JP2008233585A - Zoom lens, optical device and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has high optical performance even though having a wide view angle and wherein a ghost and a flare are reduced. <P>SOLUTION: In the zoom lens provided with, from an object side in order along an optical axis, a first lens group G1 having negative refractive force, a second lens group G2 having positive refractive force, a third lens group G3 having negative refractive force, a fourth lens group G4 having positive refractive force and a fifth lens group G5 having positive refractive force, transverse magnification and the like of the fifth lens group G5 satisfy a prescribed conditional formula, a reflection preventing film is provided on at least one surface of optical surfaces of the first lens group G1 and the reflection preventing film includes at least one layer formed by using a wet process. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zoom lens suitable for a single-lens reflex camera, a digital camera, or the like.

Conventionally, as a large-aperture wide-angle zoom lens used in a single-lens reflex camera, a digital camera, or the like, a 4-group zoom lens or a 5-group zoom lens preceded by a lens group having negative refractive power has been disclosed (for example, a patent) Reference 1 and Patent Reference 2). In recent years, with respect to such zoom lenses, not only aberration performance but also ghost and flare, which are one of the factors that impair optical performance, have become increasingly demanding, and therefore anti-reflection applied to the lens surface. Higher performance is required for the film, and multilayer film design technology and multilayer film formation technology continue to advance to meet the demand (see, for example, Patent Document 3).
JP 2001-174704 A JP 2001-318314 A JP 2000-356704 A

  Conventionally, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, In the zoom lens equipped with the zoom lens, although the angle of view has achieved 80 degrees or more in the wide-angle end state, there has been a problem that it is very difficult to satisfactorily correct astigmatism and coma. For example, in the disclosure example of Patent Document 1, although the lens group having negative refractive power is a 5-group zoom lens preceded by a large aperture with an aperture ratio of about 2.8, the maximum angle of view is only about 75 degrees. In addition, in the disclosure example of Patent Document 2, although the maximum field angle is more than 100 degrees in the 5-group zoom lens preceded by the lens group having negative refractive power, the zoom ratio is as small as less than 2.7 times, The F number is only about 4.

  In addition, there is a problem that reflected light that becomes ghost or flare is likely to be generated from the optical surface of the front lens in such a zoom lens.

  The present invention has been made in view of such a problem, and provides a zoom lens, an optical apparatus, and an imaging method that have high optical performance while having a wide angle of view and further reduce ghost and flare. The purpose is to do.

  In order to achieve such an object, the zoom lens according to the first aspect of the present invention includes a first lens group having a negative refractive power and a second lens having a positive refractive power, which are arranged in order from the object side along the optical axis. A lens group, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power, from the wide-angle end state to the telephoto end state When zooming, the first lens group once moves to the image side and then moves to the object side, the distance between the first lens group and the second lens group is reduced, and the second lens group and the second lens group are reduced. The distance between the third lens group is increased, the distance between the third lens group and the fourth lens group is reduced, and the distance between the fourth lens group and the fifth lens group is increased. .

In the wide-angle end state, the fifth lens is measured in the optical axis direction from the rear principal point of the fourth lens group, where the focal length of the entire system is fw and the lateral magnification of the fifth lens group is β5. When the front principal point position of the group is S45w, the following expressions 0.6 <β5 <0.9 and S45w / fw <−0.15
The antireflection film is provided on at least one of the optical surfaces in the first lens group, and the antireflection film includes at least one layer formed by using a wet process. Is done.

  In the above-described invention, it is preferable that the antireflection film is a multilayer film, and the layer formed by using the wet process is the most surface layer among the layers constituting the multilayer film.

In the above-described invention, when the refractive index of the layer formed using the wet process is nd, the following formula nd ≦ 1.30
It is preferable to satisfy the following conditions.

  A zoom lens according to a second aspect of the invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, arranged in order from the object side along the optical axis, and a negative lens group. A third lens group having a refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power, and at the time of zooming from the wide-angle end state to the telephoto end state, The first lens group once moves to the image side and then moves to the object side, the distance between the first lens group and the second lens group is reduced, and the distance between the second lens group and the third lens group. Is enlarged, the distance between the third lens group and the fourth lens group is reduced, and the distance between the fourth lens group and the fifth lens group is enlarged.

In the wide-angle end state, the focal length of the entire system is fw, the lateral magnification of the fifth lens group is β5, and the fifth lens group is measured in the optical axis direction from the rear principal point of the fourth lens group. Where S45w is the front principal point position of the following equation: 0.6 <β5 <0.9 and S45w / fw <−0.15
The antireflection film is provided on at least one of the optical surfaces in the first lens group, and the antireflection film includes at least one layer having a refractive index of 1.30 or less. Composed.

  In the above-described invention, it is preferable that the antireflection film is a multilayer film, and the layer having a refractive index of 1.30 or less is the most surface layer among the layers constituting the multilayer film.

  In each of the above-described inventions, it is preferable that an aperture stop is disposed closer to the object side than the most object side surface in the third lens group, and the optical surface is concave with respect to the aperture stop.

In each of the above-described inventions, when the F number of the entire system in the telephoto end state is Fnot, the focal length of the entire system in the telephoto end state is ft, and the focal length of the first lens group is f1, −1.8 <f1 × Fnot / ft <−1.0
It is preferable to satisfy the following conditions.

  In each of the above-described inventions, the fifth lens group includes a cemented positive lens composed of a positive lens and a negative lens that are arranged in order from the object side along the optical axis and have a convex surface facing the object side. It is preferable.

  In each of the above inventions, the fourth lens group includes a cemented positive lens of a negative lens and a biconvex positive lens arranged in order from the object side along the optical axis, and one or more positive lenses. It is preferable that it is comprised.

  In each of the above-described inventions, at least one of the fourth lens group and the fifth lens group includes at least one aspheric lens, and the aspheric lens goes from the lens center to the periphery. Accordingly, it is preferable that the positive refractive power becomes weaker.

In each of the above-described inventions, the second lens group includes at least one aspheric lens and at least one positive lens, and the Abbe number of the positive lens in the second lens group is determined. When νd, the following equation νd> 70
It is preferable to satisfy the following conditions.

In each of the above-described inventions, the second lens group includes a front group having a positive refractive power and a rear group having a positive refractive power arranged in order from the object side along the optical axis, and is infinite. Focusing from a far object to a short distance object is performed by moving the front group along the optical axis. When the focal length of the front group is f2a and the focal length of the rear group is f2b, the following formula 1 .1 <f2a / f2b <1.5
It is preferable to satisfy the following conditions.

  The optical apparatus according to the present invention is an optical apparatus having a zoom lens for forming an image of an object on a predetermined image plane, wherein the zoom lens is a zoom lens according to each invention.

  In addition, the imaging method according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a negative refraction arranged in order from the object side along the optical axis. A zoom lens including a third lens group having a power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power; An image forming method for forming an image on the top, wherein when the zoom is changed from the wide-angle end state to the telephoto end state, the first lens group once moves to the image side and then moves to the object side. The distance between the second lens group is reduced, the distance between the second lens group and the third lens group is enlarged, the distance between the third lens group and the fourth lens group is reduced, and the second lens group is reduced. An interval between the four lens groups and the fifth lens group is increased.

In the wide-angle end state, the focal length of the entire system is fw, the lateral magnification of the fifth lens group is β5, and the fifth lens group is measured in the optical axis direction from the rear principal point of the fourth lens group. Where S45w is the front principal point position of the following equation: 0.6 <β5 <0.9 and S45w / fw <−0.15
The anti-reflection film is provided on at least one of the optical surfaces in the first lens group, and the anti-reflection film includes at least one layer formed using a wet process. It is characterized by that.

  According to the present invention, it is possible to obtain high optical performance while having a wide angle of view, and to further reduce ghosts and flares.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. A single-lens reflex camera CAM provided with a zoom lens according to the present application is shown in FIG. This single-lens reflex camera CAM includes a zoom lens ZL, a mirror M, an image pickup device CCD for photographing, a focusing screen F, a pentaprism P, and an eyepiece lens EL. The mirror M, the image sensor CCD, the focusing screen F, the pentaprism P, and the eyepiece lens EL are built in the camera body B, and the zoom lens ZL is detachably attached to the camera body B.

  The zoom lens ZL forms an image of a subject (object) on the image sensor CCD or the focusing screen F. The mirror M is inserted at an angle of 45 degrees with respect to the optical axis passing through the zoom lens ZL. In normal times (in a shooting standby state), the mirror M reflects light from the subject passing through the zoom lens ZL to reflect the focus plate. An image is formed on F, and when the shutter is released, it is in a mirror-up state and jumps up so that light from the subject passing through the zoom lens ZL forms an image on the image sensor CCD. That is, the image sensor CCD and the focusing screen F are disposed at optically conjugate positions.

  The pentaprism P reverses the subject image (inverted image) on the focusing screen F formed by the zoom lens ZL vertically and horizontally to make it an erect image, and the eyepiece EL makes the subject image converted into an erect image by the pentaprism P. Is imaged on an eye point (not shown). Thereby, the subject image formed on the focusing screen F by the zoom lens ZL can be observed by the eyepiece lens EL.

  By the way, as shown in FIG. 1, for example, the zoom lens ZL includes a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power arranged in order from the object side along the optical axis. G2, a third lens group G3 having a negative refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. When zooming from the wide-angle end state to the telephoto end state, the first lens group G1 once moves to the image side and then moves to the object side, and the distance between the first lens group G1 and the second lens group G2 is reduced. Then, the distance between the second lens group G2 and the third lens group G3 is enlarged, the distance between the third lens group G3 and the fourth lens group G4 is reduced, and the fourth lens group G4 and the fifth lens group G5 The interval between is increased.

  In FIG. 1, a surface on which an image of a subject (object) is formed by the zoom lens ZL is indicated by an image plane I. In addition, an antireflection film is provided on at least one of the optical surfaces in the first lens group G1, and the antireflection film is configured to include at least one layer formed by using a wet process, which will be described in detail later. Is done.

  In the wide-angle end state, the fifth lens group measured in the optical axis direction from the rear principal point of the fourth lens group G4 with the focal length of the entire system as fw and the lateral magnification of the fifth lens group G5 as β5. When the front principal point position of G5 is S45w, the conditions represented by the following conditional expressions (1) and (2) are satisfied.

0.6 <β5 <0.9 (1)
S45w / fw <−0.15 (2)

  In general, a multi-group zoom lens preceded by a lens group having negative refractive power is suitable for a large-aperture wide-angle zoom lens. However, in order to have an angle of view exceeding 80 degrees and a zoom ratio of about 2.8 times and a large aperture ratio of F number of about 2.8, sufficient performance can be obtained with a four-group configuration. Can not. Therefore, it is necessary to consider a configuration including five groups or more. However, when the number of groups is six or more, the mechanism for zooming becomes complicated and large. On the other hand, in the case of the five-group configuration, if the fifth lens group is a lens group having negative refractive power, the lateral magnification of the fifth lens group exceeds 1, so that the aberration from the first lens group to the fourth lens group Therefore, it is difficult to sufficiently perform aberration correction in order to secure the above performance.

  On the other hand, in the zoom lens ZL according to the present embodiment, the fifth lens group G5 is a lens group having a positive refractive power, and the power arrangement of the entire five groups is optimized, thereby achieving a wide angle of view. The zoom lens ZL having high optical performance and an optical apparatus (single-lens reflex camera CAM) including the zoom lens ZL can be provided. Further, an antireflection film is provided on at least one of the optical surfaces in the first lens group G1, and the antireflection film includes at least one layer formed by using a wet process. Ghosts and flares can be further reduced.

  Here, the conditional expression (1) will be described. Conditional expression (1) defines the lateral magnification of the fifth lens group G5 within an appropriate range. By making the lateral magnification of the fifth lens group G5 positive and 1 or less as in the conditional expression (1), the combined focal length from the first lens group G1 to the fourth lens group G4 is shortened by the fifth lens group G5. can do. Therefore, the combined focal length from the first lens group G1 to the fourth lens group G4 can be made longer than when the fifth lens group G5 is included. As a result, the combined focal length from the first lens group G1 to the fourth lens group G4 can be set longer, and the generated aberration can be reduced.

  When the condition exceeds the upper limit value of the conditional expression (1), the refractive power by the fifth lens group G5 is reduced, and the above effect is diminished so as to satisfactorily correct coma, distortion, and astigmatism. Dependence on the lens group increases, and it becomes difficult to correct aberration variation from the wide-angle end state to the telephoto end state in a balanced manner. On the other hand, when the condition is lower than the lower limit value of the conditional expression (1), the focal length of the fifth lens group G5 is shortened, the spherical aberration and coma aberration of the fifth lens group G5 itself are increased, and the desired performance and F It becomes difficult to secure enough numbers. In order to secure the effect of the present application, it is preferable to set the upper limit of conditional expression (1) to 0.85. In order to secure the effect of the present application, it is preferable to set the lower limit of conditional expression (1) to 0.75.

  Conditional expression (2) defines the front principal point position of the fifth lens group G5 measured in the optical axis direction from the rear principal point of the fourth lens group G4 within an appropriate range. In the fifth lens group G5, it is desirable that the front principal point position of the fifth lens group G5 measured from the rear principal point of the fourth lens group G4 be as close as possible to the object side as in the conditional expression (2). Accordingly, the focal lengths of the fourth lens group G4 and the fifth lens group G5 required for obtaining the lateral magnification of the conditional expression (1) can be set longer, and the fourth lens group G4 and the fifth lens group are set. Spherical aberration generated by G5, particularly coma aberration at the wide-angle end state, can be reduced, and a desired high field angle, high zoom ratio, large aperture ratio, and high optical performance can be obtained. In order to secure the effect of the present application, it is preferable to set the upper limit of conditional expression (2) to −0.3.

  In addition, when the antireflection film is a multilayer film, the layer formed using the wet process is preferably the most surface 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.

  Moreover, when the refractive index of the layer formed using the 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.

  Further, by providing an aperture stop closer to the object side than the most object side surface in the third lens group G3, various aberrations such as spherical aberration can be favorably corrected, but an antireflection film is provided. The optical surface is preferably concave with respect to such an aperture stop. In this way, a ghost is easily generated on the concave surface with respect to the aperture stop, so that ghost and flare can be effectively reduced.

  Note that the antireflection film is not limited to a wet process, and may include at least one layer having a refractive index of 1.30 or less (by a dry process or the like). Even if it does in this way, the effect similar to the case where a wet process is used can be acquired. 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. The optical surface on which the antireflection film is provided is preferably concave with respect to the aperture stop.

  Further, when the F number of the entire system in the telephoto end state is Fnot, the focal length of the entire system in the telephoto end state is ft, and the focal length of the first lens group G1 is f1, the following conditional expression (3) is satisfied. It is preferable that the conditions expressed are satisfied.

  −1.8 <f1 × Fnot / ft <−1.0 (3)

  Conditional expression (3) defines the focal length of the first lens group G1 within an appropriate range. When the condition exceeds the upper limit value of the conditional expression (3), the refractive power of the first lens group G1 is increased, which is advantageous for reducing the outer diameter of the lens and ensuring the back focus. It is difficult to correct the coma aberration and distortion aberration, and spherical aberration and coma aberration in the telephoto end state in a balanced manner. On the other hand, when the condition is less than the lower limit value of conditional expression (3), the lens outer diameter increases, which is not preferable. In addition, distortion and coma become worse, and high optical performance cannot be obtained. In order to secure the effect of the present application, it is preferable to set the upper limit of conditional expression (3) to −1.3. In order to secure the effect of the present application, it is preferable to set the lower limit of conditional expression (3) to −1.7.

  The fifth lens group G5 preferably includes a cemented positive lens composed of a positive lens and a negative lens, which are arranged in order from the object side along the optical axis and have a convex surface directed toward the object side.

  By adopting such a configuration, there are many advantages over a configuration in which a negative lens and a positive lens are joined in order from the object side, which is often observed in the past. It becomes so-called telephoto lens type in order from the object side, that is, a positive lens and a negative lens, and it becomes easy to bring the front principal point position of the fifth lens group G5 closer to the object side, so it is easy to satisfy the conditional expression (2). Further, by bringing the negative lens to the image plane side, the effect of correcting the insufficient correction of distortion on the wide angle side due to the first lens group G1 being a negative lens, and the fluctuation of the image plane due to zooming Correction is expected. Also, from the viewpoint of the amount of peripheral light, the positive lens of the fifth lens group G5 has a strong effect of reducing the peripheral light beam height, which is advantageous for reducing the lens diameter.

  The fourth lens group G4 is composed of a cemented positive lens of a negative lens and a biconvex positive lens arranged in order from the object side along the optical axis, and one or more positive lenses. preferable.

  By adopting such a configuration, there are more advantages than a configuration in which a positive lens and a negative lens are joined in order from the object side, which is often seen in the past. Contrary to the case of the fifth lens group G5, in the order from the object side, a negative lens, a positive lens, and a positive lens form a so-called retrofocus lens type, and the rear principal point position of the fourth lens group G4 is defined as the image plane. Since it becomes easy to approach the side, conditional expression (2) is easily satisfied. In addition, the fourth lens group G4 and the fifth lens group G5 as a whole are front-back symmetric optical systems having negative lenses on the front and rear sides, and are lenses that are strong against a wide angle of view. This is a lens type often used in eyepiece systems that require a wide angle of view and flatness of the image plane. Thereby, it is possible to form an image on the image plane with almost no aberration with respect to the substantially parallel light beam emitted from the third lens group G3.

  In addition, at least one of the fourth lens group G4 and the fifth lens group G5 includes at least one aspheric lens, and the aspheric lens has a positive refractive power as it goes from the lens center to the periphery. It is preferable to become weak. By including an aspherical surface in the positive lens of the fourth lens group G4 or the fifth lens group G5, it is possible to effectively correct especially spherical aberration, coma and peripheral curvature at peripheral image height.

  The second lens group G2 includes at least one aspheric lens and at least one positive lens. The d-line (wavelength λ = 587.6 nm) of the positive lens in the second lens group G2. It is preferable that the condition represented by the following conditional expression (4) is satisfied when the Abbe number with respect to νd is νd.

  νd> 70 (4)

  Conditional expression (4) defines the configuration of the second lens group G3. In the zoom type in which the first lens group G1 has negative power, the second lens group G2 has the highest marginal light beam (the light beam having the highest incident height among the incident light beams parallel to the optical axis). The effect on upper chromatic aberration is very large. Therefore, if a positive lens satisfying conditional expression (4) is used, axial chromatic aberration can be corrected well. However, many glass materials satisfying conditional expression (4) generally have a low refractive index, and correction of spherical aberration tends to be insufficient. Therefore, by using an aspheric lens in combination with the second lens group G2, axial chromatic aberration and spherical aberration can be corrected satisfactorily at the same time. In order to secure the effect of the present application, it is preferable to set the lower limit of conditional expression (4) to 80.

  The second lens group G2 includes a front group having a positive refractive power and a rear group having a positive refractive power arranged in order from the object side along the optical axis. Focusing is performed by moving the front group along the optical axis, and when the focal length of the front group is f2a and the focal length of the rear group is f2b, the condition expressed by the following conditional expression (5) Is preferably satisfied.

  1.1 <f2a / f2b <1.5 (5)

  Conditional expression (5) defines the ratio of the focal lengths of the front group and the rear group of the second lens group G2. When the condition is lower than the lower limit value of the conditional expression (5), the difference in the focusing movement amount between the wide-angle side and the telephoto side becomes large, and the air space necessary for focusing becomes large. In addition, the variation of spherical aberration at the time of focusing becomes large, and high optical performance cannot be obtained. On the other hand, when the condition exceeds the upper limit value of the conditional expression (5), the difference in focusing movement amount between the wide angle side and the telephoto side becomes large, and the air space necessary for focusing becomes large. Absent. Or, spherical aberration deteriorates and high optical performance cannot be obtained.

  In order to secure the effect of the present application, it is preferable to set the upper limit of conditional expression (5) to 1.4. In order to further secure the effect of the present application, it is more preferable to set the upper limit of conditional expression (5) to 1.3. In order to secure the effect of the present application, it is preferable to set the lower limit of conditional expression (5) to 1.15.

  Embodiments of the present application will be described below with reference to the accompanying drawings. The first to fourth examples described below are examples of the zoom lens according to the present application. Details of the antireflection film provided on these zoom lenses will be described separately after each example.

(First embodiment)
The first embodiment of the present application will be described below. FIG. 1 is a lens configuration diagram of a zoom lens according to the first example. The zoom lens ZL according to the first example includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative lens arranged in order from the object side along the optical axis. And a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power, and from the wide-angle end state W to the telephoto end state T. During zooming, the first lens group G1 once moves to the image plane I side and then moves to the object side, and the second lens group G2, the third lens group G3, and the fourth lens group G4 all move to the object side. The fifth lens group G5 is fixed.

  The first lens group G1 is arranged in order from the object side along the optical axis, and has a negative meniscus lens L11 having a convex surface facing the object side and an aspheric surface on the image surface I side, and a biconcave negative lens L12. And a positive meniscus lens L13 having a convex surface facing the object side, and an antireflection film is provided on the lens surface on the image plane I side of the negative meniscus lens L11 and the lens surface on the object side of the negative lens L12.

  The second lens group G2 includes a front group G2a having a positive refractive power and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The front group G2a includes a biconvex positive lens L21 having an aspheric surface on the object side surface, and a negative cemented lens L22 of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens. The rear group G2b includes a biconvex positive lens L23.

  The third lens group G3 is arranged in order from the object side along the optical axis, a negative cemented lens L31 of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and a concave surface facing the object side And a negative meniscus lens L32. The fourth lens group G4 includes, in order from the object side along the optical axis, a positive cemented lens L41 of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens, and a surface on the image plane I side. And a biconvex positive lens L42 having an aspherical surface. The fifth lens group G5 includes a positive cemented lens L51 including a positive meniscus lens having a convex surface directed toward the object side and a negative meniscus lens having a convex surface directed toward the object side.

  Note that focusing from an infinitely distant object to a close object is performed by moving the front group G2a in the image plane I direction. The aperture stop S is disposed adjacent to the object side from the most object side surface in the third lens group G3, and is integrated with the third lens group G3 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  Tables 1 to 4 shown below are tables listing values of specifications in the first to fourth examples. In [Overall specifications] in each table, f indicates a focal length, FNO indicates an F number, and 2ω indicates an angle of view (unit: degree). In [Lens Data], the surface number is the order of the lens surfaces counted from the object side, r is the radius of curvature of the lens surfaces, d is the surface spacing, and nd is for the d-line (wavelength λ = 586.6 nm). The refractive index νd represents the Abbe number with respect to the d-line (wavelength λ = 586.6 nm).

  Further, an aspherical surface in [lens data] is marked with * and the paraxial radius of curvature is indicated in the column of the radius of curvature r, and Κ and each aspherical coefficient are described in the column of [Aspherical data]. The aspherical surface shown in [Aspherical surface data] has a height in the direction perpendicular to the optical axis as y, a displacement amount in the optical axis direction at the height y as X (y), and the radius of curvature of the reference spherical surface (paraxial) When the radius of curvature is r, the cone coefficient is Κ, and the n-th order (n = 4, 6, 8, 10, 12) aspherical coefficient is Cn, the following aspherical expression is used.

X (y) = (y ² / r) / {1+ (1−Κ × y ² / r ² ) ^1/2 }
+ C4 × y ⁴ + C6 × y ⁶ + C8 × y ⁸ + C10 × y ¹⁰ + C12 × y ¹²

  In [variable interval data], the focal length f and each variable interval in the wide-angle end state, the intermediate focal length state, and the telephoto end state are shown. [Condition corresponding value] indicates the value of each conditional expression. Note that the radius of curvature “r = ∞” indicates a plane, and the refractive index of air nd = 1.00000 is omitted.

  In all the following specification values, “mm” is generally used as the focal length f, radius of curvature r, surface interval d and other lengths, etc. unless otherwise specified, but the optical system is proportional. Even if it is enlarged or proportionally reduced, the same optical performance can be obtained. Further, the unit is not limited to “mm”, and other appropriate units may be used. The description of these symbols is the same in the other examples below.

  Table 1 below shows specifications in the first embodiment. The surface numbers 1 to 28 in Table 1 correspond to the surfaces 1 to 28 in FIG.

(Table 1)
[Overall specifications]
f = 24.78 to 67.7
2ω = 82.2 to 35.4
FNO = 2.91
[Lens data]
Surface number r d nd νd
Object ∞ ∞
1 148.55 3.2 1.744429 49.52
2 * 26.69 15.05
3-140.00 2.20 1.618000 63.33
4 170.00 0.20
5 59.74 4.00 1.860740 23.06
6 96.63 D6
7 * 58.54 0.09 1.553890 38.09
8 60.61 5.13 1.816000 46.62
9 -4381.42 8.35
10 79.18 1.54 1.846660 23.78
11 30.73 8.00 1.456000 91.20
12 -637.46 D12
13 59.59 4.84 1.882997 40.76
14 -925.95 D14
15 Aperture stop 1.65
16 -468.53 3.00 1.860740 23.06
17 -41.13 1.15 1.729157 54.68
18 58.99 3.13
19 -40.45 1.15 1.729157 54.68
20 -129.43 D20
21 249.89 1.20 1.846660 23.78
22 61.26 6.50 1.497000 81.61
23 -33.18 0.20
24 499.94 3.25 1.495500 81.36
25 * -150.00 D25
26 37.97 4.80 1.497000 81.61
27 337.67 1.40 1.805181 25.42
28 69.31 Bf
Image plane ∞
[Aspherical data]
Surface number Κ C4 C6 C8
2 -0.18970 × 10 ^-1 + 3.9947 × 10 ^-6 -1.0319 × 10 ^-9 + 7.4218 × 10 ^-12
7 -2.2290 × 10 ^-1 -1.1042 × 10 ^-7 -4.2572 × 10 ^-10 + 2.1178 × 10 ^-12
25 -9.5432 + 3.2539 × 10 ^-6 + 1.1325 × 10 ^-9 + 4.9837 × 10 ^-12
Surface number C10 C12
2 -1.0720 × 10 ^-14 + 6.8060 × 10 ^-18
7 -2.0591 × 10 ^-15 0.0000
25 -8.3197 × 10 ^-15 0.0000
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state f 24.78 51.92 67.70
D6 48.16 9.18 1.85
D12 7.59 7.59 7.59
D14 1.35 20.98 28.94
D20 16.60 6.77 1.60
D25 1.50 14.05 24.18
[Conditional value]
Conditional expression (1) β5 = 0.82
Conditional expression (2) S45w / fw = −0.47
Conditional expression (3) f1 × Fnot / ft = −1.64
Conditional expression (4) νd = 91.2
Conditional expression (5) f2a / f2b = 1.21

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (5) are satisfied.

  FIG. 2A is a diagram illustrating various aberrations in the wide-angle end state of the zoom lens according to Example 1 in the infinitely focused state, and FIG. 2B is a diagram illustrating various aberrations in the intermediate focal length state. FIG. 2C is a diagram showing various aberrations in the telephoto end state. In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the incident angle of the chief ray. D shows the aberration curve of the d-line (wavelength λ = 587.6 nm), and G shows the aberration curve of the g-line (wavelength λ = 435.8 nm).

  In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the spherical aberration diagram, the solid line indicates spherical aberration, and the broken line indicates sine condition. Further, the magnification chromatic aberration diagram shows the g-line with respect to the d-line. The description of these symbols is the same in the other examples below. As is apparent from the aberration diagrams of FIGS. 2A, 2B, and 2C, the zoom lens according to the first example has excellent correction of various aberrations and is excellent. It can be seen that it has imaging performance.

  Further, as shown in FIG. 3, when the light beam BM from the object side enters the zoom lens ZL as shown, the object side lens surface (the first ghost generation surface in the negative lens L12, whose surface number is 3), the reflected light is reflected again by the lens surface on the image plane I side of the negative meniscus lens L11 (the second ghost generation surface and its surface number is 2) and reaches the image plane I. A ghost is generated. The first ghost generation surface 3 and the second ghost generation surface 2 are both concave with respect to the aperture stop. A ghost can be effectively reduced by forming an antireflection film corresponding to a wide incident angle in a wider wavelength range on such a surface.

(Second embodiment)
The second embodiment of the present application will be described below. FIG. 4 is a lens configuration diagram of a zoom lens according to Example 2. The zoom lens ZL according to the second example includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative lens arranged in order from the object side along the optical axis. And a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power, and from the wide-angle end state W to the telephoto end state T. During zooming, the first lens group G1 once moves to the image plane I side and then moves to the object side, and the second lens group G2, the third lens group G3, and the fourth lens group G4 all move to the object side. The fifth lens group G5 is fixed.

  The first lens group G1 is arranged in order from the object side along the optical axis, and has a negative meniscus lens L11 having a convex surface facing the object side and an aspheric surface on the image surface I side, and a biconcave negative lens L12. And a positive meniscus lens L13 having a convex surface facing the object side, and an antireflection film is provided on the lens surface on the image plane I side of the negative meniscus lens L11.

  The second lens group G2 includes a front group G2a having a positive refractive power and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The front group G2a includes a biconvex positive lens L21 having an aspheric surface on the object side surface, and a negative cemented lens L22 of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens. The rear group G2b includes a biconvex positive lens L23.

  The third lens group G3 is arranged in order from the object side along the optical axis, a negative cemented lens L31 of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and a concave surface facing the object side And a negative meniscus lens L32. The fourth lens group G4 includes, in order from the object side along the optical axis, a positive cemented lens L41 of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens, and a surface on the image plane I side. And a biconvex positive lens L42 having an aspherical surface. The fifth lens group G5 includes a positive cemented lens L51 including a positive meniscus lens having a convex surface directed toward the object side and a negative meniscus lens having a convex surface directed toward the object side.

  Note that focusing from an infinitely distant object to a close object is performed by moving the front group G2a in the image plane I direction. The aperture stop S is disposed adjacent to the object side from the most object side surface in the third lens group G3, and is integrated with the third lens group G3 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  Table 2 below shows specifications in the second embodiment. The surface numbers 1 to 28 in Table 2 correspond to the surfaces 1 to 28 in FIG.

(Table 2)
[Overall specifications]
f = 24.78 to 67.7
2ω = 82.2 to 35.4
FNO = 2.91
[Lens data]
Surface number r d nd νd
Object ∞ ∞
1 125.62 3.20 1.744429 49.52
2 * 26.88 14.95
3-140.00 2.20 1.618000 63.33
4 164.53 0.20
5 53.97 4.00 1.846660 23.78
6 75.60 D6
7 * 59.74 0.10 1.553890 38.09
8 62.41 5.00 1.772500 49.60
9 -762.32 6.00
10 113.72 1.50 1.761821 26.52
11 30.03 8.30 1.497820 82.56
12 -315.20 D12
13 60.55 4.84 1.882997 40.76
14 -474.60 D14
15 Aperture stop 1.65
16 -1292.82 3.05 1.846660 23.78
17 -36.86 1.15 1.729157 54.68
18 54.86 3.30
19 -39.10 1.15 1.729157 54.68
20 -139.40 D20
21 285.08 1.20 1.805181 25.42
22 46.73 7.11 1.497820 82.56
23 -32.76 0.20
24 508.57 2.80 1.516330 64.14
25 * -127.81 D25
26 39.24 5.05 1.497820 82.56
27 599.11 1.40 1.805181 25.42
28 74.82 Bf
Image plane ∞
[Aspherical data]
Surface number Κ C4 C6 C8
2 -1.4380 × 10 ^-1 + 3.8749 × 10 ^-6 -2.2610 × 10 ^-10 + 6.0954 × 10 ^-12
7 -4.5880 × 10 ^-1 -2.4347 × 10 ^-7 -1.2907 × 10 ^-10 + 1.7953 × 10 ^-12
25 +13.380 + 3.3574 × 10 ^-6 + 3.1407 × 10 ^-9 -8.1398 × 10 ^-12
Surface number C10 C12
2 -8.9785 × 10 ^-15 + 6.5290 × 10 ^-18
7 -1.9730 × 10 ^-15 0.0000
25 + 1.4058 × 10 ^-14 0.0000
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state f 24.78 51.92 67.70
D6 47.46 9.09 1.87
D12 7.35 7.35 7.35
D14 1.35 19.10 26.58
D20 16.24 6.48 1.60
D25 1.40 14.23 23.79
[Conditional value]
Conditional expression (1) β5 = 0.82
Conditional expression (2) S45w / fw = −0.50
Conditional expression (3) f1 × Fnot / ft = −1.62
Conditional expression (4) νd = 82.60
Conditional expression (5) f2a / f2b = 1.23

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (5) are satisfied.

  FIG. 5A is a diagram of various aberrations in the wide-angle end state of the zoom lens according to Example 2 in the infinitely focused state, and FIG. 5B is a diagram of various aberrations in the intermediate focal length state. FIG. 5C shows various aberrations in the telephoto end state. As is apparent from the respective aberration diagrams of FIGS. 5A, 5B, and 5C, the zoom lens according to Example 2 is excellent in correcting various aberrations. It can be seen that it has imaging performance.

(Third embodiment)
The third embodiment of the present application will be described below. FIG. 6 is a lens configuration diagram of a zoom lens according to Third Example. The zoom lens ZL according to the third example includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative lens arranged in order from the object side along the optical axis. And a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power, and from the wide-angle end state W to the telephoto end state T. During zooming, the first lens group G1 once moves to the image plane I side and then moves to the object side, and the second lens group G2, the third lens group G3, and the fourth lens group G4 all move to the object side. The fifth lens group G5 is fixed.

  The first lens group G1 is arranged in order from the object side along the optical axis, and has a negative meniscus lens L11 having a convex surface facing the object side and an aspheric surface on the image surface I side, and a biconcave negative lens L12. And a positive meniscus lens L13 having a convex surface facing the object side, and an antireflection film is provided on the object side lens surface of the positive meniscus lens L13.

  The second lens group G2 includes a front group G2a having a positive refractive power and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The front group G2a includes a positive meniscus lens L21 having an aspheric surface on the object side surface, and a positive cemented lens L22 of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens. The rear group G2b Is composed of a biconvex positive lens L23.

  The third lens group G3 is arranged in order from the object side along the optical axis, a negative cemented lens L31 of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and a concave surface facing the object side And a negative meniscus lens L32. The fourth lens group G4 includes, in order from the object side along the optical axis, a positive cemented lens L41 of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens, and a surface on the image plane I side. And a positive meniscus lens L42 having an aspherical surface and a concave surface facing the object side. The fifth lens group G5 includes a positive cemented lens L51 including a biconvex positive lens and a biconcave negative lens.

  Note that focusing from an infinitely distant object to a close object is performed by moving the front group G2a in the image plane I direction. The aperture stop S is disposed adjacent to the object side from the most object side surface in the third lens group G3, and is integrated with the third lens group G3 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  Table 3 below shows specifications in the third embodiment. The surface numbers 1 to 29 in Table 3 correspond to the surfaces 1 to 29 in FIG.

(Table 3)
[Overall specifications]
f = 24.78 to 67.7
2ω = 82.2 to 35.4
FNO = 2.92
[Lens data]
Surface number r d nd νd
Object ∞ ∞
1 124.77 3.00 1.744429 49.52
2 * 27.48 14.50
3-140.00 2.20 1.618000 63.33
4 170.00 0.20
5 52.25 4.00 1.846660 23.78
6 69.81 D6
7 * 60.50 0.10 1.553890 38.09
8 63.21 4.78 1.772500 49.60
9 12779.25 5.40
10 111.76 1.75 1.761821 26.52
11 30.78 8.40 1.497820 82.56
12 -209.11 D12
13 61.32 4.70 1.882997 40.76
14 -438.25 D14
15 Aperture stop 1.65
16 -669.73 3.40 1.846660 23.78
17 -36.02 1.10 1.696797 55.53
18 60.85 3.05
19 -42.21 1.05 1.729157 54.68
20 -274.34 D20
21 234.05 1.10 1.805181 25.42
22 42.64 7.14 1.497820 82.56
23 -33.19 0.20
24-605.58 2.50 1.772500 49.60
25 * -136.80 0.08 1.553890 38.09
26 -130.93 D26
27 40.74 5.15 1.497820 82.56
28 -910.23 1.40 1.805181 25.42
29 87.90 Bf
Image plane ∞
[Aspherical data]
Surface number Κ C4 C6 C8
2 -1.5280 × 10 ^-1 + 3.7704 × 10 ^-6 -5.3623 × 10 ^-10 + 6.7695 × 10 ^-12
7 -1.8520 × 10 ^-1 -4.3765 × 10 ^-7 -2.3315 × 10 ^-10 + 2.3862 × 10 ^-12
25 +11.437 + 2.8992 × 10 ^-6 + 3.8341 × 10 ^-9 -1.2929 × 10 ^-11
Surface number C10 C12
2 -1.0431 × 10 ^-14 + 7.4566 × 10 ^-18
7 -2.8617 × 10 ^-15 0.0000
25 + 2.1850 × 10 ^-14 0.0000
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state f 24.78 52.00 67.70
D6 48.09 9.21 1.85
D12 7.53 7.53 7.53
D14 1.35 18.90 26.53
D20 16.45 6.51 1.60
D26 1.30 14.47 23.86
[Conditional value]
Conditional expression (1) β5 = 0.82
Conditional expression (2) S45w / fw = −0.44
Conditional expression (3) f1 × Fnot / ft = −1.65
Conditional expression (4) νd = 82.60
Conditional expression (5) f2a / f2b = 1.25

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (5) are satisfied.

  FIG. 7A is a diagram illustrating various aberrations in the wide-angle end state of the zoom lens according to Example 3 in the infinite focus state, and FIG. 7B is a diagram illustrating various aberrations in the intermediate focal length state. FIG. 7C shows various aberrations in the telephoto end state. As is apparent from the aberration diagrams of FIGS. 7A, 7B, and 7C, the zoom lens according to Example 3 is excellent in correcting various aberrations. It can be seen that it has imaging performance.

(Fourth embodiment)
The fourth embodiment of the present application will be described below. FIG. 8 is a lens configuration diagram of a zoom lens according to Example 4. The zoom lens ZL according to Example 4 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative lens arranged in order from the object side along the optical axis. And a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power, and from the wide-angle end state W to the telephoto end state T. During zooming, the first lens group G1 once moves to the image plane I side and then moves to the object side, and the second lens group G2, the third lens group G3, and the fourth lens group G4 all move to the object side. The fifth lens group G5 is fixed.

  The first lens group G1 is arranged in order from the object side along the optical axis, and has a negative meniscus lens L11 having a convex surface facing the object side and an aspheric surface on the image surface I side, and a biconcave negative lens L12. And a positive meniscus lens L13 having a convex surface facing the object side, both lens surfaces of the negative meniscus lens L11, both lens surfaces of the negative lens L12, and both lens surfaces of the positive meniscus lens L13, that is, The antireflection film is provided on all the lens surfaces in the first lens group G1.

  The second lens group G2 includes a front group G2a having a positive refractive power and a rear group G2b having a positive refractive power, which are arranged in order from the object side along the optical axis. The front group G2a includes a positive meniscus lens L21 having an aspheric surface on the object side surface, and a positive cemented lens L22 of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens, and the rear group G2b Is composed of a biconvex positive lens L23.

  The third lens group G3 is arranged in order from the object side along the optical axis, a negative cemented lens L31 of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and a concave surface facing the object side And a negative meniscus lens L32. The fourth lens group G4 includes, in order from the object side along the optical axis, a positive cemented lens L41 of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens, and a surface on the image plane I side. And a positive meniscus lens L42 having an aspherical surface and a concave surface facing the object side. The fifth lens group G5 includes a positive cemented lens L51 including a biconvex positive lens and a biconcave negative lens.

  Note that focusing from an infinitely distant object to a close object is performed by moving the front group G2a in the image plane I direction. The aperture stop S is disposed adjacent to the object side from the most object side surface in the third lens group G3, and is integrated with the third lens group G3 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  Table 4 below shows specifications in the fourth embodiment. The surface numbers 1 to 29 in Table 4 correspond to the surfaces 1 to 29 in FIG.

(Table 4)
[Overall specifications]
f = 24.78 to 67.7
2ω = 82.2 to 35.4
FNO = 2.92
[Lens data]
Surface number r d nd νd
Object ∞ ∞
1 120.00 3.00 1.744429 49.52
2 * 27.87 14.50
3-140.00 2.20 1.618000 63.33
4 87.55 0.20
5 56.59 4.00 1.903660 31.31
6 100.69 D6
7 * 60.51 0.10 1.553890 38.09
8 63.20 4.51 1.772500 49.60
9 -9682.46 6.00
10 117.81 1.47 1.761821 26.52
11 30.70 8.40 1.497820 82.56
12 -195.19 D12
13 59.30 4.85 1.882997 40.76
14 -527.45 D14
15 Aperture stop 1.65
16 -516.24 3.46 1.860740 23.06
17 -34.64 1.10 1.754998 52.32
18 61.49 2.97
19 -42.94 1.05 1.754998 52.32
20 -139.62 D20
21 234.05 1.10 1.805181 25.42
22 48.37 7.00 1.497820 82.56
23 -32.58 0.20
24 -784.30 2.50 1.772500 49.60
25 * -136.22 0.09 1.553890 38.09
26 -150.00 D26
27 40.92 6.00 1.497820 82.56
28 -276.81 1.40 1.805181 25.42
29 95.99 Bf
Image plane ∞
[Aspherical data]
Surface number Κ C4 C6 C8
2 -1.2870 × 10 ^-1 + 3.7539 × 10 ^-6 -1.7076 × 10 ^-9 + 1.0990 × 10 ^-11
7 + 1.1000 × 10 ^-1 -5.5738 × 10 ^-7 + 1.2030 × 10 ^-10 + 1.3357 × 10 ^-12
25 +9.4244 + 2.5528 × 10 ^-6 + 8.0499 × 10 ^-9 -5.1196 × 10 ^-11
Surface number C10 C12
2 -1.6921 × 10 ^-14 + 1.1239 × 10 ^-17
7 -1.7946 × 10 ^-15 0.0000
25 + 1.9412 × 10 ^-13 -2.7823 × 10 ^-16
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state f 24.78 52.00 67.70
D6 48.45 12.43 1.85
D12 7.39 7.39 7.39
D14 1.35 16.36 26.28
D20 16.95 8.43 1.60
D26 1.30 11.68 24.04
[Conditional value]
Conditional expression (1) β5 = 0.81
Conditional expression (2) S45w / fw = -0.51
Conditional expression (3) f1 × Fnot / ft = −1.65
Conditional expression (4) νd = 82.60
Conditional expression (5) f2a / f2b = 1.27

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (5) are satisfied.

  FIG. 9A is a diagram of various aberrations in the wide-angle end state of the zoom lens according to Example 4 at the infinite focus state, and FIG. 9B is a diagram of various aberrations in the intermediate focal length state. FIG. 9C shows various aberrations in the telephoto end state. As is apparent from the aberration diagrams of FIGS. 9A, 9B, and 9C, the zoom lens according to Example 4 is excellent in that various aberrations are corrected satisfactorily. It can be seen that it has imaging performance.

  Here, the antireflection film used in the zoom lenses of the first to fourth embodiments will be described. FIG. 10 is a diagram showing 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. Further, 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, the seventh layer 101g made of a mixture of silica and magnesium fluoride 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. In the sol-gel method, an optical thin film material sol is applied on the optical surface of an optical member, a gel film is deposited, and then immersed in a liquid. This is a method for producing a film by vaporizing and drying. 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 sol liquid prepared by the hydrofluoric acid / magnesium acetate method was apply | coated by the spin coat method, and the layer which consists of a mixture of the silica and magnesium fluoride used as the 7th layer 101g was formed. Form. The reaction formula when prepared by the hydrofluoric acid / magnesium acetate method is shown in the following formula (6).

    2HF + Mg (CH3COO) 2 → MgF2 + 2 + CH3COOH (6)

  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, several to several tens of atoms or molecules are gathered to form particles with a size of several nanometers to several tens of nanometers. Secondary particles are formed and the secondary particles are deposited to form the seventh layer 101g.

The optical performance of the antireflection film 101 formed in this way will be described with reference to the spectral characteristics shown in FIG. FIG. 11 shows the spectral characteristics when a light ray is vertically incident when the antireflection film 101 is designed under the conditions shown in Table 5 below when the reference wavelength λ is 550 nm. Table 5 shows aluminum oxide as Al ₂ O ₃ , titanium oxide-zirconium oxide mixture as ZrO ₂ + TiO ₂ , silica and magnesium fluoride as SiO ₂ + MgF ₂ , and a reference wavelength λ of 550 nm. Table 4 shows design values when the substrate has four kinds of refractive indexes of 1.46, 1.62, 1.74, and 1.85.

(Table 5)
Substance Refractive index Optical film thickness Optical film thickness Optical film thickness Optical film thickness Medium Air 1
7th layer SiO ₂ + MgF ₂ 1.26 0.275λ 0.268λ 0.271λ 0.269λ
6th layer ZrO ₂ + TiO ₂ 2.12 0.045λ 0.057λ 0.054λ 0.059λ
5th layer Al ₂ O ₃ 1.65 0.212λ 0.171λ 0.178λ 0.162λ
4th layer ZrO ₂ + TiO ₂ 2.12 0.077λ 0.127λ 0.13λ 0.158λ
3rd layer Al ₂ O ₃ 1.65 0.288λ 0.122λ 0.107λ 0.08λ
Second layer ZrO ₂ + TiO ₂ 2.12 0 0.059λ 0.075λ 0.105λ
1st layer Al ₂ O ₃ 1.65 0 0.257λ 0.03λ 0.03λ
Substrate refractive index 1.46 1.62 1.74 1.85

  As can be seen from FIG. 11, the reflectance is suppressed to 0.2% or less over the entire wavelength range of 420 nm to 720 nm.

  In the zoom lens of the first example, the refractive index of the negative meniscus lens L11 is 1.744429, and the refractive index of the negative lens L12 is 1.618000. Therefore, the lens on the image plane I side in the negative meniscus lens L11. It is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.74 on the surface, and an antireflection film corresponding to the refractive index of the substrate of 1.62 on the object side lens surface of the negative lens L12. Can be used.

  In the zoom lens of the second example, since the refractive index of the negative meniscus lens L11 is 1.744429, the refractive index of the substrate corresponds to the lens surface on the image plane I side of the negative meniscus lens L11. It is possible to use an antireflection film. In the zoom lens of the third example, since the refractive index of the positive meniscus lens L13 is 1.846660, the reflection on the object side lens surface of the positive meniscus lens L13 corresponds to the refractive index of the substrate corresponding to 1.85. It is possible to use a prevention film.

  In the zoom lens of the fourth example, the refractive index of the negative meniscus lens L11 is 1.744429, the refractive index of the negative lens L12 is 1.618000, and the refractive index of the positive meniscus lens L13 is 1.903660. is there. Therefore, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.74 on the lens surfaces on both sides of the negative meniscus lens L11, and the refractive index of the substrate on the lens surfaces on both sides of the negative lens L12. An antireflection film corresponding to 1.62 can be used, and an antireflection film corresponding to a refractive index of the substrate of 1.85 can be used on both lens surfaces of the positive meniscus lens L13.

  In this way, by applying the antireflection film of the present embodiment to the zoom lenses of the first to fourth examples, the maximum field angle includes a wide field angle of 80 degrees or more, and a change of about 2.7 times. A high-power zoom lens having a magnification ratio and a large aperture ratio with an F number of about 2.8 and a low ghost and a low flare can be obtained.

  The antireflection film 101 can be used as an optical element provided on the optical surface of a plane-parallel plate, or can be used provided on the optical surface of a lens formed in a curved surface.

  Next, a modified example of the antireflection film will be described. This antireflection film consists of five layers and is configured under the conditions shown in Table 6 below. Note that the sol-gel method described above is used to form the fifth layer. Table 6 shows design values when the reference wavelength λ is 550 nm and the refractive index of the substrate is 1.52.

(Table 6)
Material Refractive index Optical film thickness Medium Air 1
Fifth layer Mixture of silica and magnesium fluoride 1.26 0.269λ
Fourth layer Titanium oxide-zirconium oxide mixture 2.12 0.043λ
Third layer Aluminum oxide 1.65 0.217λ
Second layer Titanium oxide-zirconium oxide mixture 2.12 0.066λ
First layer Aluminum oxide 1.65 0.290λ
Substrate BK7 1.52

  FIG. 12 shows spectral characteristics when light is vertically incident on the antireflection film of the modification. As can be seen from FIG. 12, the reflectance is suppressed to 0.2% or less over the entire wavelength range of 420 nm to 720 nm. FIG. 13 shows spectral characteristics when the incident angles are 30, 45, and 60 degrees.

  For comparison, FIG. 14 shows the spectral characteristics at the time of normal incidence of a multilayer broadband antireflection film formed by only a dry process such as a conventional vacuum deposition method and configured under the conditions shown in Table 7 below. FIG. 15 shows the spectral characteristics when the incident angles are 30, 45, and 60 degrees.

(Table 7)
Material Refractive index Optical film thickness Medium Air 1
7th layer MgF ₂ 1.39 0.243λ
Sixth layer Titanium oxide-zirconium oxide mixture 2.12 0.119λ
5th layer Aluminum oxide 1.65 0.057λ
Fourth layer Titanium oxide-zirconium oxide mixture 2.12 0.220λ
Third layer Aluminum oxide 1.65 0.064λ
Second layer Titanium oxide-zirconium oxide mixture 2.12 0.057λ
First layer Aluminum oxide 1.65 0.193λ
Substrate BK7 1.52

  Comparing the spectral characteristics of the modification shown in FIGS. 12 and 13 with the spectral characteristics of the conventional example shown in FIGS. 14 and 15, the low reflectance of the antireflection film 101 according to the modification can be clearly seen.

  As an example of the present application, a five-group lens system is shown, but a lens system in which an additional lens group is added to the five-group lens system is an equivalent lens system in which the effect of the present application is inherent. Needless to say. In addition, in the configuration in each lens group, it goes without saying that a lens group in which an additional lens is added to the configuration in the embodiment is an equivalent lens group in which the effect of the present application is inherent.

  Further, the above-described embodiment is merely an example, and is not limited to the above-described configuration and shape, and can be appropriately modified and changed within the scope of the present application.

1 is a lens configuration diagram of a zoom lens according to Example 1. FIG. (A) is various aberration diagrams in the wide-angle end state in the infinite focus state of the zoom lens according to Example 1, (b) is various aberration diagrams in the intermediate focal length state, and (c) is It is an aberration diagram in the telephoto end state. FIG. 3 is a configuration diagram of a zoom lens according to the first example, in which incident light rays are reflected by a first ghost generation surface and a second ghost generation surface. It is a lens block diagram of the zoom lens which concerns on 2nd Example. (A) is various aberration diagrams in the wide-angle end state in the infinite focus state of the zoom lens according to Example 2, (b) is various aberration diagrams in the intermediate focal length state, and (c) is It is an aberration diagram in the telephoto end state. It is a lens block diagram of the zoom lens which concerns on 3rd Example. (A) is various aberration diagrams in the wide-angle end state in the infinite focus state of the zoom lens according to Example 3, (b) is various aberration diagrams in the intermediate focal length state, and (c) is It is an aberration diagram in the telephoto end state. It is a lens block diagram of the zoom lens which concerns on 4th Example. (A) is various aberration diagrams in the wide-angle end state in the infinite focus state of the zoom lens according to Example 4, (b) is various aberration diagrams in the intermediate focal length state, and (c) is It is an aberration diagram in the telephoto end state. It is explanatory drawing which shows the 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 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 spectral characteristic of the anti-reflective film produced with the prior art. It is a schematic block diagram of a single-lens reflex camera.

Explanation of symbols

CAM single-lens reflex camera (optical equipment)
ZL Zoom lens I Image plane G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G5 Fifth lens group 101 Antireflection film 101a First layer 101b Second layer 101c Third layer 101d Fourth Layer 101e 5th layer 101f 6th layer 101g 7th layer 102 Optical member

Claims (14)

A first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, arranged in order from the object side along the optical axis, and positive A fourth lens group having a refractive power and a fifth lens group having a positive refractive power;
Upon zooming from the wide-angle end state to the telephoto end state, the first lens group once moves to the image side and then moves to the object side, and the distance between the first lens group and the second lens group is reduced. The distance between the second lens group and the third lens group is enlarged, the distance between the third lens group and the fourth lens group is reduced, and the distance between the fourth lens group and the fifth lens group is reduced. Is configured to expand,
In the wide-angle end state, the focal length of the entire system is fw, the lateral magnification of the fifth lens group is β5, and the fifth lens group is measured in the optical axis direction from the rear principal point of the fourth lens group. When the front principal point position is S45w, the following formula 0.6 <β5 <0.9
And S45w / fw <−0.15
While satisfying the conditions of
An antireflection film is provided on at least one of the optical surfaces in the first lens group, and the antireflection film is configured to include at least one layer formed using a wet process. Zoom lens. The antireflection film is a multilayer film,
The zoom lens 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. When the refractive index of the layer formed by using the wet process is nd, the following formula nd ≦ 1.30
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition. A first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, arranged in order from the object side along the optical axis, and positive A fourth lens group having a refractive power and a fifth lens group having a positive refractive power;
Upon zooming from the wide-angle end state to the telephoto end state, the first lens group once moves to the image side and then moves to the object side, and the distance between the first lens group and the second lens group is reduced. The distance between the second lens group and the third lens group is enlarged, the distance between the third lens group and the fourth lens group is reduced, and the distance between the fourth lens group and the fifth lens group is reduced. Is configured to expand,
In the wide-angle end state, the focal length of the entire system is fw, the lateral magnification of the fifth lens group is β5, and the front side of the fifth lens group is measured in the optical axis direction from the rear principal point of the fourth lens group. When the principal point position is S45w, the following formula 0.6 <β5 <0.9
And S45w / fw <−0.15
While satisfying the conditions of
An antireflection film is provided on at least one of the optical surfaces of the first lens group, and the antireflection film includes at least one layer having a refractive index of 1.30 or less. Zoom lens to be used. The antireflection film is a multilayer film,
5. The zoom lens according to claim 4, wherein the layer having a refractive index of 1.30 or less is the most surface layer among the layers constituting the multilayer film. An aperture stop is disposed closer to the object side than the most object side surface of the third lens group,
The zoom lens according to claim 1, wherein the optical surface is a concave surface with respect to the aperture stop. When the F-number of the entire system in the telephoto end state is Fnot, the focal length of the entire system in the telephoto end state is ft, and the focal length of the first lens group is f1, the following formula: −1.8 <f1 × Fnot /Ft<−1.0
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.   The fifth lens group includes a positive cemented lens composed of a positive lens and a negative lens arranged in order from the object side along the optical axis and having a convex surface facing the object side. The zoom lens according to any one of claims 1 to 7.   The fourth lens group includes a cemented positive lens of a negative lens and a biconvex positive lens arranged in order from the object side along the optical axis, and one or more positive lenses. The zoom lens according to any one of claims 1 to 8. At least one of the fourth lens group and the fifth lens group is configured to have at least one aspheric lens,
10. The zoom lens according to claim 1, wherein the aspherical lens has a positive refractive power that decreases from the lens center toward the periphery. The second lens group includes at least one aspheric lens and at least one positive lens,
When the Abbe number of the positive lens in the second lens group is νd, the following equation νd> 70
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition. The second lens group includes a front group having a positive refractive power and a rear group having a positive refractive power arranged in order from the object side along the optical axis. Focusing is performed by moving the front group along the optical axis,
When the focal length of the front group is f2a and the focal length of the rear group is f2b, the following expression 1.1 <f2a / f2b <1.5
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition. In an optical apparatus equipped with a zoom lens that forms an image of an object on a predetermined image plane,
The optical apparatus, wherein the zoom lens is the zoom lens according to any one of claims 1 to 12. A first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, arranged in order from the object side along the optical axis, and positive An image forming method for forming an image of the object on a predetermined image plane by using a zoom lens including a fourth lens group having a refractive power and a fifth lens group having a positive refractive power. ,
Upon zooming from the wide-angle end state to the telephoto end state, the first lens group once moves to the image side and then moves to the object side, and the distance between the first lens group and the second lens group is reduced. The distance between the second lens group and the third lens group is enlarged, the distance between the third lens group and the fourth lens group is reduced, and the distance between the fourth lens group and the fifth lens group is reduced. Is configured to expand,
In the wide-angle end state, the focal length of the entire system is fw, the lateral magnification of the fifth lens group is β5, and the front side of the fifth lens group is measured in the optical axis direction from the rear principal point of the fourth lens group. When the principal point position is S45w, the following formula 0.6 <β5 <0.9
And S45w / fw <−0.15
While satisfying the conditions of
An image forming apparatus comprising: an antireflection film provided on at least one of the optical surfaces of the first lens group, wherein the antireflection film includes at least one layer formed by a wet process. Method.

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