JPH0593866A - Zoom lens including wide angle - Google Patents

Abstract

PURPOSE:To obtain the compact zoom lens that is a high-power-variation zoom lens, which is suitable for-a compact camera and has a X 42.5 high power variation rate including a wide angle in a power variation range, and small in front lens diameter and rear lens diameter while securing the sufficient quantity of marginal light at the wide-angle end, and need not be machined and assembled with high precision. CONSTITUTION:This zoom lens is a three-group zoom lens which consists of a 1st lens group with negative refracting power, a 2nd lens group with positive refracting power, and a 3rd lens group with negative refracting power in order from an object side and monotoneously decreases the interval between the 1st and 2nd lens groups and the interval between the 2nd and 3rd lens groups for power variation from the wide-angle end to the telephoto end; and an aperture stop is arranged between the 1st and 2nd lens groups and moved together with the 2nd lens group at the time of power variation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens, and more particularly to a zoom lens suitable for a lens-shutter compact camera and the like in which the back focus is less restricted.

[0002]

2. Description of the Related Art A zoom lens for a camera, which has a high zoom ratio of 2.5 times or more including a wide angle in its zoom range, is disclosed in Japanese Patent Laid-Open No. Sho 58-58.
The ones described in Japanese Patent Application Laid-Open No. 75108 and Japanese Patent Laid-Open No. 58-79213 are known. These are a first lens group having a negative focal length, a second lens group having a positive focal length, and The third lens unit has a negative focal length, and each lens unit is independently moved to realize a high zoom ratio without increasing the amount of aberration. However, these zoom lenses are intended to be used as interchangeable lenses for single-lens reflex cameras, and because of their long back focus and long lens length, they have a large front lens diameter and are too large to be used as zoom lenses for compact cameras. is there.

On the other hand, as a high zoom lens including a wide angle for a compact camera, for example, Japanese Patent Laid-Open No. 2-23841 is known.
A zoom lens such as Japanese Patent No. 7 is known, and it has the same configuration as that described above, but it increases the amount of change in the air gap between the second lens group and the third lens group, and the refraction of the third lens group. The power is increased to increase the zooming load on the third lens group. As a result, a compact lens with a short back focus and a short length from the lens tip to the imaging surface is realized. However, in this zoom lens, it becomes difficult to secure the peripheral light amount at a wide angle, and if a sufficient peripheral light amount is obtained, the front lens diameter becomes considerably large. As a result, particularly when focusing is performed by moving the first lens group to the front, the load on the drive mechanism for autofocus becomes large, which is not preferable. Also, since the back focus at the wide-angle end is too short, dust and dirt on the final surface of the lens are easily captured in the photograph. Further, since the zooming load on the third lens group is large, the paraxial lateral magnification of the third lens group becomes too large at the telephoto end, and an error in the air gap between the second lens group and the third lens group is brought into focus. The effect is too great and the lens is difficult to process and assemble.

[0004]

DISCLOSURE OF THE INVENTION The present invention is a zoom lens having a high zoom ratio of 2.5 times or more including a wide angle in a zoom range, and a front lens diameter and a rear lens diameter are ensured while securing a sufficient peripheral light amount at the wide angle end. An object of the present invention is to provide a compact zoom lens having a small ball diameter and not requiring high precision in processing and assembling.

[0005]

In order to achieve the above object, the zoom lens according to the present invention has, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a negative lens group. The third lens unit having a refracting power of 1 is used to monotonically decrease the distance between the first lens unit and the second lens unit and the distance between the second lens unit and the third lens unit during zooming from the wide-angle end to the telephoto end. In the three-group zoom lens, an aperture stop is arranged between the first lens group and the second lens group, and is moved together with the second lens group during zooming.

If the focal length of the i-th lens unit is fi and the focal length of the entire system at the wide-angle end is fw, the following conditional expression is satisfied. 1.2 <| f ₃ | / fw <1.7 (1) 0.28 <fbw / D <0.6 ··· (3) 1.2 <| f 1 | / fw <1.6 ··· (4) 1.5 <| f 3 | / f 2 <1・ ・ ・ (5) where m ₂ w: Paraxial lateral magnification of the second lens group at the wide-angle end m ₂ t: Paraxial lateral magnification of the second lens group at the telephoto end fw: Total at the wide-angle end Focal length of the system ft: Focal length of the whole system at the telephoto end fbw: Back focus at the wide-angle end fi: Focal length of the i-th lens group D: Diagonal length of screen

[0007]

The zoom lens of the present invention has a negative, positive, and negative three-group configuration, and each group is independently moved so that the two groups, the second lens group and the third lens group, are responsible for zooming. Therefore, high zooming can be achieved without increasing the amount of movement of each lens group for zooming. Also, by making the focal length of each lens group from the object side negative, positive, negative, the angle of the off-axis oblique ray bundle with respect to the optical axis is made small at the intermediate portion of the lens and the portion passing through the second lens group. As shown in FIG. 1, the heights h ₁ and h ₃ of the oblique rays passing through the first lens group and the third lens group before and after the second lens group from the optical axis can be reduced. This effect becomes remarkable at the wide-angle end, and the lens system for the front lens and the rear lens can be kept small even if the angle is widened. In addition, when the angle of view is widened, generally, the problem of the reduction of the image plane illuminance in the peripheral portion of the screen due to the influence of the cosine fourth law becomes a problem. A stop is placed, and the refraction of this lens group increases the entrance pupil as the angle of view increases.
The aperture efficiency can be increased, the influence of the cosine fourth law can be mitigated, and a sufficient peripheral light amount ratio can be obtained. Further, since the diaphragm is arranged near the second lens group between the first lens group and the second lens group, the entrance pupil is located in front of the diaphragm position at the wide-angle end where the distance between the first lens group and the second lens group widens. Therefore, the height of the oblique ray bundle passing through the first lens group can be further reduced, and the diameter of the front lens element can be reduced. Generally, in a lens shutter, after a hole of an aperture stop spreads around the optical axis to reach a predetermined size, the shutter blades move so as to become smaller and close again. Considering this, it is possible to increase the ratio of the exposure amount to the central part of the peripheral part of the screen by passing the oblique ray bundle through the center of the aperture stop, and reduce the influence of the decrease in image plane illuminance. However, if an aperture stop is arranged as in the present invention, the diameter of the front lens can be made relatively small even through the oblique ray bundle as described above.

Further, in this type of zoom lens, it is easy to be affected by the decentering of the second lens group, and when the aperture stop is arranged inside the second lens group, it becomes difficult to align the optical axes of the lenses before and after that. However, in the zoom lens according to the present invention, since the lens forming the second lens group is fixed in one lens barrel member, the optical axis shift of the lens hardly occurs.

If the focal length of the third lens unit falls below the lower limit of conditional expression (1), the back focus at the wide-angle end becomes too short, and the Petzval sum tends to have a large negative value, resulting in large astigmatism. If the upper limit is exceeded, the refracting power of the third lens group becomes weak and the zoom ratio becomes large, so that the air gap at the wide-angle end of the first lens group and the second lens group becomes too large. In addition, the back focus becomes too long, and the total length becomes extremely large. Therefore, the diameter of the lens in front of the lens also becomes large.

The zoom lens of the present invention has three movable lens groups, and the paraxial image forming magnifications of the second lens group and the third lens group are changed to change the magnification, but the second lens group and the third lens are used. The property of the zoom lens depends on the ratio of zooming load to the group.
Conditional expression (2) relates to the ratio of the magnification variation load, and represents that the second lens group bears the majority of the magnification variation. Generally, in the three-group zoom lens as in the present invention, the paraxial image forming magnification of the third negative lens group is larger than 1 in the entire zoom range and becomes a considerably large value at the telephoto end. That is, when the value goes below the lower limit of the conditional expression (2), the change m ₃ t / m ₃ w in the ratio of the zooming load of the third lens group becomes large, and m ₃ t becomes large. The change of the back focus with respect to the change of the air gap between the second lens group and the third lens group is (m ₃ t) ² times, so when m ₃ t becomes large, a member such as a cam that controls the lens position is required. The accuracy will be severe. If the lower limit of conditional expression (2) is exceeded, the so-called telephoto type property becomes stronger at the wide-angle end, and it becomes difficult to secure the peripheral light amount, and the front lens diameter and the rear lens diameter must be increased. If the upper limit of conditional expression (2) is exceeded, the retrofocus type characteristics become stronger, the back focus, the total lens length, etc. become longer, and the front lens diameter also becomes larger. Further, at the telephoto end, the influence of the air gap between the first lens group and the second lens group on the focus becomes large, and similarly the required accuracy of the mechanism becomes high, which is not preferable.

Conditional expression (3) is a condition relating to back focus at the wide-angle end. If the upper limit of conditional expression (3) is exceeded, the back focus and lens overall length become long in the entire zoom range, and the front lens diameter becomes remarkable. It becomes large and does not become a lens suitable for a compact camera. On the other hand, when the value goes below the lower limit, the back focus at the wide-angle end becomes short, dust and dirt on the final lens surface are easily reflected in the image, and the rear lens diameter becomes large, which tends to cause the camera body to become large. Further, if the back focus is large, the angle of incidence of the oblique ray bundle incident on the peripheral portion of the screen at the wide-angle end becomes large, and the flatness of the imaging surface is likely to be unfavorable. Also, in the case of a camera that uses film, it is easy for light to come in through the gap between the light-shielding frame in front of the film and the film, and when there is a strong light source at the corner of the screen due to backlight shooting, etc. There is a fear of doing so.

Conditional expressions (4) and (5) are conditional expressions (2) and
With a zoom lens that satisfies (3), it is easy to balance the size, aberration correction, and ease of making.
If the upper limit of conditional expression (4) is exceeded, the first lens group at the wide-angle end,
The air gap of the second lens group becomes large, the total length of the lens becomes long, and the viewfinder field and the strobe irradiation light are obstructed. On the contrary, if the lower limit is exceeded, the Petzval sum becomes a large negative value, and it becomes difficult to correct field curvature and astigmatism. Further, at the telephoto end, the influence of the error in the distance between the first lens group and the second lens group on the focus becomes large, and the processing accuracy of the cam and the like becomes severe, which is not preferable.

If the upper limit of conditional expression (5) is exceeded, the negative refractive power of the third lens group becomes too weak, and the overall length at the wide-angle end becomes too long. On the other hand, when the value goes below the lower limit, the Petzval sum becomes a large negative value, and it becomes difficult to correct field curvature and astigmatism.

[0014]

EXAMPLES Examples of the present invention will be shown below to further describe the details of the invention. In the embodiment of the present invention, the first lens group is set to 1
It is composed of one to two negative lenses and one positive lens, and the negative lens having the strongest refracting power is arranged on the most object side. Due to the refracting action of the first lens on the oblique rays, The effective diameter is made smaller. The second lens group includes at least two positive lenses and at least one negative lens, and the positive lenses are arranged before and after the negative lens. The third lens group is composed of at least one positive lens and at least one negative lens, and the negative lens is arranged closest to the image side, and the effective diameter of the final lens becomes small as in the case of the first lens group. I am trying. Further, in this embodiment, aspherical surfaces are used for the second lens group and the third lens group, and spherical aberration and field curvature are satisfactorily corrected. Particularly, in the second and sixth embodiments, the cost is reduced by using the plastic aspherical lens.

In the fourth embodiment, the first lens group is composed of two lenses, a negative meniscus lens and a positive meniscus lens.
The weight of the lens group is reduced, which is advantageous when focusing on the front lens.

Further, the zoom lens according to the present invention includes the first and third zoom lenses.
The average value of the refractive index of the negative lens of the lens group is N ₁ n,
Let N ₃ n be the average value of the Abbe numbers be ν ₁ n and ν ₃ n, and similarly represent the positive lenses as N ₁ p, N ₃ p, ν ₁ p and ν ₃ p, the following conditions must be satisfied: Is desirable. N ₁ n, N ₃ n> 1.7 (6) ν ₁ n, ν ₃ n> 40 (7) 1.8> N ₁ p, N ₃ p> 1.65 (8) ν ₁ p, ν ₃ p <35 (9) If the lower limit of conditional expression (6) is exceeded, the Petzval sum becomes negative and large, and the field curvature is overcorrected, which is not preferable. If the lower limit of conditional expression (7) is exceeded, axial chromatic aberration becomes excessive, and positive lateral chromatic aberration becomes large on the telephoto side, which is not preferable. If the lower limit of conditional expression (8) is exceeded, spherical aberration will increase, and the difference in coma aberration between the wide-angle side and the telephoto side will increase, making correction difficult. If the upper limit is exceeded, the Petzval sum will become negative and large, which is not desirable. .. If the upper limit of conditional expression (9) is exceeded, axial chromatic aberration becomes excessive, positive chromatic aberration of magnification becomes large on the telephoto side, and the difference in lateral chromatic aberration between the wide-angle side and the telephoto side becomes large, which is not desirable.

In the zoom lens of the present invention, focusing can be performed by moving the whole or a part of the first lens group or the third lens group, and the lens diameter is small, so the load on the drive mechanism is small. In particular, when the entire first lens group or a part thereof is extended and focused, the amount of extension does not change due to zooming, so that the focusing mechanism can be simplified.

The data of the examples are shown below. In each symbol in the table, R is the radius of curvature of each refracting surface, D is the refracting surface interval, and Nd
Is the refractive index of the lens material, νd is the Abbe number, f is the focal length of the entire lens system, ω is the half angle of view, and F is the F number. The surface marked with "*" is an aspherical surface. The shape of the aspherical surface has the X axis in the optical axis direction and the Y axis in the direction perpendicular to the optical axis, and the light traveling direction is positive, K, When A ₁ and A ₂ are aspherical coefficients, they are expressed by the following mathematical formula 1.

[0019]

[Equation 1]

Example 1 f = 29.0 to 78.1 FNo. = 3.88 to 7.64 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 182.460 1.00 1.77250 49.6 2 16.690 4.00 3 58.147 1.40 1.78590 44.2 4 40.683 0.20 5 20.332 3.80 1.76182 26.6 6 45.383 Variable diaphragm ∞ 0.50 7 * 15.536 3.00 1.51633 64.1 8 -91.673 0.30 9 33.120 1.00 1.84666 23.8 10 13.988 8.82 1.53172 48.9 11 314.545 Variable 12 * -51.827 4.55 1.74077 27.8 13 -19.949 4.00 14 -10.719 1.20 1.78590 44.2 15 -35.269 D ₆ D ₁₂ f Fb 21.54 8.50 29.00 16.76 9.7 27.36 47.99 29.61 2.00 6.24 78.17 49.93 Aspheric coefficient 7th surface 12th surface _{K = -2.00292 K = -43.0287 A 1} = 3.48976 × 10 -5 A 1 = -3.93627 × 10 -5 A 2 = -1.27320 × 10 -7 A 2 = 2.91172 × 10 ^-7 | f ₃ | /fw=1.49 first lens effective diameter: 2 .9 relative illumination at the wide-angle end 9% image height: 32.1%

Example 2 f = 29.0 to 78.1 FNo. = 3.80 to 7.64 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 276.098 1.00 1.77250 49.6 2 17.256 3.30 3 200.000 1.20 1.78590 44.2 4 62.685 1.20 5 22.713 4.00 1.68893 31.1 6 79.032 Variable aperture ∞ 0.50 7 15.667 3.00 1.51633 64.1 8 57.877 0.50 9 * 18.000 2.00 1.49200 57.0 10 18.399 0.50 11 19.830 1.00 1.84666 23.8 12 10.640 6.00 1.53172 48.9 13 -202.054 Variable 14 -22.012 2.50 1.49200 57.0 15 * -23.000 0.20 16 1155.394 2.60 1.74077 27.8 17 -41.670 4.00 18 -12.388 1.20 1.77250 49.6 19 -46.416 D ₆ D ₁₃ f Fb 19.91 10.10.29.00 15.60 8.7.6 76.70 47.98 29.24 2.00 7 .63 78.05 50.20 = -0.986835 aspherical coefficients ninth surface fifteenth surface _{K K = -0.613391 A 1 = -5.48519} × 10 -6 A 1 = -1.62410 × 10 - ⁶ A ₂ = -1.11554 x 10 ^-7 A ₂ = -1.23460 x 10 ^-7 | f ₃ | / fw = 1.41 First lens effective diameter: 23.6 Wide-angle end 90% Peripheral light quantity ratio at image height: 28.6%

Example 3 f = 29.0 to 78.2 FNo. = 3.89 to 7.64 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 227.776 1.00 1.77250 49.6 2 17.164 4.83 3 19.919 3.80 1.76182 26.6 4 32.465 Variable aperture ∞ 0.50 5 * 15.881 3.00 1.51633 64.1 6 -111.587 0.30 7 36.553 2.00 1.84666 23.8 8 14.510 6.00 1.53172 48.9 9 -333.494 Variable 10 * -49.420 3.96 1.74077 27.8 11 -19.925 4.00 12 -10.789 1.20 1.78590 44.2 13 -35.949 D ₄ D ₉ f Fb 22. 10 10.62 29.00 15.92 9.47 9.31 48.00 28.62 2.00 8.04 78.17 48.70 Aspheric coefficient 5th surface 10th surface K = -2.11872 K _{= -38.5331 A 1 = 3.54833 × 10} -5 A 1 = -4.00287 × 10 -5 A 2 = -1.26508 × 10 -7 A 2 = 2.91266 × 10 -7 | f 3 | /Fw=1.45 First lens effective diameter: 25.7 Wide-angle end 90% at image height Side light amount ratio: 32.1%

Example 4 f = 29.0 to 78.2 FNo. = 3.84 to 7.64 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 198.092 1.00 1.77250 49.6 2 16.324 4.42 3 19.114 3.80 1.76182 26.6 4 32.307 Variable aperture ∞ 0.50 5 * 14.601 3.00 1.51633 64.1 6 -93.769 0.30 7 33.384 1.50 1.84666 23.8 8 14.188 0.50 9 16.044 6.00 1.53172 48.9 10 -513.037 Variable 11 * -49.344 5.00 1.74077 27.8 12 -20.726 4.00 13 -11.055 1.20 1.78590 44.2 14 -39.304 D ₄ D ₉ df Fb 21.73 10.68 29.00 00 14.81 9.50 9.50 47.96 27.13 2.50 8.02 78.21 47.48 Aspheric coefficient 5th surface 11th surface K = -1 _{.90593 K = -37.7212 A 1 = 4.14158} × 10 -5 A 1 = -3.93644 × 10 -5 A 2 = -1.24279 × 10 -7 A 2 = 2.91237 × 10 -7 | f ₃ | /fw=1.33 First lens effective diameter: 25.9 Wide-angle end 90% Peripheral light quantity ratio at image height: 33.0% m ₂ t / m ₂ w = 1.66 0.8ft / fw = 2.16 fbw / D = 0.34 | f 1 | /fw=1.45 | f 3 | / f 2 = 1.60

Example 5 f = 29.0 to 78.2 FNo. = 4.01 to 7.64 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 81.106 1.00 1.77250 49.6 2 16.329 4.00 3 96.835 1.40 1.78590 44.2 4 39.942 0.38 5 20.832 3.80 1.68893 31.1 6 74.280 Variable 7 * 14.317 3.00 1.51633 64.1 8 1205.802 0.30 9 26.972 1.00 1.84666 23.8 10 13.429 7.45 1.53172 48.9 11 100.693 Variable 12 * -57.653 2.73 1.74077 27.8 13 -21.702 4.00 14 -9.747 1.20 1.78590 44.2 15 -25.289 D ₄ D ₉ D f Fb 25.59 7.97 29.00 00.19.21 10.97 7.69 48.00 30.86 2.50 7.17 78.18 49.83 Aspheric coefficient 7th surface 12th surface K = -2 _{.03950 K = -58.2778 A 1 = 5.71192} × 10 -5 A 1 = -3.64688 × 10 -5 A 2 = -1.25122 × 10 -7 A 2 = 2.98226 × 10 -7 | f ₃ | /fw=1.49 First lens effective diameter: 26.4 Wide angle Edge light ratio at 90% image height: 31.6% m ₂ t / m ₂ w = 1.80 0.8ft / fw = 2.16 fbw / D = 0.44 | f 1 | /fw=1.48 | f 3 | / f 2 = 1.74

Example 6 f = 29.0 to 78.2 FNo. = 3.50 to 7.38 ω = 36.7 ° to 15.5 ° Surface number RD Nd νd 1 ∞ 1.00 1.77250 49.6 2 17.633 1.89 3 22.119 1.50 1.78590 44.2 4 19.535 1.00 5 18.487 4.00 1.68893 31.1 6 42.344 Variable 7 14.583 3.00 1.51633 64.1 8 33.024 0.50 9 * 18.000 2.00 1.49200 57.0 10 18.399 0.50 11 16.007 1.00 1.84666 23.8 12 8.853 6.00 1.53172 48.9 13 -136.393 Variable 14 -22.012 2.50 1.49200 57.0 15 * -23.000 0.19 16 495.763 2.60 1.74077 2 17 -35.199 6.28 18 -12.147 1.20 1.77250 49.6 19 -79.327 D ₆ D ₁₃ f Fb 18.39 7.60 29.00 00 13.22 7.79 6.80 47.99 24.28 1.6 5.885 78 .19 42.10 aspherical coefficients ninth surface fifteenth surface _{K = -0.798786 K = 1.79876 A 1} = -1.37432 × 10 -5 A 1 = 8.59424 × 10 -6 A 2 = - 8.222209 × 10 ⁻⁸ A ₂ = −1.28769 × 10 ^-7 | f ₃ | /fw=1.41 First lens effective diameter: 27.0 Wide-angle end 90% peripheral light amount ratio at image height: 34.8% m ₂ t / m ₂ w = 1.71 0.8ft / fw = 2.16 fbw / D = 0.31 | f 1 | /fw=1.36 | f 3 | / f 2 = 1.70

[0026]

According to the present invention, if the aperture stop is arranged as described above, as shown in each of the embodiments, the front lens diameter and the rear lens diameter are maintained while maintaining a sufficient peripheral light amount ratio at the wide-angle end. It is possible to obtain a wide-angle, high-magnification zoom lens that is 2.5 times or more smaller than the angle of view ω = 36 °. Therefore, the weight of the first lens group and the third lens group can be reduced, and the first lens group or the third lens group can be reduced.
It is most suitable for a camera that moves the lens group for focusing. Further, a zoom lens having a small precision required for processing and assembling a cam or the like and easy to manufacture is realized, and it is possible to obtain a zoom lens in which aberrations are well corrected.
Further, the zoom lens of the present invention can be extremely miniaturized because the lens diameter is small if the air space between the lens groups is reduced during storage by using a mechanism such as a collapsible mechanism.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a passage path of oblique rays passing through a center of an aperture stop at a wide-angle end of a zoom lens according to the present invention.

FIG. 2 is a sectional view of a first embodiment of a zoom lens according to the present invention,
The scaling method is also shown.

FIG. 3 is an aberration diagram at the wide-angle end of Embodiment 1 of the zoom lens of the present invention.

FIG. 4 is an aberration diagram of a middle focus of Example 1 of the zoom lens of the present invention.

FIG. 5 is an aberration diagram at a telephoto end of Embodiment 1 of the zoom lens according to the present invention.

FIG. 6 is a sectional view of a zoom lens according to a second embodiment of the present invention.

FIG. 7 is an aberration diagram at a wide-angle end of Example 2 of the zoom lens according to the present invention.

FIG. 8 is an aberration diagram of a middle focus of Embodiment 2 of the zoom lens of the present invention.

FIG. 9 is an aberration diagram at a telephoto limit of Embodiment 2 of the zoom lens according to the present invention.

FIG. 10 is a sectional view of a zoom lens according to a third embodiment of the present invention.

FIG. 11 is an aberration diagram at a wide-angle end of Example 3 of the zoom lens according to the present invention.

FIG. 12 is an aberration diagram of a middle focus of Embodiment 3 of the zoom lens of the present invention.

FIG. 13 is an aberration diagram of Example 3 of the zoom lens according to the present invention at the telephoto end.

FIG. 14 is a sectional view of a zoom lens according to a fourth embodiment of the present invention.

FIG. 15 is an aberration diagram at a wide-angle end of Embodiment 4 of the zoom lens according to the present invention.

FIG. 16 is an aberration diagram of a middle focal point of Example 4 of the zoom lens according to the present invention.

FIG. 17 is an aberration diagram at a telephoto limit of Embodiment 4 of the zoom lens according to the present invention.

FIG. 18 is a sectional view of a fifth embodiment of a zoom lens according to the present invention.

FIG. 19 is an aberration diagram at a wide-angle end of Example 5 of the zoom lens according to the present invention.

FIG. 20 is an aberration diagram of a middle focus of Embodiment 5 of the zoom lens of the present invention.

FIG. 21 is an aberration diagram of Example 5 of the zoom lens according to the present invention at the telephoto end.

FIG. 22 is a sectional view of a zoom lens according to a sixth embodiment of the present invention.

FIG. 23 is an aberration diagram at a wide-angle end of Example 6 of the zoom lens according to the present invention.

FIG. 24 is an aberration diagram of a middle focal point of Embodiment 6 of the zoom lens according to the present invention.

FIG. 25 is an aberration diagram at a telephoto limit of Embodiment 6 of the zoom lens according to the present invention.

[Explanation of symbols]

In the aberration diagram, “d” and “g” are spherical aberrations with respect to the d line and the g line, “SC” is a sine condition, and “ΔS” and “Δ”.
“M” represents a sagittal image plane and a meridional image plane, respectively.

Claims (4)

[Claims] 1. A lens system having, from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power in order from a wide-angle end to a telephoto end. When doubling,
In a three-group zoom lens that monotonically reduces the distance between the first lens group and the second lens group and the distance between the second lens group and the third lens group, an aperture stop is arranged between the first lens and the second lens group. And a zoom lens including a wide angle, which moves together with the second lens group during zooming. 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied, where f _{3 is} the focal length of the third lens group and fw is the focal length of the entire system at the wide-angle end. .2 <| f ₃ | / fw <1.7 3. A change from a wide-angle end to a telephoto end, which comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. When doubling,
In a three-group zoom lens that moves three lens groups so as to monotonically decrease the distance between the first lens group and the second lens group and the distance between the second lens group and the third lens group, the following conditions must be satisfied. Zoom lens featuring 0.28 <fww / D <0.6 where m ₂ w: paraxial lateral magnification of the second lens group at the wide-angle end m ₂ t: paraxial lateral magnification of the second lens group at the telephoto end fw: wide-angle end Focal length of the entire system at ft: focal length of the entire system at the telephoto end fbw: back focus at the wide-angle end D: diagonal length of the screen 4. The zoom lens according to claim 3, wherein the following condition is satisfied: 1.2 <| f ₁ | / fw <1.6 1.5 <| f ₃ | / f ₂ <1 .8 where fi: focal length of the i-th lens group