JP2005106878A - Super-wide angle lens system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance inner focus type super-wide angle lens whose system is compact and where aberration fluctuation due to focusing is little though it is a super-wide angle lens whose photographic viewing angle exceeds 120°. <P>SOLUTION: The super-wide angle lens system is constituted of a 1st lens group having negative refractive power and a rear group having positive refractive power in order from an object side, and the 1st lens group is constituted of a 1A lens group having negative refractive power and a 1B lens group having negative refractive power. Furthermore, the 1A lens group is constituted of two lenses, such as, a negative meniscus lens as a 1st lens L1 and a negative meniscus lens as a 2nd lens L2, and the 1B lens group is constituted by including a negative meniscus lens using an aspherical surface as a 3rd lens L3 and a negative meniscus lens using an aspherical surface as a 4th lens L4, and is moved to the object side in the case of focusing. The super-wide angle lens system satisfies a fixed condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultra-wide-angle lens suitable for a single-lens reflex camera, an electronic still camera, a video camera, or the like whose field angle at the wide-angle end exceeds 120 degrees.

  Conventionally, super wide-angle zoom lenses generally have an angle of view of about 100 to 110 degrees. In addition, no short focus lens with an angle of view exceeding 120 degrees was present except for fish eye lenses with different projection methods. As a conventional example, there is one disclosed in Japanese Patent Laid-Open No. 2001-124985 assuming that the angle of view exceeds 120 degrees, but it cannot be applied to a single-lens reflex type with a long back focus. In addition, as a legend constituted by a retro focus type effective for a single-lens reflex camera having a long back focus, an angle of view is 118 to 9 degrees, Japanese Patent Laid-Open Nos. 2001-159732 and 2001-166206, and an angle of view is 113. JP-A 04-15612, JP-A 04-275515, etc. are known as those having ˜114 degrees. However, these lenses have a problem that it is difficult to process a large-aperture aspherical lens used in the front group having a large effective diameter.

JP 2001-124985 A JP 2001-159732 A JP 2001-166206 A Japanese Patent Laid-Open No. 04-15612 Japanese Patent Laid-Open No. 04-275515

  In a single-lens reflex camera that generally employs a quick return mirror, it is necessary to take a long back focus in order to avoid a mirror hit, and the negative refractive power of the first lens group increases as the lens becomes an ultra-wide angle lens. It is necessary to have a retro focus configuration. Here, a negative meniscus lens having a strong refractive power is required for the first lens L1, but distortion occurs with respect to the peripheral luminous flux of the lens having a wide angle of view. In order to correct distortion, a plurality of lenses including a positive lens are required. However, as the number of lens elements increases, the first lens group becomes enlarged, which not only increases the lens diameter and weight, but also negative. Since the concave side curvature of the meniscus lens is a shape close to a hemisphere, lens processing becomes difficult. In order to avoid this, it is effective to make the surface close to the object surface aspherical, such as the first lens L1, for example, but making the large-aperture lens aspherical greatly increases the manufacturing cost. This leads to a decrease in mass productivity and is not desirable.

  Accordingly, by appropriately arranging the configuration of the first lens group, it is a problem to realize a lightweight and compact super wide-angle lens while performing sufficient aberration correction without using a large-aperture aspheric lens.

  An object is to provide a high-performance inner focus type super-wide-angle lens with a compact system and less aberration fluctuations due to focusing, even though it is a super-wide-angle lens with a shooting angle of view exceeding 120 degrees.

In order from the object side, there are a first lens unit having a negative refractive power and a rear group having a positive refractive power, and the first lens group has a first A lens group having a negative refractive power and a negative refractive power. The first lens group includes a first meniscus lens as the first lens L1 and a negative meniscus lens as the second lens L2, and the first lens group includes an aspherical surface as the third lens L3. A negative meniscus lens using a lens and a negative meniscus lens using an aspherical surface for the fourth lens L4. The first B lens group is moved to the object side during focusing, and satisfies the following conditions: Let
(1) 1.1 <| f ₁ / f _w | <1.6
(2) 0.5 <f _1B / f _1A <2.0
However,
f _w : Focal length of the entire optical system at the wide-angle end f ₁ : Focal length f _1A of the first lens group f _1B : Focal length f _{1B of the} first A lens group: Focal length of the first B lens group

Further, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive or negative refractive power are provided. With the zooming from the high angle side to the telephoto side, the distance between the first lens group and the second lens group is narrowed, the distance between the second lens group and the third lens group is narrowed, and the third lens group and the fourth lens group are A configuration in which the distance between the lens groups is widened to satisfy the following conditions.
(3) 2.5 <f ₂ / f _w <5.0
(4) 10.0 <f ₄ / f _w |
However,
f ₂ : Focal length of the second lens group f ₄ : Focal length of the fourth lens group

  The present invention divides a first lens group having negative refractive power into a first A lens group and a first B lens group, and moves only a relatively compact first B lens group to the object side to perform focusing. Therefore, there is no need to move a large and heavy lens group such as the first lens L1 of the super-wide-angle lens at the time of focusing, and there is an advantage that quick focusing is possible. In addition, the first lens group of the ultra-wide-angle lens tends to have a large negative refractive power. By appropriately dividing the power arrangement in the first lens group, it is possible to suppress aberration fluctuations due to focusing.

  In the present invention, as the first A lens group, negative meniscus lenses having convex surfaces facing the object side are employed for the first lens L1 and the second lens L2. In order to have an appropriate incident angle and reflection angle with respect to an angle of view exceeding 120 degrees, the generation of astigmatism is suppressed by appropriately distributing power between the two lenses.

  Further, as the first B lens group, the third lens L3 is a negative meniscus having a convex surface on the R1 surface, but the convex surface of the R1 surface has a sharp convex power up to the middle portion with respect to the power of the central portion. An aspherical surface is used which shows a shape that has a gentle convex power from the middle to the periphery.

  By using an aspherical surface that has a stronger convex power from the center, the same effect as a convex lens is produced, and distortion and lateral chromatic aberration are corrected. However, since the angle of view is a super-wide-angle lens far exceeding 90 degrees, correcting the aberration at the intermediate portion results in overcorrection at the peripheral portion. In view of this, the convex power has a gradual shape from the middle to the periphery, thereby reducing the overcorrection.

However, this is still insufficient for correcting the aberration of a super-wide-angle lens having an angle of view of 120 degrees or more. Therefore, by using an aspheric surface for the fourth lens L4 having the same negative meniscus shape, It has a role to correct aberrations that have been overcorrected.
In this way, by using an aspherical surface for the third lens L3 and the fourth lens L4 having a diameter of about 30 mm without using an aspherical surface for the lenses having the large diameters of the first lens L1 and the second lens L2, 120 degrees. A sufficiently compact first lens group can be obtained by adopting a structure that corrects sufficient aberrations for an angle of view exceeding 10 mm without using a convex lens, and provides an appropriate incident angle up to the peripheral luminous flux. ing.

Conditional expression (1) defines the ratio between the focal length f _w of the entire system at the wide-angle end and the focal length f ₁ of the first lens group. If the lower limit of conditional expression (1) is exceeded, the negative refractive power of the first lens group becomes strong, which is advantageous for compactness, but it becomes difficult to correct distortion. Exceeding the upper limit of conditional expression (1) is advantageous for correcting distortion, but is disadvantageous for making compact.

Conditional expression (2) defines the ratio between the focal length f _1A of the first A lens group and the focal length f _1B of the first B lens group. Condition (2) The focal length f _1B of the 1B lens group exceeds the lower limit becomes longer in, the focus movement amount increases, the first lens group unit is large diameter, first at the same time that the lens weight increase Manufacturing of the lens L1 and the second lens L2 becomes difficult. If the upper limit of conditional expression (2) is exceeded, the focal length f _1B of the 1B lens group will be shortened, making it difficult to correct the astigmatism fluctuation due to focusing.

Condition (3) is obtained by defining the ratio of the focal length f ₂ of the focal length f _w and the second lens unit of the entire system at the wide angle end. If the lower limit of conditional expression (3) is exceeded, the negative refractive power of the second lens group becomes too strong and the curvature of each surface becomes tight, making it difficult to correct coma and astigmatism. If the upper limit of conditional expression (3) is exceeded, the power of the second lens group becomes loose, which is advantageous for aberration correction, but the amount of movement of the second lens group becomes large and it is difficult to make it compact.

Condition (4) is obtained by defining the ratio of the focal length f ₄ of the focal length f _w of the fourth lens group of the entire system at the wide angle end. When the lower limit of conditional expression (4) is exceeded, the negative refractive power of the fourth lens group becomes too strong, and at the same time the positive refractive power of the third lens group becomes strong, and the peripheral luminous flux from the fourth lens group to the film surface is emitted. Since the angle is tight, it is difficult to correct astigmatism. If the upper limit of conditional expression (4) is exceeded, the exit angle to the peripheral light beam from the fourth lens group to the film surface becomes loose, which is advantageous for correcting astigmatism. The problem is that the rays of light increase and the lens diameter increases.

  According to the present invention, there is an effect that an ultra high angle lens having an angle of view exceeding 120 degrees at the wide angle end can be configured.

の式で表される。 Numerical examples of the super wide-angle zoom lens according to the present invention are shown in Example 1, Example 2, and Example 3. Here, f is the focal _{length, f NO} is the F-number, 2 [omega represents an angle of view. r is the radius of curvature of the i-th lens surface in order from the object side, d is the i-th lens thickness and air spacing in order from the object side, and n is the d-line of the i-th lens in order from the object side (= 587. 6 nm) Refractive index, ν is the Abbe number of the i-th lens in order from the object side.
The expression representing the aspherical shape is as follows: when the optical axis is the height perpendicular to the optical axis, the radius of curvature is the nth-order aspherical coefficient,

It is expressed by the following formula.

(Overall specifications)
f = 12.45-16.97-23.03 mm
f _No = 4.63 to 5.16 to 5.87
2ω = 122.2 ° to 104.6 ° to 86.4 °
(Lens specifications)
Number r d n ν
[1] 31.4230 1.6000 1.84666 23.8
[2] 22.1730 5.7700
[3] 25.5320 1.5000 1.84666 23.8
[4] 17.7310 11.470
[5] 54.5410 1.5000 1.73077 40.7
[6] 21.5050 3.2780
[7] 27.9050 50.1000 1.551840 52.1
[8] 33.1520 1.1000 1.77250 49.6
[9] 14.8460 7.3650
[10] -31.0010 1.0000 1.49700 81.6
[11] 47.1310 0.1500
[12] 29.7410 6.0170 1.67270 32.2
[13]-44.8190 Variable [14] 36.5970 0.9000 1.77250 49.6
[15] 9.8160 3.8810 1.71736 29.5
[16] 104.2440 Variable [17] 22.4060 3.5790 1.5516 64.2
[18] -14.3540 0.9000 1.734234 38.0
[19] 18.6600 3.4120 1.48749 70.4
[20]-17.4100 Variable [21]-22.1680 0.9000 1.83481 42.7
[22] 12.9280 3.4620 1.49700 81.6
[23] -90.1010 0.1500
[24] 27.8900 5.0730 1.49700 81.6
[25]-19.9210 0.1500
[26] -66.8050 4.2930 1.49700 81.6
[27]-15.5750 0.1500
[28] 480.0860 1.5000 1.81474 37.0
[29] 29.3040
(Variable interval in zooming)
f 12.45 16.97 23.03
d13 24.5960 12.140 140 2.8500
d16 1.5450 1.5810 0.7000
d20 0.9000 1.8110 3.0360
(Aspheric coefficient)
r5
A ₄ = 7.5221081 × 10 ⁻⁵
A ₆ = −2.4780504 × 10 ⁻⁷
A ₈ = 1.1491923 × 10 ⁻⁹
A ₁₀ = −2.1110936 × 10 ⁻¹²
r7
A ₄ = −7.2288616 × 10 ⁻⁵
A ₆ = 3.9919302 × 10 ⁻⁷
A ₈ = −1.1999784 × 10 ⁻⁹
A ₁₀ = 3.5004977 × 10 ⁻¹²
r28
A ₄ = −3.9442222 × 10 ⁻⁵
A ₆ = −9.2949610 × 10 ⁻⁷
A ₈ = 3.0830092 × 10 ⁻⁹
A ₁₀ = −8.77958053 × 10 ⁻¹²

(Overall specifications)
f = 12.45 to 16.53-23.07 mm
f _No = 4.65 to 5.12 to 5.87
2ω = 122.2 ° to 106.0 ° to 86.2 °
(Lens specifications)
Number r d n ν
[1] 31.9060 1.6000 1.84666 23.8
[2] 22.1730 5.7860
[3] 25.5140 1.5000 1.84666 23.8
[4] 17.7300 11.1960
[5] 51.5690 1.5000 1.73077 40.5
[6] 21.5050 3.0440
[7] 27.0700 0.1000 1.51840 52.1
[8] 31.2260 1.1000 1.77250 49.6
[9] 15.1610 7.4930
[10] -31.0720 1.0000 1.49700 81.6
[11] 50.9730 0.1500
[12] 31.4470 5.7370 1.67270 32.2
[13] -47.6030 Variable [14] 28.1150 0.9000 1.77250 49.6
[15] 9.9270 3.6080 1.71736 29.5
[16] -376.0460 Variable [17] 26.9030 3.2290 1.51680 64.2
[18] -15.4400 0.9000 1.723434 38.0
[19] 20.0730 3.0790 1.48749 70.4
[20] -20.0730 Variable [21] -22.1520 0.9000 1.83481 42.7
[22] 14.0370 3.7720 1.49700 81.6
[23] -49.4240 0.1500
[24] 33.3050 5.7660 1.49700 81.6
[25] -17.9570 0.1500
[26] -86.2140 4.6800 1.49700 81.6
[27]-16.5940 0.1500
[28] -77.6520 1.5000 1.814474 37.0
[29] 48.8910
(Variable interval in zooming)
f 12.45 16.53 23.07
d13 24.3270 12.8100 2.8500
d16 2.6420 2.2710 0.7000
d20 0.9000 2.1870 4.3770
(Aspheric coefficient)
r5
A ₄ = 7.8179172 × 10 ⁻⁵
A ₆ = -2.7969058 × 10 ⁻⁷
A ₈ = 1.4531984 × 10 ⁻⁹
A ₁₀ = −2.8112808 × 10 ⁻¹²
r7
A ₄ = −7.0067259 × 10 ⁻⁵
A ₆ = 3.6188391 × 10 ⁻⁷
A ₈ = −1.1995162 × 10 ⁻⁹
A ₁₀ = 3.8289879 × 10 ⁻¹²
r28
A ₄ = −3.8904562 × 10 ⁻⁵
A ₆ = −7.2370018 × 10 ⁻⁷
A ₈ = 5.776155 × 10 ⁻⁹
A ₁₀ = −3.6326879 × 10 ⁻¹²

(Overall specifications)
f = 12.45 to 14.76 to 23.05 mm
f _NO = 4.66 to 4.92 to 5.85
2ω = 12.2 ° to 112.6 ° to 85.8 °
(Lens specifications)
Number r d n ν
[1] 31.2870 1.6000 1.84666 23.8
[2] 22.1730 5.8520
[3] 25.5570 1.5000 1.84666 23.8
[4] 17.7310 10.6206
[5] 43.0160 1.5000 1.73077 40.7
[6] 21.5050 3.2940
[7] 30.9720 0.1000 1.51840 52.1
[8] 36.0610 1.1000 1.77250 49.6
[9] 15.3880 7.0060
[10] -37.7550 1.0000 1.49700 81.6
[11] 43.7420 0.1500
[12] 28.5720 5.0710 1.67270 32.2
[13]-60.9390 Variable [14] 26.4670 0.9000 1.77250 49.6
[15] 9.7600 3.1700 1.71736 29.5
[16] -17677.6100 Variable [17] 31.6390 2.9180 1.551680 64.2
[18] -15.6780 0.9000 1.7342342 38.0
[19] 28.3800 3.1230 1.48749 70.4
[20] -20.3800 Variable [21] -20.8100 0.9000 1.83481 42.7
[22] 16.5850 4.1220 1.49700 81.6
[23] -39.5180 0.1500
[24] 39.9200 6.7770 1.49700 81.6
[25] -17.9960 0.1500
[26] -333.9090 5.0190 1.49700 81.6
[27] -20.1740 0.1500
[28] -82.3390 1.5000 1.81474 37.0
[29] 60.9520
(Variable interval in zooming)
f 12.45 14.46 23.07
d13 23.1530 16.2750 2.8500
d16 3.0950 3.6570 0.7000
d20 0.9000 2.1670 6.1330
(Aspheric coefficient)
r5
A ₄ = 7.0626968 × 10 ⁻⁵
A ₆ = −2.2057471 × 10 ⁻⁷
A ₈ = 1.1403764 × 10 ⁻⁹
A ₁₀ = −2.0648920 × 10 ⁻¹²
r7
A ₄ = −6.220113 × 10 ⁻⁵
A ₆ = 3.314259 × 10 ⁻⁷
A ₈ = −8.9919434 × 10 ⁻⁹
A ₁₀ = 2.38771438 × 10 ⁻¹²
r28
A ₄ = −2.8150499 × 10 ⁻⁵
A ₆ = −4.5498365 × 10 ⁻⁷
A ₈ = 1.2238447 × 10 ⁻⁹
A ₁₀ = −1.69871438 × 10 ⁻¹²

The values of the conditional expressions of the present invention for the examples are as follows.
Conditional Example Example 1 Example 2 Example 3
(1) f ₁ / f _w -1.3918 -1.33872 -1.3690
(2) f _1B / f _1A 0.9030 0.9415 0.8928
_{(3) f 2 / f w} 3.6317 3.3761 3.3939
(4) f ₄ / f _w -14.6079 915.5397 13.3915

1 is a lens configuration diagram of Example 1. FIG. FIG. 4 is an aberration diagram at Example 1 at the wide-angle end. FIG. 6 is an aberration diagram for Example 1 at the intermediate focal length. FIG. 4 is an aberration diagram for Example 1 at the telephoto end. 6 is a lens configuration diagram of Example 2. FIG. FIG. 4 is an aberration diagram at Example 2 at the wide-angle end. FIG. 6 is an aberration diagram for Example 2 at the intermediate focal length. FIG. 6 is an aberration diagram at Example 2 at a telephoto end. 6 is a lens configuration diagram of Example 3. FIG. FIG. 6 is an aberration diagram at Example 3 at the wide-angle end. FIG. 6 is an aberration diagram for Example 3 at the intermediate focal length. FIG. 6 is an aberration diagram at Example 1 at the telephoto end.

Explanation of symbols

G1 1st lens group G1A 1A lens group G1B 1B lens group G2 2nd lens group G3 3rd lens group G4 4th lens group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens

Claims (2)

In order from the object side, there are a first lens unit having a negative refractive power and a rear group having a positive refractive power, and the first lens group has a first A lens group having a negative refractive power and a negative refractive power. The first lens group includes a first meniscus lens as the first lens L1 and a negative meniscus lens as the second lens L2, and the first lens group includes an aspherical surface as the third lens L3. A negative meniscus lens using a lens and a negative meniscus lens using an aspherical surface for the fourth lens L4. The first B lens group is moved to the object side during focusing, and satisfies the following conditions: Super wide-angle lens system.
(1) 1.1 <| f ₁ / f _w | <1.6
(2) 0.5 <f _1B / f _1A <2.0
However,
f _w : Focal length of the entire optical system at the wide-angle end f ₁ : Focal length f _1A of the first lens group f _1B : Focal length f _{1B of the} first A lens group: Focal length of the first B lens group In order from the object side, there are a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive or negative refractive power. With the zooming from the wide angle side to the telephoto side, the distance between the first lens group and the second lens group is narrowed, the distance between the second lens group and the third lens group is narrowed, and the third lens group and the fourth lens group. The super-wide-angle lens system according to claim 1, wherein the distance of is wide and satisfies the following conditions.
(3) 2.5 <f ₂ / f _w <5.0
(4) 10.0 <f ₄ / f _w |
However,
f ₂ : Focal length of the second lens group f ₄ : Focal length of the fourth lens group

Images