JP5621562B2 - Photographic lens, optical apparatus equipped with the photographic lens - Google Patents

Description

The present invention includes a photographing lens, relates to an optical equipment provided with the photographic lens.

  Conventionally, various lens types have been proposed for optical systems that achieve good imaging performance from an infinite object point to a close object point. For example, an in-focus optical system with a four-group configuration (see, for example, Patent Document 1) and an optical system with a two-group configuration (see, for example, Patent Document 2) have been proposed. In recent years, for optical systems that achieve good imaging performance from infinity to near-distance objects, not only aberration performance but also ghost and flare, which are factors that impair optical performance The demands on the anti-reflection coating applied to the lens surface are also demanding higher performance, and multilayer film design technology and multilayer film formation technology continue to advance to meet the demand ( For example, see Patent Document 3).

JP 2009-63715 A JP 2007-86308 A JP 2000-356704 A

  However, since the number of groups is large in the 4-group configuration, the optical system tends to be large. In the two-group configuration, the optical system can be easily miniaturized, but there is a problem that the amount of movement necessary for focusing increases. At the same time, there has been a problem that reflected light that is ghost or flare is likely to be generated from the optical surface of such a photographing lens.

  The present invention has been made in view of such problems, and it is possible to obtain a good imaging performance from an infinite object point to a close object point by reducing the ghost and flare while reducing the size of the optical system. An object of the present invention is to provide a possible photographing lens.

In order to solve the above problems, the present invention provides:
From the object side,
A first lens group having a positive refractive power;
An aperture stop,
A second lens group having a positive refractive power;
A third lens group having a negative refractive power and substantially consisting of three lens groups ;
When focusing from an infinite object point to a short-distance object point, the first lens group and the second lens group independently move on the optical axis to the object side,
The first lens group is in order from the object side.
A front group having negative refractive power;
A rear group having a positive refractive power,
The front group is composed of a positive lens and a negative lens in order from the object side,
An antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film includes at least one layer formed using a wet process. Provide a taking lens.

  The present invention also provides an optical apparatus comprising the photographing lens.

According to the present invention, there is provided a photographic lens capable of obtaining a good imaging performance from an infinite object point to a short-distance object point while reducing the ghost and flare while reducing the size of the optical system, and the photographic lens. It was it is possible to provide an optical equipment.

It is sectional drawing which shows the structure of the imaging lens concerning 1st Example. FIG. 3A is a diagram illustrating various aberrations of the photographing lens according to the first example. FIG. 9A is a diagram illustrating various aberrations in the infinite focus state, and FIG. It is sectional drawing which shows the structure of the imaging lens concerning 1st Example, Comprising: It is a figure explaining an example of a mode that the incident light ray reflects in the 1st ghost generating surface and the 2nd ghost generating surface. It is sectional drawing which shows the structure of the imaging lens concerning 2nd Example. FIG. 7A is a diagram illustrating various aberrations of the photographing lens according to the second example, FIG. 9A is a diagram illustrating various aberrations in the infinite focus state, and FIG. It is sectional drawing which shows the structure of the imaging lens concerning 3rd Example. FIG. 6A is a diagram illustrating various aberrations of the photographing lens according to Example 3, wherein FIG. 9A is a diagram illustrating various aberrations in the infinite focus state, and FIG. It is sectional drawing which shows the structure of the imaging lens concerning 4th Example. FIG. 9A is a diagram illustrating various aberrations of the photographing lens according to the fourth example, in which FIG. 10A is a diagram illustrating aberrations in an infinite focus state, and FIG. It is sectional drawing which shows the structure of the imaging lens concerning 5th Example. FIG. 6A is a diagram illustrating various aberrations of the photographing lens according to Example 5, where FIG. 9A is a diagram illustrating aberrations in the infinite focus state, and FIG. 1 is a cross-sectional view of a digital single-lens reflex camera equipped with a photographic lens according to the present embodiment. It is a flowchart for demonstrating the manufacturing method of the imaging lens concerning this embodiment. It is explanatory drawing which shows an example of the layer structure of an antireflection film. It is a graph which shows the spectral characteristic of an antireflection film. It is a graph which shows the spectral characteristics of the antireflection film concerning a modification. It is a graph which shows the incident angle dependence of the spectral 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 of the spectral characteristic 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. First, the photographing lens SL according to the present embodiment has, in order from the object side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a positive refractive power, and a negative refractive power. And a third lens group. The first lens group includes, in order from the object side, a front group having negative refractive power and a rear group having positive refractive power. The front group includes a positive lens and a negative lens in order from the object side. Have.

Then, when focusing from an infinite object point to a short-distance object point, the first lens group and the second lens group, which are focusing lens groups, are independently moved to the object side on the optical axis. The photographic lens according to the present embodiment has a three-group configuration to reduce the overall length, and by independently moving the first lens group and the second lens group, a high connection from an infinite object point to a short-distance object point is achieved. Image performance can be obtained. In addition, since the two lens groups having positive refractive power are independently moved when focusing, it is possible to obtain good imaging performance while suppressing the movement amount of each lens group.
The first lens group includes a front group having a negative refractive power on the object side and a rear group having a positive refractive power on the image side, thereby reducing the distance between the object and the first lens group. It is possible to increase the distortion, and it is possible to satisfactorily correct distortion aberration when focusing from an infinite object point to a short distance object point. The photographic lens according to the present embodiment has a front lens group composed of a positive lens and a negative lens, so that coma aberration is mainly achieved with a positive lens in focusing from an infinite object point to a close object point. Correcting and correcting the distortion with the negative lens can achieve good imaging performance.

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

  In the photographic lens according to the present embodiment, the antireflection film is preferably a multilayer film, and the layer formed using 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, it is possible to reduce the reflection of light and further reduce ghosts and flares.

  In the photographing lens according to the present embodiment, it is preferable that the refractive index nd is 1.30 or less, where nd is the refractive index of the layer formed using the wet process. In this way, since the difference in refractive index with air can be reduced, it is possible to reduce the reflection of light and further reduce ghosts and flares.

  In the photographic lens according to the present embodiment, the optical surface provided with the antireflection film is at least one of the first lens group and the second lens group, and the optical surface is viewed from an aperture stop. The surface is preferably concave. Since a ghost is likely to occur on a concave lens surface as viewed from the aperture stop, ghosts and flares can be effectively reduced by forming an antireflection film on such a surface.

  In the photographing lens according to the present embodiment, it is preferable that the concave surface provided with the antireflection film is a lens surface on the image plane side. Since a ghost is likely to occur on a concave lens surface as viewed from the aperture stop, ghosts and flares can be effectively reduced by forming an antireflection film on such a surface.

  In the photographic lens according to the present embodiment, it is preferable that the concave surface provided with the antireflection film is a lens surface on the object side. Since a ghost is likely to occur on a concave lens surface as viewed from the aperture stop, ghosts and flares can be effectively reduced by forming an antireflection film on such a surface.

  In the photographing lens according to the present embodiment, the optical surface provided with the antireflection film is at least one surface of the third lens group, and the optical surface is a concave surface when viewed from the image plane. It is preferable that Since a ghost is likely to occur on the concave lens surface as viewed from the image plane, ghosts and flares can be effectively reduced by doing so.

  In the photographic lens according to the present embodiment, it is preferable that the concave surface when viewed from the image surface provided with the antireflection film is a lens surface on the image surface side. Since a ghost is likely to occur on a concave lens surface when viewed from the image surface, ghosts and flares can be effectively reduced by forming an antireflection film on such a surface.

  In the photographic lens according to the present embodiment, it is preferable that the concave surface when viewed from the image surface provided with the antireflection film is a lens surface on the object side. Since a ghost is likely to occur on a concave lens surface when viewed from the image surface, ghosts and flares can be effectively reduced by forming an antireflection film on such a surface.

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

In addition, it is desirable that the photographic lens according to the present embodiment satisfies the following conditional expression (1).
(1) 1.38 <(− f1F) / f1R <3.00
However, f1F is the focal length of the front group, and f1R is the focal length of the rear group.

Conditional expression (1) is a conditional expression that defines an appropriate range for the ratio of the focal length of the front group and the focal length of the rear group of the first lens group. By satisfying conditional expression (1), it is possible to increase the distance between the object and the lens at the time of short-distance shooting, and it is possible to satisfactorily correct various aberrations such as distortion.
The first lens group has a negative and positive refractive power arrangement in the front group and the rear group, and the front lens group having a negative refractive power is arranged closest to the object side. When being extended, the distance between the object and the front group having negative refractive power can be increased.
If the upper limit of conditional expression (1) is exceeded, the negative refractive power in the first lens group will be weakened, so that spherical aberration and curvature of field can be corrected well. Along with shortening, negative distortion occurs. Since negative distortion becomes large especially at close-up shooting, it is not preferable in terms of imaging performance.
In addition, by setting the upper limit of conditional expression (1) to 2.80, it is possible to correct distortion more satisfactorily and make the effect of the present embodiment more reliable. Further, by setting the upper limit value of conditional expression (1) to 2.50, it is possible to correct distortion more satisfactorily and further ensure the effect of the present embodiment.
When the lower limit of conditional expression (1) is not reached, the refractive power of the front group increases and the negative refractive power of the first lens group increases, so when focusing from an infinite object point to a close object point, Spherical aberration and curvature of field are insufficiently corrected, which is not preferable for imaging performance.
By setting the lower limit of conditional expression (1) to 1.40, spherical aberration and curvature of field can be corrected more satisfactorily and the effect of this embodiment can be made more reliable. Further, by setting the lower limit value of conditional expression (1) to 1.45, spherical aberration and curvature of field can be corrected more satisfactorily, and the effect of this embodiment can be further ensured.

In addition, it is desirable that the photographing lens according to the present embodiment satisfies the following conditional expression (2).
(2) 0.50 <f1R / f <1.20
Here, f1R is the focal length of the rear group, and f is the focal length at the time of focusing on the entire system at infinity.

Conditional expression (2) is a conditional expression in which the focal length of the rear group of the first lens group is defined by the focal length of the entire photographing lens system. Satisfying the conditional expression (2) makes it possible to satisfactorily correct spherical aberration that occurs during close-up shooting and to ensure high imaging performance from an infinite object point to a close object point.
If the upper limit of conditional expression (2) is exceeded, the refractive power of the rear group becomes weak, and the spherical aberration that occurs during short-distance shooting becomes insufficiently corrected.
Note that by setting the upper limit of conditional expression (2) to 1.15, spherical aberration that occurs during close-up shooting can be corrected more satisfactorily, and the effects of the present embodiment can be made more reliable. In addition, by setting the upper limit value of conditional expression (2) to 1.10, spherical aberration that occurs during close-up shooting can be corrected more satisfactorily, and the effects of the present embodiment can be further ensured.
If the lower limit of conditional expression (2) is not reached, the refractive power of the rear group will increase, and spherical aberration that occurs during close-up shooting will be overcorrected.
Note that, by setting the lower limit value of conditional expression (2) to 0.55, spherical aberration that occurs during close-up shooting can be corrected more favorably, and the effects of the present embodiment can be made more reliable. In addition, by setting the lower limit value of conditional expression (2) to 0.57, it is possible to correct spherical aberration that occurs during close-up shooting more satisfactorily and to further ensure the effect of the present embodiment.

  In the photographing lens according to the present embodiment, it is desirable that the distance between the first lens group and the second lens group changes during focusing. With this configuration, it is possible to improve field curvature at the time of focusing on a short-distance object point.

In addition, it is desirable that the photographing lens according to the present embodiment satisfies the following conditional expression (3).
(3) 4.00 <(− f3) / f1 <10.00
Here, f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group.

Conditional expression (3) is a conditional expression that defines an appropriate range of the ratio between the focal length of the first lens group and the focal length of the third lens group. When the conditional expression (3) is satisfied, the field curvature generated in the focusing lens group from the object point at infinity to the object point at the short distance can be corrected favorably by the third lens group.
If the upper limit value of conditional expression (3) is exceeded, the refractive power of the third lens group will weaken, and the field curvature cannot be corrected well. In particular, it is desirable to satisfy this conditional expression (3) in order to satisfactorily correct field curvature during close-up shooting.
Note that by setting the upper limit of conditional expression (3) to 9.50, it is possible to correct the curvature of field more satisfactorily and to ensure the effect of the present embodiment. Further, by setting the upper limit value of conditional expression (3) to 9.00, it is possible to correct the curvature of field more satisfactorily and further ensure the effect of the present embodiment.
If the lower limit of conditional expression (3) is not reached, the refractive power of the third lens group will increase, and the field curvature cannot be corrected well.
Note that by setting the lower limit value of conditional expression (3) to 0.405, the curvature of field can be corrected more favorably and the effect of the present embodiment can be made more reliable. Further, by setting the lower limit value of conditional expression (3) to 0.410, it is possible to correct the curvature of field more satisfactorily and further ensure the effect of the present embodiment.

In addition, it is desirable that the photographing lens according to the present embodiment satisfies the following conditional expression (4).
(4) 0.20 <d / f <0.33
Here, d is the air space on the optical axis between the most image side lens surface of the front group and the most object side lens surface of the rear group, and f is the focal length at the time of focusing on the entire system at infinity.

Conditional expression (4) is a conditional expression in which the air space on the optical axis between the front group and the rear group of the first lens group is defined by the focal length of the entire taking lens system. By satisfying conditional expression (4), it is possible to satisfactorily correct field curvature and distortion while miniaturizing the entire system.
If the upper limit value of conditional expression (4) is exceeded, the entire system becomes large. In addition, distortion becomes worse.
Note that by setting the upper limit value of conditional expression (4) to 0.320, the entire system can be made more compact, and distortion effects can be corrected more satisfactorily and the effects of the present embodiment can be made more reliable. . In addition, by setting the upper limit value of conditional expression (4) to 0.315, the entire system can be further reduced in size, and distortion can be corrected more satisfactorily to further ensure the effect of the present embodiment. .
If the lower limit of conditional expression (4) is not reached, the curvature of field deteriorates.
Note that by setting the lower limit value of conditional expression (4) to 0.250, the curvature of field can be corrected more satisfactorily and the effect of the present embodiment can be made more reliable. Further, by setting the lower limit value of conditional expression (4) to 0.280, it is possible to correct the curvature of field more satisfactorily and further ensure the effect of the present embodiment.

In addition, it is desirable that the photographing lens according to the present embodiment satisfies the following conditional expression (5).
(5) 0.40 <(− f1Fn) / f <0.90
Here, f1Fn is the focal length of the negative lens constituting the front group of the first lens group, and f is the focal length at the time of focusing on the entire system at infinity.

Conditional expression (5) is a conditional expression that defines an appropriate range for the ratio of the focal length of the negative lens constituting the front group of the first lens group and the focal length at the time of focusing on infinity of the entire system. . By satisfying conditional expression (5), it is possible to correct various aberrations satisfactorily with the front lens group of the first lens group having two lenses.
If the upper limit of conditional expression (5) is exceeded, the negative refractive power of the first lens group will be weakened, so that field curvature and distortion cannot be corrected well.
In addition, by setting the upper limit value of conditional expression (5) to 0.89, it is possible to correct the curvature of field and distortion more satisfactorily and make the effect of the present embodiment more reliable. Further, by setting the upper limit value of conditional expression (5) to 0.88, it is possible to correct the curvature of field and distortion more satisfactorily and further ensure the effect of this embodiment.
If the lower limit of conditional expression (5) is not reached, the negative refracting power of the first lens group becomes strong, so that the field curvature cannot be corrected well.
In addition, by setting the lower limit value of conditional expression (5) to 0.45, it is possible to correct the curvature of field more satisfactorily and to ensure the effect of the present embodiment. In addition, by setting the lower limit value of conditional expression (5) to 0.48, it is possible to correct the field curvature more satisfactorily and further ensure the effect of the present embodiment.

In addition, it is desirable that the photographic lens according to the present embodiment satisfies the following conditional expression (6).
(6) 0.60 <X1 / f <0.90
However, X1 is the absolute value of the amount of movement of the first lens unit on the optical axis when focusing from infinity to the closest object point, and f is the focal length of the entire system when focusing on infinity.

Conditional expression (6) shows the absolute value of the movement amount on the optical axis of the first lens group when focusing on the closest object point from infinity, as the focal length of the entire photographing lens system at the time of focusing on infinity. It is a defined conditional expression. By satisfying conditional expression (6), the amount of movement of the first lens unit on the optical axis when focusing on the object point closest to infinity can be made appropriate.
If the upper limit of conditional expression (6) is exceeded, the amount of various aberrations such as field curvature will decrease, but the amount of movement of the first lens group will increase, and the optical system will become larger.
By setting the upper limit value of conditional expression (6) to 0.88, the amount of movement of the first lens group can be made more appropriate while suppressing the amount of various aberrations such as field curvature, and the effect of the present embodiment. Can be made more reliable. Further, by setting the upper limit of conditional expression (6) to 0.85, the amount of movement of the first lens unit can be made more appropriate while suppressing the generation of various aberrations such as field curvature, and the effect of the present embodiment. Can be further ensured.
If the lower limit of conditional expression (6) is not reached, the optical system can be miniaturized, but the refractive power of the first lens group is increased and various aberrations such as field curvature are likely to occur.
By setting the lower limit of conditional expression (6) to 0.65, various aberrations such as field curvature can be corrected more favorably while reducing the size of the optical system, and the effects of the present embodiment can be made more reliable. Can do. Further, by setting the lower limit value of conditional expression (6) to 0.70, various aberrations such as field curvature can be corrected more satisfactorily while downsizing the optical system, and the effects of this embodiment can be further ensured. Can do.

In addition, it is desirable that the photographing lens according to the present embodiment satisfies the following conditional expression (7).
(7) 0.70 <X2 / f <0.90
However, X2 is the absolute value of the amount of movement of the second lens unit on the optical axis when focusing from infinity to the closest object point, and f is the focal length of the entire system when focusing on infinity.

Conditional expression (7) expresses the absolute value of the amount of movement on the optical axis of the second lens group when focusing on the closest object point from infinity as the focal length of the entire photographing lens system at the time of focusing on infinity. It is a defined conditional expression. By satisfying conditional expression (7), the amount of movement of the second lens group on the optical axis when focusing on the object point closest to infinity can be made appropriate.
When the upper limit of conditional expression (7) is exceeded, the amount of aberrations such as field curvature is reduced, but the amount of movement of the second lens group is increased, and the optical system is enlarged.
By setting the upper limit of conditional expression (7) to 0.88, the optical system can be made more compact while suppressing the amount of various aberrations such as curvature of field, and the amount of movement of the second lens group is more appropriate. The effect of this embodiment can be made more reliable. Further, by setting the upper limit of conditional expression (7) to 0.85, the optical system can be further miniaturized while suppressing the amount of occurrence of various aberrations such as curvature of field, and the amount of movement of the second lens group is more appropriate. The effect of this embodiment can be further ensured.
If the lower limit of conditional expression (7) is not reached, the optical system can be miniaturized, but the refractive power of the second lens group becomes stronger, and various aberrations such as field curvature tend to occur.
By setting the lower limit of conditional expression (7) to 0.71, various aberrations such as field curvature can be corrected more favorably while reducing the size of the optical system, and the effects of this embodiment can be made more reliable. Can do. Further, by setting the lower limit value of conditional expression (7) to 0.72, various aberrations such as field curvature can be corrected more satisfactorily while downsizing the optical system, and the effect of this embodiment can be further ensured. it can.

  In addition, it is desirable that the photographing lens according to the present embodiment has an aspheric lens in at least one of the front group, the rear group, and the second lens group of the first lens group. When an aspherical lens is provided in the front group of the first lens group, coma and distortion can be favorably corrected when focusing from an infinite object point to a close object point. In addition, when the positive lens in the rear group of the first lens group and the aspheric lens in the second lens group are used, it is possible to satisfactorily correct spherical aberration when focusing from an infinite object point to a near object point. .

  FIG. 12 is a schematic cross-sectional view of a digital single-lens reflex camera 1 (hereinafter simply referred to as a camera) as an optical apparatus provided with a photographic lens SL shown in a first embodiment described later. In this camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 (shooting lens SL) and imaged on the focusing screen 4 via the quick return mirror 3. The light imaged on the focusing screen 4 is reflected a plurality of times in the pentaprism 5 and guided to the eyepiece lens 6. Thus, the photographer can observe the object (subject) image as an erect image through the eyepiece 6.

  Further, when a release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light of an object (subject) (not shown) condensed by the photographing lens 2 is captured on the image sensor 7. Form an image. Thereby, the light from the object (subject) is captured by the image sensor 7 and recorded as an object (subject) image in a memory (not shown). In this way, the photographer can shoot an object (subject) with the camera 1. Note that the camera 1 shown in FIG. 12 may hold the photographic lens SL in a detachable manner, or may be formed integrally with the photographic lens SL. The camera 1 may be a so-called single-lens reflex camera or a compact camera without a quick return mirror or the like. The camera 1 can be mounted not only with the first embodiment described above but also with a photographic lens of another embodiment.

  Hereinafter, an outline of a method for manufacturing the photographic lens SL according to the present embodiment will be described with reference to FIG. First, each lens is arranged and a lens group is prepared (step S100). Specifically, in the present embodiment, for example, in the case of a first example to be described later, the front group G1F of the first lens group G1 is, in order from the object side, a biconvex positive lens L11 and a biconcave negative lens L12. The rear lens group G1R of the first lens group G1 is arranged with a cemented lens of a biconvex positive lens L13 and a biconcave negative lens L14 in order from the object side. Configure. Further, the second lens group G2 includes, in order from the object side, a biconcave negative lens L21, a positive meniscus lens L22 having a convex surface facing the image surface side, and a biconvex positive lens L23. To do. The third lens group G3 includes a negative meniscus lens L31 having a concave surface facing the image surface side and a biconvex positive lens L32 in order from the object side. The aperture stop S is arranged between the rear group G1R of the first lens group G1 and the second lens group G2. The lens groups prepared in this manner are arranged in a lens barrel to manufacture the photographing lens SL.

  At this time, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 are arranged so as to move independently on the optical axis to the object side. (Step S200). Thus, the production of the taking lens according to the present embodiment is completed.

(Example)
Hereinafter, each example according to the present embodiment will be described with reference to the accompanying drawings. 1, 4, 6, 8 and 10 show the configurations of the photographing lenses SL1 to SL5.
(First embodiment)
As shown in FIG. 1, the photographic lens SL1 according to the first example includes, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens having a positive refractive power. It is composed of a group G2 and a third lens group G3 having negative refractive power. Then, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 (focusing lens group) each independently extend on the optical axis to the object side. To focus on a finite distance object.
The first lens group G1 includes, in order from the object side, a front group G1F having negative refractive power and a rear group G1R having positive refractive power. The front group G1F includes, in order from the object side, a cemented lens of a biconvex positive lens L11 and a biconcave negative lens L12. Note that the cemented lens may have a configuration in which a positive meniscus lens and a negative meniscus lens are cemented. The biconcave negative lens L12 has a surface having an absolute value of the radius of curvature smaller than the absolute value of the radius of curvature of the object-side surface on the image surface side, so that the object point from the infinite distance to the short distance object point. The coma and distortion are corrected. The rear group G1R is composed of a cemented lens of a biconvex positive lens L13 and a biconcave negative lens L14 in order from the object side. Thus, by disposing the front lens group G1F, which is a negative lens group, on the object side in the first lens group G1, the object and the biconvex positive lens L11 when the first lens group G1 is extended in focus. The interval is made longer.

  The second lens group G2 includes, in order from the object side, a biconcave negative lens L21, a positive meniscus lens L22 having a convex surface facing the image surface, and a biconvex positive lens L23. . Since the first lens group G1 has a positive refractive power, the light flux from the object converges and reaches the second lens group G2. For this reason, a biconcave negative lens L21 is arranged on the object side in the second lens group G2, and the light beam is once diverged. Then, by arranging a positive meniscus lens L22 and a biconvex positive lens L23 on the image side of the negative lens L21, spherical aberration and coma are corrected well.

  The third lens group G3 includes, in order from the object side, a negative meniscus lens L31 having a concave surface directed toward the image surface side, and a biconvex positive lens L32. The third lens group G3 ensures a long back focus and corrects curvature of field. doing. The third lens group G3 may be arranged with a positive lens and a negative lens in order from the object side.

  The aperture stop S is disposed between the rear group G1R of the first lens group G1 and the second lens group G2. The aperture stop S can be disposed between the front group G1F and the rear group G1R of the first lens group G1. It is also possible to arrange an aperture stop S in the second lens group G2.

  In the first example, an antireflection film described later is formed on the image side lens surface of the positive meniscus lens L22 of the second lens group G2 and the object side lens surface of the negative meniscus lens L31 of the third lens group G3. Has been.

  Table 1 below lists values of specifications of the photographing lens SL1 according to the first example. In Table 1 (various data), f is the focal length at infinity focusing of the entire system, FNO is the F number, ω is the half angle of view (unit is “°”), and Y is the image height. , TL represents the total length of the optical system, and Bf represents the back focus. Further, in (lens surface data), the surface number indicates the order of the lens surfaces from the object side along the traveling direction of the light beam, the surface interval indicates the interval on the optical axis from each optical surface to the next optical surface, The refractive index and the Abbe number indicate values for the d-line (λ = 587.6 nm), respectively.

  In (variable interval data), the photographic lens SL1 according to the first embodiment is in focus at infinity, the intermediate shooting distance state (shooting magnification -0.5 times state), and the closest shooting distance state (shooting magnification). The variable interval in the -1.0 times state. Also, d0 is the axial air space between the object and the first lens group G1, d1 is the axial air space between the first lens group G1 and the second lens group G2, and d2 is the second lens group G2 and the third lens group G2. Each of the on-axis air gaps with the lens group G3 is shown, and d0, d1, and d2 change during zooming.

  In (conditional expression corresponding value), f1F is the focal length of the front group G1F, f1R is the focal length of the rear group G1R, f is the focal length at the time of focusing on the entire system at infinity, and f1 is the first lens. The focal length of the group G1, f3 is the focal length of the third lens group G3, f1Fn is the focal length of the negative lens L12 that constitutes the front group G1F of the first lens group G1, and X1 and X2 are from infinity to the nearest The absolute values of the movement amounts on the optical axis of the first lens group G1 and the second lens group G2 when focusing on an object point are respectively shown. In the following embodiments, the description of the reference numerals is the same unless otherwise specified.

  The unit of focal length, curvature radius, surface interval, and other lengths listed in all the following specifications is generally “mm”, but the optical system may be proportionally enlarged or reduced. Since equivalent optical performance can be obtained, the present invention is not limited to this. The curvature radius “∞” indicates a plane, and the refractive index of air 1.000 is omitted. In addition, description of these codes | symbols and description of a specification table are the same also in a subsequent example, and description in a subsequent example is abbreviate | omitted.

(Table 1) First Example

(Various data)
F.NO = 2.887
f = 40
ω = 20.479
Y = 15.00
TL = 92.518
Bf = 39.818

(Lens surface data)
Surface number Curvature radius Surface spacing Refractive index Abbe number object surface ∞
1 39.6938 3.5 1.743997 44.79
2 -216.2230 1.5 1.516330 64.14
3 13.1290 12.5
4 34.1159 6.1 1.699998 48.08
5 -14.9811 1.5 1.581439 40.75
6 265.8581 2.5
7 (Aperture S) ∞ (d1)
8 -33.7748 1.4 1.740769 27.79
9 41.5423 1.7
10 -60.0662 3.3 1.651597 58.55
11 -26.1423 0.2
12 54.7001 3.9 1.740999 52.64
13 -34.9008 (d2)
14 229.2568 1.6 1.772499 49.60
15 37.7106 1.0
16 70.8279 3.6 1.548141 45.78
17 -91.4184 39.8
Image plane ∞

(Variable interval data)
Infinity Medium shooting distance Closest shooting distance
d0 ∞ 78.087 38.206
d1 7.200 6.688 7.253
d2 1.200 16.234 31.200

(Values for conditional expressions)
(1) (−f1F) /f1R=1.49
(2) f1R / f = 0.966
(3) (−f3) /f1=4.38
(4) d / f = 0.313
(5) (−f1Fn) /f=0.60
(6) X1 / f = 0.551
(7) X2 / f = 0.750

  2A and 2B show various aberration diagrams of the photographing lens SL1 according to the first example. FIG. 2A is a diagram illustrating various aberrations in the infinite focus state, and FIG. 2B is a diagram illustrating various aberrations in the closest photographing distance state. is there. In each aberration diagram, the solid line in the astigmatism diagram indicates the sagittal image plane, the broken line indicates the meridional image plane, FNO indicates the F-number, NA indicates the object-side NA at the closest shooting distance, and Y indicates the image. Represents high. In each aberration diagram, d and g represent aberrations at the d-line (λ = 587.6 nm) and g-line (λ = 435.8 nm), respectively. As is apparent from these aberration diagrams, in the first embodiment, although each lens group is composed of a very small number of lenses, each aberration from the infinite object point to the near object point is excellent. You can see that it has been corrected. It can also be seen that the distortion variation is small.

  FIG. 3 shows a state in which a ghost is generated by the light beam BM incident from the object side in the photographing lens SL1 of the first embodiment. In FIG. 3, when a light beam BM from the object side is incident on the photographing lens SL1 as shown in the drawing, it is reflected by the lens surface on the object side (the first ghost generating surface whose surface number is 14) in the negative meniscus lens L31. Then, the reflected light is reflected again by the image side lens surface of the positive meniscus lens L22 (the second ghost generation surface and its surface number is 11) and reaches the image surface I, thereby generating a ghost. . The first ghost generating surface (surface number 14) is a concave lens surface as viewed from the image plane, and the second ghost generating surface (surface number 11) is a concave lens as viewed from the aperture stop. Surface. 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)
FIG. 4 is a diagram illustrating a configuration of the photographic lens SL2 according to the second example. The photographic lens SL2 according to the second example includes, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and negative refraction. And a third lens group G3 having power. Then, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 (focusing lens group) each independently extend on the optical axis to the object side. To focus on a finite distance object.
The first lens group G1 includes, in order from the object side, a front group G1F having negative refractive power and a rear group G1R having positive refractive power. The front group G1F includes, in order from the object side, a positive meniscus lens L11 having a convex surface directed toward the object side, and an absolute value of the radius of curvature of the image side surface with the concave surface facing the image surface. The negative meniscus lens L12 is smaller than the absolute value of the lens, and corrects coma and distortion well while ensuring negative refractive power. The rear group G1R includes, in order from the object side, a biconvex positive lens L13 and a biconcave negative lens L14 whose absolute value of the curvature radius of the object side surface is smaller than the absolute value of the curvature radius of the image side surface. The lens is composed of a cemented lens, and spherical aberration and axial chromatic aberration are corrected by using the cemented lens while ensuring a strong positive refractive power.

  The second lens group G2, in order from the object side, includes an aperture stop S, a biconcave negative lens L21, a positive meniscus lens L22 having a convex surface facing the image surface, and a biconvex positive lens L23. It is composed of Since the first lens group G1 has a positive refractive power, the light flux from the object converges and reaches the second lens group G2. For this reason, a biconcave negative lens L21 is arranged on the object side in the second lens group G2, and the light beam is once diverged. Then, by arranging the positive meniscus lens L22 and the biconvex positive lens L23 on the image side of the negative lens L21, spherical aberration and coma are corrected well.

  The third lens group G3 includes, in order from the object side, a biconcave negative lens L31 in which the absolute value of the curvature radius of the image side surface is smaller than the absolute value of the curvature radius of the object side surface, and a biconvex shape positive lens. The lens L32 is configured to ensure a long back focus and correct curvature of field.

  In the second embodiment, an image surface side lens surface of the biconcave negative lens L31 of the third lens group G3 and an object side lens surface of the biconvex positive lens L32 of the third lens group G3 will be described later. An antireflection film is formed.

  Table 2 below lists values of specifications of the second embodiment.

(Table 2) Second Example

(Various data)
F.NO = 2.887
f = 40
ω = 20.479
Y = 15.00
TL = 92.122
Bf = 39.818

(Lens surface data)
Surface number Curvature radius Surface spacing Refractive index Abbe number object surface ∞
1 34.4867 3.4 1.805181 25.42
2 52.7011 0.3
3 29.4779 1.9 1.743997 44.79
4 13.3614 12.5
5 36.4689 6.1 1.772499 49.60
6 -17.2077 1.5 1.548141 45.78
7 118.9407 (d1)
8 (Aperture S) ∞ 7.2
9 -25.3642 1.4 1.740769 27.79
10 44.3873 1.7
11 -58.1179 3.3 1.651597 58.55
12 -23.8313 0.2
13 56.5111 3.9 1.740999 52.64
14 -33.0293 (d2)
15 -707.1640 1.6 1.772499 49.60
16 38.5522 0.8
17 58.7991 3.0 1.548141 45.78
18 -64.8622 39.8
Image plane ∞

(Variable interval data)
Infinity Medium shooting distance Closest shooting distance
d0 ∞ 77.315 37.556
d1 2.404 1.780 2.335
d2 1.100 16.186 31.100

(Values for conditional expressions)
(1) (-f1F) /f1R=1.63
(2) f1R / f = 0.768
(3) (−f3) /f1=5.43
(4) d / f = 0.313
(5) (−f1Fn) /f=0.86
(6) X1 / f = 0.748
(7) X2 / f = 0.750

  FIG. 5 shows various aberration diagrams of the taking lens SL2 according to the second example, where (a) shows various aberrations in the infinite focus state, and (b) shows various aberrations in the closest photographing distance state. It is. As is apparent from these respective aberration diagrams, in the second embodiment, although each lens group is composed of a very small number of lenses, each aberration is corrected well from infinity to a short distance object point. I understand that. It can also be seen that the distortion variation is small.

(Third embodiment)
FIG. 6 is a diagram illustrating a configuration of the photographing lens SL3 according to the third example. The taking lens SL3 according to the third example includes, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a negative refraction. And a third lens group G3 having power. Then, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 (focusing lens group) each independently extend on the optical axis to the object side. To focus on a finite distance object.
The first lens group G1 includes, in order from the object side, a front group G1F having negative refractive power and a rear group G1R having positive refractive power. The front group G1F includes, in order from the object side, a biconvex positive lens L11 whose absolute value of the curvature radius of the object side surface is smaller than the absolute value of the curvature radius of the image side surface, and the curvature radius of the image side surface. The negative lens L12 has a biconcave shape whose absolute value is smaller than the absolute value of the radius of curvature of the object side surface, and corrects coma aberration and distortion aberration while ensuring negative refractive power. Yes. The rear group G1R includes, in order from the object side, a negative meniscus having a biconvex positive lens L13 and a concave surface facing the object side, the absolute value of the radius of curvature of the object side surface being smaller than the absolute value of the curvature radius of the image side surface. The lens is composed of a cemented lens with the lens L14, and spherical aberration and axial chromatic aberration are corrected by using the cemented lens while ensuring a strong positive refractive power.

  The second lens group G2, in order from the object side, includes an aperture stop S, a biconcave negative lens L21, a positive meniscus lens L22 having a convex surface facing the image surface, and a biconvex positive lens L23. It is composed of Since the first lens group G1 has a positive refractive power, the light flux from the object converges and reaches the second lens group G2. For this reason, a biconcave negative lens L21 is arranged on the object side in the second lens group G2, and the light beam is once diverged. Then, by arranging the positive meniscus lens L22 and the biconvex positive lens L23 on the image side of the negative lens L21, spherical aberration and coma are corrected well.

  The third lens group G3 includes, in order from the object side, a negative meniscus lens L31 having a concave surface facing the image surface side and an absolute value of the curvature radius of the image side surface smaller than the absolute value of the curvature radius of the object side surface, Consisting of a convex positive lens L32, it ensures a long back focus and corrects curvature of field.

  In the third embodiment, an antireflection film described later is formed on the image side lens surface of the positive meniscus lens L22 of the second lens group G2 and the object side lens surface of the negative meniscus lens L31 of the third lens group G3. Has been.

  Table 3 below lists values of specifications of the third example.

(Table 3) Third Example

(Various data)
F.NO = 2.892
f = 45
ω = 18.456
Y = 15.00
TL = 92.908
Bf = 38.500

(Lens surface data)
Surface number Curvature radius Surface spacing Refractive index Abbe number object surface ∞
1 34.8272 3.4 1.805181 25.42
2 -1179.9200 0.8
3 -155.4560 1.9 1.698947 30.13
4 16.7393 13.0
5 30.1013 6.1 1.743997 44.79
6 -21.1253 1.5 1.581439 40.75
7 -84.6331 (d1)
8 (Aperture S) ∞ 7.2
9 -21.7172 1.4 1.740769 27.79
10 41.7635 2.0
11 -37.1989 3.3 1.651597 58.55
12 -22.6795 0.2
13 74.3167 3.9 1.740999 52.64
14 -32.1787 (d2)
15 290.1463 1.6 1.772499 49.60
16 25.4736 0.8
17 26.4901 3.8 1.548141 45.78
18 -153.8880 38.5
Image plane ∞

(Variable interval data)
Infinity Medium shooting distance Closest shooting distance
d0 ∞ 92.212 47.351
d1 2.406 1.874 1.653
d2 1.102 18.798 36.100

(Values for conditional expressions)
(1) (−f1F) /f1R=1.70
(2) f1R / f = 0.700
(3) (−f3) /f1=9.36
(4) d / f = 0.289
(5) (−f1Fn) /f=0.48
(6) X1 / f = 0.661
(7) X2 / f = 0.778

  FIG. 7 shows various aberration diagrams of the photographic lens SL3 according to the third example. (A) is a diagram of various aberrations in the infinite focus state, and (b) is a diagram of various aberrations in the closest photographing distance state. It is. As is apparent from these respective aberration diagrams, in the third example, although each lens group is composed of a very small number of lenses, each aberration from the infinite object point to the near object point is excellent. You can see that it has been corrected. It can also be seen that the distortion variation is small.

(Fourth embodiment)
FIG. 8 is a diagram showing a configuration of the taking lens SL4 according to the fourth example. The photographic lens SL4 according to the fourth example includes, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a negative refraction. And a third lens group G3 having power. Then, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 (focusing lens group) each independently extend on the optical axis to the object side. To focus on a finite distance object.
The first lens group G1 includes, in order from the object side, a front group G1F having negative refractive power and a rear group G1R having positive refractive power. The front group G1F includes, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side and an absolute value of the radius of curvature of the object side surface being smaller than the absolute value of the curvature radius of the image side surface; A negative meniscus lens L12 having a concave surface and an absolute value of the radius of curvature of the surface on the image side smaller than the absolute value of the radius of curvature of the surface on the object side. Distortion is corrected well. The rear group G1R includes, in order from the object side, a negative meniscus having a biconvex positive lens L13 and a concave surface facing the object side, the absolute value of the radius of curvature of the object side surface being smaller than the absolute value of the curvature radius of the image side surface. The lens is composed of a cemented lens with the lens L14, and spherical aberration and axial chromatic aberration are corrected by using the cemented lens while ensuring a strong positive refractive power.

  The second lens group G2 includes, in order from the object side, an aperture stop S, a negative biconcave lens L21, a positive meniscus lens L22 having a convex surface facing the image plane, and a biconvex positive lens L23. It is configured. Since the first lens group G1 has a positive refractive power, the light flux from the object converges and reaches the second lens group G2. For this reason, a biconcave negative lens L21 is arranged on the object side in the second lens group G2, and the light beam is once diverged. Then, by arranging the positive meniscus lens L22 and the biconvex positive lens L23 on the image side of the negative lens L21, spherical aberration and coma are corrected well.

  The third lens group G3 includes, in order from the object side, a biconcave negative lens L31 in which the absolute value of the curvature radius of the image side surface is smaller than the absolute value of the curvature radius of the object side surface, and a biconvex shape positive lens. The lens L32 is configured to ensure a long back focus and correct curvature of field.

  In the fourth embodiment, an antireflection film described later on the object-side lens surface of the positive meniscus lens L11 of the first lens group G1 and the object-side lens surface of the biconvex positive lens L13 of the first lens group G1. Is formed.

  Table 4 below shows values of specifications of the fourth embodiment.

(Table 4) Fourth Example

(Various data)
F.NO = 2.830
f = 50
ω = 16.591
Y = 15.00
TL = 95.504
Bf = 38.500

(Lens surface data)
Surface number Curvature radius Surface spacing Refractive index Abbe number object surface ∞
1 34.0919 3.4 1.805181 25.42
2 78.2611 0.8
3 84.8565 1.9 1.698947 30.13
4 18.1430 14.2
5 25.7196 7.0 1.743997 44.79
6 -26.0123 1.5 1.581439 40.75
7 -1407.4300 (d1)
8 (Aperture S) ∞ 7.2
9 -22.7294 1.4 1.728250 28.46
10 31.5074 2.0
11 -38.9885 3.1 1.620411 60.29
12 -22.7280 0.2
13 47.0519 3.7 1.693495 50.81
14 -33.1230 (d2)
15 -190.2480 1.6 1.743997 44.79
16 26.9892 0.8
17 28.9798 4.7 1.581439 40.75
18 -86.9708 38.5
Image plane ∞

(Variable interval data)
Infinity Medium shooting distance Closest shooting distance
d0 ∞ 102.988 53.175
d1 2.404 1.728 1.419
d2 1.100 18.846 36.100

(Values for conditional expressions)
(1) (-f1F) /f1R=2.50
(2) f1R / f = 0.575
(3) (−f3) /f1=6.62
(4) d / f = 0.284
(5) (−f1Fn) /f=0.67
(6) X1 / f = 0.680
(7) X2 / f = 0.700

  FIG. 9 is a diagram illustrating various aberrations of the photographic lens SL4 according to the fourth example. FIG. 9A is a diagram illustrating various aberrations in the infinitely focused state, and FIG. 9B is a diagram illustrating various aberrations in the closest photographing distance state. It is. As is apparent from these respective aberration diagrams, in the fourth example, although each lens group is composed of a very small number of lenses, each aberration from the infinite object point to the short distance object point is excellent. You can see that it has been corrected. It can also be seen that the distortion variation is small.

(5th Example)
FIG. 10 is a diagram illustrating a configuration of the photographic lens SL5 according to the fifth example. The taking lens SL5 according to the fifth example includes, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and negative refraction. And a third lens group G3 having power. Then, when focusing from an infinite object point to a short-distance object point, the first lens group G1 and the second lens group G2 (focusing lens group) each independently extend on the optical axis to the object side. To focus on a finite distance object.
The first lens group G1 includes, in order from the object side, a front group G1F having negative refractive power and a rear group G1R having positive refractive power. The front group G1F includes, in order from the object side, a cemented lens of a positive meniscus lens L11 having a convex surface facing the object side and a negative meniscus lens L12 having a concave surface facing the image surface side. The cemented lens may be configured by cementing a biconvex positive lens and a biconcave negative lens. The negative meniscus lens L12 includes a coma from an infinite object point to a short-distance object point by configuring the image side surface with a surface having an absolute value of the radius of curvature smaller than the absolute value of the radius of curvature of the object side surface. Aberration and distortion are corrected. The rear group G1R is composed of a cemented lens of a biconvex positive lens L13 and a biconcave negative lens L14 in order from the object side. Thus, by arranging the front lens group G1F, which is a negative lens group, on the object side in the first lens group G1, the distance between the object and the positive meniscus lens L11 when the first lens group G1 is extended during focusing is increased. Try to be long.

  The second lens group G2 includes, in order from the object side, a biconcave negative lens L21, a positive meniscus lens L22 having a convex surface facing the image surface, and a biconvex positive lens L23. . Since the first lens group G1 has a positive refractive power, the light beam from the object converges and reaches the second lens group G2. For this reason, a biconcave negative lens L21 is arranged on the object side in the second lens group G2, and the light beam is once diverged. Then, by arranging the positive meniscus lens L22 and the biconvex positive lens L23 on the image side of the negative lens L21, spherical aberration and coma are corrected well.

  The third lens group G3 includes, in order from the object side, a biconcave negative lens L31 and a biconvex positive lens L32. The third lens group G3 ensures a long back focus and corrects curvature of field. The third lens group G3 may be arranged with a positive lens and a negative lens in order from the object side.

  The aperture stop S is disposed between the rear group G1R of the first lens group G1 and the second lens group G2. The aperture stop S can be disposed between the front group G1F and the rear group G1R of the first lens group G1. It is also possible to arrange the aperture stop S in the second lens group G2.

  In the fifth embodiment, an aspherical surface is introduced into each lens group to improve the imaging performance. Specifically, by reducing the image side surface of the negative meniscus lens L12 to an aspherical surface, the variation range of the distortion aberration from infinity to the same magnification is achieved. Further, by making the image side surface of the biconvex positive lens L23 an aspherical surface, fluctuations in coma from infinity to equal magnification are suppressed. In addition, the curvature of field is corrected by introducing an aspherical surface to the image side surface of the biconcave negative lens L31.

  In the fifth embodiment, an antireflection film described later on the object-side lens surface of the positive meniscus lens L11 of the first lens group G1 and the object-side lens surface of the biconvex positive lens L13 of the first lens group G1. Is formed.

Table 5 below shows values of specifications of the fifth embodiment. In (Aspherical data), the paraxial radius of curvature, the conic constant, and the aspherical coefficient when the shape of the aspherical surface shown in (Lens surface data) is expressed by the following equation are shown.
S (y) = (y ² / r) / {1+ (1−κ × y ² / r ² ) ^1/2 }
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰
Here, y is the height in the direction perpendicular to the optical axis, S (y) is the distance (sag amount) along the optical axis from the tangent plane of each aspheric surface at the height y to each aspheric surface, r Is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and An is the nth-order aspherical coefficient. In the fifth embodiment, the secondary aspheric coefficient A2 is zero. In the following examples, “E−n” indicates “× 10 ⁻ⁿ ”. The aspherical surfaces are marked with * on the left side of the surface number.

(Table 5) Fifth Example

(Various data)
F.NO = 2.870
f = 40
ω = 20.504
Y = 15.00
TL = 94.159
Bf = 39.819

(Lens surface data)
Surface number Curvature radius Surface spacing Refractive index Abbe number object surface ∞
1 39.0832 3.5 1.882997 40.76
2 289.4752 1.5 1.516330 64.14
* 3 13.0001 12.5
4 39.0426 6.1 1.699998 48.08
5 -14.3688 1.5 1.581439 40.75
6 193.6469 2.5
7 (Aperture S) ∞ (d1)
8 -36.6799 1.4 1.755199 27.51
9 46.3094 1.7
10 -75.9583 3.3 1.729157 54.68
11 -28.3466 0.24
12 54.4214 3.9 1.729157 54.68
* 13 -36.7891 (d2)
14 -134.9520 1.6 1.804000 46.57
* 15 44.8591 1.0
16 95.5721 3.6 1.720000 41.98
17 -56.128 39.8
Image plane ∞

(Aspheric data)
Surface number κ A4 A6 A8 A10
3 1.0000 0.00000E + 00 -4.37302E-09 0.00000E + 00 0.OOOOOE + 00
13 1.1778 0.00000E + 00 0.00000E + 00 0.00000E + 00 0.OOOOOE + 00
15 0.7665 0.00000E + 00 0.00000E + 00 0.OOOOOE + 00 0.OOOOOE + 00

(Variable interval data)
Infinity Medium shooting distance Closest shooting distance
d0 ∞ 77.055 36.881
d1 8.000 7.925 8.799
d2 2.000 16.714 31.500

(Values for conditional expressions)
(1) (-f1F) /f1R=1.44
(2) f1R / f = 1.091
(3) (−f3) /f1=4.03
(4) d / f = 0.313
(5) (−f1Fn) /f=0.66
(6) X1 / f = 0.557
(7) X2 / f = 0.737

  FIG. 11 shows various aberrations of the taking lens SL5 according to the fifth example. (A) is a diagram showing various aberrations in the infinite focus state, and (b) is a diagram showing various aberrations in the closest photographing distance state. is there. As is clear from these aberration diagrams, in the fifth example, although each lens group is composed of a very small number of lenses, each aberration from the infinite object point to the near object point is excellent. You can see that it has been corrected. It can also be seen that the distortion variation is small.

  Next, an antireflection film (also referred to as a multilayer broadband antireflection film) used for the photographing lenses SL1 to SL5 (hereinafter collectively referred to as SL) according to the embodiment will be described. FIG. 14 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 (b).

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

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

  The optical performance of the optical member having the antireflection film 101 formed as described above will be described with reference to 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 Al2O3, a mixture of titanium oxide and zirconium oxide is represented by ZrO2 + TiO2, and a mixture of magnesium fluoride and silica is represented by MgF2 + SiO2.

  FIG. 15 shows the spectral characteristics when light rays are perpendicularly incident on an optical member in which the reference wavelength λ is 550 nm and the optical film thickness of each layer of the antireflection film 101 is designed in Table 6.

  From FIG. 15, 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. It has been found that the spectral characteristics are almost the same as when the wavelength λ is 550 nm.

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

  Next, a modified example of the antireflection film will be described. This antireflection film consists 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.

  FIG. 16 shows the spectral characteristics when light enters perpendicularly to an optical member having an antireflection film whose optical film thickness is designed with a refractive index of the substrate of 1.52 and a reference wavelength λ of 550 nm in Table 7. Yes. It can be seen from FIG. 16 that the antireflection film of the present modification 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 whose optical film thickness is designed with the reference wavelength λ as the d-line (wavelength 587.6 nm) hardly affects the spectral characteristics, and the spectral characteristics shown in FIG. It is known to have almost the same characteristics as

  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. 16 and 17 do not show the spectral characteristics of the optical member having the antireflection film with the refractive index of 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.

(Table 7)
Material Refractive index Optical film thickness Optical film thickness Medium Air 1
5th layer MgF2 + SiO2 1.26 0.275λ 0.269λ
4th layer ZrO2 + TiO2 2.12 0.045λ 0.043λ
3rd layer Al2O3 1.65 0.212λ 0.217λ
Second layer ZrO2 + TiO2 2.12 0.077λ 0.066λ
1st layer Al2O3 1.65 0.288λ 0.290λ
Refractive index of substrate 1.46 1.52

  For comparison, FIG. 18 shows an example of an antireflection film formed only by a dry process such as a conventional vacuum deposition method. FIG. 18 shows the spectral characteristics when a light beam is perpendicularly incident on an optical member designed with an antireflection film configured under the conditions shown in Table 8 below at a refractive index of 1.52 of the same substrate as in Table 7. FIG. 19 shows spectral characteristics when the incident angles of light rays to the optical member having the spectral characteristics shown in FIG. 18 are 30, 45, and 60 degrees, respectively.

(Table 8)
Material Refractive index Optical film thickness Medium Air 1
7th layer MgF2 1.39 0.243λ
6th layer ZrO2 + TiO2 2.12 0.119λ
5th layer Al2O3 1.65 0.057λ
4th layer ZrO2 + TiO2 2.12 0.220λ
3rd layer Al2O3 1.65 0.064λ
Second layer ZrO2 + TiO2 2.12 0.057λ
1st layer Al2O3 1.65 0.193λ
Refractive index of substrate 1.52

  When comparing the spectral characteristics of the optical member having the antireflection film according to this embodiment shown in FIGS. 15 to 17 with the spectral characteristics of the conventional example shown in FIGS. It can be seen that the corner also has a lower reflectivity and has a lower reflectivity over a wider band.

  Next, an example in which the antireflection films shown in Tables 6 and 7 are applied to the first to fifth examples described above will be described.

  In the photographic lens SL1 of the first example, the refractive index of the positive meniscus lens L22 in the second lens group G2 is nd = 1.615597 as shown in Table 1, and the negative meniscus lens in the third lens group G3. Since the refractive index of L31 is nd = 1.77499, the antireflection film 101 (see Table 6) corresponding to the refractive index of the substrate of 1.62 is used on the image surface side lens surface of the positive meniscus lens L22. By using an antireflection film (see Table 6) having a refractive index of the substrate of 1.74 on the object-side lens surface of the negative meniscus lens L31, reflected light from each lens surface can be reduced, and ghost and Flare can be reduced.

  In the photographic lens SL2 of the second embodiment, the refractive index of the negative biconcave lens L31 in the third lens group G3 is nd = 1.77499, as shown in Table 2, and the third lens group Since the refractive index of the G3 biconvex positive lens L32 is nd = 1.548141, the refractive index of the substrate corresponds to the lens surface on the image plane side of the biconcave negative lens L31. By using the antireflection film 101 (see Table 6) and using the antireflection film (see Table 7) corresponding to the refractive index of the substrate of 1.52 on the object-side lens surface of the biconvex positive lens L32. The reflected light from each lens surface can be reduced, and ghost and flare can be reduced.

  In the photographic lens SL3 of the third example, the refractive index of the positive meniscus lens L22 of the second lens group G2 is nd = 1.615597 as shown in Table 3, and the negative index of the third lens group G3. Since the refractive index of the meniscus lens L31 is nd = 1.77499, the antireflection film 101 (see Table 6) corresponding to the refractive index of the substrate corresponding to 1.62 is formed on the lens surface on the image surface side of the positive meniscus lens L22. By using an antireflection film (see Table 6) corresponding to the refractive index of the substrate of 1.74 on the object-side lens surface of the negative meniscus lens L31, the reflected light from each lens surface can be reduced, and the ghost And flare can be reduced.

  Further, in the photographing lens SL4 of the fourth example, the refractive index of the positive meniscus lens L11 of the first lens group G1 is nd = 1.805181 as shown in Table 4, and both of the first lens group G1. Since the refractive index of the convex positive lens L13 is nd = 1.7439797, the antireflective film 101 corresponding to the refractive index of the substrate corresponding to 1.85 is formed on the object-side lens surface of the positive meniscus lens L11 (Table 6). And an antireflection film 101 (see Table 6) corresponding to a refractive index of the substrate of 1.74 is used on the object-side lens surface of the biconvex positive lens L13. Reflected light can be reduced, and ghost and flare can be reduced.

  In the photographic lens SL5 of the fifth example, the refractive index of the positive meniscus lens L11 in the first lens group G1 is nd = 1.882997 as shown in Table 5, and both of the first lens group G1. Since the refractive index of the convex lens L13 is nd = 1.699998, the antireflection film 101 (see Table 6) corresponding to the refractive index of the substrate of 1.85 is used on the object-side lens surface of the positive meniscus lens L11. By using an antireflection film 101 (see Table 6) having a refractive index of the substrate of 1.74 on the object side lens surface of the biconvex positive lens L13, reflected light from each lens surface is reduced. 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 the above description and examples, the three-group configuration is shown, but the above-described configuration conditions and the like can be applied to other group configurations such as the fourth group, the fifth group, and the like. 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 or a plurality of lens groups, or a partial lens group may be moved along the optical axis to be a focusing lens group that performs focusing from an object at infinity to a near object. In this case, the focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, it is desirable that the first lens group G1 and the second lens group G2 be the focusing lens group.

  Image stabilization that corrects image blur caused by camera shake by moving the lens group or partial lens group so as to have a component perpendicular to the optical axis, or by rotating (swinging) the lens group or partial lens group in the in-plane direction including the optical axis It may be a lens group. In particular, it is preferable that at least a part of the third lens group G3 is an anti-vibration lens group.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. It is preferable that the lens surface is a spherical surface or a flat surface because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembly adjustment is prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. In addition, when the lens surface is aspheric, this aspherical surface is an aspherical surface by grinding, a glass mold aspherical surface made of glass with an aspherical shape, and a composite type in which resin is formed on the glass surface in an aspherical shape. 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 S is preferably disposed on the image plane side of the rear group G1R, but may be disposed between the front group G1F and the rear group G1R. An aperture stop S may be disposed in the second lens group G2. In addition, a lens frame may be used instead of a member as an aperture stop.

  In the photographing lens SL according to the present embodiment, it is preferable that the first lens group G1 has one positive lens component and one negative lens component. In the photographic lens SL according to this embodiment, it is preferable that the second lens group G2 has two positive lens components and one negative lens component. In the second lens group G2, it is preferable that the lens components are arranged in order of negative positive / negative in order from the object side with an air gap interposed therebetween. Further, in the photographic lens SL according to the present embodiment, it is preferable that the third lens group G3 has one positive lens component and one negative lens component.

  In addition, in order to explain this application in an easy-to-understand manner, the configuration requirements of the embodiment have been described, but it goes without saying that the present application is not limited to this. Further, the effects of the present application can be obtained even when the lens data is proportionally enlarged or reduced.

As described above, according to the present invention, it is possible to further reduce ghosts and flares, and to obtain a good imaging performance from an infinite object point to a close object point while reducing the size of the optical system with a simple lens configuration. It is possible to provide a photographing lens that can be used, an optical apparatus including the same, and a manufacturing method.

SL (SL1 to SL5) Shooting lens G1 First lens group
G1F front group
G1R Rear group G2 Second lens group
G3 Third lens group
G4 4th lens group
S Aperture stop 1 Digital single-lens reflex camera (optical equipment)
101 Antireflection film 101a 1st layer 101b 2nd layer 101c 3rd layer 101d 4th layer 101e 5th layer 101f 6th layer 101g 7th layer 102 Optical member

Claims (19)

From the object side,
A first lens group having a positive refractive power;
An aperture stop,
A second lens group having a positive refractive power;
A third lens group having a negative refractive power and substantially consisting of three lens groups ;
When focusing from an infinite object point to a short-distance object point, the first lens group and the second lens group independently move on the optical axis to the object side,
The first lens group is in order from the object side.
A front group having negative refractive power;
A rear group having a positive refractive power,
The front group is composed of a positive lens and a negative lens in order from the object side,
An antireflection film is provided on at least one of the optical surfaces of the first lens group to the third lens group, and the antireflection film includes at least one layer formed using a wet process. Shooting lens. The antireflection film is a multilayer film,
The photographing 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.   The photographic lens according to claim 1, wherein nd is 1.30 or less, where nd is a refractive index of a layer formed by using the wet process.   The optical surface provided with the antireflection film is at least one surface of the first lens group and the second lens group, and the optical surface is a concave surface when viewed from the aperture stop. The photographing lens according to any one of claims 1 to 3.   The photographic lens according to claim 4, wherein the concave surface is a lens surface on the image plane side.   The photographic lens according to claim 4, wherein the concave surface is an object side lens surface.   2. The optical surface provided with the antireflection film is at least one surface of the third lens group, and the optical surface is a concave surface when viewed from the image surface. 4. The taking lens according to any one of 3 above.   The photographic lens according to claim 7, wherein the concave surface is a lens surface on an image plane side.   The photographing lens according to claim 7, wherein the concave surface is an object side lens surface. The photographic lens according to claim 1, wherein the following condition is satisfied.
1.38 <(− f1F) / f1R <3.00
However,
f1F: focal length of the front group,
f1R: focal length of the rear group. The photographing lens according to any one of claims 1 to 10, wherein the following condition is satisfied.
0.50 <f1R / f <1.20
However,
f1R: focal length of the rear group,
f: Focal length when focusing on infinity of the entire system   The photographing lens according to claim 1, wherein an interval between the first lens group and the second lens group changes during focusing. The photographing lens according to claim 1, wherein the following condition is satisfied.
4.00 <(− f3) / f1 <10.00
However,
f1: the focal length of the first lens group,
f3: focal length of the third lens group The photographing lens according to claim 1, wherein the following condition is satisfied.
0.20 <d / f <0.33
However,
d: an air space on the optical axis between the most image side lens surface of the front group and the most object side lens surface of the rear group;
f: Focal length when focusing on infinity of the entire system The photographing lens according to claim 1, wherein the following condition is satisfied.
0.40 <(− f1Fn) / f <0.90
However,
f1Fn: focal length of the negative lens constituting the front group,
f: Focal length when focusing on infinity of the entire system. The photographic lens according to claim 1, wherein the following condition is satisfied.
0.60 <X1 / f <0.90
However,
X1: absolute value of the amount of movement of the first lens unit on the optical axis when focusing from infinity to the closest object point;
f: Focal length when focusing on infinity of the entire system. The photographing lens according to claim 1, wherein the following condition is satisfied.
0.70 <X2 / f <0.90
However,
X2: absolute value of the amount of movement on the optical axis of the second lens group when focusing from infinity to the closest object point;
f: Focal length when focusing on infinity of the entire system.   18. The photographic lens according to claim 1, further comprising an aspheric lens in at least one of the front group, the rear group, and the second lens group.   An optical apparatus comprising the photographic lens according to claim 1.

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