JP4445603B2 - Telephoto zoom lens - Google Patents

Description

【００１７】

【００１８】

【００１９】
【発明の効果】
本発明によれば、物体側より順に正、負、正からなる３群ズーム方式で、ズーム比が３倍程度の高性能コンパクトな望遠ズームが従来のズームより４乃至５枚少ない構成枚数で大きなコストダウンが可能である。
【図面の簡単な説明】
【図１】本発明の数値実施例１のレンズ構成図である。
【図２】本発明の数値実施例２のレンズ構成図である。
【図３】本発明の数値実施例３のレンズ構成図である。
【図４】本発明の数値実施例１の広角端の収差図である。
【図５】本発明の数値実施例１の望遠端の収差図である。
【図６】本発明の数値実施例２の広角端の収差図である。
【図７】本発明の数値実施例２の望遠端の収差図である。
【図８】本発明の数値実施例３の広角端の収差図である。
【図９】本発明の数値実施例３の望遠端の収差図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a compact telephoto zoom lens having a zoom ratio of about 3 times used for a single-lens reflex camera, a digital camera, or the like.
[0002]
[Prior art]
Conventionally, a telephoto zoom lens having a zoom ratio of about 3 times, such as a single-lens reflex camera or a digital camera, has many four-group zoom lenses as disclosed in JP-A-60-1114814, and has a positive refractive power. About 15 in total: 3 for 1 lens group, 3 for 2nd lens group for negative refractive power, 2 for 3rd lens group for positive refractive power, 7 for 4th lens group for positive refractive power It was often composed of.
[0003]
[Problems to be solved by the invention]
As disclosed in Japanese Patent Laid-Open No. 60-1114814, a four-group zoom lens composed of about 15 lenses is used for multi-group zoom when zooming from the wide-angle end to the telephoto end. However, there are problems such as an increase in movable parts, a complicated barrel structure, poor productivity, and high cost.
[0004]
Accordingly, an object of the present invention is to provide a high-performance and compact zoom lens while the zoom ratio is about 3 times and the number of components is as small as ten.
[0005]
In order to design a high-performance and compact zoom lens with a small number of components, it is necessary to have an appropriate power arrangement and lens configuration for each group. Therefore, in the present invention, the first group including the negative lens and the positive lens in order from the object side, the second group of negative refractive power including the negative single lens and the cemented lens, and the third group of positive refractive power are the front part. consists rear, front is a cemented lens and a single lens having a positive refractive power, the rear consists arrangement two negative meniscus lens having a concave surface directed toward the object side are arranged with a large air gap, the telephoto end from the wide-angle end In zooming, the first and third lens groups are moved in the object direction while increasing the air gap between the first lens group and the second lens group and reducing the gap between the second lens group and the third lens group. (1) 0.65 <| fII / fw | <0.75
(2) 0.77 <| fIII / fw | <0.80
(3) 1.00 <| fIII / fII | <1.20
(4) 2.60 <| fI / fIII | <3.20
Conditions were given.
However,
fw: focal length at the wide angle end fI: focal length of the first lens group fII: focal length of the second lens group fIII: focal length of the third lens group
[0006]
Also, the third lens group with a large degree of freedom in lens configuration is arranged with a large air gap between the cemented lens and the single lens with positive refractive power at the front, and two negative meniscus lenses with the concave surface facing the object side at the rear. The focal length of the negative lens is (5) 1.60 <| f9 / fIII | <2.00
(6) 1.60 <| f10 / fIII | <2.0
It was possible to make it high performance and compact.
However,
f9: focal length of the object-side negative lens at the rear of the third lens group f10: focal length of the image-side negative lens at the rear of the third lens group.
[0007]
Conditional expressions (1) to (4) define the focal lengths of the three groups. Conditional expression (1) is a condition for the focal length of the second group that greatly contributes to zooming as a variator. If the lower limit is exceeded, the power of the second lens becomes strongly negative, which is effective in reducing the size of the lens system, but it is not preferable because the Petzpearl sum becomes negative and the field curvature becomes overcorrected. If the upper limit is exceeded, the negative power of the second lens group becomes weak and the absolute value of the radius of curvature of each surface increases, so that aberrations due to the second group can be corrected well, but the amount of movement for variable magnification on the other hand The negative side of the increase in size and interaction with other groups will become conspicuous.
[0008]
Conditional expression (2) defines the power of the third lens group, but the third lens group has not only the main role as a master lens, but also a function of a compensator and a zooming function for reducing zooming aberration fluctuations. The power setting is important. If the lower limit is exceeded, the power of the third lens group becomes strong and coma increases in the entire zoom range, and it is difficult to correct spherical aberration, especially on the wide side. Exceeding the upper limit is not preferable because the power of the third lens group becomes weak, which increases the amount of movement and increases the size of the system.
[0009]
Conditional expression (3) is a condition regarding the refractive power ratio of the third lens group and the second lens group. In the present invention, a good aberration correction is realized over the entire zoom range by balancing the refractive power ratio between the second group and the third group with zooming from wide angle to telephoto. If the upper limit of conditional expression (3) is exceeded, the refractive power of the second group becomes strong, and the back focus on the telescope becomes large, which is not preferable for downsizing. If the lower limit is exceeded, the refractive power of the third group becomes strong, making it difficult to correct aberration fluctuations off-axis during zooming, and hindering performance improvement.
[0010]
Conditional expression (4) defines the relationship between the positive powers of the first group and the third group with the second group negative power interposed therebetween, and is a condition that guarantees good correction of coma and distortion. If the power of the first lens group exceeds the lower limit and becomes relatively stronger than the third lens group, it is not preferable for correcting the spherical aberration on the telephoto side, and conversely if it exceeds the upper limit, it is not preferable for spherical aberration on the wide angle side. Further, when the upper limit is exceeded, performance deterioration due to an increase in the feeding amount at a short distance, difficulty in designing the lens barrel, and the like occur.
[0011]
Conditional expressions (5) and (6) are power specifications of the two negative lenses constituting the rear part of the third group. Unlike the first and second groups, where the configuration is limited by a thin lens, the third group must be configured with a large overall lens length. Therefore, the configuration of the third group is important because it is greatly related to lens performance and compactness. In the present invention, high performance and compactness are realized by a configuration in which the third lens unit has a positive power front portion and two meniscus negative lenses having a concave surface facing the object side with a large air gap. Conditional expressions (5) and (6) indicate that the two lens powers are substantially equal. However, if the lower limit is exceeded, the positive power of the front part constituting the third group becomes stronger and aberrations due to zooming. This is not preferable because of a large fluctuation. If the upper limit is exceeded, the respective powers of the components of the third group become loose, and it is inevitable that the system becomes large, and this is not preferable for correcting astigmatism. In addition, it is a condition that the two negative lenses have a concave surface facing the object side to correct the off-axis performance satisfactorily. If the balance between the two powers is lost, the coma aberration deteriorates, which is not preferable.
[0012]
【Example】
Numerical Example 1, Numerical Example 2, and Numerical Example 3 of the high variable magnification zoom lens of the present invention are shown below.
[0013]
1 is a lens configuration diagram of Numerical Example 1, FIG. 2 is a lens configuration diagram of Numerical Example 2, and FIG. 3 is a lens configuration diagram of Numerical Example 3. 1 to 3, I is a first lens group having a positive refractive power, II is a second lens group having a negative refractive power, and III is a third lens group having a positive refractive power. 4 is an aberration diagram at the wide-angle end of Numerical Example 1 of the present invention, FIG. 5 is an aberration diagram at the telephoto end of Numerical Example 1 of the present invention, and FIG. 6 is an aberration diagram at the wide-angle end of Numerical Example 2 of the present invention. 7 is an aberration diagram at the telephoto end of Numerical Example 2 of the present invention, FIG. 8 is an aberration diagram at the wide-angle end of Numerical Example 3 of the present invention, and FIG. 9 is an aberration at the telephoto end of Numerical Example 3 of the present invention. FIG.
[0014]
As shown in the present embodiment, a telephoto lens having a zoom ratio of about 3 and good aberration correction can be realized with a small number of components without using an aspherical surface.
[0015]
In Numerical Examples 1 to 3, f is a focal length, Fno is an F number, ω is a half angle of view, ri is a radius of curvature of the i-th lens surface in order from the object side, and di is an i-th in order from the object side. The th lens thickness, the air gap, and ni and vi are respectively the i th lens refractive index and the Abbe number in order from the object side.
[0016]

[0017]

[0018]

[0019]
【The invention's effect】
According to the present invention, a high-performance compact telephoto zoom with a zoom ratio of about 3 times is larger with the number of constituent elements 4 to 5 less than the conventional zoom in the three-group zoom system in order from the object side. Cost reduction is possible.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram of Numerical Example 1 of the present invention.
FIG. 2 is a lens configuration diagram of Numerical Example 2 of the present invention.
FIG. 3 is a lens configuration diagram of Numerical Example 3 of the present invention.
FIG. 4 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.
FIG. 5 is an aberration diagram at the telephoto end according to Numerical Example 1 of the present invention.
FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.
FIG. 7 is an aberration diagram at the telephoto end according to Numerical Example 2 of the present invention.
FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.
FIG. 9 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

Claims (1)

A second lens unit of negative refractive power for the first unit having a positive refractive power composed of two negative lenses and a positive lens in order from the object side, a negative single lens and a cemented lens, the third lens unit of positive refractive power becomes, the third group consists of front and rear, front is a cemented lens and a single lens having a positive refractive power, the rear is two negative meniscus lens having a concave surface directed toward the object side are arranged in a large air gap In the zooming from the wide-angle end to the telephoto end, the air gap between the first lens group and the second lens group is enlarged, and the gap between the second lens group and the third lens group is reduced. A telephoto zoom lens characterized in that the first and third lens units move in the object direction and satisfy the following conditions.
(1) 0.65 <| fII / fw | <0.75
(2) 0.77 <| fIII / fw | <0.80
(3) 1.00 <| fIII / fII | <1.20
(4) 2.60 <| fI / fIII | <3.20
(5) 1.60 <| f9 / fIII | <2.00
(6) 1.60 <| f10 / fIII | <2.0
However,
fw: Focal length fI at the wide angle end: Focal length fII of the first lens group: Focal length fIII of the second lens group: Focal length f3 of the third lens group f9: Focal length f10 of the object side negative lens at the rear of the third lens group : The focal length of the image-side negative lens at the rear of the third lens unit.

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