JPH11258506A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high power zoom lens having high optical performance over the whole variable power range while shortening the whole lens length satisfying specific conditions at the time of changing power from the wide angle end to its telephone end with respect to a five-group zoom lens. SOLUTION: The lens system has five lens groups consisting of a 1st group L1 having positive refractive power, a 2nd group L2 having negative refractive power, a 3rd group L3 having positive refractive power, a 4th group L4 having negative refractive power, and 5th group L5 having positive refractive power. At the time of changing power from the wide angle end to the telephoto end, conditions D1W<D1T, D2W>D2T, D3W<D3T, D4W>D4T, 3.3<β2T/β2W<6.6, 0.18<f1/fT<0.33 are satisfied. The DiW and DiT are air intervals between the i-th and (i+1)th groups on the wide angle end and the telephoto end, the β2W, β2T are horizontal power values on the wide angle end and telephoto end of the 2nd group L2, the f1 is the focal distance of the 1st group L1, and the fT expresses the focal distance of the telephoto end of the whole system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly, to a zoom lens having a photographing angle of view of about 73 degrees at the wide-angle end, an F-number of about 3.6 to 5.9, and a zoom ratio of about 11. The present invention relates to a zoom lens having a high zoom ratio suitable for a photographic camera, a video camera, an electronic still camera, and the like having excellent optical performance.

[0002]

2. Description of the Related Art Conventionally, a photographing system such as a photographic camera or a video camera has been required to have a zoom lens having a high zoom ratio, a wide angle of view, and a high contrast and high optical performance over the entire zoom range. I have.

[0003] For example, in Japanese Patent Application Laid-Open Nos. 57-2014 and 60-39613, the positive,
A zoom lens with five lens groups of negative, positive, negative, and positive refractive power, a wide angle of view with a shooting angle of view of about 75 degrees at the wide angle end, and a zoom ratio of about 5 with a high zoom ratio. Has been proposed.
Japanese Patent Application Laid-Open No. 5-119260 has five lens groups having the same refractive power arrangement as described above, and has a wide angle of view of about 75 degrees at a wide-angle end and a zoom ratio of about 3.5 to 7 times. 2. Description of the Related Art A zoom lens having an angle of view and a high zoom ratio has been proposed. In addition, Japanese Unexamined Patent Publication No.
In Japanese Patent No. 70708, positive, negative, positive,
A zoom lens has been proposed which includes five lens groups having positive and negative refractive power, has a shooting angle of view of about 70 degrees at the wide-angle end, and has a zoom ratio of about 7.

[0004]

Generally, in a zoom lens, there is a demand for a high zoom ratio as well as a compact lens system as a whole. In order to increase the zoom ratio of the zoom lens, the refractive power of the lens unit that contributes to zooming is increased to increase the zooming effect, or the amount of movement of the lens unit that contributes to zooming is increased.

[0005] In order to achieve a high zoom ratio, it is necessary to appropriately set the moving conditions of each lens unit and the refractive power of each lens unit during zooming. If these elements are not properly set, the occurrence of various aberrations accompanying zooming will increase, and it will be difficult to obtain images of good image quality over the entire zoom range.

According to the present invention, in a five-unit zoom lens, the photographing angle of view at the wide-angle end is 73 degrees by appropriately setting the moving conditions of each lens unit mainly for zooming and the refractive power of each lens unit. SUMMARY OF THE INVENTION It is an object of the present invention to provide a zoom lens having high optical performance over the entire zoom range with a zoom ratio of about 11.

In addition, the present invention uses a rear focus and an inner focus method suitable for an auto-focus mechanism as a focus method in a five-group zoom lens, and moves each lens group to perform the refracting power and zooming of each lens group. It is an object of the present invention to provide a high-magnification zoom lens having high optical performance over the entire zoom range while shortening the overall length of the lens by appropriately setting conditions and the like.

[0008]

According to the present invention, there is provided a zoom lens comprising: (1-1) a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power in order from the object side. Group, fourth with negative refractive power
Group, and a fifth lens group having a positive refractive power. The fifth lens group has a positive refractive power. At the time of zooming from the wide-angle end to the telephoto end, the distance between the lens groups changes, and the i-th lens unit and the (i + 1) -th lens unit The air spacings at the wide-angle end and the telephoto end are DiW and DiT, respectively, the lateral magnifications at the wide-angle end and the telephoto end of the second group are β2W and β2T, the focal length of the first group is f1, and the focal length of the entire system is f1. FT focal length
D1W <D1T (1) D2W> D2T (2) D3W <D3T (3) D4W> D4T (4) 3.3 <β2T / β2W <6. 6 (5) 0.18 <f1 / fT <0.33 (6)

[0009]

1 to 3 are sectional views of a lens at a wide angle end according to Numerical Examples 1 to 3 of the present invention. FIGS. 4 and 5 are aberration diagrams of an object at infinity at the wide angle end and a close object according to Numerical Embodiment 1 of the present invention. FIGS. 6 and 7 are close to an infinite object at the telephoto end of Numerical Embodiment 1 of the present invention. 8 and 9 are aberration diagrams for an object at infinity and a close object at the wide-angle end according to Numerical Embodiment 2 of the present invention, and FIGS. 10 and 11 are telephoto ends for Numerical Embodiment 2 of the present invention. Of aberrations of an object at infinity and a close object, FIGS. 12 and 13
14A and 14B are aberration diagrams of an object at infinity and a close object at the wide-angle end according to Numerical Embodiment 3 of the present invention. FIGS. 14 and 15 show Numerical Embodiment 3 of the present invention.
FIG. 7 is an aberration diagram of an object at infinity and a close object at the telephoto end of FIG.

In the figure, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Denotes a fourth unit having a negative refractive power, L5 denotes a fifth unit having a positive refractive power, and
P denotes an aperture, which is provided in front of the third lens group. Aperture SP
Is moving integrally with the third lens unit with zooming.

In the numerical examples 1, 2 and 3 shown in FIGS. 1 to 3, when changing the magnification from the wide-angle end to the telephoto end, each lens unit is moved to the object side as indicated by an arrow. At this time, in each numerical example, the first lens unit and the second lens unit as in the conditional expressions (1) to (4) are used.
Each lens group such that the distance between the groups increases, the distance between the second and third groups decreases, the distance between the third and fourth groups increases, and the distance between the fourth and fifth groups decreases. Is moved to the object side.
Although the stop SP is moved integrally with the third lens unit, it may be moved independently.

In the present embodiment, by moving all the lens units from the first unit to the fifth unit at the time of zooming as described above, zooming is shared by a plurality of lens units in a well-balanced manner. Zooming is performed efficiently while miniaturization is achieved, and aberration correction in the entire zoom range is satisfactorily performed.

Focusing from an object at infinity to a close object is performed by moving the first unit and the second unit integrally or independently to the image plane side.

In this embodiment, in order to simplify the lens barrel structure, the first and second units are moved integrally. By adopting such a focusing method, the overall length of the lens at the wide-angle end can be made compact, and the amount of peripheral light can be easily secured as compared with focusing by the front lens feeding method.

In the present invention, each element is set so as to satisfy the conditional expressions (5) and (6).

Conditional expression (5) defines the range of the zoom ratio of the second lens unit from the wide-angle end to the telephoto end. In order to maintain good optical performance while achieving high zoom ratio and compactness of the zoom lens, each lens group must have an appropriate zoom ratio, and in particular, increase the zoom ratio by the second group. is necessary. During zooming from the wide-angle end to the telephoto end, the lateral magnification of the second unit changes with the change in the distance between the first and second units. Therefore, a large change in the lateral magnification can be given to the second lens unit by increasing the difference in the amount of extension between the first lens unit and the second lens unit during zooming, and a high zoom ratio of the zoom lens can be achieved. If the zoom ratio of the second lens unit becomes smaller than the lower limit value of conditional expression (5), the variable power sharing to other lens units becomes large in order to increase the zoom ratio of the lens.

Although the first and second lens units have a variable power distribution, the other lens units other than the second lens unit need to provide a moving space in the lens barrel in advance. or,
If the upper limit is exceeded, the amount of extension of the first lens unit due to zooming becomes very large, and the structure is burdensome.

Conditional expression (6) relates to the ratio of the focal length of the first lens unit to the focal length of the entire system at the telephoto end. The focal length of the first lens group is made relatively short and the overall length of the lens is shortened. In particular, by reducing the light beam diameter of light incident on the image side from the second lens group at the telephoto end and reducing the aperture diameter, the lens outer diameter is reduced. This is a condition for reducing. If the focal length of the first lens unit is too short below the lower limit, aberrations on the telephoto side, particularly spherical aberrations, which occur in this lens unit become extremely large, and this is mutually corrected by the second and subsequent lens units. It will be difficult to do. If the upper limit value is exceeded, in addition to the above-mentioned object of compactness, in addition to a large amount of lens movement for obtaining a desired zoom ratio, it becomes difficult to hold the lens barrel.

In order to correct various aberrations caused by the second unit having a large variable power, it is desirable that the second unit is composed of four negative lenses and one positive lens.
Specifically, the second lens unit includes, in order from the object side, a meniscus negative lens having a convex surface facing the object side, and both lens surfaces having a strong refractive power on the object side as compared with the image surface side. It is preferable to have a lens, a positive lens having both lens surfaces convex, and a negative lens having a concave surface having a stronger refractive power directed toward the object side than the image surface side.

The third lens unit is composed of a cemented lens composed of a negative lens and a positive lens, and a positive lens whose both lens surfaces are convex. Of these, it is preferable to use an aspheric lens for at least one lens surface. According to this, it is possible to reduce spherical aberration, field curvature, and coma generated in the first and second units.

The fourth unit is composed of a cemented lens in which a positive lens whose convex surface faces the image surface side and a negative lens whose both lens surfaces are concave are cemented, and the lens surfaces on the object side and the image surface side are concave. This is preferable for reducing aberration fluctuations due to zooming.

The fifth unit includes a positive lens and a negative lens,
From the viewpoint of aberration correction, it is preferable to use a cemented lens in which the lens surfaces of the object side and the image plane side are convex, and a cemented lens of a positive lens having a convex surface facing the image plane and a negative 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 or air gap,
Ni and νi are the refractive index and Abbe number of the material of the i-th lens. In the aspherical shape, the radius of curvature at the center of the lens surface is R, the optical axis direction (the traveling direction of light) is the X axis, the direction perpendicular to the optical axis is the Y axis, and A, B, C, D, E Are the aspheric coefficients, respectively.

[0024]

(Equation 1) It is assumed that The notation of “ex” is “× 1”.
0- ^X ". Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[0025]

[Outside 1]

[0026]

[Outside 2]

[0027]

[Outside 3]

[0028]

[Table 1]

[0029]

As described above, according to the present invention, in the five-unit zoom lens, the wide-angle lens can be obtained by appropriately setting the moving conditions of each lens unit mainly for zooming and the refracting power of each lens unit. It is possible to achieve a zoom lens having a high optical performance over the entire zooming range with a shooting angle of view at the end of about 73 degrees and a zoom ratio of about 11.

Further, by moving the first unit and the second unit during focusing, it is possible to achieve a zoom lens capable of obtaining good optical performance over the entire object distance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a lens at a wide-angle end according to a second numerical embodiment of the present invention.

FIG. 3 is a sectional view of a lens at a wide angle end according to Numerical Embodiment 3 of the present invention.

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

FIG. 5 is an aberration diagram of a close object at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is an aberration diagram of an object at infinity at a telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 7 is an aberration diagram of a close object at a telephoto end according to Numerical Embodiment 1 of the present invention;

FIG. 8 is an aberration diagram of an object at infinity at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an aberration diagram of a close object at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 10 is an aberration diagram of an object at infinity at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 11 is an aberration diagram of a close object at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 12 is an aberration diagram of an object at infinity at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 13 is an aberration diagram of a close object at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 14 is an aberration diagram of an object at infinity at a telephoto end according to Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram of a close object at the telephoto end according to 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 SP Aperture IP image plane d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane

Claims (4)

[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 negative refractive power, and a positive refractive power in order from the object side. The fifth lens unit has a fifth lens unit. When the magnification is changed from the wide-angle end to the telephoto end, the distance between the lens units changes. The air spacing is DiW, DiT, the lateral magnification of the second group at the wide-angle end and the telephoto end is β2W, β2T, the focal length of the first group is f1, and the focal length of the entire system at the telephoto end is f.
When T, the zoom lens satisfies the following condition: D1W <D1T D2W> D2T D3W <D3T D4W> D4T 3.3 <β2T / β2W <6.6.18 <f1 / fT <0.33 lens. 2. The zoom lens according to claim 1, wherein the first lens unit and the second lens unit are moved on an optical axis to perform focusing. 3. The second lens unit includes, in order from the object side, a meniscus-shaped negative lens having a convex surface facing the object side, and both lens surfaces having a stronger refractive power on the object side than the image surface side have a concave negative surface. 3. The zoom lens according to claim 1, further comprising a lens, a positive lens having both lens surfaces convex, and a negative lens having a concave surface having a stronger refractive power on the object side than on the image surface side. 4. The zoom lens according to claim 1, wherein said third group has at least one aspheric surface.