JP3352263B2 - 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 zoom lens, and in particular, has a photographic field angle of about 82 degrees at the wide angle end and an F-number of 2.8.
A high zoom ratio suitable for a photographic camera, a video camera, an electronic still camera, etc., having good optical performance over the entire zoom range of about 3.3 to 4.1 and a zoom ratio of about 3.3 to 4.1; The present invention relates to a wide-angle zoom lens.

[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 five-unit zoom lens composed of five lens units having positive, negative, positive, negative, and positive refractive powers in order from the object side, the photographic field angle at the wide angle end is 82 degrees. In order to maintain a high optical performance over the entire zoom range and achieve a predetermined aperture ratio while achieving a wide angle of view and a high zoom ratio of about 3 to 4, each lens group constituting a lens system It is important to appropriately set the optical constants of.

For example, in the above-described five-unit zoom lens,
Unless the conditions for moving each lens unit during zooming, the refractive power of each lens unit, and the zooming ratio and magnification of the second unit that performs zooming, are not set properly, the occurrence of various aberrations increases, and all zooming occurs. It becomes difficult to obtain images of good image quality over the range.

According to the present invention, in a five-unit zoom lens, the moving conditions of each lens unit mainly due to zooming, the refractive power of each lens unit, and the imaging magnification of the second unit are appropriately set. It is an object of the present invention to provide a zoom lens having a high optical performance over the entire zoom range with a photographing angle of view at the wide angle end of about 82 degrees and a zoom ratio of about 3 to 4, and a camera using the same.

[0007]

A zoom lens according to the present invention comprises, in order from the object side, 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. A fourth lens group having a negative refractive power and a fifth lens group having a positive refractive power, and when zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group increases. The distance between the second lens group and the third lens group is reduced, the distance between the third lens group and the fourth lens group is increased, and the distance between the fourth lens group and the fifth lens group is reduced. 0.18 <| β2W | <where the imaging magnification at the wide-angle end of the second lens group at an infinity object is β2W and the focal length of the i-th group is fi. 0.255 ‥‥‥ (1) 0.7 <f5 / | f4 | <1.2 ‥‥‥ (2) It is a symptom.

[0008]

1 to 5 are sectional views of a lens at a wide angle end according to Numerical Examples 1 to 5 of the present invention. 6 to 10 are graphs showing various aberrations of Numerical Examples 1 to 5 of the present invention. In the aberration diagrams, (A) shows the wide-angle end, and (B) shows the telephoto end.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, L4
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. IP is an image plane.

In this embodiment, upon zooming from the wide-angle end to the telephoto end, the first and second lens units are moved toward the object side as indicated by arrows.
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. I have. The stop SP is moved integrally with the third lens unit.

In this embodiment, by moving the five lens units during zooming in this way, the zooming is shared among a plurality of lens units in a well-balanced manner, so that the zooming can be performed efficiently, and especially, the intermediate zoom. The aberration correction in the region is performed well.

In this embodiment, as described above, the refracting power of the five lens units and the conditions for moving each of the lens units upon zooming are set, and the imaging magnification β for the infinity object at the wide-angle end of the second unit.
2W or the ratio of the focal lengths of the fourth and fifth lens units, f5 / | f4
Is satisfied so as to satisfy the conditional expressions (1) and (2).

Next, the technical meaning of the conditional expressions (1) and (2) will be described. Conditional expression (1) defines the imaging magnification of the second lens unit at infinity at the wide-angle end. Exceeding the lower limit means that the focal length of the first lens unit becomes too long. It is difficult to shorten the overall length. Exceeding the upper limit means that the focal length of the first lens unit becomes too short, which is advantageous for shortening the overall length of the lens, but makes aberration correction difficult and disadvantageous for widening the angle of view.

Conditional expression (2) defines the ratio of the focal length of the fifth lens group to the focal length of the fourth lens group, and is intended mainly to achieve a wide angle and to secure a predetermined back focus. If the focal length of the fifth lens unit is shorter than the lower limit and the fifth lens unit is short, it is advantageous for widening the angle and securing the back focus. If the focal length of the fifth lens unit becomes longer than the lower limit, it is advantageous for aberration correction, but it becomes difficult to widen the angle and make it compact.

In the present invention, with the above-described lens configuration, the photographic field angle at the wide-angle end is 82 degrees, and a wide field of view has a zoom ratio of about 3 to 4 and an F number of about 2.8 to 3.6. A zoom lens having good optical performance over a range is obtained.

Further, in the present invention, focusing is performed by moving the second unit, thereby preventing an increase in the lens outer diameter of the first unit as compared with the case where focusing is performed by the first unit. The shortest possible shooting distance has been reduced. Also, by using an aspherical surface having a shape in which the positive refractive power becomes weaker from the center of the lens toward the periphery of the lens in the fifth lens unit, mainly spherical aberration, astigmatism, and curvature of field are corrected in a well-balanced manner. I have. In particular, high-order field curvature on the wide-angle side is favorably corrected.

The zoom lens according to the present invention can be achieved by satisfying the above-mentioned conditions. However, it is possible to satisfactorily correct aberration fluctuations when widening the angle of view and increasing the zoom ratio, thereby achieving high optical performance. To achieve this, it is preferable to satisfy at least one of the following conditions.

(1-1) The first group includes a cemented lens formed by joining a negative meniscus lens having a convex surface facing the object side and a positive lens, and a positive meniscus lens having a convex surface facing the object side. The second group includes a meniscus negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, a positive lens having both convex lens surfaces, and a negative lens having a concave surface facing the object side. Is to have. As a result, the outer diameter of the lens of the first group is reduced to achieve compactness,
In addition, various aberrations are satisfactorily corrected over the entire zoom range while widening the angle of view at the wide angle end.

(1-2) The third group is a cemented lens in which a negative meniscus lens having a convex surface facing the object side and a positive lens having both convex lens surfaces are joined, and both positive lens surfaces are convex. That is, it has a lens. This allows
While ensuring a predetermined zoom ratio, the occurrence of various aberrations due to zooming is reduced. In particular, spherical aberration is favorably corrected over the entire zoom range.

(1-3) The fifth lens unit includes two positive lenses each having a convex surface on both lens surfaces and a negative lens having a concave surface facing the object side. As a result, variations in various aberrations such as spherical aberration due to zooming are corrected in a well-balanced manner.

[0021]

[0022]

( 1-4 ) When the combined focal length of the first lens unit and the second lens unit at the wide-angle end is f12w, and the focal length of the entire system at the wide-angle end is fw, 5.8 <f1 / | f2 | <7 ‥‥‥ ( 3 ) 1.4 <f5 / | f12w | <2.5 ‥‥‥ ( 4 ) 0.8 <f3 / fw <1.1 ‥‥‥ ( 5 ) 1.0 <f5 / | f4 | <1.1 ‥‥‥ ( 6 ).

Conditional expression ( 3 ) defines the ratio of the focal length of the first lens unit to the focal length of the second lens unit, and mainly reduces the lens outer diameter of the third lens unit at the telephoto end and achieves high zooming. When the positive refractive power of the first lens unit is increased beyond the lower limit, aberrations on the telephoto side, particularly spherical aberration, generated in the first lens unit are increased, and this is corrected by other lens units in a well-balanced manner. It becomes difficult to do. If the positive refractive power of the first lens unit is weakened beyond the upper limit, it becomes difficult to reduce the size of the first lens unit.

Conditional expression ( 4 ) defines the ratio of the focal length of the fifth lens unit to the composite focal length of the first lens unit and the second lens unit at infinity at the wide-angle end. It is for achieving compactness and high performance while securing
If the positive refractive power of the fifth lens unit is increased beyond the lower limit value, it is advantageous for securing the back focus. However, various aberrations generated in the fifth lens unit, particularly the curvature of field, increase, and this is reduced to other lens units. And it is difficult to make a good correction. If the positive refractive power of the fifth lens unit is weakened beyond the upper limit, it becomes difficult to secure the back focus and to make the lens compact.

Conditional expression ( 5 ) defines the ratio of the focal length of the third lens unit to the focal length of the entire system at the wide-angle end.
If the positive refractive power of the third lens unit is increased beyond the lower limit value, it is advantageous for compactness. However, various aberrations, particularly spherical aberration, generated in the third lens unit become large, and this is well balanced by other lens units. It becomes difficult to correct. If the positive refractive power of the third lens unit is weakened beyond the upper limit, the effect of multi-grouping is reduced, and the overall length of the lens and the outer diameter of the lens are increased.

The conditional expression ( 6 ) further specifies the numerical range of the conditional expression (2), whereby a zoom lens having a photographic field angle of about 82 degrees at the wide-angle end and a zoom ratio of about 4 can be easily realized. It has gained.

( 1-5 ) When the imaging magnification of the second lens group at the telephoto end at infinity is β2T, the following condition is satisfied: | β2T | <1 ( 7 )

When the zooming from the wide-angle end to the telephoto end is satisfied by satisfying the condition of the conditional expression ( 7 ), focusing from an object at infinity to a close object is performed because the imaging magnification of the second lens unit does not fall within the same magnification. In this case, the second lens unit is always moved in the same direction, thereby enabling focusing in the second lens unit.

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-described conditional expressions and various numerical values in the numerical examples.
Shown in The aspherical shape 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, and A,
When B, C, D, and E are aspheric coefficients, respectively,

[0031]

(Equation 1) It is represented by the following equation. Note that "e-0x" represents "10- ^x ".

[0032]

[Outside 1]

[0033]

[Outside 2]

[0034]

[Outside 3]

[0035]

[Outside 4]

[0036]

[Outside 5]

[0037]

[Table 1]

[0038]

As described above, according to the present invention, in the five-unit zoom lens, the moving condition of each lens unit mainly due to zooming, the refractive power of each lens unit, and the imaging magnification of the second unit By appropriately setting the zoom angle, etc., it is possible to achieve a zoom lens having a wide angle of view of about 82 degrees at the wide angle end, a wide zoom range of about 3 to 4 and a high optical performance over the entire screen. .

[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 a third numerical embodiment of the present invention;

FIG. 4 is a sectional view of a lens at a wide-angle end according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a lens at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 6 is an aberration diagram of a numerical example 1 of the present invention.

FIG. 7 is an aberration diagram of a numerical example 2 of the present invention.

FIG. 8 is an aberration diagram of a numerical example 3 of the present invention.

FIG. 9 is an aberration diagram of a numerical example 4 of the present invention.

FIG. 10 is an aberration diagram of a numerical example 5 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit L5 Fifth lens unit SP Aperture F Image plane d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-230285 (JP, A) JP-A-5-119260 (JP, A) JP-A-1-154014 (JP, A) JP-A-63- 266415 (JP, A) JP-A-57-2014 (JP, A) JP-A-57-164710 (JP, A) JP-A-60-39613 (JP, A) JP-A-8-94932 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (8)

(57) [Claims] A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, in order from the object side; Fifth of positive refractive power
With a lens group, when zooming from the wide-angle end to the telephoto end,
The distance between the first lens group and the second lens group increases,
A zoom lens that moves so that the distance between the lens group and the third lens group decreases, the distance between the third lens group and the fourth lens group increases, and the distance between the fourth lens group and the fifth lens group decreases. 0.18 <| β2W | <0.255 0 where β2W is the imaging magnification when the object at infinity is at the wide-angle end of the second lens unit, and fi is the focal length of the i-th unit. 0.7 <f5 / | f4 | <1.2. 2. When the combined focal length of the first lens unit and the second lens unit at the wide-angle end is f12w, and the focal length of the entire system at the wide-angle end is fw, 5.8 <f1 / | f2 | <71. 4 <f5 / | f12w | <2.5 0.8 <f3 / fw <1.1 1.0 <f5 / | f4 | <1.1 2 zoom lens. 3. The first lens group includes a cemented lens in which a negative meniscus lens having a convex surface facing the object side and a positive lens are joined, and a positive meniscus lens having a convex surface facing the object side. The second lens group includes a meniscus negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, a positive lens having both lens surfaces convex, and a negative lens having a concave surface facing the object side. The zoom lens according to claim 1, wherein Wherein said third lens group cemented lens negative lens and both lens surfaces of the meniscus form convex toward the object side is joined to the positive lens convex, and a positive lens of both lens surfaces is convex The zoom lens according to claim 1, further comprising: a zoom lens. 5. The zoom lens according to claim 1, wherein said fifth lens group includes two positive lenses each having a convex surface on both lens surfaces and a negative lens having a concave surface facing the object side. 6. When was .beta.2T imaging magnification when the infinite object at the telephoto end of the second lens group | .beta.2T | <zoom lens according to claim 1, characterized by satisfying one condition:. 7. The zoom lens according to claim 1, wherein the focusing is performed by moving said second lens group. 8. A camera comprising the zoom lens according to claim 1.