JP2581199B2 - Small zoom lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a small zoom lens composed of two lens groups suitable for a lens shutter camera, a video camera, and the like, and in particular, appropriately sets the lens configuration of each lens group. By doing so, aberration correction can be performed well and the entire lens length
The present invention relates to a small-sized zoom lens for reducing the distance from the lens surface to the image plane).

(Prior 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, even in the field of a small camera such as a lens shutter camera which does not perform lens replacement, it is desired to mount a zoom lens, and a small zoom lens having the same length as a conventionally used single focus lens is demanded.

The present applicant has previously disclosed JP-A-57-201213 and JP-A-60-201213.
No. 170816, JP-A-60-191216, JP-A-62-56
No. 917, etc., composed of two lens groups of a first group having a positive refractive power and a second group having a negative refractive power in order from the object side,
We proposed a small zoom lens that changes the magnification by changing the distance between both lens groups.

In this publication, a positive / negative refractive power arrangement is adopted in order from the object side to achieve a zoom lens having a high optical performance with a relatively short back focus and a short overall lens length.

In addition, Japanese Patent Laid-Open No. 62-284319 discloses a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. Both lens units are moved forward while changing the distance between both lens units. Discloses a zoom lens that performs variable magnification.

(Problems to be Solved by the Invention) In this zoom lens, 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 total lens length can be further reduced. It becomes possible.

However, if the refractive power of each lens group is simply increased, there is a problem that aberration fluctuations accompanying zooming become large, and it becomes difficult to satisfactorily correct them.

The present invention further improves the zoom lens proposed in each of the earlier publications of the present applicant, and by appropriately setting the lens configuration of each lens group, particularly while having a predetermined zoom ratio and a shooting angle of view, An object of the present invention is to provide a compact zoom lens having high optical performance over the entire zoom range in which the overall length of the lens is reduced.

(Means for Solving the Problems) There are two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, sequentially from the object side. The first group is a meniscus-shaped positive first lens having a convex surface facing the object side, a negative second lens having both concave lens surfaces, a positive third lens, and both lens surfaces. Has four convex positive fourth lenses, and the second group has a meniscus-shaped positive fifth lens having a convex surface facing the image surface side, and a meniscus-shaped positive fifth lens having a convex surface facing the image surface side. It has two negative sixth lenses, the focal length of the i-th lens unit is Fi, the focal length of the i-th lens is fi, the focal length of the entire system at the wide-angle end is Fw, and the first to third lenses F123, the composite focal length up to f123, counted from the object side
When the radius of curvature of the i-th lens surface is Ri, and the distance between the i-th lens surface and the (i + 1) -th lens surface is Di, 0.5 <F1 / Fw <1.0 (1) −1.5 <F2 / Fw <− 0.5 ... (2) -0.5 <F1 / f123 <0.1 ... (3) 0.75 <F1 / f4 <1.5 ... (4) -5 <f5 / F2 <-2.5 ... (5) -5 <(R3-R2) / (R3 + R2) <-2 (6) −0.5 <R4 / R5 <0.5 (7) −0.4 <D10 / F2 <−0.15 (8)

(Example) FIGS. 1 to 3 are lens cross-sectional views of Numerical Examples 1 to 3 of the present invention. In the figure, the zoom position at the wide angle end is shown.

In the figure, I is a first group having a positive refractive power, and II is a second group having a negative refractive power. By moving both lens groups toward the object side as indicated by arrows while reducing the distance between the two lens groups. Zooming is performed from the wide-angle end to the telephoto end.

In the present embodiment, the overall length of the lens is shortened, particularly the overall length of the lens at the wide-angle end, by adopting such a zoom system and the refractive power arrangement as described above.
Then, the lens configuration of each lens group, the lens shape and the refractive power of each lens group, and the like are specified so as to satisfy the above-described conditional expressions (1) to (8). High optical performance is obtained over the entire zoom range after correction.

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

Conditional expressions (1) and (2) are to appropriately set the focal length (refractive power) of the first lens unit having a positive refractive power and the second lens unit having a negative refractive power, and to balance various aberrations over the entire zoom range. This is for good correction.

If the focal length F1 of the first group exceeds the lower limit of conditional expression (1) or the focal length F2 of the second group exceeds the upper limit of conditional expression (2), the refractive power of each lens group becomes too strong. Although the overall length of the lens is shortened, it is not good because aberration fluctuations during zooming, particularly fluctuations in spherical aberration and coma, increase.

Conversely, when the focal length F1 of the first group exceeds the upper limit of conditional expression (1) or the focal length F2 of the second group exceeds the lower limit of conditional expression (2), the refractive power of each lens unit becomes weak. If it is too long, the back focus becomes too short, and the outer shape of the lens of the second group increases to secure a predetermined amount of off-axis light flux. Furthermore, the zoom stroke of the second lens unit during zooming becomes too large, and the first lens unit and the second lens unit come into contact on the telephoto side, making it difficult to obtain a sufficient zoom ratio.

Conditional expression (3) relates to the ratio of the refractive power of the first lens unit to the combined lens unit 1A from the first lens unit to the refractive power of the third lens unit. Conditional expressions (3) and (4) relate to the ratio of the refracting power of the lens, and are mainly used to favorably correct spherical aberration and distortion in zooming.

Exceeding the lower limit of conditional expression (3), the refractive power of the lens unit 1A increases in the negative direction, or exceeding the upper limit of conditional expression (4), the positive refractive power of the fourth lens becomes excessively strong. Then, the spherical aberration generated in the first lens unit increases, and it becomes difficult to correct the spherical aberration by the other lens units.

Conversely, if the value exceeds the conditional value of the conditional expression (3) or exceeds the lower limit value of the conditional expression (4), the distortion will be overcorrected, which is not good.

It is particularly preferable to set the upper limit of conditional expression (3) to about 0.05.

Conditional expression (5) is satisfied for the fifth lens that is the first lens in the second group.
It relates to the refractive power of the lens. If the positive refractive power of the fifth lens exceeds the upper limit and becomes too strong, the curvature of field in the middle portion of the screen increases. If the lower limit of conditional expression (5) is exceeded, distortion will be overcorrected over the entire zoom range, which is not good.

Conditional expression (6) relates to the shape characteristics of the air lens formed between the first lens and the second lens in the first group, and is mainly used to correct spherical aberration and coma in a well-balanced manner. It is. If the lower limit is exceeded, spherical aberration will be insufficiently corrected, and if the upper limit is exceeded, coma will increase.

Conditional expression (7) relates to the ratio of the radius of curvature of the lens surface on the image surface side of the second lens to the radius of curvature of the lens surface on the object side of the third lens, and is mainly used to favorably correct spherical aberration. Things. When the value exceeds the lower limit, the spherical aberration is overcorrected, and when the value exceeds the upper limit, the spherical aberration is undercorrected.

Conditional expression (8) relates to the air gap between the fifth lens and the sixth lens in the second group. If the distance exceeds the lower limit and the distance is too large, the back focus becomes shorter and the outer diameter of the sixth lens increases, or the fourth lens and the fifth lens come into contact on the telephoto side. You can't get it. If the interval exceeds the upper limit and the interval is too short, the field curvature in the middle of the screen increases, which is not good.

The compact zoom lens aimed at by the present invention can be achieved by satisfying the above conditions, but it is also possible to satisfactorily correct aberration fluctuations caused by zooming while further reducing the size of the entire lens system, and to achieve full zooming. To obtain high optical performance over the range, the following conditions should be satisfied.

Under the above conditions, the refractive index of the material of the i-th lens is Ni
0.02 <D2 / F1 <0.1 ... (9) 0.6 <R4 / F1 <2.0 ... (10) 0 <D4 / F1 <0.09 ... (11) 0.9 <D5 / D7 ... (12) 0.05 <R9 / F2 <12 ... (13) 0.39 <R11 / F2 <0.7 ... (14) -0.18 <N6-N5 ... (15)

Conditional expression (9) relates to the lens thickness of the first lens. If the lower limit of conditional expression (9) is exceeded, the radius of curvature of the air lens formed by the first lens and the second lens must be reduced, making it difficult to satisfactorily correct spherical aberration and coma. Come. If the value exceeds the upper limit, the outer diameter of the first lens increases, which is not good.

Conditional expression (10) relates to the radius of curvature of the lens surface on the image plane side of the second lens. If the lower limit of conditional expression (10) is exceeded, spherical aberration will be insufficiently corrected, and if the upper limit is exceeded, coma will increase.

Conditional expression (11) relates to the air gap between the second lens and the third lens. If conditional expression (11) is not satisfied, a lens system cannot be formed, or coma will increase, which is not good. It is preferable to set the condition value of the conditional expression to 0.04.

Conditional expression (12) relates to the ratio between the lens thickness of the third lens and the lens thickness of the fourth lens. If the distance D5 is smaller than the conditional expression (12) or the distance D7 is larger, it becomes difficult to satisfactorily correct the distortion.

Conditional expression (13) relates to the radius of curvature of the object-side lens surface of the fifth lens, and conditional expression (14) relates to the radius of curvature of the object-side lens surface of the sixth lens. If the lower limit of conditional expression (13) or the upper limit of conditional expression (14) is exceeded, the field curvature will increase. Conversely, if the value exceeds the upper limit of conditional expression (13) or the lower limit of conditional expression (14), distortion increases, which is not good.

Conditional expression (15) relates to the refractive indices of the materials of the fifth lens and the sixth lens, and is mainly for favorably correcting field curvature. If conditional expression (15) is not satisfied, the curvature of field increases over the entire zooming, which is not good.

In this embodiment, the aperture is between the first and second lens groups,
Alternatively, it is preferable to arrange between the third lens and the fourth lens in order to correct aberration.

Next, numerical examples of the present invention will be described. In numerical examples
Ri is the radius of curvature of the i-th lens surface in order from the object side,
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

Numerical example 1 Numerical example 2 Numerical example 3 (Effects of the Invention) According to the present invention, the lens shape, the refractive power, and the like of each lens group of a zoom lens that performs zooming by moving two lens groups having a predetermined refractive power are set as described above. A compact zoom lens having a simple configuration and high optical performance over the entire zoom range in which the overall length is reduced can be achieved.

[Brief description of the drawings]

1 to 3 are lens sectional views of Numerical Examples 1 to 3 of the present invention, and FIGS. 4 to 6 are various aberration diagrams of Numerical Examples 1 to 3 of the present invention. In the aberration diagrams, (A) is the wide-angle end, (B) is the middle, (C)
9 is an aberration diagram at a telephoto end. In the figure, I and II denote the first and second lens groups, SP denotes the aperture, and arrows denote the moving directions of the respective groups during zooming.

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 changing the distance between both lens groups to perform zooming. In the lens,
The first group is a meniscus positive first lens having a convex surface facing the object side.
Lens, negative second lens with both lens surfaces concave, positive third
The lens, and the fourth lens of the fourth positive lens having both lens surfaces convex.
The second group includes two lenses: a positive meniscus fifth lens having a convex surface facing the image surface side, and a negative meniscus sixth lens having a convex surface facing the image surface. The focal length of the i-th lens unit is Fi, and the focal length of the i-th lens unit is f.
i, Fw is the focal length of the entire system at the wide-angle end, f123 is the combined focal length from the first lens to the third lens, Ri is the radius of curvature of the i-th lens surface counted from the object side, and i is the i-th lens surface. 0.5 <F1 / Fw <1.0 −1.5 <F2 / Fw <−0.5 −0.5 <F1 / f123 <0.1 0.75 <F1 / f4 <1.5 − where Di is the distance between the lens surface and the (i + 1) th lens surface. 5 <f5 / F2 <−2.5−5 <(R3−R2) / (R3 + R2) <− 2−0.5 <R4 / R5 <0.5−0.4 <D10 / F2 <−0.15 Small zoom lens.