JP3008711B2 - 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 aberration by appropriately setting the lens configuration of each lens group. The present invention relates to a compact zoom lens having a wide angle of view and a zoom ratio of about 2, which is satisfactorily performed and reduces the overall length of the lens (the distance from the first lens surface to the image surface).

[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. 2-284109, the first group is composed of five lenses of positive, negative, negative, 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.

According to the present invention, in a so-called two-group zoom lens, by appropriately setting the lens configuration of each lens group, it is possible to shorten the overall length of the lens, particularly while having a wide angle of view at a zoom ratio of about 2. It is another object of the present invention to provide a compact zoom lens having high optical performance over the entire zoom range.

[0015]

According to the present invention, there is provided a compact zoom lens comprising: (a) a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side. A first lens unit having a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the object side, and at least one positive lens; The second group has a positive lens and at least two negative lenses, and the Abbe number of the material of the negative lens closest to the image plane in the second group is νrn. When the total thickness of the lenses in the group is 群 D1 and the focal length of the entire system at the wide-angle end is Fw, 57 <νrn (A-1) 0.5 <ΣD1 / Fw <1.0 (A-2) The following condition is satisfied.

In particular, when the focal lengths of the first and second groups are f1 and f2, respectively, and the distance from the first lens surface to the final lens surface of the second group is TD2, 1.2 <Fw / f1 <1.7... (A-3) -0.8 <TD2 / F2 <-0.5 (a-4)

(B) A small lens unit having two lens units, a first unit having a positive refractive power and a second unit having a negative refractive power, in order from the object side. In the zoom lens, the first group includes a meniscus positive first lens having a convex surface facing the object side, a negative second lens having a concave lens surface on the object side, a positive third lens, and both lens surfaces having a convex surface. It has five lenses, a positive fourth lens and a meniscus-shaped negative fifth lens with the convex surface facing the image plane side, and the fourth lens and the fifth lens are cemented as a whole and are a positive laminated lens. The second group includes a meniscus positive sixth lens having a convex surface facing the image surface side, a meniscus negative seventh lens having a convex surface facing the image surface side, and a convex surface facing the image surface side. With three meniscus negative eighth lenses, and the focal length of the entire system at the wide-angle end Fw, the Abbe number of the material of said eighth lens Nyu8, the total thickness of lenses in the first group ΣD1
57 <ν8 (b-1) 0.5 <−１D1 / Fw <1.0 (b-2) .

In particular, when the Abbe number of the material of the i-th lens is νi and the average value of the refractive index of the material of the positive lens in the first group is NIP, 15 <ν4-ν5 (b− 3) NIP <1.63 (b-4) The following condition is satisfied, and a stop is arranged between the third lens and the fourth lens.

[0026]

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 figure, L1 denotes a first group having a positive refractive power, and L2 denotes a second group having a negative refractive power. While reducing the distance between the two lens groups, the two 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 is an aperture, and in Numerical Examples 1 to 3, the third lens in the first group and the fourth lens
The lens unit is disposed between the lens unit and the lens unit, and moves integrally with the first unit with zooming.

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, and 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 and aberration fluctuation accompanying zooming are corrected well, and high optical performance is obtained over the entire zoom range.

In particular, in the present invention, numerical values shown in FIGS. 1 to 3 are used to satisfactorily correct fluctuations in various aberrations such as spherical aberration and curvature of field due to zooming, and to maintain a good balance of the optical performance of the entire screen. In the first to third embodiments, the first lens unit has a meniscus positive first lens having a convex surface facing the object side, a negative second lens having a concave lens surface on the object side, a positive third lens, and both lens surfaces. Is composed of five lenses: a positive fourth lens having a convex surface, and a negative fifth meniscus lens having a convex surface facing the image surface side. If necessary, the second lens and the third lens are joined.
Further, the fourth lens and the fifth lens are cemented. And
A positive meniscus sixth lens having the second lens unit convex toward the image plane side
Lens, meniscus negative seventh lens with convex surface facing image surface side
It comprises three lenses: a lens and a meniscus-shaped negative eighth lens with the convex surface facing the image plane side.

In the first to third numerical embodiments, the stop is arranged between the third lens and the fourth lens in the first lens unit, so that the lens diameter can be effectively increased when widening the angle of view. Preventing.

In the first to third numerical embodiments, the size of the entire lens system is reduced while satisfying each conditional expression in the above-described lens configuration, 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 expressions (a-1) and (b-1) are to appropriately set the Abbe number of the material of the negative lens (eighth lens) closest to the image plane in the second lens unit, and The purpose is to satisfactorily correct the accompanying change in chromatic aberration of magnification. If the conditional expression is not satisfied, the fluctuation of chromatic aberration of magnification accompanying zooming becomes large, and the optical performance is greatly reduced.

Conditional expressions (a-2) and (b-2) are to appropriately set the ratio between the total thickness of the lenses in the first lens unit and the refractive power of the entire system at the wide-angle end, and This is for obtaining high optical performance while preventing an increase in the lens diameter. If the total thickness of the lenses in the first group exceeds the upper limit of this conditional expression and becomes too thick, the diameter of the front lens increases. On the other hand, if the thickness is less than the lower limit value, too much flare is generated over the entire screen, which is not good.

Conditional expression (a-3) is to appropriately set the ratio between the refractive power of the first lens unit and the refractive power of the entire system at the wide-angle end, and to reduce the zoom ratio by 2 while mainly reducing the size of the entire lens system. This is to reduce the occurrence of various aberrations due to zooming when obtaining the degree.
If the refractive power of the first lens unit becomes too strong beyond the upper limit value of conditional expression (A-3), various aberrations such as spherical aberration and coma aberration increase with zooming. If the refractive power of the first lens unit becomes weaker than the lower limit, the amount of movement of the first lens unit due to zooming increases in order to secure a predetermined zoom ratio, and the overall length of the lens becomes longer. Not so good.

Conditional expression (a-4) is used to appropriately set the ratio between the refractive power in the second unit and the total length of the lens in the second unit, and to reduce fluctuations in various aberrations mainly due to zooming. It is. If the refractive power of the second lens unit becomes too strong beyond the upper limit value of conditional expression (a-4), fluctuations of various aberrations such as curvature of field and distortion due to zooming will increase. On the other hand, if the refractive power of the second lens unit is too weak below the lower limit, the amount of movement of the second lens unit for securing a predetermined zoom ratio increases, and the overall length of the lens becomes longer.

Conditional expression (b-3) appropriately sets the difference between the Abbe numbers of the materials of the positive fourth lens and the negative fifth lens in the first group, and favorably corrects mainly axial chromatic aberration. It is for. If the difference between the Abbe numbers of the materials of the two lenses is too small outside the conditional expression (b-3), axial chromatic aberration will increase over the entire zoom range, which is not good.

Conditional expression (b-4) is for appropriately setting the refractive index of the material of the positive lens in the first lens unit, and for mainly maintaining good image plane characteristics. If conditional expression (b-4) is not satisfied and the average refractive index is too high, the Petzval sum will increase in the negative direction, making it difficult to satisfactorily correct astigmatism.

In the present invention, more preferably, n1P <
It is good to be 1.6.

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 aspheric surface has an X-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When A, B, C, D, and E are each aspheric coefficients

[0059]

(Equation 1) It is represented by the following equation.

Table 1 shows the relationship with each conditional expression in each numerical example.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. (Numerical Example 1) F = 28.93 to 54.59 FNO = 1: 4.1 to 7.72 ω = 73.6 ° to 43.3 ° R 1 = 20.47 D 1 = 2.16 N 1 = 1.58144 ν 1 = 40.8 R 2 = 38.45 D 2 = 2.08 R 3 = -17.61 D 3 = 4.16 N 2 = 1.85026 ν 2 = 32.3 R 4 = -40.37 D 4 = 5.00 N 3 = 1.54814 ν 3 = 45.8 R 5 = -21.22 D 5 = 1.00 R 6 = (Aperture) D 6 = 1.00 R 7 = 22.21 D 7 = 4.50 N 4 = 1.51633 ν 4 = 64.2 R 8 = -8.41 D 8 = 1.50 N 5 = 1.83400 ν 5 = 37.2 R 9 = -14.32 D 9 = Variable R10 = -29.25 D10 = 2.60 N 6 = 1.60342 ν 6 = 38.0 R11 = -14.25 D11 = 2.14 R12 = -14.19 D12 = 1.30 N 7 = 1.71300 ν 7 = 53.8 R13 = -86.46 D13 = 4.65 R14 = -12.57 D14 = 1.50 N 8 = 1.60311 ν 8 = 60.7 R15 = -43.61

[0062]

[Table 1] (Numerical Example 2) F = 28.95 to 54.50 FNO = 1: 4.1 to 7.72 ω = 73.6 ° to 43.3 ° R 1 = 23.69 D 1 = 2.14 N 1 = 1.63636 ν 1 = 35.4 R 2 = 48.84 D 2 = 1.95 R 3 = -18.86 D 3 = 4.84 N 2 = 1.85026 ν 2 = 32.3 R 4 = -50.35 D 4 = 4.97 N 3 = 1.60342 ν 3 = 38.0 R 5 = -24.68 D 5 = 1.00 R 6 = (Aperture) D 6 = 1.00 R 7 = 22.86 D 7 = 5.00 N 4 = 1.51742 ν 4 = 52.4 R 8 = -8.20 D 8 = 1.50 N 5 = 1.80518 ν 5 = 25.4 R 9 = -14.13 D 9 = Variable R10 = -27.24 D10 = 3.00 N 6 = 1.66680 ν 6 = 33.0 R11 = -14.50 D11 = 2.30 R12 = -13.67 D12 = 1.30 N 7 = 1.71300 ν 7 = 53.8 R13 = -75.02 D13 = 4.38 R14 = -13.48 D14 = 1.50 N 8 = 1.60311 ν 8 = 60.7 R15 = -52.56

[0063]

[Table 2] (Numerical Example 3) F = 28.95 to 54.50 FNO = 1: 4.1 to 7.72 ω = 73.6 ° to 43.3 ° R 1 = 28.11 D 1 = 1.85 N 1 = 1.72825 ν 1 = 28.5 R 2 = 47.51 D 2 = 1.84 R 3 = -17.38 D 3 = 4.58 N 2 = 1.85026 ν 2 = 32.3 R 4 = -49.56 D 4 = 4.61 N 3 = 1.62004 ν 3 = 36.3 R 5 = -24.54 D 5 = 1.00 R 6 = (Aperture) D 6 = 1.00 R 7 = 21.33 D 7 = 5.00 N 4 = 1.51742 ν 4 = 52.4 R 8 = -8.00 D 8 = 1.50 N 5 = 1.80518 ν 5 = 25.4 R 9 = -13.57 D 9 = Variable R10 = -28.53 D10 = 3.00 N 6 = 1.64769 ν 6 = 33.8 R11 = -14.73 D11 = 2.46 R12 = -13.11 D12 = 1.30 N 7 = 1.71300 ν 7 = 53.8 R13 = -35.70 D13 = 2.96 R14 = -14.12 D14 = 1.50 N 8 = 1.60311 ν 8 = 60.7 R15 = -132.94

[0064]

[Table 3]

[0070]

[Table 4]

[0071]

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. Therefore, 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.

[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

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (5)

(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 has a positive lens with a convex surface facing the object side, a negative lens with a concave surface facing the object side, at least one positive lens, and a negative lens, and the second group has a positive lens and at least The optical system has two negative lenses, the Abbe number of the material of the negative lens closest to the image plane in the second group is νrn, the total thickness of the lenses in the first group is ΔD1, and the total thickness at the wide-angle end is ΔD1. A compact zoom lens, which satisfies a condition of 57 <νrn 0.5 <ΣD1 / Fw <1.0, where Fw is a focal length of the system. 2. The focal lengths of the first and second lens units are each f
1, f2, where TD2 is the distance from the first lens surface of the second group to the last lens surface, 1.2 <Fw / f1 <1.7-0.8 <TD2 / F2 <-0.5 2. The compact zoom lens according to claim 1, wherein the condition is satisfied. 3. 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 positive meniscus first lens having a convex surface facing the object side, a negative second lens having a concave lens surface on the object side,
A positive third lens, a positive fourth lens having both lens surfaces convex,
The lens has five meniscus-shaped negative fifth lenses with the convex surface facing the image surface side, and the fourth lens and the fifth lens are made of a cemented positive lens as a whole, and
The second group includes 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 shape having a convex surface facing the image surface side. , The focal length of the entire system at the wide-angle end is Fw, the Abbe number of the material of the eighth lens is ν8, and the total thickness of the lenses in the first group is A small zoom lens characterized by satisfying the following condition: ＜ D1 57 <ν8 0.5 <ΣD1 / Fw <1.0 4. An Abbe number of a material of the i-th lens is ν.
4. The small-sized lens according to claim 3, wherein, when an average value of refractive indices of materials of the positive lens in the first group is NIP, a condition of 15 <ν4-ν5 NIP <1.63 is satisfied. Zoom lens. 5. The compact zoom lens according to claim 4, wherein a stop is arranged between said third lens and said fourth lens.