# US 9,519,124 B2 · Single focal length lens system and image pickup apparatus using the same

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- Number: US 9,519,124 B2
- Document ID: US9519124B2
- Status: Granted
- Kind: B2
- Application number: 14/522,128
- Filed: 2014-10-23
- Published: 2015-04-23
- Granted: 2016-12-13
- Earliest claimed: 2013-10-23
- Assignees: Olympus Corporation
- Applicants: Olympus Corporation
- Inventors: Takashi Fujikura; Kazuteru Kawamura
- Web page: https://patentgrep.com/patent/US9519124B2

## CPC

- G02B 13/02: Telephoto objectives, i.e. systems of the type + - in which the distance from the front vertex to the image plane is less than the equivalent focal length
- G02B 9/64: having more than six components
- G02B 27/646: {compensating for small deviations, e.g. due to vibration or shake (movement of one or more optical elements for control of motion blur in cameras, projectors or printers G03B2205/0007; image stabilisation in cameras peculiar to the presence or use of an electronic image sensor H04N23/68)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A single focal length lens system includes a front lens unit having a positive refractive power, and a rear lens unit. The front lens unit includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power, and both the first lens unit and the second lens unit include a positive lens and a negative lens. The rear lens unit includes a focusing lens unit and a first predetermined lens unit. The first predetermined lens unit has a refractive power having a sign different from a refractive power of the focusing lens unit, and does not move at the time of focusing. The front lens unit does not include a lens which moves, and the rear lens unit does not include a lens which moves except at the time of focusing.

## Claims

### Claim 1

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction,
wherein a position of the front lens unit is fixed, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing.

### Claim 2 (depends on 1)

The single focal length lens system according to claim 1, wherein the rear lens unit has a negative refractive power as a whole.

### Claim 3 (depends on 1)

The single focal length lens system according to claim 1, wherein no other lens is disposed between the third lens unit and the focusing lens unit.

### Claim 4 (depends on 1)

The single focal length lens system according to claim 1,
the single focal length lens system includes an aperture stop which is disposed between the third lens unit and the focusing lens unit.

### Claim 5 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (1) is satisfied:
0.20<fFF/f<0.90 (1)
where,
fFF denotes a focal length of the front lens unit, and
f denotes a focal length of the single focal length lens system at the time of focusing at an object at infinity.

### Claim 6 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (2) is satisfied:
0.30<|fG1/fG2|<2.00 (2)
where,
fG1 denotes a focal length of the first lens unit, and
fG2 denotes a focal length of the second lens unit.

### Claim 7 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (3) is satisfied:
−2.50<fG2/f<−0.10 (3)
where,
fG2 denotes the foal length of the second lens unit, and
f denotes the focal length of the single focal length lens system at the time of focusing at an object at infinity.

### Claim 8 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (4) is satisfied:
0<MGG2 (4)
where,
MGG2 denotes a lateral magnification of the second lens unit at the time of focusing at an object at infinity.

### Claim 9 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (5) is satisfied:
0.20<fFF/fG3<2.00 (5)
where,
fFF denotes the focal length of the front lens unit, and
fG3 denotes a focal length of the third lens unit.

### Claim 10 (depends on 1)

The single focal length lens system according to claim 1, wherein
the rear lens unit includes a focusing lens unit having a negative refractive power which moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and a lens unit having a positive refractive power, and
only the focusing lens unit moves in the optical axial direction at the time of focusing.

### Claim 11 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (6) is satisfied:
0.06<|ffo/f|<0.35 (6)
where,
f denotes the foal length of the single focal length lens system at the time of focusing at an object at infinity, and
ffo denotes a focal length of the focusing lens unit.

### Claim 12 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (7) is satisfied:
1.60<fG2/ffo<10.0 (7)
where,
ffo denotes the focal length of the focusing lens unit, and
fG2 denotes the focal length of the second lens unit.

### Claim 13 (depends on 1)

The single focal length lens system according to claim 1, wherein the front lens unit includes a positive lens which satisfies the following conditional expression (8):
80<vdFp<98 (8)
where,
vdFp denotes Abbe number for one of the positive lenses in the front lens unit.

### Claim 14 (depends on 1)

The single focal length lens system according to claim 1, wherein
the focusing lens unit is the only lens unit which moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the rear lens unit includes a lens unit having a positive refractive power which is disposed on the image side of the focusing lens unit, immediately after the focusing lens unit, and
the following conditional expression (9) is satisfied:
0.05<fFop/f<1.00 (9)
where,
fFop denotes a focal length of the lens unit having a positive refractive power which is disposed on the image side of the focusing lens unit, immediately after the focusing lens unit, and
f denotes the focal length of the single focal length lens system at the time of focusing at an object at infinity.

### Claim 15 (depends on 1)

The single focal length lens system according to claim 1, wherein
the focusing lens unit is the only lens unit which moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the rear lens unit has a lens unit having a positive refractive power which is disposed on the image side of the focusing lens unit, immediately after the focusing lens unit, and which includes a positive lens and a negative lens.

### Claim 16 (depends on 1)

The single focal length lens system according to claim 1, wherein
the rear lens unit includes an image-motion correcting lens unit, and
the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the single focal length lens system.

### Claim 17 (depends on 16)

The single focal length lens system according to claim 16, wherein
the rear lens unit includes a second predetermined lens unit which is disposed immediately before the image-motion correcting lens unit, and
the second predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the image-motion correcting lens unit.

### Claim 18 (depends on 16)

The single focal length lens system according to claim 16, wherein
the rear lens unit includes a third predetermined lens unit which is disposed immediately after the image-motion correcting lens unit, and
the third predetermined lens unit has a refractive power having a sign different from a sign of the refractive power of the image-motion correcting lens unit.

### Claim 19 (depends on 16)

The single focal length lens system according to claim 16, wherein
the image-motion correcting lens unit includes a plurality of lenses and a predetermined lens, and
the plurality of lenses have a refractive power having a sign same as the sign of the refractive power of the image-motion correcting lens unit, and
the predetermined lens has a refractive power having a sign different from the sign of the refractive power of the image-motion correcting lens unit.

### Claim 20 (depends on 16)

The single focal length lens system according to claim 16, wherein
the rear lens unit includes a second predetermined lens unit which is disposed immediately before the image-motion correcting lens unit and a third predetermined lens unit which is disposed immediately after the image-motion correcting lens unit, and
each of the second predetermined lens unit and the third predetermined lens unit has a refractive power having a sign different from the sign of the refractive power of the image-motion correcting lens unit.

### Claim 21 (depends on 16)

The single focal length lens system according to claim 16, wherein the image-motion correcting lens unit has a negative refractive power.

### Claim 22 (depends on 1)

The single focal length lens system according to claim 1, wherein the focusing lens unit satisfies the following conditional expression (10):
0.9<|(MGfoback)2×{(MGfo)2−1}|<3.50 (10)
where,
MGfo denotes a lateral magnification of the focusing lens unit in an arbitrary focused state, and
MGfoback denotes a lateral magnification of the overall optical system between the focusing lens unit and the image plane, in an arbitrary focused state.

### Claim 23 (depends on 1)

The single focal length lens system according to claim 1, wherein the single focal length lens system includes an image-motion correcting lens unit which satisfies the following conditional expression (11):
2.00<|MGISback×(MGIS×1)|<7.50 (11)
where,
MGIS denotes a lateral magnification of the image-motion correcting lens unit in an arbitrary focused state, and
MGISback denotes a lateral magnification of an overall optical system between the image-motion correcting lens unit and the image plane, in an arbitrary focused state.

### Claim 24 (depends on 1)

The single focal length lens system according to claim 1, wherein the second lens unit includes a negative lens which satisfies the following conditional expression (12):
20.0<vG2nMAX<65.0 (12)
where,
vG2nMAX denotes a maximum Abbe number from among Abbe numbers for the negative lenses in the second lens unit.

### Claim 25 (depends on 1)

The single focal length lens system according to claim 1, wherein the third lens unit is a lens unit which is disposed nearest to the image in the front lens unit.

### Claim 26 (depends on 1)

The single focal length lens system according to claim 1, wherein the total number of lenses included in the focusing lens unit is not more than two.

### Claim 27 (depends on 1)

The single focal length lens system according to claim 1, wherein the focusing lens unit consists of two lenses namely, a positive lens and a negative lens.

### Claim 28 (depends on 1)

The single focal length lens system according to claim 1, wherein
the focusing lens unit has a negative refractive power, and
a lens unit which does not move in the optical axial direction at the time of focusing is a lens unit having a positive refractive power of which, a position is fixed all the time, and
the rear lens unit includes a image-motion correcting lens unit and the lens unit having a positive refractive power of which, the position is fixed all the time, and
the image-motion correcting lens unit is disposed on the image side of the lens unit having a positive refractive power, of which, the position is fixed all the time, and moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the single focal length lens system, and
the lens unit having a positive refractive power of which, the position is fixed all the time, is disposed on the image side of the image-motion correcting lens unit.

### Claim 29 (depends on 1)

The single focal length lens system according to claim 1, wherein only the focusing lens unit is a lens unit which is movable in the optical axial direction.

### Claim 30 (depends on 16)

The single focal length lens system according to claim 16, wherein only the focusing lens unit and a image-motion correcting lens unit are the lens units which are movable.

### Claim 31 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (13) is satisfied:
0≦|f/rG2b|<7.0 (13)
where,
f denotes the focal length of the single focal length lens system at the time of focusing at an object at infinity, and
rG2b denotes a paraxial radius of curvature of a lens surface on the object side of the focusing lens unit, immediately before the focusing lens unit.

### Claim 32 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (14) is satisfied:
0.5≦φfo/φLa≦0.92 (14)
where,
φfo denotes a maximum effective aperture from among effective apertures of lenses in the focusing lens unit, and
φLa denotes a maximum effective aperture of a lens positioned nearest to the image in the single focal length lens system.

### Claim 33 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (15) is satisfied:
0.023≦Dsfo/DLTL≦0.110 (15)
where,
Dsfo denotes a distance on the optical axis from the aperture stop up to a lens surface nearest to an object of the focusing lens unit,
DLTL denotes a distance on the optical axis from a lens surface nearest to the object of the single focal length lens system up to an image plane, and
both Dsfo and DLTL are distances at the time of focusing at an object at infinity.

### Claim 34 (depends on 1)

The single focal length lens system according to claim 1, wherein the following conditional expression (16) is satisfied:
0.2≦Dsfo/φs≦0.8 (16)
where,
Dsfo denotes the distance on the optical axis from the aperture stop up to a lens surface nearest to an object of the focusing lens unit, and is a distance at the time of focusing at an object at infinity, and
Φs denotes a maximum diameter of the aperture stop.

### Claim 35 (depends on 1)

The single focal length lens system according to claim 1, wherein an optical system positioned on the image side of the focusing lens unit includes at least two positive lenses and one negative lens.

### Claim 36 (depends on 1)

An image pickup apparatus comprising:
an optical system; and
an image pickup element which has an image pickup surface, and which converts an image formed on the image pickup surface by the optical system to an electric signal, wherein
the optical system is a single focal length lens system according to claim 1.

### Claim 37

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the rear lens unit includes a focusing lens unit having a negative refractive power which moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and a lens unit having a positive refractive power, and
only the focusing lens unit moves in the optical axial direction at the time of focusing.

### Claim 38

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the focusing lens unit is the only lens unit which moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the rear lens unit has a lens unit having a positive refractive power which is disposed on the image side of the focusing lens unit, immediately after the focusing lens unit, and which includes a positive lens and a negative lens.

### Claim 39

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the rear lens unit includes an image-motion correcting lens unit, and
the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the single focal length lens system.

### Claim 40

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the focusing lens unit satisfies the following conditional expression (10):
0.9<|(MGfoback)2×{(MGfo)2−1}|<3.50 (10)
where,
MGfo denotes a lateral magnification of the focusing lens unit in an arbitrary focused state, and
MGfoback denotes a lateral magnification of the overall optical system between the focusing lens unit and the image plane, in an arbitrary focused state.

### Claim 41

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the single focal length lens system includes an image-motion correcting lens unit which satisfies the following conditional expression (11):
2.00<|MGISback×(MGIS×1)|<7.50 (11)
where,
MGIS denotes a lateral magnification of the image-motion correcting lens unit in an arbitrary focused state, and
MGISback denotes a lateral magnification of an overall optical system between the image-motion correcting lens unit and the image plane, in an arbitrary focused state.

### Claim 42

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the total number of lenses included in the focusing lens unit is not more than two.

### Claim 43

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the focusing lens unit consists of two lenses namely, a positive lens and a negative lens.

### Claim 44

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the focusing lens unit has a negative refractive power, and
a lens unit which does not move in the optical axial direction at the time of focusing is a lens unit having a positive refractive power of which, a position is fixed all the time, and
the rear lens unit includes a image-motion correcting lens unit and the lens unit having a positive refractive power of which, the position is fixed all the time, and
the image-motion correcting lens unit is disposed on the image side of the lens unit having a positive refractive power, of which, the position is fixed all the time, and moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the single focal length lens system, and
the lens unit having a positive refractive power of which, the position is fixed all the time, is disposed on the image side of the image-motion correcting lens unit.

### Claim 45

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the following conditional expression (15) is satisfied:
0.023≦Dsfo/DLTL≦0.110 (15)
where,
Dsfo denotes a distance on the optical axis from the aperture stop up to a lens surface nearest to an object of the focusing lens unit,
DLTL denotes a distance on the optical axis from a lens surface nearest to the object of the single focal length lens system up to an image plane, and
both Dsfo and DLTL are distances at the time of focusing at an object at infinity.

### Claim 46

A single focal length lens system comprising in order from an object side to an image side along an optical axis:
a front lens unit having a positive refractive power; and
a rear lens unit, wherein
the front lens unit 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 third lens unit having a positive refractive power, and
both the first lens unit and the second lens unit include a positive lens and a negative lens, and
the rear lens unit includes in order from the object side to the image side, a focusing lens unit and a first predetermined lens unit, and
the focusing lens unit moves along the optical axis at the time of focusing from an object at infinity to an object at a close distance, and
the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the focusing lens unit, and does not move in an optical axial direction at the time of focusing, and
the front lens unit does not include a lens which moves in the optical axial direction, and
the rear lens unit does not include a lens which moves in the optical axial direction except at the time of focusing, and
the following conditional expression (16) is satisfied:
0.2≦Dsfo/φs≦0.8 (16)
where,
Dsfo denotes the distance on the optical axis from the aperture stop up to a lens surface nearest to an object of the focusing lens unit, and is a distance at the time of focusing at an object at infinity, and
Φs denotes a maximum diameter of the aperture stop.