
2 24.3470 6.4422
3 46.8800 1.5000 1.77250 49.61
4 30.0000 0.1000 1.52050 50.97
5 * 28.1565 10.0000
6 39.4043 6.0000 1.83481 42.76
7 799.7751 1.3000 1.51823 58.82
8 50.6325 (d1)
9 34.7711 5.7076 1.80400 46.58
10 -127.3217 4.2607
11 0.0000 1.8217 (Aperture)
12 311.4924 1.2000 1.58144 40.98
13 50.7052 5.0000
14 -23.2205 1.4000 1.78472 25.64
15 45.6877 4.0000 1.59319 67.90
16 -102.0531 0.5000
17 224.5463 3.3243 1.77250 49.62
18 * -72.9478 1.1000
19 -271.1411 4.5000 1.80400 46.60
20 -28.5408 (Bf)
Image plane ∞
[Aspherical data]
5th surface κ = 1.0000, A4 = -3.78292E-06, A6 = -3.64587E-09, A8 = -1.01198E-11, A10 = 3.37967E-15
18th surface κ = 1.0000, A4 = 1.43983E-05, A6 = 6.14666E-11, A8 = 0.00000E + 00, A10 = 0.00000E + 00
[Variable interval data]
Infinity short distance D0 = ∞ 200.0000
d1 = 11.3148 4.5052

  FIGS. 9A to 9B are graphs showing various aberrations of the optical system WL4 according to the fourth example. Here, FIG. 9A is a diagram of various aberrations when focusing on infinity, and FIG. 9B is a diagram of various aberrations when focusing on short distance (D0 = 200 mm). From the respective aberration diagrams, it can be seen that in the fourth example, various aberrations are corrected satisfactorily and the imaging performance is excellent. As a result, by mounting the optical system WL4 of the fourth embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  Table 5 below shows the values corresponding to the conditional expressions in the respective examples.

(Table 5)
First Example Second Example Third Example Fourth Example Conditional Expression (1) 1.33 1.56 1.57 1.11
Conditional expression (2) 0.43 0.87 0.66 0.38
Conditional expression (3) 2.03 1.90 1.52 1.79
Conditional expression (4) 1.37 1.33 1.38 1.28
Conditional expression (5) 2.78 2.53 2.10 2.29
Conditional expression (6) 1.83481 1.83481 1.81600 1.83481
Conditional expression (7) 42.76 42.76 46.62 42.76

  Thus, it can be seen that each of the above-described conditional expressions is satisfied in each embodiment. As described above, according to each embodiment, it is possible to realize an optical system WL and an optical apparatus (digital single-lens reflex camera CAM) having good optical performance.

  Here, an antireflection film (also referred to as a multilayer broadband antireflection film) used in the optical system WL according to the present embodiment 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 (CH ₃ COO) ₂ → MgF ₂ + 2CH ₃ COOH (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 6 below. Here, in Table 6, the reference wavelength is λ, and the layers 101a (first layer) to 101g (seventh layer) of the antireflection film 101 when the refractive index (optical member) of the substrate is 1.62, 1.74, and 1.85. The optical film thickness of each layer is determined. In Table 6, aluminum oxide is represented by Al ₂ O ₃ , a titanium oxide and zirconium oxide mixture is represented by ZrO ₂ + TiO ₂ , and a mixture of magnesium fluoride and silica is represented by MgF ₂ + SiO ₂ .

(Table 6)
Material Refractive index Optical film thickness Optical film thickness Optical film thickness Medium Air 1
7th layer MgF ₂ + SiO ₂ 1.26 0.268λ 0.271λ 0.269λ
6th layer ZrO ₂ + TiO ₂ 2.12 0.057λ 0.054λ 0.059λ
5th layer Al ₂ O ₃ 1.65 0.171λ 0.178λ 0.162λ
4th layer ZrO ₂ + TiO ₂ 2.12 0.127λ 0.13λ 0.158λ
3rd layer Al ₂ O ₃ 1.65 0.122λ 0.107λ 0.08λ
Second layer ZrO ₂ + TiO ₂ 2.12 0.059λ 0.075λ 0.105λ
1st layer Al ₂ O ₃ 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 in Table 6 and the optical film thickness of each layer of the antireflection film 101 is designed.

  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 the d-line (wavelength 587.6 nm) in Table 6, 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. The antireflection film of the modification is composed of five layers, and similarly to Table 6, the optical film thickness of each layer with respect to the reference wavelength λ is designed under the conditions shown in Table 7 below. In this modification, the above-described sol-gel method is used for forming the fifth layer.

(Table 7)
Material Refractive index Optical film thickness Optical film thickness Medium Air 1
5th layer MgF ₂ + SiO ₂ 1.26 0.275λ 0.269λ
Fourth layer ZrO ₂ + TiO ₂ 2.12 0.045λ 0.043λ
3rd layer Al ₂ O ₃ 1.65 0.212λ 0.217λ
Second layer ZrO ₂ + TiO ₂ 2.12 0.077λ 0.066λ
1st layer Al ₂ O ₃ 1.65 0.288λ 0.290λ
Refractive index of substrate 1.46 1.52

FIG. 14 shows the spectral characteristics in Table 7 when light rays are perpendicularly incident on an optical member having an antireflection film having a refractive index of 1.52 and a reference wavelength λ of 550 nm and designed for each optical film thickness. Yes. From FIG. 14, it can be seen that the antireflection film of the modified example has a reflectance of 0.2% or less over the entire wavelength range of 420 nm to 720 nm. In Table 7, even an optical member having an antireflection film in which each 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 whose refractive index is 1.46 shown in Table 7, 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 spectral characteristics when a light beam is perpendicularly incident on an optical member designed with an antireflection film having the refractive index of 1.52 of the same substrate as in Table 7 and the conditions shown in Table 8 below. 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 8)
Material Refractive index Optical film thickness Medium Air 1
7th layer MgF ₂ 1.39 0.243λ
6th layer ZrO ₂ + TiO ₂ 2.12 0.119λ
5th layer Al ₂ O ₃ 1.65 0.057λ
Fourth layer ZrO ₂ + TiO ₂ 2.12 0.220λ
3rd layer Al ₂ O ₃ 1.65 0.064λ
Second layer ZrO ₂ + TiO ₂ 2.12 0.057λ
1st layer Al ₂ O ₃ 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.

  Next, examples in which the antireflection films shown in Tables 6 and 7 are applied to the first to fourth examples of the present application will be described.

  In the optical system WL1 of the first example, the refractive index nd of the third negative meniscus lens L22 constituting the second lens group G2 is nd = 1.51742 as shown in Table 1, and the second lens group The refractive index nd of the fourth positive lens L25 constituting G2 is nd = 1.77250. Therefore, an antireflection film 101 (see Table 7) with a refractive index of the substrate corresponding to 1.52 is used for the lens surface on the image plane I side in the third negative meniscus lens L22, and the fourth positive lens L25 is used. An antireflection film (see Table 6) having a refractive index of the substrate of 1.74 is used for the lens surface on the image plane I side. The lens surface (14th surface) on the image plane I side of the third negative meniscus lens L22 is a concave lens surface when viewed from the image plane I, and is on the image plane I side of the fourth positive lens L25. The lens surface (the 19th surface) is a concave lens surface when viewed from the aperture stop S. Thereby, the reflected light from each lens surface (14th surface and 19th surface) can be reduced, and a ghost and flare can be reduced.

In the optical system WL2 of the second example, the refractive index nd of the first negative meniscus lens L11 constituting the first lens group G1 is nd = 1.69679 as shown in Table 2, and the first lens group The refractive index nd of the second negative meniscus lens L12 constituting G1 is nd = 1.51680. Therefore, an antireflection film 101 (see Table 6) having a refractive index of the substrate corresponding to 1.74 is used on the image surface I side lens surface of the first negative meniscus lens L11, and the second negative meniscus lens L12. An antireflection film (see Table 7) corresponding to a refractive index of the substrate of 1.52 is used for the lens surface on the object side. The image surface I side lens surface (second surface) of the first negative meniscus lens L11 is a concave lens surface when viewed from the aperture stop S, and the object side lens of the second negative meniscus lens L12. The surface (third surface) is a concave lens surface when viewed from the aperture stop S. Thereby, the reflected light from each lens surface (the 2nd surface and the 3rd surface) can be decreased, and a ghost and flare can be reduced.

  In the optical system WL3 of the third example, as shown in Table 3, the refractive index of the fourth negative meniscus lens L22 constituting the second lens group G2 is nd = 1.75519. Therefore, an antireflection film (see Table 6) corresponding to a refractive index of the substrate of 1.74 is used on the object-side lens surface of the fourth negative meniscus lens L22. The object-side lens surface (the twelfth surface) of the fourth negative meniscus lens L22 is a concave lens surface when viewed from the image plane I. Thereby, the reflected light from each lens surface (12th surface) can be decreased, and a ghost and flare can be reduced.

  In the optical system WL4 of the fourth example, the refractive index of the fourth negative meniscus lens L22 constituting the second lens group G2 is nd = 1.58144 as shown in Table 4, and the second lens group G2 The refractive index of the second positive meniscus lens L26 constituting nd is nd = 1.80400. Therefore, an antireflection film 101 (see Table 6) corresponding to a refractive index of the substrate of 1.62 is used for the lens surface on the image plane I side of the fourth negative meniscus lens L22, and the second positive meniscus lens L26 is used. An antireflection film (see Table 6) having a refractive index of the substrate corresponding to 1.85 is used for the lens surface on the object side. The lens surface (13th surface) on the image plane I side of the fourth negative meniscus lens L22 is a concave lens surface when viewed from the image plane I, and the object side lens of the second positive meniscus lens L26. The surface (19th surface) is a concave lens surface when viewed from the aperture stop S. Thereby, the reflected light from each lens surface (the 13th surface and the 19th surface) can be reduced, and a ghost and flare can be reduced.

  In the above-described embodiment, the following description can be appropriately adopted as long as the optical performance is not impaired.

  In each of the above-described embodiments, the two-group configuration is shown. 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 zooming.

  In addition, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to be a focusing lens group that performs focusing from an object at infinity to a near object. This 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). In particular, it is preferable that at least a part of the second lens group is a focusing lens group.

  In addition, the lens group or the partial lens group is moved so as to have a component in a direction perpendicular to the optical axis, or is rotated (swayed) in the in-plane direction including the optical axis to reduce image blur caused by camera shake. A vibration-proof lens group to be corrected may be used. In particular, it is preferable that at least a part of the rear group of the second lens group is a vibration-proof lens group.

Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is 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 with a resin formed 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.

  The aperture stop is preferably disposed in the vicinity of the second lens group, but the role of the aperture stop may be substituted by a lens frame without providing a member as an aperture stop.

  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.

CAM digital SLR camera (optical device)
WL optical system G1 first lens group G2 second lens group G2a front group G2b rear group S aperture stop I image plane 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 (21)

An optical system comprising a first lens group having negative refractive power and a second lens group having positive refractive power, arranged in order from the object side along the optical axis,
When focusing from an object at infinity to an object at a finite distance, the first lens group is fixed and the second lens group is moved,
The second lens group includes a front group located on the object side with respect to the stop disposed in the second lens group, and a rear group located on the image side with respect to the stop.
An antireflection film is provided on at least one of the optical surfaces of the first lens group and the second lens group, and the antireflection film includes at least one layer formed using a wet process. ,
An optical system satisfying the following conditional expression:
0.10 <f2a / f <1.70
However,
f2a: focal length of the front group of the second lens group,
f: Focal length of the optical system in an infinitely focused state. The antireflection film is a multilayer film,
The optical system according to claim 1, wherein the layer formed by using the wet process is a layer on a most surface side among layers constituting the multilayer film.   The optical system according to claim 1 or 2, wherein a refractive index of a layer formed by using the wet process is 1.30 or less.   The optical system according to any one of claims 1 to 3, wherein the antireflection film is provided on the optical surface that is concave when viewed from the diaphragm.   5. The optical system according to claim 4, wherein the concave optical surface viewed from the diaphragm is an object-side lens surface of the lenses in the first lens group and the second lens group.   5. The optical system according to claim 4, wherein the concave optical surface when viewed from the diaphragm is a lens surface on the image plane side of the lenses in the first lens group and the second lens group.   The optical system according to claim 1, wherein the antireflection film is provided on the optical surface that is concave when viewed from the image plane.   The optical system according to claim 7, wherein the optical surface that is concave when viewed from the image plane is an object-side lens surface of a lens in the second lens group.   The optical system according to claim 7, wherein the optical surface having a concave shape when viewed from the image surface is a lens surface on an image surface side of a lens in the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <f2a / f2b <1.00
However,
f2b: focal length of the rear group of the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <(− f1) / f2 <2.50
However,
f1: the focal length of the first lens group,
f2: focal length of the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.20 <f2 / f <1.55
However,
f2: focal length of the second lens group.   The optical system according to any one of claims 1 to 12, wherein the rear group of the second lens group includes at least one aspheric lens.   The optical system according to any one of claims 1 to 13, wherein the rear group of the second lens group includes two positive lenses arranged in order from the image side along the optical axis. The optical system according to claim 1, wherein the following conditional expression is satisfied.
(−f1) / f <5.0
However,
f1: Focal length of the first lens group.   The optical system according to claim 1, wherein the first lens group includes two negative lenses arranged in order from the object side along the optical axis.   The optical system according to any one of claims 1 to 16, wherein the first lens group includes at least one aspherical lens. The first lens group includes a positive lens;
The optical system according to claim 1, wherein the following conditional expressions are satisfied.
n1p> 1.800
ν1p> 28.00
However,
n1p: average value of refractive index of the positive lens,
ν1p: average value of Abbe number of the positive lens.   19. When focusing from an object at infinity to an object at a finite distance, the front group and the rear group of the second lens group move together along the optical axis. The optical system according to one item. An optical device including an optical system that forms an image of an object on a predetermined surface,
20. The optical apparatus according to claim 1, wherein the optical system is an optical system according to any one of claims 1 to 19. An optical system manufacturing method in which a first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the object side along the optical axis,
When focusing from an object at infinity to an object at a finite distance, the first lens group is fixed and the second lens group is moved,
The second lens group includes a front group located on the object side with respect to the stop disposed in the second lens group, and a rear group located on the image side with respect to the stop.
An antireflection film is provided on at least one of the optical surfaces of the first lens group and the second lens group, and the antireflection film includes at least one layer formed using a wet process. ,
An optical system manufacturing method characterized by satisfying the following conditional expression:
0.10 <f2a / f <1.70
However,
f2a: focal length of the front group of the second lens group,
f: Focal length of the optical system in an infinitely focused state.

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