JP6172951B2 - Optical system and imaging apparatus having the same - Google Patents

Description

  The present invention relates to an optical system and an image pickup apparatus having the same, and is suitable for an image pickup optical system such as a digital still camera / digital video camera, a TV camera, a surveillance camera, and a silver salt camera.

  2. Description of the Related Art Conventionally, a macro lens or a micro lens (hereinafter, referred to as a macro lens) is used as an imaging optical system that is used in an imaging apparatus and mainly focuses on shooting a short-distance object with a shooting magnification of about the same magnification. The macro lens is designed so that it can satisfactorily photograph from an object at infinity to a short distance object with a photographing magnification of 1 or 0.5 times.

  In addition, the macro lens is designed so as to obtain a high optical performance particularly in a short-distance object as compared with a general photographing lens. However, when the photographic magnification range is further expanded, fluctuations in various aberrations accompanying focusing (focusing) become remarkable. In particular, when the photographing magnification is increased, many negative spherical aberrations are easily generated among various aberrations, and many chromatic aberrations, coma aberrations, and the like are easily generated.

  On the other hand, there is known a macro lens that employs a so-called floating method in which a plurality of lens groups are independently moved during focusing in order to reduce aberration fluctuations during focusing on a short distance object (Patent Documents 1 and 2). ).

  In the macro lens of Patent Document 1, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a negative lens having a negative refractive power. A fourth lens unit is used. When focusing from an object at infinity to a near object, the second lens unit is moved to the image side and the third lens unit is moved to the object side.

Further, in the telephoto lens capable of photographing at close range in Patent Document 2, a first lens unit having a positive refractive power, a first lens unit having a positive refractive power, and a second lens having a negative refractive power are sequentially arranged from the object side to the image side. The unit is composed of a third lens unit having a positive refractive power. When focusing from an object at infinity to an object at a short distance, the 1a lens unit and the third lens unit are moved. On the other hand, as a method for correcting various aberrations including chromatic aberration of an optical system, a method using a diffractive optical element provided with a diffractive surface (diffractive optical part) having a diffractive action on a part of a lens surface is known (patent). Reference 3).

  Patent Document 3 discloses a telephoto lens in which chromatic aberration is corrected favorably using a diffractive optical element. In Patent Document 3, the power of the first lens group is increased to shorten the entire lens length, and chromatic aberration is corrected with a diffractive optical element, and other aberrations are corrected with an aspherical surface. As a result, various aberrations are corrected and the overall size and weight are reduced.

JP 2011-13357 A JP-A-5-323191 JP 2009-271354 A

  In many imaging optical systems, it is desired that the shortest imaging distance that can be taken is short and that the entire system is small. If the entire system is reduced in size, the power of each lens is increased, and fluctuations in various aberrations during focusing increase.

  The present invention is an optical system in which fluctuations of various aberrations accompanying focusing are small at all object distances from an infinite object to a close object, high optical performance can be easily obtained at all object distances, and the entire system can be easily downsized. The purpose is to provide a system.

The optical system according to the present invention includes, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a rear group having a lens unit having a positive refractive power. An optical system,
Wherein the first lens unit and a positive refractive power lens subunit L1a and the positive refractive power of the lens subunit L1b is spaced intervals have the widest in the first lens unit, and the diffraction surface, and Including aspheric surfaces,
The second lens unit moves to the image side during focusing from an object at infinity to a near object,
The focal length of the entire system is f, the focal lengths of the first lens unit and the second lens unit are f1 and f2, respectively, the total length of the lens is L, and the distance between the partial lens group L1a and the partial lens group L1b is L1ab, When the combined focal length of the first lens unit and the second lens unit when focusing on an object at infinity is f12 ,
0.30 ≦ f1 × L / f ² ≦ 0.65
0.80 ≦ | f1 / f2 | ≦ 3.50
0.12 ≦ (L1ab / L) / (f1 / f) ≦ 0.50
| F / f12 | ≦ 0.36
It satisfies the following conditional expression.
In addition, the optical system according to the present invention includes a first lens unit having a positive refractive power in order from the object side to the image side, and a negative refractive power having a negative refractive power that moves toward the image side during focusing from an object at infinity to a short distance object. A second lens unit, a third lens unit having a positive refractive power that moves toward the object side during the focusing, and a fourth lens unit having a positive refractive power that does not move during the focusing,
The first lens unit includes a partial lens unit L1a having a positive refractive power and a partial lens unit L1b having a positive refractive power that are arranged at the widest intervals in the first lens unit, and has a diffractive surface and an aspherical surface. Including
The focal length of the entire system is f, the focal lengths of the first lens unit and the second lens unit are f1 and f2, respectively, the total length of the lens is L, and the distance between the partial lens group L1a and the partial lens group L1b is L1ab, And when
0.30 ≦ f1 × L / f ² ≦ 0.65
0.80 ≦ | f1 / f2 | ≦ 3.50
0.12 ≦ (L1ab / L) / (f1 / f) ≦ 0.50
It satisfies the following conditional expression.

  According to the present invention, variations in various aberrations accompanying focusing are small at the entire object distance from an infinite object to a close object, high optical performance can be easily obtained at the entire object distance, and the entire system can be easily downsized. Can be obtained.

Sectional drawing of the optical system of Example 1 of this invention Aberration diagram of optical system of Example 1 of the present invention Sectional drawing of the optical system of Example 2 of this invention Aberration diagram of optical system of Example 2 of the present invention Sectional drawing of the optical system of Example 3 of this invention Aberration diagram of optical system of Example 3 of the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

Embodiments of the present invention will be described below with reference to the drawings. First, prior to description of specific examples of the optical system of the present invention, configurations common to the examples will be described. The optical system of each embodiment includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a rear group in order from the object side to the image side.

The rear group includes a third lens unit having a positive refractive power. The first lens unit includes a partial lens unit L1a having a positive refractive power and a partial lens unit L1b having a positive refractive power which are arranged with the widest air interval (lens interval) in the first lens unit. The first lens unit has one or more diffractive surfaces and one or more aspheric surfaces. Further, at the time of focusing (focusing) from an object at infinity to an object at a short distance, at least the second lens unit moves to the image side .

  Here, the lens unit means a lens group composed of a single lens or a plurality of lenses that moves in the optical axis direction in accordance with the focus or the like, or a lens group composed of a fixed single lens or a plurality of lenses before and after that. A lens group that shifts in a direction perpendicular to the optical axis for optical image stabilization also corresponds to the lens unit here.

  FIG. 1 is a lens cross-sectional view at the time of focusing on an object at infinity according to Example 1 of the optical system of the present invention. FIGS. 2A, 2B, and 2C illustrate focusing on an object at infinity, an object with a shooting magnification of 0.5x (0.5 times), and an object with a shooting magnification of 1.0x in the optical system of the first embodiment. FIG. FIG. 3 is a lens cross-sectional view when focusing on an object at infinity according to the second embodiment of the optical system of the present invention. 4A, 4B, and 4C are longitudinal aberration diagrams when focusing on an object at infinity, an object with an imaging magnification of 0.5x, and an object with an imaging magnification of 1.0x in the optical system of Example 2. FIG. .

FIG. 5 is a lens cross-sectional view of the optical system according to the third embodiment of the present invention when focusing on an infinitely distant object. FIG 6 (A), (B) , (C) is a longitudinal aberration diagram at the time of focus on the object of the object and the imaging magnification 0.5 x the infinite object and the imaging magnification 0.25x in the optical system of Example 3 is there. FIG. 7 is a schematic view of the main part of the imaging apparatus of the present invention. In the lens cross-sectional view, the left side is the object side (front, enlargement side), and the right side is the image side (rear, reduction side). LO is an optical system. L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, and SP is an aperture stop. LR is the rear group.

In the first and second embodiments, the rear lens group LR has a positive third refractive power unit that moves toward the object side during focusing from an object at infinity to a short distance object and a positive refractive power that does not move during focusing. It is configured by a fourth lens unit L4. In the third embodiment, the rear group LR includes a third lens unit L3 having a positive refractive power that does not move during focusing.

  IP is an image plane, and when used as an imaging optical system of a video camera or a digital still camera, the image plane corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor. When used for a silver salt film camera, the image plane corresponds to a film plane. In the spherical aberration diagram, the solid line d represents the d line, and the alternate long and short dash line g represents the g line. In the astigmatism diagram, ΔM represents the d-line meridional image plane, and ΔS represents the d-line sagittal image plane. Distortion is represented by d-line. Fno is an F number, and ω is a half angle of view (degrees).

  In an optical system capable of forming an image from an object at infinity to a near object, various aberrations tend to fluctuate during focusing. In particular, as the maximum imaging magnification increases (the shooting distance decreases), the amount of variation in various aberrations increases. Even in a macro lens configured to have higher optical performance with respect to an object at a short distance than a general optical system, various aberrations, particularly spherical aberration, are insufficiently corrected during focusing, and chromatic aberration varies greatly.

  When the lens unit is moved during focusing, high-speed focusing is facilitated by reducing the driving load of the lens unit. As a method for driving the lens unit, for example, there is a method in which the whole or a part of the optical system is drawn out toward the object side and focused. These focusing methods tend to be difficult to focus at high speed due to a large driving load. Furthermore, the focusing method in which the entire optical system is extended toward the object side is likely to cause problems such as the front lens of the optical system contacting an object at a short distance.

  Therefore, conventionally, a macro lens that employs an inner focus method in which a part of lens units in an optical system is driven to perform focusing has been proposed. In the inner focus method, the entire lens length of the optical system does not change, and the lens unit driven by the focus can be easily reduced in weight. If so-called floating that drives a plurality of lens units is adopted, it becomes easy to satisfactorily correct various aberrations that change during focusing, and it becomes easy to reduce the driving load of each lens unit. .

  In general, in order to reduce the fluctuations of various aberrations accompanying the focus, particularly the fluctuations of spherical aberration and chromatic aberration, it is necessary to reduce the fluctuations of spherical aberration and chromatic aberration in the first lens unit. Conventionally, in order to reduce the fluctuation of spherical aberration, a plurality of lenses are used and the refractive power is shared by them. In addition, a low dispersion glass lens is used to reduce fluctuations in chromatic aberration. For this reason, a relatively large number of lenses are required, and it is difficult to increase the size and weight of the optical system.

The lens configuration of the optical system of the present invention is as follows. In order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear group LR are provided. The rear group LR includes a third lens unit L3 having a positive refractive power. The first lens unit L1 includes a partial lens group L1a having a positive refractive power and a partial lens group L1b having a positive refractive power having the widest lens interval in the first lens unit .

The first lens unit L1 has at least one diffractive surface and at least one aspheric surface. Further, the second lens unit L2 moves to the image plane side when focusing from an object at infinity to an object at a short distance.

The focal length of the entire system is f, and the focal lengths of the first lens unit L1 and the second lens unit L2 are f1 and f2, respectively. Let L be the total lens length (the length from the first lens surface to the final lens surface plus the back focus). The interval between the partial lens unit L1a and the partial lens unit L1b is L1ab. At this time,
0.30 ≦ f1 × L / f ² ≦ 0.65 (1)
0.80 ≦ | f1 / f2 | ≦ 3.50 (2)
0.12 ≦ (L1ab / L) / (f1 / f) ≦ 0.50 (3)
The following conditional expression is satisfied.

In each embodiment, the first lens unit L1 includes a plurality of partial lens groups (lens units) having different optical functions in terms of aberration correction. In each embodiment, among the plurality of lenses constituting the first lens unit L1, the lens is divided into two partial lens groups , a partial lens group L1a and a partial lens group L1b, at a location where the air interval is maximum.

  The first lens unit L1 has one or more diffractive surfaces and one or more aspheric surfaces. Further, the first lens unit L1 is configured with a relatively small number of lenses. The spherical aberration that can be reduced by sharing the refractive power among a plurality of lenses is reduced with a small number of lenses by using an aspherical surface. Further, the chromatic aberration is favorably corrected with a small number of lenses by using a diffraction surface. Suppression of fluctuations of various aberrations accompanying focusing and reduction in size and weight of the entire system are achieved by providing the first lens unit L1 with a diffractive surface and an aspherical surface.

  Conditional expression (1) and conditional expression (2) are mainly for reducing various aberrations that fluctuate during focusing and reducing the size of the entire system. When the focal length f1 of the first lens unit L1 is reduced beyond the lower limit values of the conditional expressions (1) and (2), various aberrations such as spherical aberration increase, making it difficult to correct them. If the focal length f1 of the first lens unit L1 exceeds the upper limit values of the conditional expressions (1) and (2), it becomes difficult to reduce the size of the entire system.

Conditional expression (3) is mainly for reducing various aberrations that vary during focusing, particularly spherical aberration. In a focused state on an object at infinity, various aberrations such as spherical aberration are well corrected in the combined system of the first lens unit L1 and the second lens unit L2. At this time, negative spherical aberration occurs in the partial lens unit L1a and the partial lens unit L1b , and positive spherical aberration occurs in the second lens unit L2, which are in a canceling relationship with each other.

  On the other hand, in the state of focusing on an object at a short distance, since the second lens unit L2 moves to the image side, the generation amount of spherical aberration is reduced. At this time, in order to prevent the spherical aberration in the combined system of the first lens unit L1 and the second lens unit L2 from being insufficiently corrected, the spherical aberration of the first lens unit L1 can be displaced in the positive direction. Good.

When the distance L1ab between the partial lens unit L1a and the partial lens unit L1b becomes smaller than the lower limit value of the conditional expression (3), the amount of displacement of the first lens unit L1 in the positive direction of the spherical aberration becomes insufficient during focusing. As a result, it becomes difficult to reduce the variation of spherical aberration. If the distance L1ab is larger than the upper limit of the conditional expression (3), the constituent lens length of the first lens unit L1 becomes large, and it becomes difficult to reduce various aberrations such as spherical aberration and coma aberration. Miniaturization becomes difficult.

  In order to further reduce fluctuations in various aberrations during focusing and to have high optical performance, the numerical ranges of conditional expressions (1) to (3) are preferably set to the following ranges.

0.35 ≦ f1 × L / f ² ≦ 0.60 (1a)
0.90 ≦ | f1 / f2 | ≦ 3.00 (2a)
0.15 ≦ (L1ab / L) / (f1 / f) ≦ 0.48 (3a)
More desirably, the numerical range of the conditional expression (1a) to the conditional expression (3a) is set to the following range.

0.38 ≦ f1 × L / f ² ≦ 0.58 (1b)
1.00 ≦ | f1 / f2 | ≦ 2.50 (2b)
0.18 ≦ (L1ab / L) / (f1 / f) ≦ 0.45 (3b)
In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions.

Let f12 be the combined focal length of the first lens unit L1 and the second lens unit L2 when focusing on an object at infinity. The focal lengths of the partial lens unit L1a and the partial lens unit L1b are defined as f1a and f1b, respectively. Let fdoe be the focal length of at least one of the one or more diffractive surfaces. At this time, one or more of the following conditional expressions should be satisfied.

| F / f12 | ≦ 0.40 (4)
0.20 ≦ f1a / f1b ≦ 1.20 (5)
10 ≦ fdoe / f ≦ 100 (6)

  Next, the technical meaning of each conditional expression will be described. Conditional expression (4) relates to the combined focal length of the first lens unit L1 and the second lens unit L2, and is mainly for reducing fluctuations in various aberrations in focus. When the combined focal length f12 of the first lens unit L1 and the second lens unit L2 becomes smaller than the upper limit value of the conditional expression (4), fluctuations in various aberrations such as spherical aberration during focusing increase. In order to further reduce fluctuations in various aberrations at the focus and to obtain high optical performance, the numerical range of conditional expression (4) is preferably set to the following range.

| F / f12 | ≦ 0.36 (4a)
More desirably, the numerical range of the conditional expression (4) is set to the range shown below.
| F / f12 | ≦ 0.34 (4b)

Conditional expression (5) relates to the focal lengths of the partial lens unit L1a and the partial lens unit L1b in order to satisfactorily reduce spherical aberration that varies mainly during focusing. When the lower limit of conditional expression (5) is exceeded and the focal length f1a of the partial lens unit L1a is reduced, the negative spherical aberration of the partial lens unit L1a is increased. As a result, the displacement of the spherical aberration in the positive direction by the first lens unit L1 becomes excessive in a focused state on an object at a short distance.

When the focal length f1a increases beyond the upper limit value of conditional expression (5), the occurrence of negative spherical aberration by the partial lens unit L1a decreases. As a result, it is not preferable that the spherical aberration due to the first lens unit L1 is insufficiently displaced in the positive direction in a focused state on a short distance object. In order to reduce fluctuations in various aberrations in focusing, particularly spherical aberration, the numerical range of conditional expression (5) is more preferably set to the following range.

0.25 ≦ f1a / f1b ≦ 1.12 (5a)
More desirably, the numerical range of the conditional expression (5a) is set to the range shown below.
0.27 ≦ f1a / f1b ≦ 1.04 (5b)

  Conditional expression (6) is mainly for satisfactorily correcting chromatic aberration with respect to the focal length fdoe of the diffractive surface of the optical system.

  When conditional expression (6) is satisfied, it becomes easy to satisfactorily correct various aberrations, particularly chromatic aberration. If the lower limit of conditional expression (6) is exceeded and the focal length fdoe becomes small, the refractive power of the diffractive surface becomes too strong and chromatic aberration is overcorrected. In addition, the pitch of the diffraction grating becomes small, making it difficult to manufacture. When the focal length fdoe is increased beyond the upper limit value of conditional expression (6), the refractive power of the diffractive surface becomes weak and chromatic aberration is insufficiently corrected. From the viewpoint of correcting chromatic aberration, the numerical range of conditional expression (6) is more preferably set to the following range.

12 ≦ fdoe / f ≦ 90 (6a)
More preferably, the numerical range of conditional expression (6a) is set as follows.

14 ≦ fdoe / f ≦ 80 (6b)
In each embodiment, the partial lens unit L1b includes a cemented lens in which a meniscus negative lens having a convex surface directed toward the object side and a positive lens are cemented, and has a diffractive surface on the cemented lens surface of the cemented lens. This facilitates correction of chromatic aberration.

The meniscus negative lens included in the partial lens unit L1b favorably reduces the variation in spherical aberration of the first lens unit L1 when focusing from an object at infinity to an object at a short distance. In addition, by arranging the diffractive surface on the cemented surface of the cemented lens of the partial lens unit L1b , the diffractive surface is not in contact with air, and the environmental resistance is favorably maintained.

Furthermore, by disposing a diffractive surface on the partial lens unit L1b , for example, when the optical system is used in a backlight state, unnecessary light is less likely to enter the diffractive surface. Since the diffraction efficiency on the diffraction surface depends on the light incident angle, unintended light may reach the image surface due to diffractive action when unwanted light is incident, and ghosts and flares may occur. For this reason, in each embodiment, the diffractive surface is arranged in the partial lens unit L1b in which unnecessary light is difficult to be incident.

In each embodiment, the partial lens unit L1a is preferably composed of a lens having a positive refractive power (positive lens) having an aspherical surface. This makes it easy to reduce fluctuations in various aberrations during focusing.

The partial lens unit L1a is disposed closest to the object side, and the lens diameter tends to be relatively large. For this reason, reducing the number of constituent lenses of the partial lens unit L1a is effective in reducing the weight of the optical system. Therefore, in each embodiment, the partial lens unit L1a is configured by one positive lens. At this time, it is desirable to use an aspherical surface in order to correct various aberrations such as spherical aberration.

  In each embodiment, it is desirable that the first lens unit L1 does not move during focusing. According to this, problems such as contact between the front lens of the optical system and the subject are less likely to occur when photographing a short distance object. In the first and second embodiments, the third lens unit L3 moves to the object side during focusing from an object at infinity to an object at a short distance. According to this, it becomes easy to satisfactorily reduce various aberrations such as field curvature that fluctuate during focusing.

  Next, the lens configuration of each example will be described. The optical system LO of Example 1 in FIG. 1 includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, an aperture stop SP, It is composed of a group LR. The rear group LR includes, in order from the object side to the image side, a third lens unit L3 having a positive refractive power and a fourth lens unit L4 having a positive refractive power. Example 1 is a telephoto type macro lens having a focal length of 180 mm (35 mm equivalent, the same applies hereinafter) and an F number of 3.5 suitable for a single-lens reflex camera, for example.

  During focusing, the first lens unit L1 and the fourth lens unit L4 are immovable (fixed) with respect to the image plane IP. By moving the second lens unit L2 to the image plane side and the third lens unit L3 to the object side in the optical axis direction, focusing from an object at infinity to a near object is performed.

The first lens unit L1 includes a partial lens unit L1a and a partial lens unit L1b with the widest air interval as a boundary. The partial lens unit L1a is composed of one positive lens having an aspherical surface. The partial lens unit L1b includes a cemented lens in which a negative meniscus lens having a convex surface directed toward the object side and a positive lens are cemented, and has a diffractive surface on the cemented lens surface of the cemented lens.

The focal lengths f1 and f2 of the first lens unit L1 and the second lens unit L2, the focal length f of the entire optical system, the total lens length L, and the distance L1ab between the partial lens unit L1a and the partial lens unit L1b are conditional expressions (1) to (1). Conditional expression (3) is satisfied.

  In this embodiment, it is possible to photograph from an object at infinity to an object at a close distance with a photographing magnification of 1.0 (1 ×) (equal magnification). In addition, each numerical value of the optical system of the present example satisfies conditional expressions (4) to (6).

In this embodiment, by using an aspherical surface for the partial lens unit L1a and a diffractive surface for the partial lens unit L1b , the first lens unit L1 can be easily reduced in weight, and the entire optical system can be reduced in size and weight. ing.

  The lens configuration of the optical system LO of Example 2 in FIG. 3 is the same as that of Example 1 in FIG. Example 2 is a telephoto macro lens having a focal length of 180 mm and an F number of 3.6 suitable for a single-lens reflex camera, for example. The focus method is the same as in the first embodiment.

  The optical system LO of Example 3 in FIG. 5 includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, an aperture stop SP, It is composed of a group LR. The rear group LR includes a third lens unit L3 having a positive refractive power. Example 3 is a telephoto macro lens having a focal length of 180 mm and an F number of 3.5 suitable for a 35 mm single lens reflex camera.

During focusing, the first lens unit L1 and the third lens unit L3 are immovable (fixed) with respect to the image plane IP. By moving the second lens unit L2 to the image plane side in the optical axis direction, focusing from an object at infinity to an object at a short distance is performed. The first lens unit L1 includes a partial lens group L1a and a partial lens group L1b with the widest air gap as a boundary.

The partial lens unit L1a is composed of one positive lens having an aspherical surface. The partial lens unit L1b includes a cemented lens in which a negative meniscus lens having a convex surface directed toward the object side and a positive lens are cemented, and has a diffractive surface on the cemented lens surface of the cemented lens. The focal lengths f1 and f2 of the first lens unit L1 and the second lens unit L2, the focal length f of the entire optical system, the total length L of the optical system, and the interval L1ab between the partial lens group L1a and the partial lens group L1b are conditional expressions (1 To conditional expression (3).

  In this embodiment, it is possible to photograph from an object at infinity to an object at a close distance with a photographing magnification of 0.5 times. In addition, each numerical value of the optical system of the present example satisfies conditional expressions (4) to (6).

In this embodiment, by using an aspherical surface for the partial lens unit L1a and a diffractive surface for the partial lens unit L1b , the first lens unit L1 can be easily reduced in weight, and the entire optical system can be reduced in size and weight. ing.

(Numerical example)
Hereinafter, numerical examples 1 to 3 corresponding to the first to third embodiments will be described. In each numerical example, i indicates the number of the surface or optical element counted from the light incident side. For example, ri is the radius of curvature of the i-th optical surface (i-th surface). di is an axial distance between the i-th surface and the (i + 1) -th surface. The unit of ri and di is mm. ni and νdi respectively indicate the refractive index and Abbe number of the material of the i-th optical element with respect to the d-line.

  The refractive indexes of the Fraunhofer line for g-line (wavelength 435.8 nm), F-line (wavelength 486.1 nm), d-line (wavelength 587.6 nm), and C-line (wavelength 656.3 nm) are ng, nF, and nd, respectively. , NC. The Abbe number νd for the d line and the partial dispersion ratio for the g line and the F line are respectively defined as follows.

νd = (nd−1) / (nF−nC)
θgF = (ng−nF) / (nF−nC)
In each embodiment, the focal length and the like are represented by using the reference wavelength as a d-line. The aspherical shape with * next to the surface number is defined as follows: X is the amount of displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, and r is the paraxial curvature. When a radius is set, k is a conic constant, and B, C, D, E,.

  The phase φ of the diffractive surface with (diffraction) next to the surface number is given by the following equation, where m is the diffraction order of the diffracted light, λ0 is the reference wavelength, and Ci (i = 1, 2, 3,...) Represent.

  The Abbe number νdDOE for the d-line of the diffractive surface and the partial dispersion ratio θgFDOE for the g-line and the F-line are as follows when the wavelengths of the d-line, g-line, C-line, and F-line are λd, λg, λC, and λF, respectively. It is expressed by the following formula.

νdDOE = λd / (λF−λC)
θgFDOE = (λg−λF) / (λF−λC)
Thus, νdDOE and θgFDOE are −3.45 and 0.296, respectively. The dispersion characteristic of the diffractive surface has a negative value, and has an action opposite to that of a general optical material. Further, the partial dispersion ratio θgFDOE between the g-line and the F-line is smaller than that of a general optical material, which means that the linearity of the refractive index change with respect to the wavelength is high. The focal length fDOE of the diffractive surface is expressed by the following equation.

  Further, the focal length fDOE (λ) of the diffractive surface at an arbitrary wavelength λ is expressed by the following equation.

“E ± XX” means “× 10 ^{± XX} ”. Fno is an effective F number. ω is a half angle of view, and the unit is degrees. Table 1 shows the relationship between the conditional expressions described above and numerical examples.

Numerical Example 1 (Example 1)

f = 180.00 Fno = 3.50 2ω = 13.70
Surface number rd nd νd Effective diameter
1 74.723 7.76 1.71300 53.9 58.18
2 * -2053.467 20.79 57.22
3 92.378 2.00 1.85026 32.3 39.11
4 (Diffraction) 43.702 7.49 1.49700 81.5 37.21
5 -145.734 (variable) 36.41
6 308.138 1.80 1.88300 40.8 33.84
7 51.391 2.97 32.21
8 -700.120 1.60 1.77250 49.6 32.17
9 51.015 3.79 1.84666 23.8 31.74
10 171.856 (variable) 31.50
11 (Aperture) ∞ (Variable) 29.41
12 41.919 4.85 1.71300 53.9 29.86
13 723.222 0.15 29.62
14 61.532 5.56 1.60311 60.6 29.34
15 -59.970 3.08 1.63980 34.5 28.77
16 27.348 (variable) 26.61
17 -26.209 1.99 1.48749 70.2 31.36
18 -67.120 4.49 1.80518 25.4 34.56
19 -34.935 2.12 35.72
20 36.715 3.08 1.48749 70.2 38.42
21 41.629 BF 37.86
Image plane ∞

Aspheric data 2nd surface
K = -7.17943e + 003 A 4 = 4.39799e-007 A 6 = -3.86724e-011
A 8 = 2.51368e-014 A10 = -9.12999e-018

4th surface (diffractive surface)
C 2 = -6.98385e-005 C 4 = -2.91086e-008 C 6 = 6.46247e-011
C 8 = 1.91499e-013
C10 = -3.92381e-016 C12 = 1.88356e-019

Various data Maximum shooting magnification 1.00

Focal length 180.00
Magnification ∞ 0.5x 1.0x
F number 3.50 4.50 5.20
Half angle of view (degrees) 6.85 6.85 6.85
Image height 21.64 21.64 21.64
Total lens length 202.38 202.38 202.37
BF 52.18 52.18 52.18

d 5 1.99 16.82 31.96
d10 32.15 17.33 2.17
d11 17.22 7.96 1.80
d16 25.29 34.56 40.72

Entrance pupil position 159.96
Exit pupil position -73.08
Front principal point position 81.29
Rear principal point position-127.82

Lens unit data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 75.31 38.04 9.98 -24.21
2 6 -52.04 10.16 2.50 -4.27
3 12 172.65 13.65 -29.23 -32.01
4 17 278.32 11.69 19.75 13.15

Single lens Data lens Start surface Focal length
1 1 101.28
2 3 -100.81
3 4 67.91
4 6 -70.08
5 8 -61.50
6 9 84.48
7 12 62.23
8 14 51.24
9 15 -28.96
10 17 -89.64
11 18 85.18
12 20 529.38

Numerical Example 2 (Example 2)

f = 180.00 Fno = 3.64 2ω = 13.70
Surface number rd nd νd Effective diameter
1 88.437 9.52 1.48749 70.2 55.72
2 * -163.470 25.37 54.56
3 91.212 2.00 1.71736 29.5 38.46
4 (Diffraction) 51.899 6.91 1.49700 81.5 37.04
5 -165.159 (variable) 34.65
6 -1245.733 1.80 1.77250 49.6 34.10
7 73.493 2.20 32.70
8 -827.947 1.60 1.77250 49.6 32.63
9 41.267 3.76 1.84666 23.8 31.86
10 86.802 (variable) 31.49
11 (Aperture) ∞ (Variable) 30.72
12 42.178 4.67 1.80 400 46.6 30.24
13 -1657.015 0.15 29.60
14 73.087 5.22 1.61772 49.8 28.51
15 -47.997 3.00 1.69895 30.1 27.49
16 30.761 (variable) 23.79
17 -41.358 5.31 1.80518 25.4 28.02
18 -22.842 1.60 1.74320 49.3 29.16
19 -34.261 8.49 30.53
20 -26.931 2.55 1.80610 40.9 30.59
21 -44.527 0.20 33.03
22 44.209 4.18 1.57099 50.8 36.12
23 82.571 BF 35.96
Image plane ∞

Aspheric data 2nd surface
K = -1.29391e + 001 A 4 = 3.50420e-007 A 6 = -5.87683e-011
A 8 = 8.99943e-015

4th surface (diffractive surface)
C 2 = -5.65734e-005 C 4 = -6.43203e-008 C 6 = 6.34004e-011
C 8 = 1.03077e-013

Various data Maximum imaging magnification 1.00

Focal length 180.00
Magnification ∞ 0.5x 1.0x
F number 3.64 4.60 5.80
Half angle of view (degrees) 6.84 6.84 6.84
Image height 21.60 21.60 21.60
Total lens length 208.33 208.33 208.33
BF 49.99 49.99 49.99

d 5 1.92 16.06 30.21
d10 30.51 16.37 2.22
d11 15.21 6.66 1.80
d16 22.20 30.75 35.60

Entrance pupil position 156.78
Exit pupil position -66.47
Front principal point position 58.58
Rear principal point position -130.01

Lens unit data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 75.07 43.79 18.09 -23.77
2 6 -48.68 9.36 3.25 -2.77
3 12 131.42 13.03 -20.87 -24.59
4 17 580.76 22.33 30.58 15.64

Single lens Data lens Start surface Focal length
1 1 119.20
2 3 -174.86
3 4 79.59
4 6 -89.78
5 8 -50.84
6 9 89.53
7 12 51.22
8 14 47.68
9 15 -26.41
10 17 56.18
11 18 -98.08
12 20 -90.39
13 22 160.31

Numerical Example 3 (Example 3)
f
= 180.00 Fno = 3.50 2ω = 13.70
Surface number rd nd νd Effective diameter
1 69.984 7.88 1.61800 63.3 57.52
2 * -70059.029 21.22 56.57
3 103.633 2.00 1.90366 31.3 40.03
4 (Diffraction) 52.769 0.00 38.47
5 56.859 6.30 1.49700 81.5 38.50
6 -233.287 3.57 37.81
7 ∞ (variable) 35.34
8 598.033 1.80 1.83400 37.2 34.72
9 56.879 2.41 33.38
10 254.584 1.60 1.77250 49.6 33.34
11 47.552 4.27 1.80809 22.8 32.88
12 189.967 (variable) 32.63
13 (Aperture) ∞ 4.78 29.82
14 35.963 5.31 1.65160 58.5 29.12
15 -13759.718 1.00 28.25
16 97.866 4.90 1.62299 58.2 26.94
17 -47.669 2.02 1.63980 34.5 25.80
18 25.801 22.49 22.87
19 -22.078 1.97 1.48749 70.2 28.09
20 -41.906 3.70 1.80518 25.4 31.05
21 -28.653 3.00 32.31
22 42.672 3.81 1.48749 70.2 35.96
23 63.110 BF 35.70
Image plane ∞

Aspheric data 2nd surface
K = -1.51032e + 008 A 4 = 4.24859e-007 A 6 = -2.88882e-011
A 8 = -2.37944e-014 A10 = 1.35924e-017

4th surface (diffractive surface)
C 2 = -3.95578e-005 C 4 = -3.39754e-008 C 6 = 6.67252e-011
C 8 = 3.24659e-013
C10 = -1.25536e-015 C12 = 1.40535e-018

Various data Maximum imaging magnification 0.50

Focal length 180.00
Magnification ∞ 0.25x 0.5x

Focal length 180.00 180.00 180.00
F number 3.50 4.80 5.80
Half angle of view (degrees) 6.85 6.85 6.86
Image height 21.64 21.64 21.64

Total lens length 198.51 198.51 198.51
BF 61.17 61.17 61.17

d 7 0.83 13.48 27.05
d12 32.47 19.81 6.24

Entrance pupil position 157.74
Exit pupil position -58.13
Front principal point position 66.15
Rear principal point position -118.83

Lens unit data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 92.46 40.97 6.51 -30.02
2 8 -72.15 10.09 2.11 -4.46
3 13 ∞ 0.00 0.00 -0.00
4 14 297.05 13.23 -54.29 -52.96
5 19 198.03 12.49 18.10 10.78

Single lens Data lens Start surface Focal length
1 1 113.13
2 3 -122.40
3 5 92.65
4 8 -75.48
5 10 -75.95
6 11 77.45
7 14 55.06
8 16 52.13
9 17 -25.89
10 21 -98.95
11 22 100.06
12 24 254.73

In the configuration of each numerical example (each example), the values of conditional expressions (1) to (6) are shown in the following table.

  An embodiment of a digital still camera (imaging device) using the optical system shown in each of the embodiments as a photographing optical system will be described with reference to FIG.

  In FIG. 7, reference numeral 20 denotes a camera body. Reference numeral 21 denotes a photographing optical system configured by any one of the optical systems described in the first to third embodiments. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body.

  A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 denotes a finder for observing a subject image formed on the solid-state image sensor 22, which includes a liquid crystal display panel or the like.

  By using any one of the optical systems described in the first to third embodiments as a photographic optical system for a digital still camera in this way, fluctuations in various aberrations accompanying focusing from an infinite object to a short-distance object are small, and it is compact and lightweight. An optical system can be provided.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

L1 first lens unit L1a partial lens group L1b partial lens group L2 second lens unit L3 third lens unit L4 fourth lens unit SP aperture stop DOE diffraction surface

Claims (9)

An optical system comprising, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a rear group having a lens unit having a positive refractive power,
Wherein the first lens unit and a positive refractive power lens subunit L1a and the positive refractive power of the lens subunit L1b is spaced intervals have the widest in the first lens unit, and the diffraction surface, and Including aspheric surfaces,
The second lens unit moves to the image side during focusing from an object at infinity to a near object,
The focal length of the entire system is f, the focal lengths of the first lens unit and the second lens unit are f1 and f2, respectively, the total length of the lens is L, and the distance between the partial lens group L1a and the partial lens group L1b is L1ab, When the combined focal length of the first lens unit and the second lens unit when focusing on an object at infinity is f12 ,
0.30 ≦ f1 × L / f ² ≦ 0.65
0.80 ≦ | f1 / f2 | ≦ 3.50
0.12 ≦ (L1ab / L) / (f1 / f) ≦ 0.50
| F / f12 | ≦ 0.36
An optical system that satisfies the following conditional expression: When the focal lengths of the partial lens unit L1a and the partial lens unit L1b are f1a and f1b, respectively.
0.20 ≦ f1a / f1b ≦ 1.20
The optical system according to claim 1, wherein the following conditional expression is satisfied. The partial lens unit L1b includes a cemented lens in which a meniscus negative lens having a convex surface directed toward the object side and a positive lens are cemented, and the cemented surface of the cemented lens is a diffractive surface. The optical system according to 1 or 2 . When the focal length of the diffractive surface is fdoe,
10 ≦ fdoe / f ≦ 100
Optical system according to any one of claims 1 to 3, characterized by satisfying the conditional expression. The rear group includes a first in order from the object side to the image side, the positive refractive power of the third lens unit which moves from infinity to the object side during focusing to a close object, a positive refractive power which is stationary during focusing and 4 lens unit, an optical system according to any one of claims 1 to 4, characterized in that it is more configurations. The rear group includes an optical system according to any one of claims 1 to 4, characterized in that it is composed of a third lens unit of positive refractive power and does not move during focusing.   In order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power that moves to the image side during focusing from an object at infinity to a near object, and toward the object side during the focusing A third lens unit having a positive refractive power that moves, a fourth lens unit having a positive refractive power that does not move during focusing, and
  The first lens unit includes a partial lens unit L1a having a positive refractive power and a partial lens unit L1b having a positive refractive power that are arranged at the widest intervals in the first lens unit, and has a diffractive surface and an aspherical surface. Including
  The focal length of the entire system is f, the focal lengths of the first lens unit and the second lens unit are f1 and f2, respectively, the total length of the lens is L, and the distance between the partial lens group L1a and the partial lens group L1b is L1ab, And when
    0.30 ≦ f1 × L / f ² ≦ 0.65
    0.80 ≦ | f1 / f2 | ≦ 3.50
    0.12 ≦ (L1ab / L) / (f1 / f) ≦ 0.50
An optical system that satisfies the following conditional expression:   When the focal lengths of the partial lens unit L1a and the partial lens unit L1b are f1a and f1b, respectively.
    0.20 ≦ f1a / f1b ≦ 1.20
The optical system according to claim 7, wherein the following conditional expression is satisfied. An imaging apparatus comprising: the optical system according to any one of claims 1 to 8 ; and a solid-state imaging device that receives light from the optical system.