Patent Grant
9841586
1. Technical Field
The present disclosure relates to a single focal length lens system, an interchangeable lens apparatus, and a camera system.
2. Description of Related Art
In recent years, interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such interchangeable-lens type digital camera systems make it possible to photograph a high-quality image with high sensitivity, to enable high-speed focusing and high-speed image processing after the photographing, and to enable easy replacement of an interchangeable lens apparatus in accordance with a desired scene.
Conventionally, there has been a demand for a lens system which is compact and has high optical performance as a lens system used in an interchangeable lens apparatus. For example, various lens systems having a three-unit configuration have been proposed.
Unexamined Japanese Patent Publication Nos. 2012-242472 and 2013-037080 disclose a lens system having positive-negative-positive three-unit configuration. In this lens system, an aperture diaphragm is disposed in the first lens unit, and focusing is performed using the second lens unit.
The present disclosure provides a single focal length lens system that sufficiently corrects various aberrations including chromatic aberration and has high optical performance even at a peripheral section. The present disclosure also provides an interchangeable lens apparatus and a camera system which are compact, have high performance, and include the single focal length lens system.
A single focal length lens system according to the present disclosure includes, in order from an object side to an image side, a first lens unit having positive optical power and a second lens unit including a lens element that moves in a direction of an optical axis with respect to an image surface in focusing from an infinity in-focus condition to a close-object in-focus condition. The first lens unit includes an aperture diaphragm and a lens element A located on the object side of the aperture diaphragm. A lens element B having positive optical power and a lens element C having negative optical power are located on the image side of the aperture diaphragm. The following conditions (1) to (3) are satisfied.
0.647<PgFA+0.0018×vdA<0.75 (1)
0.647<PgFB+0.0018×vdB<0.75 (2)
0.647<PgFC+0.0018×vdC<0.75 (3)
where
vdA: an Abbe number of the lens element A to the d-line,
vdB: an Abbe number of the lens element B to the d-line,
vdC: an Abbe number of the lens element C to the d-line,
PgFA: a partial dispersion ratio of the lens element A for the g-line and the F-line,
PgFB: a partial dispersion ratio of the lens element B for the g-line and the F-line, and
PgFC: a partial dispersion ratio of the lens element C for the g-line and the F -line.
An interchangeable lens apparatus according to the present disclosure includes the single focal length lens system, and a lens mount section that is connectable to a camera body including an imaging device which receives an optical image formed by the single focal length lens system and converts the optical image into an electric image signal.
A camera system according to the present disclosure includes an interchangeable lens apparatus including the single focal length lens system, and a camera body that is detachably connected to the interchangeable lens apparatus through a camera mount section and includes an imaging device which receives an optical image formed by the single focal length lens system and converts the optical image into an electric image signal.
Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. It is noted, however, that descriptions in more detail than necessary will sometimes be omitted. For example, detailed descriptions of well-known items and duplicate descriptions of substantially the same configuration will sometimes be omitted. This is intended to avoid unnecessary redundancy in the following description, and to facilitate understanding of those skilled in the art.
Note that the inventor provides the accompanying drawings and the following descriptions so as to facilitate fully understanding of the present disclosure by those skilled in the art, and the accompanying drawings and the following descriptions are not intended to limit the subject matter defined by the claims.
In the present disclosure, a lens unit is a unit including at least one lens element, and optical power, a composite focal length, and the like are determined for each lens unit according to the type, the number, the arrangement, and the like of lens elements constituting the lens unit.
The direction of the arrow attached to each lens unit in each diagram indicates focusing from an infinity in-focus condition to a close-object in-focus condition. That is, the arrow indicates a direction along which second lens unit G2 described below moves in focusing from an infinity in-focus condition to a close-object in-focus condition.
In each diagram, an asterisk “*” attached to a specific surface indicates that this surface is aspheric. Further, in each diagram, symbols (+) and (−) attached to the reference symbol of each lens unit corresponds to the sign of the optical power of each lens unit. In addition, a straight line at the rightmost side in each diagram indicates a position of image surface S.
Each of the single focal length lens systems according to the first to fifth exemplary embodiments includes, in order from an object side to an image side, first lens unit G1 having positive optical power, second lens unit G2 having negative optical power, and third lens unit G3 having positive optical power. Further, aperture diaphragm P is provided in first lens unit G1.
As illustrated in
Second lens unit G2 only includes biconcave sixth lens element L6. Both surfaces of sixth lens element L6 at the object side and the image side are aspheric.
Third lens unit G3 includes biconvex seventh lens element L7 and plane parallel plate M.
In focusing from an infinity in-focus condition to a close-object in-focus condition, first lens unit G1 and third lens unit G3 are fixed with respect to image surface S, while second lens unit G2 which is a focusing lens unit moves to the image side along an optical axis.
First lens element L1 and second lens element L2 are one example of lens element A, fifth lens element L5 is one example of lens element B, and sixth lens element L6 is one example of lens element C.
As illustrated in
Second lens unit G2 only includes biconcave sixth lens element L6. Both surfaces of sixth lens element L6 at the object side and the image side are aspheric.
Third lens unit G3 includes positive meniscus seventh lens element L7 with a convex surface facing the object side, and plane parallel plate M.
In focusing from an infinity in-focus condition to a close-object in-focus condition, first lens unit G1 and third lens unit G3 are fixed with respect to image surface S, while second lens unit G2 which is a focusing lens unit moves to the image side along an optical axis.
First lens element L1 and second lens element L2 are one example of lens element A, fifth lens element L5 is one example of lens element B, and sixth lens element L6 is one example of lens element C.
As illustrated in
Second lens unit G2 only includes biconcave sixth lens element L6. Both surfaces of sixth lens element L6 at the object side and the image side are aspheric.
Third lens unit G3 includes biconvex seventh lens element L7 and plane parallel plate M.
In focusing from an infinity in-focus condition to a close-object in-focus condition, first lens unit G1 and third lens unit G3 are fixed with respect to image surface S, while second lens unit G2 which is a focusing lens unit moves to the image side along an optical axis.
At least one of first lens element L1, second lens element L2, and third lens element L3 is one example of lens element A, fifth lens element L5 is one example of lens element B, and sixth lens element L6 is one example of lens element C.
As illustrated in
Second lens unit G2 only includes biconcave sixth lens element L6. Both surfaces of sixth lens element L6 at the object side and the image side are aspheric.
Third lens unit G3 includes, in order from the object side to the image side, biconvex seventh lens element L7, negative meniscus eighth lens element L8 with a convex surface facing the object side, and plane parallel plate M. Both surfaces of seventh lens element L7 at the object side and the image side are aspheric.
In focusing from an infinity in-focus condition to a close-object in-focus condition, first lens unit G1 and third lens unit G3 are fixed with respect to image surface S, while second lens unit G2 which is a focusing lens unit moves to the image side along an optical axis.
At least one of first lens element L1, second lens element L2, third lens element L3, and fourth lens element L4 is one example of lens element A, seventh lens element L7 is one example of lens element B, and sixth lens element L6 is one example of lens element C.
As illustrated in
Second lens unit G2 only includes negative meniscus fifth lens element L5 with a convex surface facing the object side. Both surfaces of fifth lens element L5 at the object side and the image side are aspheric.
Third lens unit G3 includes, in order from the object side to the image side, biconvex sixth lens element L6, and negative meniscus seventh lens element L7 with a convex surface facing the image side.
In focusing from an infinity in-focus condition to a close-object in-focus condition, first lens unit G1 and third lens unit G3 are fixed with respect to image surface S, while second lens unit G2 which is a focusing lens unit moves to the image side along an optical axis.
At least one of first lens element L1, second lens element L2, and third lens element L3 is one example of lens element A, sixth lens element L6 is one example of lens element B, and fifth lens element L5 is one example of lens element C.
The single focal length lens systems according to the first to fifth exemplary embodiments include aperture diaphragm P, lens element A provided on the object side of aperture diaphragm P and having optical power, lens element B having positive optical power, and lens element C having negative optical power, the lens element B and the lens element C being provided on the image side of aperture diaphragm P, thereby being capable of satisfactorily correcting chromatic aberration at a peripheral section.
In the single focal length lens systems according to the first to fifth exemplary embodiments, lens element B and lens element C are provided adjacent to each other in the optical axis direction, whereby on-axis chromatic aberration and magnification chromatic aberration can satisfactorily be corrected.
In the single focal length lens systems according to the first to fifth exemplary embodiments, the focusing lens unit, which includes at least one lens element and serves as a second sub-lens unit, in second lens unit G2 includes one lens element D having negative optical power, whereby variation in aberration according to a focusing distance is small, and high-speed focusing is easily implemented due to the light weight of the focusing lens unit.
The first to fifth exemplary embodiments have been described above as illustrative examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these exemplary embodiments, and can be applied to exemplary embodiments in which various changes, replacements, additions, and omissions are made.
Conditions that a single focal length lens system like the single focal length lens systems according to the first to fifth exemplary embodiments can satisfy will be described below. Notably, a plurality of possible conditions are specified for the single focal length lens system according to each exemplary embodiment, and the configuration of a single focal length lens system satisfying all of the plurality of conditions is the most effective. However, it is possible to obtain a single focal length lens system which satisfies an individual condition to provide the effect corresponding to the individual condition.
For example, a single focal length lens system includes, in order from an object side to an image side, a first lens unit having positive optical power and a second lens unit including one lens element that moves in a direction of an optical axis with respect to an image surface in focusing from an infinity in-focus condition to a close-object in-focus condition, like the single focal length lens systems according to the first to fifth exemplary embodiments. The first lens unit includes an aperture diaphragm and lens element A disposed on the object side of the aperture diaphragm, and lens element B having positive optical power and lens element C having negative optical power are disposed on the image side of the aperture diaphragm. The single focal length lens system having the above configuration (this lens configuration is referred to as a basic configuration of exemplary embodiments hereinafter) satisfies the following conditions (1) to (3).
0.647<PgFA+0.0018×vdA<0.75 (1)
0.647<PgFB+0.0018×vdB<0.75 (2)
0.647<PgFC+0.0018×vdC<0.75 (3)
where
vdA: an Abbe number of the lens element A to the d-line,
vdB: an Abbe number of the lens element B to the d-line,
vdC: an Abbe number of the lens element C to the d-line,
PgFA: a partial dispersion ratio of the lens element A for the g-line and the F-line,
PgFB a partial dispersion ratio of the lens element B for the g-line and the F-line, and
PgFC: a partial dispersion ratio of the lens element C for the g-line and the F-line.
Conditions (1) to (3) specify the partial dispersion ratios of lens elements A to C. When the ratio becomes less than the lower limit of the conditions (1) to (3), the correction of chromatic aberration by lens elements A to C becomes excessive, which may result in unsatisfactory correction of chromatic aberration. When the ratio exceeds the upper limit of conditions (1) to (3), the correction of chromatic aberration by lens element I becomes insufficient, which may result in insufficient correction of chromatic aberration.
When at least one of the following conditions (1)′-1, (1)′-2, (1)″-1, and (1)″-2 is satisfied, the above effect can be achieved more successfully.
0.650<PgFA+0.0018×vdA (1)′-1
PgFA+0.0018×vdA<0.70 (1)′-2
0.660<PgFA+0.0018×vdA (1)″-1
PgFA+0.0018×vdA<0.67 (1)″-2
When at least one of the following conditions (2)′-1, (2)′-2, (2)″-1, and (2)″-2 is satisfied, the above effect can be achieved more successfully.
0.650<PgFB+0.0018×vdB (2)′-1
PgFB+0.0018×vdB<0.70 (2)′-2
0.660<PgFB+0.0018×vdB (2)″-1
PgFB+0.0018×vdB<0.67 (2)″-2
When at least one of the following conditions (3)′-1, (3)′-2, (3)″-1, and (3)″-2 is satisfied, the above effect can be achieved more successfully.
0.650<PgFC+0.0018×vdC (3)′-1
PgFC+0.0018×vdC<0.70 (3)′-2
0.660<PgFC+0.0018×vdC (3)″-1
PgFC+0.0018×vdC<0.67 (3)″-2
For example, it is beneficial that the single focal length lens system having the basic configuration and including lens element B, like the single focal length lens systems according to the first to fifth exemplary embodiments, satisfies the following condition (4).
−0.5<(R1B+R2B)/(R1B−R2B)<1.0 (4)
where
R1B: a radius of curvature of the surface of lens element B at the object side, and
R2B: a radius of curvature of the surface of lens element B at the image side.
Condition (4) specifies the shape factor of lens element B. When the value becomes lower than the lower limit of condition (4) or exceeds the upper limit of condition (4), aberration of ray passing near the effective diameter of lens element B increases. With this, spherical aberration and a curvature of field are likely to occur, which may result in deterioration in focusing performance.
When at least one of the following conditions (4)′-1, (4)′-2, (4)″-1, and (4)″-2 is satisfied, the above effect can be achieved more successfully.
−0.2<(R1B+R2B)/(R1B−R2B) (4)′-1
(R1B+R2B)/(R1B−R2B)<0.5 (4)′-2
0.15<(R1B+R2B)/(R1B−R2B) (4)″-1
(R1B+R2B)/(R1B−R2B)<0.25 (4)″-2
For example, it is beneficial that the single focal length lens system having the basic configuration and including lens element C, like the single focal length lens systems according to the first to fifth exemplary embodiments, satisfies the following condition (5).
0.2<(R1C+R2C)/(R1C−R2C)<3.0 (5)
where
R1C: a radius of curvature of the surface of lens element C at the object side, and
R2C: a radius of curvature of the surface of lens element C at the image side.
Condition (5) specifies the shape factor of lens element C. When the value becomes lower than the lower limit of condition (5) or exceeds the upper limit of condition (5), aberration of ray passing near the effective diameter of lens element B increases. With this, spherical aberration and a curvature of field are likely to occur, which may result in deterioration in focusing performance.
When at least one of the following conditions (5)′-1, (5)′-2, (5)″-1, and (5)″-2 is satisfied, the above effect can be achieved more successfully.
0.6<(R1C+R2C)/(R1C−R2C) (5)′-1
(R1C+R2C)/(R1C−R2C)<2.2 (5)′-2
1.0<(R1C+R2C)/(R1C−R2C) (5)″-1
(R1C+R2C)/(R1C−R2C)<1.3 (5)″-2
For example, it is beneficial that the single focal length lens system having the basic configuration, like the single focal length lens systems according to the first to fifth exemplary embodiments, satisfies the following condition (6).
0.3<|fB/fC|<2.5 (6)
where
fB: a focal length of lens element B, and
fC: a focal length of lens element C.
Condition (6) specifies a ratio of the focal length of lens element B and the focal length of lens element C. When the ratio becomes lower than the lower limit of condition (6) or exceeds the upper limit of condition (6), the relation between the compensation of chromatic aberration generated on lens element B and the compensation of chromatic aberration generated on lens element C deteriorates. Thus, focusing performance might deteriorate.
When at least one of the following conditions (6)′-1, (6)′-2, (6)″-1, and (6)″-2 is satisfied, the above effect can be achieved more successfully.
0.4<|fB/fC| (6)′-1
|fB/fC|<1.6 (6)′-2
0.48<|fB/fC| (6)″-1
|fB/fC|<0.57 (6)″-2
For example, it is beneficial that the single focal length lens system having the basic configuration and including a focusing lens unit which includes one lens element D having negative optical power, like the single focal length lens systems according to the first to fifth exemplary embodiments, satisfies the following condition (7).
0.2<|fW/fD|<3.0 (7)
where
fW: a focal length of the entire system in an infinity in-focus condition, and
fD: a focal length of lens element D.
In the first to fifth exemplary embodiments, lens element D is the same as lens element C described above.
Condition (7) specifies the focal length of lens element D. When the value becomes lower than the lower limit of condition (7), the amount of movement of the focusing lens is increased, which may lead to an increase in the total length of the entire lens system. When the value exceeds the upper limit of condition (7), large aberration occurs due to the focusing lens unit, so that the variation in aberration according to the focusing distance might be increased.
When at least one of the following conditions (7)′-1, (7)′-2, (7)″-1, and (7)″-2 is satisfied, the above effect can be achieved more successfully.
0.35<|fW/fD| (7)′-1
|fW/fD|<1.8 (7)′-2
0.50<|fW/fD| (7)″-1
|fW/fD|<0.6 (7)″-2
Each lens unit composing the single focal length lens systems according to the first to fifth exemplary embodiments may only include refractive lens element (specifically, a lens element of a type deflecting light on an interface between mediums having different refractive indices) deflecting incident ray with refraction. However, it is not limited thereto. For example, each lens unit may include a diffractive lens element which deflects incident ray with diffraction, a hybrid diffractive-refractive lens element which deflects incident ray with a combination of diffraction action and refraction action, or a gradient index lens element which deflects incident ray with gradual variation of the refractive index in a medium. In particular, when a diffraction structure is formed on the interface between mediums having different refractive indices in a hybrid diffractive-refractive lens element, wavelength dependency of diffraction efficiency can be enhanced. Thus, this is beneficial.
Camera system 100 according to the sixth exemplary embodiment includes camera body 101 and interchangeable lens apparatus 201 detachably connected to camera body 101.
Camera body 101 includes imaging device 102 that receives an optical image formed with single focal length lens system 202 of interchangeable lens apparatus 201 and converts the received optical image into an electric image signal, a liquid crystal monitor 103 that displays the image signal converted by imaging device 102, and camera mount section 104. On the other hand, interchangeable lens apparatus 201 includes single focal length lens system 202 according to any one of the first to fifth exemplary embodiments, lens barrel 203 holding single focal length lens system 202, and lens mount section 204 connected to camera mount section 104 of camera body 101. Camera mount section 104 and lens mount section 204 are physically connected to each other, and further, function as an interface that establishes electrical connection between a controller (not illustrated) mounted in camera body 101 and a controller (not illustrated) mounted in interchangeable lens apparatus 201 to enable mutual signal communication.
Since single focal length lens system 202 according to any one of the first to fifth exemplary embodiments is used in the sixth exemplary embodiment, a compact interchangeable lens apparatus having excellent focusing performance can be implemented at low cost. In addition, reduction in size and reduction in cost of entire camera system 100 according to the sixth exemplary embodiment can also be achieved.
The sixth exemplary embodiment has been described above as an illustrative example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these exemplary embodiments, and can be applied to exemplary embodiments in which various changes, replacements, additions, and omissions are made.
Numerical Examples for specifically implementing the single focal length lens systems according to the first to fifth exemplary embodiments will be described below. In each Numerical Example, the units of length are all “mm”, while the units of viewing angle are all “°” in each Table. Moreover, in each Numerical Example, r is a radius of curvature, d is an axial distance, and is a refractive index to the d-line, and vd is an Abbe number to the d-line.
Further, in each Numerical Example, nC is a refractive index to the C-line, nF is a refractive index to the F-line, and ng is a refractive index to the g-line. PgF is a partial dispersion ratio of the g-line and the F-line, and can be obtained from the following equation.
PgF=(ng−nF)/(nF−nC)
In addition, in each Numerical Example, the surface marked with * is aspheric. The aspheric shape is defined by the following equation.
where
Z: a distance from a point on the aspheric surface with height h relative to an optical axis to a tangent plane at the vertex of the aspheric surface,
h: a height relative to the optical axis,
r: a radius of curvature at the top,
κ: a conic constant, and
An: an nth-order aspheric coefficient.
The single focal length lens system according to Numerical Example 1 corresponds to the first exemplary embodiment illustrated in
The single focal length lens system according to Numerical Example 2 corresponds to the second exemplary embodiment illustrated in
The single focal length lens system according to Numerical Example 3 corresponds to the third exemplary embodiment illustrated in
The single focal length lens system according to Numerical Example 4 corresponds to the fourth exemplary embodiment illustrated in
The single focal length lens system according to Numerical Example 5 corresponds to the fifth exemplary embodiment illustrated in
The following Table 36 shows the corresponding values to the individual conditions in the single focal length lens systems of each of Numerical Examples.
As presented above, the exemplary embodiments have been described above as illustrative examples of the technology in the present disclosure. The accompanying drawings and the detailed description are provided for this purpose.
Thus, elements appearing in the accompanying drawings and the detailed description include not only those that are essential to solving the technical problems set forth herein, but also those that are not essential to solving the technical problems but are merely used to illustrate the technique disclosed herein. Therefore, those non-essential elements should not immediately be taken as being essential for the reason that they appear in the accompanying drawings and/or in the detailed description.
The exemplary embodiments above are for illustrating the technology disclosed herein, and various changes, replacements, additions, and omissions can be made without departing from the scope defined by the claims and equivalents thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-169941 | Aug 2015 | JP | national |
| 2016-115803 | Jun 2016 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20110164324 | Okumura | Jul 2011 | A1 |
| 20130033768 | Sunaga et al. | Feb 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2012-242472 | Dec 2012 | JP |
| 2013-37080 | Feb 2013 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20170059832 A1 | Mar 2017 | US |
