JP2962023B2 - Compact 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 telephoto type compact zoom lens having a long focal length suitable for a 35 mm camera, a video camera, an electronic still camera, and the like. The zoom lens system according to the present invention relates to a compact zoom lens having high optical performance over the entire zoom range with a zoom ratio of about 2.5 by moving a plurality of lens groups.

[0002]

2. Description of the Related Art Conventionally, in order to reduce the size of the entire lens system while maintaining a predetermined zoom ratio, the zoom lens is constituted by three or more lens units, and at least three lens units are moved to change the zoom ratio. Various zoom lenses have been proposed.

A zoom lens composed of five lens groups as a whole and having three or more lens groups moved during zooming has been proposed in, for example, JP-A-60-175020 and JP-A-63-189819. Have been.

Japanese Patent Application Laid-Open No. 60-175020 proposes a telephoto zoom lens having a relatively long focal length. In this publication, all of the five lens groups having a predetermined refractive power are moved or the four lens groups of the first, third, fourth, and fifth groups are moved.
The two lens groups are moved to, for example, the object side to perform zooming from the wide-angle end to the telephoto end, and have a zoom ratio of 3 and an F-number of 3.6 to 3.6.
A zoom lens of about 5.6 has been proposed.

Japanese Patent Laid-Open Publication No. Sho 63-189819 proposes a standard zoom lens having a relatively wide angle of view. In this publication, of the five lens units having a predetermined refractive power, zooming from the wide-angle end to the telephoto end is performed by changing the first unit toward the object side, integrating the third, fourth, and fifth units, or reciprocating each other. The whole is moved to the object side while changing the group interval.

As described above, the zoom type which comprises five lens groups as a whole, and performs zooming by moving three or more lens groups while maintaining a constant relationship, has a predetermined zooming ratio. Since it is easy to reduce the size of the entire lens system while securing it, it is used for zoom lenses such as 35 mm cameras and video cameras.

[0007]

In order to shorten the overall length of the lens and further downsize the entire lens system in such a zoom type, the number of lenses in each lens group is reduced or the refractive power of each lens group is reduced. It is common to take a strengthening approach.

However, if the number of lenses is simply reduced or the refractive power of each lens group is increased, the aberration correction in each lens group becomes insufficient, and the aberration variation accompanying zooming becomes large. There is a problem that it is very difficult to obtain performance.

According to the present invention, the zoom lens is composed of five lens units having a predetermined refractive power as a whole, and the refractive power of each lens unit, the moving conditions of each lens unit for performing zooming, and the like are appropriately set. Accordingly, it is an object of the present invention to provide a compact zoom lens having high optical performance over the entire zoom range and having a zoom ratio of about 2.5 while shortening the overall length of the lens.

[0010]

A compact zoom lens according to the present invention has first positive refractive power in order from the object side.
Each lens group includes five lens groups, a second group having a negative refractive power, a third group having a positive refractive power, a fourth group having a positive refractive power, and a fifth group having a negative refractive power. Is composed of two lenses, a positive lens and a negative lens. In zooming from the wide-angle end to the telephoto end, the second and fourth units are fixed, and the first, third, and fifth lenses are fixed.
The groups are independently moved in the object-side direction, the focal lengths at the wide-angle end and the telephoto end of the entire system are respectively fW and fT, the focal length of the i-th group is fi, and the first group and the second group at the wide-angle end are The focal length of the combination is f12W, the change amount of the principal point interval at the telephoto end with respect to the wide-angle end of the third and fourth units is Δe34, and the length from the first lens surface to the final lens surface of the entire system at the wide-angle end is DW, when the principal point interval between the first group and the second group at the wide-angle end is e12W, 0.09 · fT / fW <Δe34 / DW <0.15 · fT / fW (1) 24 <f5 / f12W <0.35 ‥‥‥ (2) 5 <| f12 / e12W | <15 ‥‥‥ (3)

[0011]

1 to 3 are lens sectional views of Numerical Examples 1 to 3 of the present invention. In the figure, L1 is a first group having a positive refractive power,
L2 is a second group having a negative refractive power, and L3 is a third group having a positive refractive power.
The group L4 is a fourth group having a positive refractive power, and L5 is a fifth group having a negative refractive power. Arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end.

In this embodiment, each lens unit is composed of two lenses, a positive lens and a negative lens, in order to reduce the size of the entire lens system. As shown in FIGS. A lens configuration is adopted in which a predetermined lens group is moved as shown in the figure to distribute the zooming effect in zooming to each lens group in a well-balanced manner.

When zooming from the wide-angle end to the telephoto end,
The second and fourth units are fixed, and the first, third and fifth units are independently moved in the object side direction. By configuring each lens group so as to satisfy the above-mentioned conditional expressions (1), (2), and (3), it is possible to secure a predetermined zoom ratio, shorten the overall length of the lens, and reduce the overall length of the lens system. Good optical performance is obtained over the entire zoom range while miniaturizing.

In particular, in the present embodiment, in order to reduce the size of the entire lens system and to prevent an unnecessary long back focus, the entire lens system is prevented from becoming a very strong reverse telephoto type at the wide angle end. That is, the refractive power and the paraxial arrangement of each lens group are set so as to be a relatively weak reverse telephoto type. Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) defines the amount of change in the distance between the principal points of the third and fourth units during zooming from the wide-angle end to the telephoto end with respect to the entire length of the lens at the wide-angle end. is there. Conditional expression (1)
If the distance between the principal points of the third and fourth units becomes too large at the telephoto end beyond the upper limit of the above, it is necessary to secure a large moving space for zooming at the wide-angle end so that the lens does not interfere. Occurs, and as a result, the overall length of the lens at the wide-angle end increases, which is not preferable.

If the distance between the principal points of the third lens unit and the fourth lens unit becomes too small at the telephoto end beyond the lower limit value of the conditional expression (1), the total optical length at the wide-angle end is obtained while obtaining a desired zoom ratio. In order to shorten the zoom distance, the zoom strokes of the first and fifth lens units must be increased, which is not preferable.

Conditional expression (2) defines the ratio of the focal length of the fifth lens unit to the combined focal length of the first lens unit and the second lens unit at the wide-angle end. If the negative refractive power of the fifth lens unit becomes too weak beyond the upper limit of conditional expression (2), the distortion tends to decrease. However, in order to obtain a predetermined zoom ratio, the fourth and fifth lens units are changed. Needs to be widened at the wide-angle end, and the back focus at the wide-angle end becomes longer than necessary, making it difficult to reduce the size of the entire lens system.

If the negative refractive power of the fifth lens unit is too strong beyond the lower limit of conditional expression (2), the thread-wafer type distortion will increase and the Petzval sum will increase in the negative direction.
It is difficult to satisfactorily correct the image plane characteristics, which is not preferable.

Conditional expression (3) defines the ratio of the distance between the principal points of the first and second units to the combined focal length of the first and second units at the wide-angle end. If the distance between the principal points of the first lens unit and the second lens unit becomes too small beyond the upper limit value of the conditional expression (3), the aperture diameter, which is a main factor for determining the outer diameter of the lens barrel, tends to decrease. Since the distance between the first group and the second group is increased, the peripheral light amount is reduced, and the coma aberration based on the descending ray is adversely affected.

If the lower limit of conditional expression (3) is exceeded, the stop diameter increases, the outer diameter of the lens barrel increases, and fluctuations in various aberrations such as spherical aberration and field curvature accompanying zooming occur. Undesirably increases.

By satisfying the above conditions, a compact zoom lens aimed at by the present invention can be achieved.
Furthermore, in order to obtain a compact zoom lens having high optical performance, which achieves miniaturization of the entire lens system, the first unit is composed of a meniscus negative lens having a convex surface facing the object side and a positive lens in order from the object side. The second group is composed of a negative lens having both concave lens surfaces and a positive lens, the third group is composed of a negative lens having both concave lens surfaces and a positive lens having both lens surfaces convex, and the fourth group is composed of both positive and negative lenses. The fifth lens unit is composed of a positive lens having a convex surface and a negative meniscus lens having a convex surface facing the image surface, and the fifth unit includes a positive meniscus lens having a convex surface facing the image surface and both negative surfaces having a concave surface. It is better to use a lens.

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.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in numerical examples. (Numerical Example 1) R 1 = 53.32 D 1 = 1.8 N 1 = 1.80518 ν 1 = 25.4 R 2 = 38.41 D 2 = 0.3 R 3 = 40.94 D 3 = 5.3 N 2 = 1.61271 ν 2 = 58.7 R 4 = -891.86 D 4 = variable R 5 = -42.43 D 5 = 1.0 N 3 = 1.80609 ν 3 = 40.9 R 6 = 26.24 D 6 = 2.7 N 4 = 1.80518 ν 4 = 25.4 R 7 = 1463.95 D 7 = variable R 8 = -116.97 D 8 = 1.1 N 5 = 1.84666 ν 5 = 23.7 R 9 =-85.14 D 9 = 4.1 N 6 = 1.60311 ν 6 = 60.7 R10 = -28.04 D10 = Variable R11 = 29.94 D11 = 5.2 N 7 = 1.53172 ν 7 = 48.9 R12 = -29.94 D12 = 1.0 N 8 = 1.83400 ν 8 = 37.1 R13 = -90.84 D13 = variable R14 = -96.92 D14 = 2.5 N 9 = 1.80518 ν 9 = 25.4 R15 = -28.43 D15 = 1.13 R16 = -26.79 D16 = 1.2 N10 = 1.77249 ν10 = 49.6 R17 = 43.18

[0024]

[Table 1] (Numerical example 2) R 1 = 53.18 D 1 = 1.8 N 1 = 1.80518 ν 1 = 25.4 R 2 = 38.13 D 2 = 0.3 R 3 = 40.44 D 3 = 5.3 N 2 = 1.61271 ν 2 = 58.7 R 4 = -1004.16 D 4 = variable R 5 = -42.19 D 5 = 1.0 N 3 = 1.80609 ν 3 = 40.9 R 6 = 26.46 D 6 = 2.7 N 4 = 1.80518 ν 4 = 25.4 R 7 = 5178.08 D 7 = Variable R 8 = -106.41 D 8 = 1.1 N 5 = 1.84666 ν 5 = 23.7 R 9 =-93.46 D 9 = 4.1 N 6 = 1.61271 ν 6 = 58.7 R10 = -27.95 D10 = Variable R11 = 30.63 D11 = 5.2 N 7 = 1.56137 ν 7 = 45.1 R12 = -30.63 D12 = 1.0 N 8 = 1.85025 ν 8 = 32.2 R13 = -106.95 D13 = variable R14 = -94.95 D14 = 2.5 N 9 = 1.80518 ν 9 = 25.4 R15 = -27.20 D15 = 0.63 R16 = -26.45 D16 = 1.2 N10 = 1.77249 ν10 = 49.6 R17 = 42.21

[0025]

[Table 2] (Numerical example 3) R 1 = 51.67 D 1 = 1.8 N 1 = 1.80518 ν 1 = 25.4 R 2 = 38.51 D 2 = 0.46 R 3 = 41.37 D 3 = 5.3 N 2 = 1.60311 ν 2 = 60.7 R 4 = -1683.48 D 4 = Variable R 5 = -42.66 D 5 = 1.1 N 3 = 1.80609 ν 3 = 40.9 R 6 = 26.14 D 6 = 2.7 N 4 = 1.80518 ν 4 = 25.4 R 7 = 637.55 D 7 = variable R 8 = -146.49 D 8 = 1.1 N 5 = 1.84665 ν 5 = 23.7 R 9 =-77.31 D 9 = 4.1 N 6 = 1.60311 ν 6 = 60.7 R10 = -28.88 D10 = Variable R11 = 31.03 D11 = 5.2 N 7 = 1.53171 ν 7 = 48.9 R12 = -31.03 D12 = 1.0 N 8 = 1.83400 ν 8 = 37.1 R13 = -95.26 D13 = variable R14 = -104.28 D14 = 2.5 N 9 = 1.80518 ν 9 = 25.4 R15 = -30.51 D15 = 1.44 R16 = -28.65 D16 = 1.20 N10 = 1.77249 ν10 = 49.6 R17 = 44.96

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

According to the present invention, the zoom lens is composed of five lens units having a predetermined refractive power as a whole, and the moving conditions of each lens unit and the lens configuration of each lens unit during zooming are described above. By setting as described above, the zoom ratio has high optical performance with little aberration fluctuation over the entire zoom range while shortening the entire lens length and the lens diameter.
A compact zoom lens of about 5 can be achieved.

[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 Example 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 group L2 Second group L3 Third group L4 Fourth group L5 Fifth group ΔS Sagittal image plane ΔM Meridional image plane d d-line g g-line

Claims (1)

(57) [Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a negative refractive power in order from the object side. The fifth lens unit has five lens units, and each lens unit is composed of two lenses, a positive lens and a negative lens. When zooming from the wide-angle end to the telephoto end, the second and fourth units are The first, third, and fifth units are independently moved in the object-side direction, the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fW and fT, and the focal lengths of the i-th unit are fi, The combined focal length of the first group and the second group at the wide-angle end is f12W, the change amount of the principal point interval at the telephoto end with respect to the wide-angle end of the third group and the fourth group is Δe34, The length from the first lens surface to the last lens surface is D
W, the distance between the principal points of the first group and the second group at the wide-angle end is e12W
0.09 · fT / fW <Δe34 / DW <0.15
A compact zoom lens satisfying the following condition: fT / fW 0.24 <f5 / f12W <0.35 5 <| f12 / e12W | <15