JP3119056B2 - Small zoom lens - Google Patents

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 comprising two lens groups suitable for a lens shutter camera, a video camera, and the like. In particular, the present invention relates to a zoom lens for correcting aberrations by appropriately setting the lens configuration of each lens group. The photographic angle of view at the wide-angle end is 60 degrees, and the zoom ratio is 2.
The present invention relates to a small zoom lens of about two.

[0002]

2. Description of the Related Art Recently, with the miniaturization of lens shutter cameras, video cameras, and the like, a small zoom lens having a short overall lens length has been demanded. In particular, it is desired to mount a zoom lens even in the field of a small camera such as a lens shutter camera which does not perform lens replacement, and a small zoom lens having a length similar to that of a conventionally used single focus lens is demanded.

[0003] The present applicant has previously disclosed Japanese Patent Application Laid-Open No. 57-201213.
JP-A-60-170816, JP-A-60-170816
In JP-A-191216 and JP-A-62-56917, two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, are sequentially arranged from the object side. A small so-called two-unit zoom lens that changes magnification by changing the interval has been proposed.

In this publication, a two-unit zoom lens having high optical performance which employs positive and negative refractive power arrangements in order from the object side to make the back focus relatively short and to shorten the overall length of the lens. Have achieved.

In addition, Japanese Patent Application Laid-Open Nos. Sho 62-284319, 62-256915, and 64-5
In Japanese Patent Application Laid-Open No. 2111 and Japanese Patent Application Laid-Open No. 1-193807, the first lens unit has a positive refractive power and the second lens unit has a negative refractive power, and both lens groups are moved forward while changing the distance between both lens groups. This discloses a two-unit zoom lens that changes the magnification.

In addition, Japanese Patent Application Laid-Open No.
In Japanese Patent Application Laid-Open No. 3-161422, the first group is defined as positive, negative, negative, positive,
A zoom lens that includes five positive lenses and has a shooting angle of view of about 55 degrees at the wide-angle end is disclosed.

Further, JP-A-62-90611, JP-A-62-113120, and JP-A-3-116110
In the publication, a first lens group is composed of four lenses of positive, negative, negative and positive, and a two-group zoom lens having a zoom ratio of about 1.5 is disclosed.

In Japanese Patent Application Laid-Open No. 1-288823, the first group is composed of five lenses of positive, negative, positive, positive and positive, and the second group is composed of three lenses of positive, negative and negative. The disclosed two-unit zoom lens is disclosed.

[0009]

SUMMARY OF THE INVENTION In the above-described two-unit zoom lens including the first lens unit having the positive refractive power and the second lens unit having the negative refractive power, the size of the entire lens system is reduced. To obtain good optical performance over the entire zoom range while having a zoom ratio of about 2 times, it is necessary to appropriately set the lens configuration of each lens group.

For example, the zoom lens disclosed in the above-mentioned JP-A-57-201213 and JP-A-1-193807 has a zoom ratio of about 1.5, and JP-A-63-25691.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. 5 (1993) -205, fluctuations in aberrations during zooming, particularly fluctuations in spherical aberration and field curvature, were large.

In the zoom lens disclosed in JP-A-64-52111, the F-number at the wide angle end is F4.5, and the brightness is not always sufficient.

In general, if the refractive power of both the first and second units is increased, the amount of movement of each lens unit during zooming is reduced, and the overall length of the lens can be reduced.

However, if the refractive power of each lens group is simply increased, the fluctuation of aberration due to zooming becomes large, and it becomes difficult to satisfactorily correct this.

The present invention is directed to a so-called two-unit zoom lens system in which the lens configuration of each lens unit is appropriately set, thereby reducing the overall length of the lens while having a wide angle of view at a zoom ratio of about 2.2. It is an object of the present invention to provide a compact zoom lens having high optical performance over the entire zoom range.

[0015]

A compact zoom lens according to the present invention has two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side. In a small zoom lens that changes magnification by changing the distance between groups,
The group includes a positive meniscus first lens with a convex surface facing the object side, a negative second lens with both lens surfaces concave, a positive third lens with both lens surfaces convex, and a strong refractive surface on the image surface side. The second lens unit has a positive fourth lens having both convex lens surfaces facing each other and a positive fifth lens having both convex lens surfaces facing a strong refracting surface on the image surface side. A positive meniscus sixth lens directed toward the lens, a negative seventh lens on the meniscus having a convex surface facing the image surface side, and a meniscus negative eighth lens having a convex surface facing the image surface side. The second lens and the third lens are cemented, and when the refractive index and Abbe number of the material of the i-th lens are Ni and νi, respectively, (N4 + N5) / 2 <1.5 (1) 67 <(Ν4 + ν5) / 2 (2) 1.6 <(N7 + N8) / 2 <1.7 (3) 57 <(Ν7 + ν8) / 2 (4) The following condition is satisfied.

[0016]

1 to 3 are lens sectional views of Numerical Examples 1 to 3 of the present invention. In the lens sectional views, (A) shows the zoom position at the wide angle end, (B) shows the middle position, and (C) shows the zoom position at the telephoto end.

In the drawing, L1 denotes a first group having a positive refractive power, and L2 denotes a second group having a negative refractive power. The distance between the two lens groups is reduced and both lens groups are moved toward the object side as shown by arrows. Moving the zoom from the wide-angle end to the telephoto end. SP denotes an aperture stop, which is disposed between the first lens unit and the second lens unit in the present embodiment, and moves together with the first lens unit with zooming. I
P is an image plane.

In the present embodiment, by adopting such a zoom system and the lens configuration as described above, the overall length of the lens is shortened, particularly the wide angle of view at the wide angle end and the overall length of the lens are shortened. A magnification ratio of about 2.2 and aberration variation accompanying zooming are corrected well, and high optical performance is obtained over the entire zoom range.

In particular, in the present invention, the first lens unit is moved to the object side in order to satisfactorily correct fluctuations in various aberrations such as spherical aberration and curvature of field due to zooming, and to maintain the optical performance of the entire screen in a well-balanced state. A positive meniscus first lens with a convex surface, a negative second lens with both lens surfaces concave, a positive third lens with both lens surfaces convex, and a stronger refracting surface on the image surface side than the object side. The second lens surface is composed of a positive fourth lens having a convex surface, and the second lens surface having a refraction surface stronger on the image surface side than the object side is composed of a fifth positive lens having a convex surface. The second lens and the third lens are joined as needed.
The second lens unit has a meniscus-shaped positive sixth lens having a convex surface facing the image surface side, a meniscus-shaped negative seventh lens having a convex surface facing the image surface side, and a meniscus having a convex surface facing the image surface side. It is composed of three lenses of a negative eighth lens.

Further, the stop SP is arranged between the first and second units to effectively prevent the lens diameter from increasing when widening the angle of view.

By satisfying each of the conditional expressions in the above-described lens configuration, the overall size of the lens system is reduced while ensuring high optical performance over the entire zoom range.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) is for appropriately setting the refractive index of the material of the fourth lens and the fifth lens, and mainly for favorably correcting the field curvature. If the refractive index of the material of the fourth lens and the fifth lens becomes too high beyond the upper limit of conditional expression (1), the Petzval sum increases in the negative direction, making it difficult to satisfactorily correct astigmatism. It is becoming.

Conditional expression (2) is for appropriately setting the Abbe number (dispersion) of the material of the fourth lens and the fifth lens, and favorably correcting mainly the chromatic aberration variation accompanying zooming. If the material dispersion of the fourth lens and the fifth lens exceeds the lower limit of conditional expression (2) and the dispersion of the material of the fourth lens and the fifth lens becomes too large, it becomes difficult to satisfactorily correct the fluctuation of the axial chromatic aberration caused by zooming.

Conditional expression (3) is for appropriately setting the refractive indices of the materials of the seventh and eighth lenses, and mainly for favorably correcting the field curvature similarly to conditional expression (1). . If the refractive index of the material of the seventh and eighth lenses exceeds the upper limit of conditional expression (3) and the refractive index of the material of the seventh and eighth lenses becomes too high, the Petzval sum increases in the positive direction, making it difficult to satisfactorily correct astigmatism. It is becoming. If the refractive index of the material of the seventh lens and the eighth lens is too low below the lower limit of conditional expression (3), the Petzval sum increases in the negative direction, making it difficult to satisfactorily correct astigmatism. It becomes.

Conditional expression (4) sets appropriately the Abbe number (dispersion) of the material of the seventh lens and the eighth lens, and conditional expression (2)
In the same manner as described above, the main purpose is to satisfactorily correct fluctuations in chromatic aberration due to zooming. If the variance of the material of the seventh lens and the eighth lens becomes too large beyond the lower limit of the conditional expression (4), it becomes difficult to satisfactorily correct the change of the chromatic aberration of magnification due to zooming.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. The relationship between the above-described conditional expressions and various numerical values in the numerical examples is shown in Table.
Shown in 1).

<Numerical Example 1> F = 39.2 to 82.2 fno = 1: 3.9 to 8.2 2ω = 57.8 ° to 29.5 ° R 1 = 20.78 D 1 = 2.11 N 1 = 1.64769 ν 1 = 33.8 R 2 = 61.99 D 2 = 1.31 R 3 = -18.05 D 3 = 3.98 N 2 = 1.80610 ν 2 = 41.0 R 4 = 18.05 D 4 = 3.65 N 3 = 1.51633 ν 3 = 64.2 R 5 = -39.21 D 5 = 0.41 R 6 = 184.85 D 6 = 2.30 N 4 = 1.48749 ν 4 = 70.2 R 7 = -19.79 D 7 = 0.20 R 8 = 62.61 D 8 = 2.12 N 5 = 1.48749 ν 5 = 70.2 R 9 = -26.52 D 9 = 1.20 R10 = (Aperture) D10 = Variable R11 = -39.30 D11 = 2.96 N 6 = 1.62004 ν 6 = 36.3 R12 = -18.79 D12 = 2.87 R13 = -19.37 D13 = 1.50 N 7 = 1.69680 ν 7 = 55.5 R14 = -218.06 D14 = 4.28 R15 = -15.28 D15 = 1.50 N 8 = 1.60311 ν 8 = 60.7 R16 = -45.22

[0029]

[Table 1] <Numerical Example 2> F = 39.2 to 82.1 fno = 1: 3.9 to 8.2 2ω = 57.8 ° to 29.5 ° R 1 = 20.79 D 1 = 2.07 N 1 = 1.64769 ν 1 = 33.8 R 2 = 60.83 D 2 = 1.30 R 3 = -17.77 D 3 = 4.42 N 2 = 1.80610 ν 2 = 41.0 R 4 = 17.77 D 4 = 3.20 N 3 = 1.51633 ν 3 = 64.2 R 5 = -39.27 D 5 = 0.45 R 6 = 103.57 D 6 = 2.29 N 4 = 1.48749 ν 4 = 70.2 R 7 = -19.91 D 7 = 0.20 R 8 = 72.97 D 8 = 2.09 N 5 = 1.48749 ν 5 = 70.2 R 9 = -26.00 D 9 = 1.20 R10 = (Aperture) D10 = Variable R11 = -36.69 D11 = 2.45 N 6 = 1.64769 ν 6 = 33.8 R12 = -19.62 D12 = 3.61 R13 = -19.04 D13 = 1.50 N 7 = 1.69680 ν 7 = 55.5 R14 = -635.15 D14 = 4.28 R15 = -15.64 D15 = 1.50 N 8 = 1.60311 ν 8 = 60.7 R16 = -37.03

[0030]

[Table 2] <Numerical example 3> F = 39.2 to 82.2 fno = 1: 3.9 to 8.2 2ω = 57.8 ° to 29.5 ° R 1 = 20.89 D 1 = 2.13 N 1 = 1.64769 ν 1 = 33.8 R 2 = 60.74 D 2 = 1.32 R 3 = -17.58 D 3 = 4.52 N 2 = 1.80610 ν 2 = 41.0 R 4 = 17.58 D 4 = 3.24 N 3 = 1.51633 ν 3 = 64.2 R 5 = -40.83 D 5 = 0.45 R 6 = 100.08 D 6 = 2.26 N 4 = 1.48749 ν 4 = 70.2 R 7 = -19.85 D 7 = 0.20 R 8 = 67.23 D 8 = 2.09 N 5 = 1.49831 ν 5 = 65.0 R 9 = -26.09 D 9 = 1.20 R10 = (Aperture) D10 = Variable R11 = -36.33 D11 = 2.35 N 6 = 1.64769 ν 6 = 33.8 R12 = -19.49 D12 = 3.62 R13 = -18.56 D13 = 1.50 N 7 = 1.69680 ν 7 = 55.5 R14 = -576.29 D14 = 4.28 R15 = -15.62 D15 = 1.50 N 8 = 1.56384 ν 8 = 60.7 R16 = -40.28

[0031]

[Table 3]

[0032]

According to the present invention, the total lens length can be reduced by setting the lens configuration of each lens unit of a zoom lens that performs zooming by moving two lens units having a predetermined refractive power as described above. As a result, it is possible to achieve a small-sized zoom lens having a simple configuration and high optical performance over the entire zoom range of about 2.2 with the zoom ratio of 2.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 7 is an aberration diagram at a wide angle end according to Numerical Embodiment 2 of the present invention.

FIG. 8 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit SP stop d d-line g g-line S Sagittal image plane M Meridional image plane

Claims (1)

(57) [Claims] 1. A compact zoom having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between both lens groups. In the lens, the first group includes a meniscus-shaped positive first lens having a convex surface facing the object side, a negative second lens having both lens surfaces concave, a positive third lens having both lens surfaces convex, and an image surface side. The second lens unit has a positive fourth lens whose both lens surfaces have a strong refractive surface facing the convex surface and a positive fifth lens whose both lens surfaces whose strong refractive surfaces face the image surface side are convex. A meniscus-shaped positive sixth lens having a convex surface facing the image surface side, a negative seventh lens on the meniscus having a convex surface facing the image surface side, and a meniscus-shaped negative eighth lens having a convex surface facing the image surface side And the second lens and the third lens
The lenses are cemented, and when the refractive index and Abbe number of the material of the i-th lens are Ni and νi, respectively, (N4 + N5) / 2 <1.567 <(ν4 + ν5) / 2 1.6 <(N7 + N8) / 2 <1.757 <(ν7 + ν8) / 2 A small zoom lens characterized by satisfying the following condition: