Zoom lens

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a compact zoom lens for use in digital still cameras, video cameras, and other devices that are equipped with an imaging element having a high pixel count such as a CCD.

[0002] Japanese Laid-Open Patent Publication Number Hei 5-173073 and Japanese Laid-Open Patent Publication Number Hei 6-201993 disclose conventional zoom lenses that include a first lens group with a negative refractivity; a second lens group with a positive refractivity; and a third lens group with a positive refractivity. The three lens groups include at least seven lenses arranged along an optical axis.

[0003] In recent years, there have been significant developments in the technology of solid-state imaging elements such as CCD's that are used in devices such as digital still cameras and video cameras. The increase in the density and number of pixels in these devices has led to a growing need for lenses for optical systems with superior optical characteristics. However, as devices such as digital still cameras and video cameras decrease in size, the zoom lenses mounted on these devices must become more compact, thinner, and lighter. Compactness, especially in terms of the length of the lens, is particularly important when the zoom lens is mounted on the main camera unit regardless of whether the camera is in use.

[0004] A conventional zoom lens uses at least seven lenses which requires that the zoom lens has a significant length along its optical axis. As a result, conventional zoom lenses do not meet the demands of more compact, thinner digital still cameras, video cameras, and the like.

SUMMARY OF THE INVENTION

[0005] The present invention provides a zoom lens having a compact, light, and thin design with superior optical characteristics that efficiently correct various aberrations. The zoom lens is used particularly for imaging elements with high pixel counts, wherein the zoom factor is approximately 3 and the following conditions are met: the total lens length during shooting is no more than 37 mm; the total thickness along the optical axis of the lens groups is no more than 15 mm; the back focus for placement of a low-pass filter and the like is at least 3 mm; the lens brightness (F number) at the wide-angle end is approximately 2.8; and the distortion is no more than 5%.

[0006] The zoom lens includes, from the object side to the image plane side: a first lens group having a negative overall refractivity, a second lens group having a positive overall refractivity, and a third lens group having a positive overall refractivity. The first lens group is formed from a first lens having a negative refractivity and a second lens having a positive refractivity. The second lens group is formed from a third lens, a fourth lens and a fifth lens. The third lens has a positive refractivity. The fourth and fifth lenses are joined together and have a negative refractivity. The third lens group is formed from a sixth lens having a positive refractivity.

[0007] With this structure, the total system can be formed with six lenses. Therefore, the total length and the retracted size of the zoom lens are reduced, and it is compact and thin.

[0008] The zoom lens as described above can satisfy the following conditions (1) and (2):

[0009] (1) 0.5<f2/|f1|<1.2

[0010] (2) 1.5<f3/fw<6

[0011] where fi (i=1−3) is the focal distance of the i-th lens group and fw is the focal distance of the total lens system at the wide-angle end. Distortion, lateral chromatic aberration, and the like are corrected, and the zoom lens is telecentric and compact. Other optical characteristics are also improved with this construction.

[0012] The zoom lens as described above can also satisfy the following conditions (3) and (4):

[0013] (3) v1−v2>10

[0014] (4) D2/fw>0.2

[0015] where v1 is the Abbe number of the first lens, v2 is the Abbe number of the second lens, D2 is the distance between the first lens and the second lens along the optical axis, and fw is the focal distance of the total lens system at the wide-angle end. Spherical aberration, astigmatism, distortion, and the like are corrected when these conditions are satisfied. This configuration is particularly effective for correcting chromatic aberration.

[0016] The first, third, and sixth lenses can include aspherical surfaces to correct aberrations such as spherical aberration, coma, and the like.

[0017] The aspherical surface of the first lens can be formed at the end having a smaller curvature radius or can be formed with a diminishing refractivity toward the periphery. These modifications can correct distortion.

[0018] The first lens group, the second lens group, and the third lens group can move along the optical axis during the zooming and image plane correction operations performed from the wide-angle end to the telescopic end. This structure allows for the correction of different types of aberrations at the central focal distance at a central position between the wide-angle end and the telescopic end.

[0019] The third lens group can move along the optical axis toward the image plane side and then toward the object side during the zooming and image plane correction operations performed from the wide-angle end to the telescopic end. This structure allows for the correction of astigmatism at the central focal distance at a central position between the wide-angle end and the telescopic end.

[0020] The features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]
FIG. 1 illustrates a zoom lens according to the present invention.

[0022]
FIG. 2 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of a zoom lens according to an embodiment of the present invention.

[0023]
FIG. 3 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the central position of a zoom lens according to an embodiment of the present invention.

[0024]
FIG. 4 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telescopic end of a zoom lens according to an embodiment of the present invention.

[0025]
FIG. 5 illustrates an embodiment of a zoom lens according to the present invention.

[0026]
FIG. 6 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of a zoom lens according to an alternate embodiment of the present invention.

[0027]
FIG. 7 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the central position of a zoom lens according to an alternate embodiment of the present invention.

[0028]
FIG. 8 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telescopic end of a zoom lens according to an alternate embodiment of the present invention.

[0029]
FIG. 9 illustrates an embodiment of a zoom lens according to the present invention.

[0030]
FIG. 10 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of a zoom lens according to an alternate embodiment of the present invention.

[0031]
FIG. 11 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the central position of a zoom lens according to an alternate embodiment of the present invention.

[0032]
FIG. 12 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telescopic end of a zoom lens according to an alternate embodiment of the present invention.

[0033]
FIG. 13 illustrates an embodiment of a zoom lens according to the present invention.

[0034]
FIG. 14 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of a zoom lens according to an alternate embodiment of the present invention.

[0035]
FIG. 15 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the central position of a zoom lens according to an alternate embodiment of the present invention.

[0036]
FIG. 16 illustrates spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telescopic end of a zoom lens according to an alternate embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037]
FIG. 1 illustrates the basic structure of a zoom lens according to the present invention.

[0038] From the object end to the image plane end, the zoom lens includes a first lens group I having a negative overall refractivity, a second lens group II having an positive overall refractivity, and a third lens group III having an positive overall refractivity.

[0039] The first lens group I is formed from a first lens 1 having a negative refractivity and a second lens 2 having a positive refractivity. The second lens group II is formed from a third lens 3, a fourth lens 4, and a fifth lens 5. The third lens 3 has a positive refractivity. The fourth lens 4 and the fifth lens 5 are joined together and have a negative refractivity. The third lens group III is formed from a sixth lens 6 having a positive refractivity.

[0040] A glass filter 7, such as an infrared cut filter or a low-pass filter, is positioned on the image plane side of the third lens group III which comprises the sixth lens 6. An aperture stop 8 is disposed between the second lens group II and the third lens group III, i.e., the second lens 2 and the third lens 3.

[0041] The first lens group I, the second lens group II, and the third lens group III can move independently along the optical axis X. Therefore, the zoom factor can be adjusted from the wide-angle to the telescopic end, and the image plane can be corrected accordingly. By adjusting the zoom scale from the wide-angle to the telescopic end, the third lens group III moves toward the image plane side and then toward the object side.

[0042] The composite focal distance of the first lens group I is represented by f1, the composite focal distance of the second lens group II is represented by f2, the focal distance of the lens system at the wide-angle end is represented by fw, the focal distance of the lens system at the telescopic end is represented by ft, and the focal distance of the lens system at the central region is represented by fm. The lens surfaces of the first lens 1 through the sixth lens 6 are represented by Si (i=1-4, 6-12); the respective curvature radii of the surfaces Si are represented by Ri (i=1-4, 6-12); the refractivity of the i-th lens relative to line d is represented by Ni (i=1-6); and the Abbe number is represented by vi (i=1-6).

[0043] For the glass filter 7, the surfaces are represented by Si (i=13, 14), the curvature radii of the surfaces Si are represented by Ri (i=13, 14), the refractivity relative to line d is represented by N7, and the Abbe number is represented by v7. The thickness of the individual lenses and the distances between each of the elements along the optical axis X from the first lens 1 to the glass filter 7 are represented by Di (i=1-13) as shown in FIG. 1.

[0044] The fourth lens 4 and the fifth lens 5, which comprise the second lens group II, are joined together at the surface S9 where the lenses have matching curvature radii R9. If the fourth lens 4 and the fifth lens 5 were replaced by a single lens, the resulting color aberration would be difficult to correct and would affect high resolution imaging. Additionally, automatic centering would be difficult due to the exact similarity between the curvature radii of the two sides of the lens. By separately preparing and then joining the fourth lens 4 and the fifth lens 5, color aberration can be corrected. Furthermore, the lenses can be centered separately.

[0045] Since the image-side surface S2 of the first lens 1 has a smaller curvature radius than the object-side surface S1 of the first lens 1, surface S2 is aspherical. The negative refractivity of this aspherical surface decreases toward the periphery in order to correct distortion. Similarly, the object-side surface S6 of the third lens 3 is aspherical in order to correct spherical aberration. Furthermore, the image-side surface S12 of the sixth lens 6 is aspherical in order to correct coma.

[0046] Thus, the correction of various types of aberration can be accomplished by using aspherical surfaces for the first lens 1 having a negative refractivity, the third lens 3 having a positive refractivity, and the sixth lens 6 having a positive refractivity.

[0047] The aspherical surfaces are defined by the following equation:

Z=Cy

2
/[1+(1−εC2y2)1/2]+Dy4+Ey6+Fy8+G

[0048] where Z is the distance from the tangent plane at the apex of the aspherical surface to a point on the aspherical surface; y is the height from the optical axis X; C is the curvature (1/R) at the apex of the aspherical surface; ε is the conic constant; and D, E, F, and G are the aspherical surface coefficients.

[0049] The first, second, and third lens groups are constructed to satisfy the following:

[0050] (1)0.5<f2/|f1|<1.2

[0051] (2) 1.5<f3/fw<6

[0052] where f1, f2, and f3 are the focal distances of the first, second, and third lens groups respectively and fw is the focal distance of the lens system at the wide-angle end.

[0053] Condition (1) defines the appropriate ratio between the focal distances of the first lens group I and the second lens group II. If the upper limit is exceeded, correction becomes difficult, especially for distortion and lateral chromatic aberration. Dropping below the lower limit makes it difficult to achieve a zoom ratio of approximately 3. By satisfying condition (1), a zoom ratio of approximately 3 can be achieved with good optical characteristics and a compact design.

[0054] Condition (2) defines the appropriate focal distance for the third lens group III. If the upper limit is exceeded, the exit pupil position approaches the image plane, making telecentricity difficult to obtain. Dropping below the lower limit makes it difficult to provide a compact overall design for the zoom lens. Thus, by satisfying the condition (2), a compact design can be achieved while maintaining telecentricity and resulting in a zoom lens suitable for imaging elements with high pixel counts.

[0055] The first lens group I is prepared to satisfy the following conditions:

[0056] (3) v1−v2>10

[0057] (4) D2/fw>0.2

[0058] where v1 is the Abbe number of the first lens 1, v2 is the Abbe number of the second lens 2, D2 is the distance between the first lens 1 and the second lens 2 along the optical axis X, and fw is the focal distance for the entire lens system at the wide-angle end.

[0059] By satisfying condition (3), the zoom lens provides effective correction, especially for chromatic aberration.

[0060] By satisfying condition (4), the zoom lens provides effective correction of various aberrations such as spherical aberration.

[0061] Table 1 shows the numerical specifications for the zoom lens of a first embodiment under the conditions (1), (2), (3), and (4), such that f2/|f1|=0.803, f3/fw=2.371, v1−v2=20.0, and D2/fw=0.498. Table 2 shows the numerical data for the individual lens surfaces. Table 3 shows the numerical data relating to the aspherical surfaces S2, S6, and S12. Table 4 shows the focal distances for the lens system at the wide-angle end fw, the central position fm, and the telescopic end ft and the distances D4, D10, and D12 along the optical axis X.

[0062] FIGS. 2-4 are aberration line drawings indicating spherical aberration, astigmatism, distortion, and lateral chromatic aberration. In FIGS. 2-4, 6-8, 10-12, and 14-16, d represents the aberration due to line d, F represents aberration due to line F, c represents aberration due to line c, SC represents the offense against the sine condition, DS represents sagittal plane aberration, and DT represents meridional plane aberration.

1TABLE 1Object distance∞Thickness of third lens2.50(mm)group III (mm)Focal distance5.02Total thickness of all14.20(mm)9.84lens groups14.50(mm)F number2.84Back focus (air3.4674.13conversion)3.2675.31(mm)3.467Exit pupil position−23.35Angle of view60.2°(mm)+106.96(2ω)31.7°+28.4321.9°Total lens length30.20Focal distance f1−12.048(mm)28.79(mm)31.54Total lens system34.25Focal distance f29.680length32.64(mm)(mm)35.58Thickness of first lens6.05Focal distance f311.904group I (mm)(mm)Thickness of second5.65Focal distance of the5.02lens group II(includes iris)lens system at the(mm)wide-angle end fw(mm)

[0063]

2

TABLE 2

Curvature
Distance
Refractivity

Surface
radius (mm)
(mm)
(d line)
Abbe number

S1
R1:
104.066
D1:
1.500
N1: 1.80432
ν1: 40.9

S2
R2:
5.331

*

D2:
2.500

S3
R3:
9.019
D3:
2.050
N2: 1.92286
ν2: 20.9

S4
R4:
15.838

D4:
variable

S5
Aperture stop

D5:
0.600

S6
R6:
8.187
D6:
1.800
N3: 1.51450
ν3: 63.1

*

S7
R7:
−16.300

D7:
0.200

S8
R8:
5.422
D8:
2.250
N4: 1.78590
ν4: 43.9

S9
R9:
−8.995
D9:
0.800
N5: 1.72825
ν5: 28.3

S10
R10:
3.049

D10:
variable

S11
R11:
21.331
D11:
2.500
N6: 1.58323
ν6: 59.5

S12
R12:
−9.849

*

D12:
variable

S13
R13:
∞
D13:
1.700
N7: 1.51680
ν7: 64.2

S14
R14:
∞

* Aspherical surface

[0064]

3

TABLE 3

Aspherical surface

coefficient
Numerical Data

Surface S2

ε
0.3580000

D
0.9228168 × 10−4

E
−0.3438605 × 10−5

F
0.3772979 × 10−6

G
−0.1120333 × 10−7

Surface S6

ε
−0.9500000

D
−0.6632119 × 10−4

E
−0.1910034 × 10−4

F
0.4364795 × 10−5

G
−0.4848686 × 10−6

Surface S12

ε
−2.7500000

D
−0.1259369 × 10−4

E
−0.9450508 × 10−5

F
−0.3946424 × 10−6

G
0.4700000 × 10−7

[0065]

4

TABLE 4

Wide-Angle End
Central Position
Telescopic End

f
(mm)
5.02
(fw)
9.84
(fm)
14.50
(ft)

D4
(mm)
12.000

4.628

1.894

D10
(mm)
4.000

9.965

15.443

D12
(mm)
1.346

1.146

1.346

[0066] For the wide-angle, central, and telescopic positions of the lens system, the total lens length (from the front surface S1 of the first lens 1 to the back surface S12 of the sixth lens 6) is 30.20 mm, 28.79 mm, and 31.54 mm; the total lens system length (from the front surface S1 of the first lens 1 to the image plane, including the cover glass of the CCD) is 34.25 mm, 32.64 mm, and 35.58 mm; the back focus (air conversion) is 3.467 mm, 3.267 mm, and 3.467 mm; the exit pupil position is −23.35 mm, +106.96 mm, and +28.43 mm; and the F number is 2.84, 4.13, and 5.31.

[0067]
FIG. 5 shows the basic structure of a second embodiment of the zoom lens. The structure of this zoom lens is identical to the structure of the first embodiment described above except for the different lens specifications.

[0068] Table 5 shows the lens specifications for a second embodiment under the conditions (1), (2), (3), and (4), such that f2/|f1|=0.799, f3/fw=2.455, v1−v2=20.0, and D2/fw=0.515. Table 6 shows the numerical data for the individual lens surfaces. Table 7 shows the numerical data relating to the aspherical surfaces S2, S6, and S12. Table 8 shows the focal distances for the lens system at the wide-angle end fw, the central position fm, and the telescopic end ft and the distances D4, D10, and D12 along the optical axis X.

[0069]
FIGS. 6, 7, and 8 are aberration line drawings indicating spherical aberration, astigmatism, distortion, and lateral chromatic aberration.

5TABLE 5Object distance∞Thickness of third lens2.50(mm)group III (mm)Focal distance4.85Total thickness of all14.20(mm)9.425lens groups14.00(mm)F number2.84Back focus (air3.4824.08conversion)3.2825.25(mm)3.482Exit pupil position−22.19Angle of view61.9°(mm)+162.68(2ω)33.0°+30.7922.6°Total lens length30.48Focal distance f1−12.120(mm)28.43(mm)30.79Total lens system34.55Focal distance f29.687length32.29(mm)(mm)34.85Thickness of first lens6.05Focal distance f311.905group I (mm)(mm)Thickness of second5.65Focal distance of the4.85lens group II(includes iris)lens system at the(mm)wide-angle end fw(mm)

[0070]

6

TABLE 6

Curvature
Distance
Refractivity

Surface
radius (mm)
(mm)
(d line)
Abbe number

S1
R1:
133.073
D1:
1.500
N1: 1.80432
ν1: 40.9

S2
R2:
5.265

*

D2:
2.500

S3
R3:
9.175
D3:
2.050
N2: 1.92286
ν2: 20.9

S4
R4:
17.230

D4:
variable

S5
Aperture stop

D5:
0.600

S6
R6:
7.947
D6:
1.800
N3: 1.51450
ν3: 63.1

*

S7
R7:
−16.294

D7:
0.200

S8
R8:
5.516
D8:
2.250
N4: 1.78590
ν4: 43.9

S9
R9:
−8.243
D9:
0.800
N5: 1.72825
ν5: 28.3

S10
R10:
3.049

D10:
variable

S11
R11:
24.708
D11:
2.500
N6: 1.58323
ν6: 59.5

S12
R12:
−9.297

*

D12:
variable

S13
R13:
∞
D13:
1.700
N7: 1.51680
ν7: 64.2

S14
R14:
∞

* aspherical surface

[0071]

7

TABLE 7

Aspherical surface

coefficient
Numerical Data

Surface S2

ε
0.3200000

D
0.9296380 × 10−4

E
−0.3433510 × 10−5

F
0.3767930 × 10−6

G
−0.1128770 × 10−7

Surface S6

ε
−0.9450000

D
−0.6634860 × 10−4

E
−0.1909890 × 10−4

F
0.4364860 × 10−5

G
−0.4848650 × 10−6

Surface S12

ε
−2.7000000

D
−0.1259450 × 10−4

E
−0.9452220 × 10−5

F
−0.3950320 × 10−6

G
0.4693460 × 10−7

[0072]

8

TABLE 8

Wide-Angle End
Central Position
Telescopic End

f
(mm)
4.850
(fw)
9.425
(fm)
14.000
(ft)

D4
(mm)
12.514

4.847

1.910

D10
(mm)
3.770

9.385

14.681

D12
(mm)
1.361

1.161

1.361

[0073] For the wide-angle, central, and telescopic positions of the lens system in this second embodiment described above, the total lens length (from the front surface S1 of the first lens 1 to the back surface S12 of the sixth lens 6) is 30.48 mm, 28.43 mm, and 30.79 mm; the total lens system length (from the front surface S1 of the first lens 1 to the image plane, including the cover glass of the CCD) is 34.55 mm, 32.29 mm, and 34.85 mm; the back focus (air conversion) is 3.482 mm, 3.282 mm, and 3.482 mm; the exit pupil position is −22.19 mm, +162.68 mm, and +30.79 mm; and the F number is 2.84, 4.08, and 5.25.

[0074]
FIG. 9 shows the basic structure of a third embodiment of the zoom lens. The structure of this zoom lens is identical to the embodiments described above except for the different lens specifications.

[0075] Table 9 shows the lens specifications for the third embodiment under the conditions (1), (2), (3), and (4), such that f2/|f1|=0.754, f3/fw=2.390, v1−v2=17.100, and D2/fw=0.390. Table 10 shows the numerical data for the individual lens surfaces. Table 11 shows the numerical data relating to the aspherical surfaces S2, S6, and S12. Table 12 shows the focal distances for the lens system at the wide-angle end fw, the central position fm, and the telescopic end ft and the distances D4, D10, and D12 along the optical axis X.

[0076]
FIGS. 10, 11, and 12 are aberration line drawings indicating spherical aberration, astigmatism, distortion, and lateral chromatic aberration.

9TABLE 9Object distance∞Thickness of third lens2.50(mm)group III (mm)Focal distance5.893Total thickness of all14.15(mm)11.440lens groups17.000(mm)F number2.85Back focus (air3.4794.12conversion)3.0795.27(mm)3.479Exit pupil position−24.3Angle of view60.8°(mm)+424.6(2ω)32.4°+41.9822.1°Total lens length32.282Focal distance f1−14.109(mm)30.312(mm)32.634Total lens system36.340Focal distance f210.638length33.970(mm)(mm)36.692Thickness of first lens5.70Focal distance f314.085group I (mm)(mm)Thickness of second5.95Focal distance of the5.893lens group II(includes iris)lens system at the(mm)wide-angle end fw(mm)

[0077]

10

TABLE 10

Curvature
Distance
Refractivity

Surface
radius (mm)
(mm)
(d line)
Abbe number

S1
R1:
162.368
D1:
1.400
N1: 1.80432
ν1: 40.9

S2
R2:
5.683

*

D2:
2.300

S3
R3:
10.056
D3:
2.000
N2: 1.84666
ν2: 23.8

S4
R4:
25.123

D4:
variable

S5
Aperture stop

D5:
0.600

S6
R6:
8.809
D6:
1.800
N3: 1.51450
ν3: 63.1

*

S7
R7:
−17.740

D7:
0.250

S8
R8:
5.968
D8:
2.250
N4: 1.78590
ν4: 43.9

S9
R9:
−11.149
D9:
0.800
N5: 1.72825
ν5: 28.3

S10
R10:
3.348

D10:
variable

S11
R11:
17.042
D11:
2.500
N6: 1.58323
ν6: 59.5

S12
R12:
−15.002

*

D12:
variable

S13
R13:
∞
D13:
1.700
N7: 1.51680
ν7: 64.2

S14
R14:
∞

* aspherical surface

[0078]

11

TABLE 11

Aspherical surface

coefficient
Numerical Data

Surface S2

ε
0.3291658

D
0.5744836 × 10−4

E
−0.1527527 × 10−5

F
0.1266336 × 10−6

G
−0.3326889 × 10−8

Surface S6

ε
−0.8754729

D
−0.4108016 × 10−4

E
−0.8628161 × 10−5

F
0.1449087 × 10−5

G
−0.1167419 × 10−6

Surface S12

ε
−3.8631148

D
−0.4226433 × 10−5

E
−0.3977215 × 10−5

F
−0.1203615 × 10−6

G
0.8336490 × 10−8

[0079]

12

TABLE 12

Wide-Angle End
Central Position
Telescopic End

f
(mm)
5.893
(fw)
11.440
(fm)
17.000
(ft)

D4
(mm)
13.113

4.855

1.483

D10
(mm)
4.318

10.607

16.300

D12
(mm)
1.358

0.958

1.358

[0080] For the wide-angle, central, and telescopic positions of the lens system in this third embodiment described above, the total lens length (from the front surface S1 of the first lens 1 to the back surface S12 of the sixth lens 6) is 32.282 mm, 30.312 mm, and 32.634 mm; the total lens system length (from the front surface S1 of the first lens 1 to the image plane, including the cover glass of the CCD) is 36.340 mm, 33.970 mm, and 36.692 mm; the back focus (air conversion) is 3.479 mm, 3.079 mm, and 3.479 mm; the exit pupil position is −24.3 mm, +424.6 mm, and +41.98 mm; and the F number is 2.85, 4.12, and 5.27.

[0081]
FIG. 13 shows the basic structure of a fourth embodiment of the zoom lens. The structure of this zoom lens is identical to the structure described above except for the different lens specifications.

[0082] Table 13 shows the lens specifications for the fourth embodiment under the conditions (1), (2), (3), and (4), such that f2/|f1|=0.749, f3/fw=2.493, v1−v2=17.100, and D2/fw=0.407. Table 14 shows numerical data for the individual lens surfaces. Table 15 shows numerical data relating to the aspherical surfaces. Table 16 shows the focal distances for the lens system at the wide-angle end fw, the central position fm, and the telescopic end ft and the distances D4, D10, and D12 along the optical axis X.

[0083]
FIGS. 14, 15, and 16 are aberration line drawings indicating spherical aberration, astigmatism, distortion, and lateral chromatic aberration.

13TABLE 13Object distance∞Thickness of third lens2.50(mm)group III (mm)Focal distance5.650Total thickness of all14.15(mm)11.002lens groups16.300(mm)F number2.83Back focus (air3.4074.04conversion)3.2075.17(mm)3.407Exit pupil position−21.75Angle of view62.8°(mm)−573.63(2ω)33.6°+47.7323.0°Total lens length32.312Focal distance f1−14.184(mm)29.513(mm)31.808Total lens system36.298Focal distance f210.608length33.299(mm)(mm)35.794Thickness of first lens5.70Focal distance f314.084group I (mm)(mm)Thickness of second5.95Focal distance of the5.650lens group II(includes iris)lens system at the(mm)wide-angle end fw(mm)

[0084]

14

TABLE 14

Curvature
Distance
Refractivity

Surface
radius (mm)
(mm)
(d line)
Abbe number

S1
R1:
111.036
D1:
1.400
N1: 1.80432
ν1: 40.9

S2
R2:
5.459

*

D2:
2.300

S3
R3:
10.375
D3:
2.000
N2: 1.84666
ν2: 23.8

S4
R4:
29.658

D4:
variable

S5
Aperture stop

D5:
0.600

S6
R6:
9.954
D6:
1.800
N3: 1.60602
ν3: 57.4

*

S7
R7:
−22.683

D7:
0.250

S8
R8:
6.037
D8:
2.500
N4: 1.78590
ν4: 43.9

S9
R9:
−8.461
D9:
0.800
N5: 1.72825
ν5: 28.3

S10
R10:
3.364

D10:
variable

S11
R11:
14.100
D11:
2.500
N6: 1.60602
ν6: 57.4

S12
R12:
−20.181

*

D12:
variable

S13
R13:
∞
D13:
1.700
N7: 1.51680
ν7: 64.2

S14
R14:
∞

* aspherical surface

[0085]

15

TABLE 15

Aspherical surface

coefficient
Numerical Data

Surface S2

ε
−0.22000

D
0.39183 × 10−3

E
0.67725 × 10−5

F
−0.35091 × 10−6

G
0.68138 × 10−8

Surface S6

ε
−1.03604

D
−0.33027 × 10−4

E
−0.55396 × 10−5

F
−0.35091 × 10−6

G
0.68138 × 10−8

Surface S12

ε
0.00000

D
0.11533 × 10−3

E
−0.85084 × 10−5

F
0.33444 × 10−6

G
−0.41000 × 10−8

[0086]

16

TABLE 16

Wide-Angle End
Central Position
Telescopic End

f
(mm)
5.650
(fw)
11.002
(fm)
16.300
(ft)

D4
(mm)
13.400

4.640

1.373

D10
(mm)
4.103

10.064

15.625

D12
(mm)
1.286

1.086

1.286

[0087] For the wide-angle, central, and telescopic positions of the lens system in the fourth embodiment described above, the total lens length (from the front surface S1 of the first lens 1 to the back surface S12 of the sixth lens 6) is 32.312 mm, 29.513 mm, and 31.808 mm; the total lens system length (from the front surface S1 of the first lens 1 to the image plane, including the cover glass of the CCD) is 36.298 mm, 33.299 mm, and 35.794 mm; the back focus (air conversion) is 3.407 mm, 3.207 mm, and 3.407 mm; the exit pupil position is −21.75 mm, −573.63 mm, and +47.73 mm; and the F number is 2.83, 4.04, and 5.17.

[0088] The zoom lens according to the present invention provides superior optical characteristics, corrects various types of aberration effectively, and is compact, slim, lightweight, and inexpensive to produce.

[0089] The zoom lens is effective particularly when the zoom factor is approximately 3 and when coupled with an imaging element with a high pixel count and a high pixel density. The total lens length during shooting should be no more than 37 mm. The total thickness along the optical axis of the lens groups should be no more than 15 mm. The back focus for placement of a low-pass filter and the like should be at least 3 mm. The lens brightness (F number) at the wide-angle end should be approximately 2.8. Furthermore, the distortion should be no more than 5%.

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