# Patent

## Title
Single focal length lens system, interchangeable lens apparatus, and camera system

## Abstract

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 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. Abbe numbers of the lens elements A, B, and C to the d-line and partial dispersion ratios of the lens elements A, B, and C for the g-line and the F-line satisfy a predetermined relation.

## Background
BACKGROUND
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.
SUMMARY
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.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a lens arrangement diagram of a single focal length lens system in an infinity in-focus condition according to a first exemplary embodiment (Numerical Example 1);
FIG. 2A is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 1;
FIG. 2B is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 1;
FIG. 2C is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 1;
FIG. 3 is a lens arrangement diagram of a single focal length lens system in an infinity in-focus condition according to a second exemplary embodiment (Numerical Example 2);
FIG. 4A is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 2;
FIG. 4B is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 2;
FIG. 4C is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 2;
FIG. 5 is a lens arrangement diagram of a single focal length lens system in an infinity in-focus condition according to a third exemplary embodiment (Numerical Example 3);
FIG. 6A is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 3;
FIG. 6B is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 3;
FIG. 6C is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 3;
FIG. 7 is a lens arrangement diagram of a single focal length lens system in an infinity in-focus condition according to a fourth exemplary embodiment (Numerical Example 4);
FIG. 8A is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 4;
FIG. 8B is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 4;
FIG. 8C is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 4;
FIG. 9 is a lens arrangement diagram of a single focal length lens system in an infinity in-focus condition according to a fifth exemplary embodiment (Numerical Example 5);
FIG. 10A is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 5;
FIG. 10B is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 5;
FIG. 10C is a longitudinal aberration diagram of the single focal length lens system in an infinity in-focus condition according to Numerical Example 5; and
FIG. 11 is a schematic configuration diagram of an interchangeable-lens type digital camera system according to a sixth exemplary embodiment.



DETAILED DESCRIPTION
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.
First to Fifth Exemplary Embodiments
FIGS. 1, 3, 5, 7, and 9 are each a lens arrangement diagram of a single focal length lens system according to each of the first to fifth exemplary embodiments, and each diagram illustrates the single focal length lens system in an infinity in-focus condition.
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.
First Exemplary Embodiment
As illustrated in FIG. 1, first lens unit G1 includes, in order from an object side to an image side, positive meniscus first lens element L1 with a convex surface facing the object side, negative meniscus second lens element L2 with a convex surface facing the object side, aperture diaphragm P, biconcave third lens element L3, biconvex fourth lens element L4, and biconvex fifth lens element L5. Both surfaces of second lens element L2 at the object side and the image side are aspheric, the surface of the third lens element L3 at the object side is aspheric, and both surfaces of the fifth lens element L5 at the object side and the image side are aspheric.
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.
Second Exemplary Embodiment
As illustrated in FIG. 3, first lens unit G1 includes, in order from an object side to an image side, positive meniscus first lens element L1 with a convex surface facing the object side, negative meniscus second lens element L2 with a convex surface facing the object side, aperture diaphragm P, biconcave third lens element L3, biconvex fourth lens element L4, and biconvex fifth lens element L5. Third lens element L3 and fourth lens element L4 out of these elements are cemented to each other. Both surfaces of fifth lens element L5 at the object side and the image side are aspheric.
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.
Third Exemplary Embodiment
As illustrated in FIG. 5, first lens unit G1 includes, in order from an object side to an image side, positive meniscus first lens element L1 with a convex surface facing the object side, negative meniscus second lens element L2 with a convex surface facing the object side, biconcave third lens element L3, aperture diaphragm P, biconvex fourth lens element L4, and biconvex fifth lens element L5. The surface of third lens element L3 at the object side is aspheric, and the surface of fifth lens element L5 at the object side is aspheric.
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.
Fourth Exemplary Embodiment
As illustrated in FIG. 7, first lens unit G1 includes, in order from an object side to an image side, positive meniscus first lens element L1 with a convex surface facing the object side, negative meniscus second lens element L2 with a convex surface facing the object side, biconcave third lens element L3, biconvex fourth lens element L4, aperture diaphragm P, and biconvex fifth lens element L5. Third lens element L3 and fourth lens element L4 out of these elements are cemented to each other.
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.
Fifth Exemplary Embodiment
As illustrated in FIG. 9, first lens unit G1 includes, in order from an object side to an image side, positive meniscus first lens element L1 with a convex surface facing the object side, biconcave second lens element L2, positive meniscus third lens element L3 with a convex surface facing the image side, aperture diaphragm P, and biconvex fourth lens element L4. Both surfaces of third lens element L3 at the object side and the image side are aspheric.
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.
Sixth Exemplary Embodiment
FIG. 11 is a schematic configuration diagram of an interchangeable-lens type digital camera system according to a sixth exemplary embodiment.
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. FIG. 11 illustrates the case in which the single focal length lens system according to the first exemplary embodiment is used as single focal length lens system 202.
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.




  
    
      
        z
        =
        
          
            
              
                h
                2
              
              /
              r
            
            
              1
              +
              
                
                  1
                  -
                  
                    
                      (
                      
                        1
                        +
                        κ
                      
                      )
                    
                    ⁢
                    
                      
                        (
                        
                          h
                          /
                          r
                        
                        )
                      
                      2
                    
                  
                
              
            
          
          +
          
            ∑
            
              
                A
                n
              
              ⁢
              
                h
                n
              
            
          
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          1
        
        ]
      
    
  




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.
FIGS. 2A, 2B, 2C, 4A, 4B, 4C, 6A, 6B, 6C, 8A, 8B, 8C, 10A, 10B, and 10C are longitudinal aberration diagrams of the single focal length lens systems according to Numerical Examples 1 to 5 in an infinity in-focus condition.
FIGS. 2A, 4A, 6A, 8A, and 10A show spherical aberration (SA(mm)). FIGS. 2B, 4B, 6B, 8B, and 10B show astigmatism (AST(mm)). FIGS. 2C, 4C, 6C, 8C, and 10C show distortion (DIS (%)). In each spherical aberration diagram, a vertical axis indicates F-number (indicated as F in each diagram), and the solid line, the short dash line, and the long dash line indicate the characteristics to the d-line, the F-line, and the C-line, respectively. In each astigmatism diagram, the vertical axis indicates an image height (indicated as H in each diagram), and the solid line and the dash line indicate characteristics to a sagittal plane (indicated as “s” in each diagram) and a meridional plane (indicated as “m” in each diagram), respectively. In each distortion diagram, the vertical axis indicates an image height (indicated as H in each diagram).
NUMERICAL EXAMPLE 1
The single focal length lens system according to Numerical Example 1 corresponds to the first exemplary embodiment illustrated in FIG. 1. Table 1 shows the surface data 1 of the single focal length lens system according to Numerical Example 1, Table 2 shows the surface data 2, Table 3 shows the aspherical data, Table 4 shows various data, Table 5 shows the single lens data, Table 6 shows the lens unit data, and Table 7 shows the lens unit magnification.







TABLE 1







(Surface data 1)











Surface number
r
d
nd
vd





Object surface
∞
Variable




 1
21.82570
5.31700
1.90366
31.3


 2
66.51370
2.05780


 3*
96.74280
2.00000
1.52996
55.8


 4*
9.12840
11.49760 


 5 (Diaphragm)
∞
3.51470


 6*
−25.38440
1.20000
1.63550
23.9


 7
83.34490
0.72520


 8
55.28840
4.88430
1.72916
54.7


 9
−17.10090
0.15000


10*
35.67000
5.98630
1.52996
55.8


11*
−22.19540
Variable


12*
−149.80450
2.00000
1.63550
23.9


13*
12.61840
Variable


14
48.71060
6.07790
1.84666
23.8


15
−35.34990
11.43000 


16
∞
4.20000
1.51680
64.2


17
∞
BF


Image surface
∞
















TABLE 2







(Surface data 2)













Surface number
nC
nF
ng
PgF

















Object surface







 1
1.89526
1.92412
1.94128
0.59467



 2



 3
1.52713
1.53662
1.54205
0.57218



 4



 5 (Diaphragm)



 6
1.62800
1.65460
1.67140
0.63158



 7



 8
1.72510
1.73844
1.74571
0.54521



 9



10
1.52713
1.53662
1.54205
0.57218



11



12
1.62800
1.65460
1.67140
0.63158



13



14
1.83649
1.87209
1.89413
0.61908



15



16
1.51432
1.52237
1.52667
0.53418



17

















TABLE 3





(Aspherical data)















Surface No. 3


K = 0.00000E+00, A4 = 1.95207E−05, A6 = −9.81210E−08, A8 =


2.71450E−10


A10 = 0.00000E+00, A12 = 0.00000E+00


Surface No. 4


K = 0.00000E+00, A4 = 1.69672E−06, A6 = 9.39629E−08,


A8 = −5.08386E−09


A10 = 0.00000E+00, A12 = 0.00000E+00


Surface No. 6


K = 0.00000E+00, A4 = −1.15216E−04, A6 = 5.29641E−08,


A8 = −2.99237E−10


A10 = 0.00000E+00, A12 = 0.00000E+00


Surface No. 10


K = 0.00000E+00, A4 = 1.38272E−05, A6 = −9.10686E−08, A8 =


1.02820E−09


A10 = −5.48203E−12, A12 = 0.00000E+00


Surface No. 11


K = 0.00000E+00, A4 = 1.72020E−05, A6 = 1.51350E−07, A8 =


0.00000E+00


A10 = 0.00000E+00, A12 = 0.00000E+00


Surface No. 12


K = 2.28019E−15, A4 = 6.80547E−06, A6 = −5.02168E−07, A8 =


4.09336E−09


A10 = −1.25341E−11, A12 = 2.28019E−15


Surface No. 13


K = −6.36846E−01, A4 = 2.38781E−05, A6 = −8.31023E−07, A8 =


6.38516E−09


A10 = −2.15468E−11, A12 = 0.00000E+00
















TABLE 4







(Various data)











Infinity
973
248














Focal length
25.8748
25.8727
25.6433


F-number
1.76015
1.76848
1.79547


Viewing angle
22.6837
22.6293
22.4573


Image height
10.8150
10.8150
10.8150


Overall length of lens system
72.9999
73.0140
72.9984


BF
1.00013
1.00018
1.00015


d0
∞
900.0000
175.0000


d11
1.9000
2.2645
3.6419


d13
9.0590
8.7085
7.3155


Entrance pupil position
24.2227
24.2227
24.2227


Exit pupil position
−305.2179
−263.1768
−167.9363


Front principal point position
47.9111
47.5545
45.8944


Back principal point position
47.1252
46.4150
43.9872
















TABLE 5







(Single lens data)









Lens
Initial surface
Focal length












1
1
34.0270


2
3
−19.1709


3
6
−30.4877


4
8
18.4371


5
10
26.7764


6
12
−18.2261


7
14
25.0236
















TABLE 6







(Lens unit data)
















Front
Back





Overall
principal
principal



Initial

length of
point
point


Lens unit
surface
Focal length
lens unit
position
position















1
1
17.81257
37.33290
35.47462
36.56059


2
12
−18.22608
2.00000
1.12249
1.90545


3
14
25.02360
21.70790
1.97260
6.07737
















TABLE 7







(Lens unit magnification)












Initial





Lens unit
surface
Infinity
973
248














1
1
0.00000
−0.01941
−0.09246


2
12
4.33097
4.31177
4.23532


3
14
0.33540
0.33540
0.33540









NUMERICAL EXAMPLE 2
The single focal length lens system according to Numerical Example 2 corresponds to the second exemplary embodiment illustrated in FIG. 3. Table 8 shows the surface data 1 of the single focal length lens system according to Numerical Example 2, Table 9 shows the surface data 2, Table 10 shows the aspherical data, Table 11 shows various data, Table 12 shows the single lens data, Table 13 shows the lens unit data, and Table 14 shows the lens unit magnification.







TABLE 8







(Surface data 1)













Surface number
r
d
nd
vd

















Object surface
∞
Variable





 1
25.02720
4.87800
1.90366
31.3



 2
94.79720
3.17490



 3
55.65910
1.20000
1.49700
81.6



 4
8.91430
8.54800



 5 (Diaphragm)
∞
5.76680



 6
−14.43470
1.00000
1.75211
25.0



 7
41.97300
4.82520
1.77250
49.6



 8
−16.89330
0.15000



 9*
22.00960
9.03320
1.52996
55.8



10*
−15.81130
Variable



11*
−86.95920
1.40000
1.63550
23.9



12*
17.63200
Variable



13
25.93640
5.18220
1.94595
18.0



14
220.08890
11.43000 



15
∞
4.20000
1.51680
64.2



16
∞
BF



Image surface
∞

















TABLE 9







(Surface data 2)













Surface number
nC
nF
ng
PgF

















Object surface







 1
1.89526
1.92412
1.94128
0.59467



 2



 3
1.49514
1.50123
1.50451
0.53875



 4



 5 (Diaphragm)



 6
1.74352
1.77355
1.79214
0.61909



 7
1.76780
1.78336
1.79193
0.55025



 8



 9
1.52713
1.53662
1.54205
0.57218



10



11
1.62800
1.65460
1.67140
0.63158



12



13
1.93123
1.98383
2.01825
0.65443



14



15
1.51432
1.52237
1.52667
0.53418



16

















TABLE 10





(Aspherical data)















Surface No. 9


K = 0.00000E+00, A4 = −2.86768E−05, A6 = −5.27238E−08, A8 =


5.67553E−11


A10 = −2.80993E−12, A12 = 0.00000E+00


Surface No. 10


K = 0.00000E+00, A4 = 6.69403E−05, A6 = −5.91281E−08, A8 =


0.00000E+00


A10 = 0.00000E+00, A12 = 0.00000E+00


Surface No. 11


K = 2.28019E−15, A4 = 5.73625E−06, A6 = 6.21066E−07,


A8 = −7.51177E−09


A10 = 2.85176E−11, A12 = 2.28019E−15


Surface No. 12


K = 7.26541E−01, A4 = −2.96497E−05, A6 = 6.16921E−07,


A8 = −7.30393E−09


A10 = 1.96498E−11, A12 = 0.00000E+00
















TABLE 11







(Various data)











Infinity
970
245














Focal length
24.2168
24.0471
23.3004


F-number
1.76129
1.76009
1.75371


Viewing angle
24.3618
24.4568
24.8092


Image height
10.8150
10.8150
10.8150


Overall length of lens system
70.0042
70.0051
70.0109


BF
1.01426
1.01502
1.01771


d0
∞
900.0000
175.0000


d10
1.9000
2.3133
3.8717


d12
6.3016
5.8885
4.3332


Entrance pupil position
20.6816
20.6816
20.6816


Exit pupil position
−148.8612
−138.3937
−108.7145


Front principal point position
40.9854
40.5618
38.9025


Back principal point position
45.7873
45.3271
43.8622
















TABLE 12







(Single lens data)









Lens
Initial surface
Focal length












1
1
36.4213


2
3
−21.5404


3
6
−14.1731


4
7
16.1703


5
9
18.9282


6
11
−22.9485


7
13
30.6832
















TABLE 13







(Lens unit data)
















Front
Back





Overall
principal
principal



Initial

length of
point
point


Lens unit
surface
Focal length
lens unit
position
position















1
1
18.51518
38.57610
36.32860
38.47542


2
11
−22.94845
1.40000
0.70802
1.25644


3
13
30.68317
20.81220
−0.35120
3.63305
















TABLE 14







(Lens unit magnification)











Lens unit
Initial surface
Infinity
970
245














1
1
0.00000
−0.02017
−0.09603


2
11
3.21318
3.19538
3.12832


3
13
0.40706
0.40703
0.40694









NUMERICAL EXAMPLE 3
The single focal length lens system according to Numerical Example 3 corresponds to the third exemplary embodiment illustrated in FIG. 5. Table 15 shows the surface data 1 of the single focal length lens system according to Numerical Example 3, Table 16 shows the surface data 2, Table 17 shows the aspherical data, Table 18 shows various data, Table 19 shows the single lens data, Table 20 shows the lens unit data, and Table 21 shows the lens unit magnification.







TABLE 15







(Surface data 1)













Surface number
r
d
nd
vd

















Object surface
∞
Variable





 1
26.34740
4.82410
1.90366
31.3



 2
95.31930
3.50000



 3
51.30700
1.20000
1.48749
70.4



 4
9.22560
13.50000 



 5*
−19.43460
1.00000
1.63550
23.9



 6
51.75270
1.16220



 7 (Diaphragm)
∞
0.00000



 8
86.29710
4.82920
1.72916
54.7



 9
−15.83660
0.20000



10*
32.54860
7.05470
1.53380
55.6



11
−21.70610
Variable



12*
−90.79550
1.40000
1.63550
23.9



13*
14.57300
Variable



14
42.24090
5.76770
1.92119
24.0



15
−49.71390
14.25450 



16
∞
4.20000
1.51680
64.2



17
∞
BF



Image surface
∞

















TABLE 16







(Surface data 2)













Surface number
nC
nF
ng
PgF

















Object surface







 1
1.89526
1.92412
1.94128
0.59467



 2



 3
1.48535
1.49227
1.49594
0.53049



 4



 5
1.62800
1.65460
1.67140
0.63158



 6



 7 (Diaphragm)



 8
1.72510
1.73844
1.74571
0.54521



 9



10
1.53100
1.54060
1.54600
0.56232



11



12
1.62800
1.65460
1.67140
0.63158



13



14
1.91020
1.94865
1.97250
0.62010



15



16
1.51432
1.52237
1.52667
0.53418



17

















TABLE 17





(Aspherical data)















Surface No. 5


K = 0.00000E+00, A4 = −7.66900E−05, A6 = 0.00000E+00, A8 =


0.00000E+00


A10 = 0.00000E+00


Surface No. 10


K = 0.00000E+00, A4 = −1.28009E−05, A6 = −8.00822E−08, A8 =


0.00000E+00


A10 = 0.00000E+00


Surface No. 12


K = 0.00000E+00, A4 = −6.90258E−06, A6 = −7.04833E−08, A8 =


3.07942E−10


A10 = −4.21582E−13


Surface No. 13


K = 0.00000E+00, A4 = −3.69945E−05, A6 = −1.61692E−07,


A8 = −3.62657E−10


A10 = 0.00000E+00
















TABLE 18







(Various data)











Infinity
973
248
















Focal length
25.7099
25.6841
25.3688



F-number
1.73731
1.75106
1.79970



Viewing angle
22.8143
22.6065
21.8726



Image height
10.8150
10.8150
10.8150



Overall length of
72.9997
73.0053
73.0024



lens system



BF
0.99974
0.99978
0.99978



d0
∞
900.0000
175.0000



d11
1.9000
2.3179
3.9020



d13
7.2076
6.7952
5.2082



Entrance pupil
29.2007
29.2007
29.2007



position



Exit pupil position
−65.5789
−63.5328
−56.3758



Front principal
44.9825
44.5475
42.6578



point position



Back principal
47.2899
46.6032
44.2866



point position

















TABLE 19







(Single lens data)









Lens
Initial surface
Focal length












1
1
38.9993


2
3
−23.2913


3
5
−22.1119


4
8
18.7246


5
10
25.5510


6
12
−19.6585


7
14
25.5593
















TABLE 20







(Lens unit data)
















Front
Back





Overall
principal
principal



Initial

length of
point
point


Lens unit
surface
Focal length
lens unit
position
position















1
1
19.28173
37.27020
35.74611
36.89902


2
12
−19.65851
1.40000
0.73383
1.28222


3
14
25.55935
24.22220
1.42185
5.52532
















TABLE 21







(Lens unit magnification)












Initial





Lens unit
surface
Infinity
973
248














1
1
0.00000
−0.02104
−0.10071


2
12
5.81305
5.79211
5.71138


3
14
0.22938
0.22938
0.22938









NUMERICAL EXAMPLE 4
The single focal length lens system according to Numerical Example 4 corresponds to the fourth exemplary embodiment illustrated in FIG. 7. Table 22 shows the surface data 1 of the single focal length lens system according to Numerical Example 4, Table 23 shows the surface data 2, Table 24 shows the aspherical data, Table 25 shows various data, Table 26 shows the single lens data, Table 27 shows the lens unit data, and Table 28 shows the lens unit magnification.







TABLE 22







(Surface data 1)











Surface number
r
d
nd
vd





Object surface
∞
Variable




 1
23.87850
4.30000
2.00069
25.5


 2
127.86160
1.52650


 3
183.86990
0.70000
1.51742
52.1


 4
10.05570
7.32680


 5
−14.14930
2.77000
1.75211
25.0


 6
22.42770
5.15000
1.72916
54.7


 7
−18.52000
0.60000


 8 (Diaphragm)
∞
1.70000


 9
36.68800
5.50000
1.80420
46.5


10
−51.79840
Variable


11*
253.21040
2.50000
1.53380
55.6


12*
22.11050
Variable


13*
31.35910
6.50000
1.53380
55.6


14*
−20.34910
3.54720


15
−30.62420
1.00000
1.58144
40.9


16
−82.33480
10.80000 


17
∞
4.20000
1.51680
64.2


18
∞
1.00000


19
∞
BF


Image surface
∞
















TABLE 23







(Surface data 2)











Surface number
nC
nF
ng
PgF





Object surface






1
1.98941
2.02872
2.05283
0.61349


2


3
1.51444
1.52436
1.52990
0.55883


4


5
1.74352
1.77355
1.79214
0.61909


6
1.72510
1.73844
1.74571
0.54521


7


8


9
1.79900
1.81630
1.82594
0.55785


10


11
1.53100
1.54060
1.54600
0.56232


12


13
1.53100
1.54060
1.54600
0.56232


14


15
1.57723
1.59145
1.59965
0.57667


16


17
1.51432
1.52237
1.52667
0.53418


18


19
















TABLE 24





(Aspherical data)















Surface No. 11


K = 0.00000E+00, A4 = 1.61276E−05, A6 = −5.81668E−07,


A8 = −2.09502E−09


A10 = 7.71341E−10, A12 = −2.10800E−11, A14 = 2.38633E−13,


A16 = −1.00673E−15


Surface No. 12


K = 0.00000E+00, A4 = 1.81047E−05, A6 = 1.27838E−06,


A8 = −1.03829E−07


A10 = 3.56865E−09, A12 = −6.09424E−11, A14 = 5.06181E−13,


A16 = −1.58084E−15


Surface No. 13


K = 0.00000E+00, A4 = 1.78062E−05, A6 = 2.01697E−07,


A8 = −9.59188E−09


A10 = 2.58013E−10, A12 = −3.40082E−12, A14 = 2.22992E−14,


A16 = −5.27487E−17


Surface No. 14


K = 0.00000E+00, A4 = 4.87160E−05, A6 = −1.55628E−07, A8 =


3.63235E−09


A10 = −5.25127E−11, A12 = 9.47811E−13, A14 = −9.91324E−15, A16 =


4.47375E−17
















TABLE 25







(Various data)











Infinity
1011
246
















Focal length
25.8784
26.0073
26.0867



F-number
1.76012
1.79041
1.91463



Viewing angle
23.6324
23.1232
21.1160



Image height
10.8150
10.8150
10.8150



Overall length of
71.0046
71.0088
71.0046



lens system



BF
0.00461
0.00488
0.00594



d0
∞
939.5121
175.0000



d10
2.3500
3.4869
8.6131



d12
9.5295
8.3965
3.2651



Entrance pupil
19.8824
19.8824
19.8824



position



Exit pupil position
−64.2371
−62.2690
−53.0287



Front principal
35.3363
34.9025
32.1589



point position



Back principal
45.1263
44.2883
41.1597



point position

















TABLE 26







(Single lens data)









Lens
Initial surface
Focal length












1
1
28.7470


2
3
−20.5869


3
5
−11.1722


4
6
14.6906


5
9
27.4664


6
11
−45.5552


7
13
24.1767


8
15
−84.4622
















TABLE 27







(Lens unit data)
















Front
Back





Overall
principal
principal



Initial

length of
point
point


Lens unit
surface
Focal length
lens unit
position
position















1
1
30.51097
29.57330
26.42482
32.69836


2
11
−45.55524
2.50000
1.79263
2.65653


3
13
31.31949
26.04720
0.86548
5.09828
















TABLE 28







(Lens unit magnification)












Initial





Lens unit
surface
Infinity
1011
246














1
1
0.00000
−0.03262
−0.17852


2
11
2.83624
2.81144
2.69906


3
13
0.29905
0.29904
0.29900









NUMERICAL EXAMPLE 5
The single focal length lens system according to Numerical Example 5 corresponds to the fifth exemplary embodiment illustrated in FIG. 9. Table 29 shows the surface data 1 of the single focal length lens system according to Numerical Example 5, Table 30 shows the surface data 2, Table 31 shows the aspherical data, Table 32 shows various data, Table 33 shows the single lens data, Table 34 shows the lens unit data, and Table 35 shows the lens unit magnification.







TABLE 29







(Surface data 1)











Surface number
r
d
nd
vd





Object surface
∞
Variable




 1
24.71640
3.70750
1.94595
18.0


 2
178.46780
1.84880


 3
−255.15060
0.70000
1.84666
23.8


 4
11.73970
15.17090 


 5*
−273.46320
5.36000
1.53380
55.6


 6*
−19.32630
1.03570


 7 (Diaphragm)
∞
1.46430


 8
28.39560
4.14820
1.72916
54.7


 9
−89.34800
Variable


10*
42.81990
2.35890
1.63550
23.9


11*
10.59360
Variable


12
22.14210
5.91100
1.53380
55.6


13
−24.38950
7.61930


14
−14.84820
0.80000
1.51680
64.2


15
−30.35070
10.43010 


16
∞
4.20000
1.51680
64.2


17
∞
BF


Image surface
∞
















TABLE 30







(Surface data 2)











Surface number
nC
nF
ng
PgF














Object surface






1
1.93123
1.98383
2.01825
0.65443


2


3
1.83649
1.87209
1.89413
0.61908


4


5
1.53100
1.54060
1.54600
0.56232


6


7


8
1.72510
1.73844
1.74571
0.54521


9


10
1.62800
1.65460
1.67140
0.63158


11


12
1.53100
1.54060
1.54600
0.56232


13


14
1.51432
1.52237
1.52667
0.53418


15


16
1.51432
1.52237
1.52667
0.53418


17
















TABLE 31





(Aspherical data)















Surface No. 5


K = −1.40898E+01, A4 = −4.06632E−05, A6 = 5.24314E−07,


A8 = −1.82351E−08


A10 = 2.58975E−10, A12 = −6.08695E−13, A14 = −1.20636E−14, A16 =


7.23165E−17


Surface No. 6


K = −1.07472E+00, A4 = −3.07368E−05, A6 = −7.85089E−08, A8 =


2.97635E−10


A10 = −1.04537E−10, A12 = 2.75209E−12, A14 = −2.53195E−14, A16 =


8.30044E−17


Surface No. 10


K = 1.21551E+01, A4 = −2.15878E−04, A6 = 2.35425E−06,


A8 = −2.98953E−08


A10 = 7.56047E−11, A12 = 5.37545E−12, A14 = −7.93906E−14, A16 =


3.37126E−16


Surface No. 11


K = −5.98312E−01, A4 = −2.46478E−04, A6 = 3.41000E−06,


A8 = −3.62066E−08


A10 = −8.31722E−10, A12 = 3.90458E−11, A14 = −5.34728E−13, A16 =


2.51787E−15
















TABLE 32







(Various data)











Infinity
1014
255














Focal length
24.1502
24.0731
23.6389


F-number
1.78016
1.80136
1.88535


Viewing angle
24.1239
23.8739
22.9258


Image height
10.8150
10.8150
10.8150


Overall length of lens system
74.5756
74.5965
74.6096


BF
0.99270
1.01329
1.02616


d0
∞
939.5121
180.0000


d9
1.3821
1.7376
3.2117


d11
7.4461
7.0909
5.6170


Entrance pupil position
20.6022
20.6022
20.6022


Exit pupil position
−40.6406
−40.3034
−38.8601


Front principal point position
30.7436
30.4380
29.0865


Back principal point position
50.4254
49.9107
47.9575
















TABLE 33







(Single lens data)









Lens
Initial surface
Focal length












1
1
29.9777


2
3
−13.2400


3
5
38.6744


4
8
29.9969


5
10
−22.7979


6
12
22.7474


7
14
−57.2563
















TABLE 34







(Lens unit data)
















Front
Back





Overall
principal
principal



Initial

length of
point
point


Lens unit
surface
Focal length
lens unit
position
position















1
1
18.63567
33.43540
27.15524
39.49239


2
10
−22.79789
2.35890
1.97254
2.84690


3
12
29.78519
28.96040
−2.87687
2.63961
















TABLE 35







(Lens unit magnification)












Initial





Lens unit
surface
Infinity
1014
255














1
1
0.00000
−0.01966
−0.09885


2
10
15.61636
15.73302
15.75216


3
12
0.08298
0.08229
0.08186









The following Table 36 shows the corresponding values to the individual conditions in the single focal length lens systems of each of Numerical Examples.








TABLE 36








Numerical Example












Condition
1
2
3
4
5
















(1)
0.0018 × νdA + PgFA
0.6726(L2)
0.6856(L2)
0.6746(L3)
0.6641(L3)
0.6726(L3)


(2)
0.0018 × νdB + PgFB
0.6726(L5)
0.6726(L5)
0.6624(L5)
0.6624(L7)
0.6624(L6)


(3)
0.0018 × νdC + PgFC
0.6746(L6)
0.6641(L6)
0.6746(L6)
0.6624(L6)
0.6746(L5)


(4)
(R1B − R2B) − (R1B + R2B)
0.23(L5)
0.16(L5)
0.20(L5)
0.21(L7)
−0.05(L6)


(5)
(R1C + R2C)/(R1B − R2C)
0.84(L6)
0.66(L6)
0.72(L6)
1.19(L6)
1.66(L5)


(6)
|fB/fC|
−1.47(L5)
−0.82(L5)
−1.30(L5)
−0.53(L7)
−1.00(L6)


(7)
|fW/fD|
−1.42(L6)
−1.06(L6)
−1.31(L6)
−0.57(L6)
−1.06(L5)





*Note 1:


The reference symbol of the lens element used is written in the parenthesis following each numerical value.


*Note 2:


The minimum value out of the corresponding lens elements is shown for conditions (1) to (3).






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.

## Claims

1. A single focal length lens system comprising, 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,
wherein 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, and
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.

2. The single focal length lens system according to claim 1, wherein the lens element B and the lens element C are disposed so as to be adjacent to each other in the direction of the optical axis.

3. The single focal length lens system according to claim 1, wherein the lens element B satisfies the following condition (4):


−0.5<(R1B+R2B)/(R1B−R2B)<1.0   (4)


where
R1B: a radius of curvature of a surface of the lens element B at the object side, and
R2B: a radius of curvature of a surface of the lens element B at the image side.

4. The single focal length lens system according to claim 1, wherein the lens element C satisfies the following condition (5):


0.2<(R1C+R2C)/(R1C−R2C)<3.0   (5)


where
R1C: a radius of curvature of a surface of the lens element C at the object side, and
R2C: a radius of curvature of a surface of the lens element C at the image side.

5. The single focal length lens system according to claim 1, wherein the lens element B and the lens element C satisfy the following condition (6):


0.3<|fB/fc|<2.5   (6)


where
fB: a focal length of the lens element B, and
fC: a focal length of the lens element C.

6. The single focal length lens system according to claim 1,
wherein the second lens unit includes one lens element D having negative optical power, and satisfies the following condition (7);


0.2<|fW/fD|<3.0   (7)



where
fW; a focal length of an entire system in an infinity in-focus condition, and
fD: a focal length of the lens element D.

7. An interchangeable lens apparatus comprising;
the single focal length lens system according to claim 1; 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.

8. A camera system comprising;
an interchangeable lens apparatus including the single focal length lens system according to claim 1; 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.