JP2002350725A - Compact zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a compact zoom lens whose angle of view at a wide end is set to a wide angle of about 70 deg. and whose zoom ratio is set to about 2.5. SOLUTION: This zoom lens is equipped with a front group lens 10 constituted of 1st to 4th lenses and having positive power, and a rear group lens 20 constituted of 5th to 7th lenses and having negative power, equipped with plastic aspherical lenses as the 1st lens 11 and the 5th lens 21, and constituted to satisfy conditional expressions -2.8<f1 /f12 <-2.1, 1.3<fw/f1 <1.6, -1.1<f2 /f1 <-0.8, nd>1.80 and νd>37.3 when it is assumed that the respective focal distances of the front group lens 10, the rear group lens 20 and the 2nd lens 12 are f1 , f2 and f12 , the focal distance at the wide end is (fw), the refractive index of the 2nd lens 12 is (nd) and an Abbe number is νd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small zoom lens provided in a compact camera or the like.

[0002]

2. Description of the Related Art As a small-sized zoom lens, a lens system in which the number of lenses is reduced and the number of lenses is reduced to two has been proposed. (JP-A-10-232350, JP-A-2000-241703, etc.)

Further, this type of small zoom lens is provided with an aspherical lens made of plastic to reduce the cost.

[0004]

The above-mentioned conventional small zoom lens is advantageous for miniaturization and cost reduction. However, the angle of view at the wide end is as narrow as about 60 °, so that it is practically impossible. Not always preferred.

A small zoom lens having a wide angle of view of about 70 ° at the wide end has been proposed. (JP-A-07-2
34363) However, this small zoom lens is costly because a glass mold is used as the aspherical lens.

Specifically, an aspherical glass mold lens is several times to several tens times more expensive than a plastic mold lens, so that the cost of the zoom lens increases.

In view of the above circumstances, the present invention provides an inexpensive small zoom lens having a two-group lens configuration and having a lens angle of view of about 70 ° at the wide end and a zoom ratio of about 2.5 times. The purpose is to:

[0008]

According to the present invention, a first lens having a positive or negative power having a convex surface on the object side, a second lens having a biconcave surface, and a third lens having a biconvex surface are provided. , A fourth lens is arranged in order from the object side, and at least one fifth lens of a front lens having a positive power as a whole and a positive or negative power having a concave surface on the object side. A sixth lens of negative power having a concave side, a rear group lens having a configuration having negative power as a whole, and the first lens and the fifth lens are it constitutes at least one surface as a plastic lens having an aspherical, the focal length f ₂ of the focal length f _1, the rear lens of the front lens _group, and a focal length fw of the wide end, the second lens has a focal length f ₁₂ , Refractive index nd, Abbe number νd _{-2.8 <f 1 / f 12 <} -2.1 1.3 <fw / f 1 <1.6 -1.1 <f 2 / f 1 <-0.8 nd> 1.80 νd> 37 A small-sized zoom lens characterized by having a configuration satisfying the following condition is proposed.

[0009]

The compact zoom lens constructed as described above has a two-group lens construction by reducing the number of lenses.
By satisfying the above-described conditional expressions, it is possible to obtain a lens performance with an angle of view at the wide end of about 70 °, a zoom ratio of about 2.5 times, and a plastic lens. Since a spherical lens is provided, a small zoom lens that is advantageous in reducing costs is provided.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an optical system diagram of a small zoom lens shown as a first embodiment.
Reference numeral 20 denotes a rear group lens, and reference numeral 30 denotes an aperture. This optical system indicates the lens position at the wide end.

The front lens group 10 includes a first lens 11 having a positive or negative power having a convex surface facing the object side, a second lens 12 having a biconcave surface, a third lens 13 having a biconvex surface, and a fourth lens having a biconvex surface. 14 is a lens system arranged in order from the object side.

The first lens 11 of the front lens group 10 is
A plastic aspheric lens having an aspherical object side surface, and a second lens 12 and a third lens 13
Is formed as a laminated lens.

Further, the front lens group 10 described above, first to fourth lenses of the lens system overall positive power - formed having a focal length that are set to be f _1.

The second lens 12 of the front lens group 10 is made of glass having a refractive index nd and an Abbe number νd.
There as a lens focal length _{f 12.}

That is, the front lens group 10 has a relationship of −2.8 <f ₁ / f ₁₂ <−2.1 (1) nd> 1.80... .. (2) νd> 37.3...... (3)

On the other hand, the rear lens group 20 includes a fifth lens 21 having a concave surface facing the object side, a sixth lens 22 having a concave surface facing the object side, and a seventh lens 22 having a concave surface facing the object side. This is a lens system in which the lenses 23 are arranged in order from the object side.

The fifth lens 21 of the rear group lens 20 is
And the object side surface aspheric and the plastic aspherical lens, also the rear unit lens 20 is formed such that the focal length becomes f _2.

Furthermore, small's constructed as described above - zoom lens, the focal length _{f 1} of the focal length fw and the front lens group 10 of the wide _{end, 1.3 <fw / f 1 <} 1.6 ......... Satisfies the conditional expression (4) and the focal length f of the front lens group 10
₁ and the focal length _{f 2} of the rear lens group 20 has a configuration which satisfies the conditional expression _{-1.1 <f 2 / f 1 <} -0.8 .................. (5).

In the above-mentioned small zoom lens, when zooming from the wide side to the telephoto side, the front group lens 10 and the rear group lens 20 move to the subject side and the front group lens 1
The focal length of the lens system is changed while reducing the distance between 0 and the optical axis of the rear lens group 20.

The stop 30 provided in the air space between the front lens group 10 and the rear lens group 20 moves integrally with the front lens group 10.

With the above arrangement, a small zoom lens having a zoom ratio of about 2.5 times is obtained, and by satisfying the conditional expressions (1) to (5), the image at the wide end is obtained. Since a wide angle of view with an angle of 70 ° can be obtained, and the first lens 11 and the fifth lens 21 are plastic aspheric lenses, a small zoom lens suitable for cost reduction can be obtained.

When the value is below the lower limit value of the conditional expression (1), the power of the second lens 12 is too strong to make it difficult to correct aberrations.
(The distance between the seventh lens 23 and the image plane) becomes small, and the lens diameter of the seventh lens 23 of the rear group lens 20 becomes large.

Next, regarding the small zoom lens according to the first embodiment, the radius of curvature ri, interval (thickness of lens, lens interval) di, refractive index ni, Abbe number ν of each lens are described.
A first embodiment in which i is specifically determined and executed will be described. The surface numbers indicate the respective surfaces of the small zoom lens shown in FIG.
Is r ₁ to r ₁₄ , and di is d ₁ to d ₁₄ .

[0024]

As can be seen from the lens configuration data,
Distance _{d 8} Gaz between the diaphragm 30 fifth lens 21 - vary from 7.026 to 1.200 by timing, also,
Seventh lens 23 is moved in the range of _d 14 = 5.629 to 37.084.

Also, the first lens 11 and the fifth lens 21
The aspherical surface is formed according to the following equation. Z = ch²/ [1+ ｛1- (1 + k) c
²h²｝^1/2] + Ah⁴ + Bh⁶+ Ch⁸+ Dh¹⁰

FIGS. 2 and 3 show the spherical aberration, astigmatism, distortion, and chromatic aberration of magnification obtained by the small zoom lens of Example 1 described above. In this figure, g indicates the characteristic at each wavelength of 435.800 nm, c indicates the characteristic at each wavelength of 656.300 nm. Each is shown.

FIG. 4 is a perspective view of a small zoom shown in the second embodiment.
FIG. 2 is an optical system diagram of a lens. In the small zoom lens according to this embodiment, the third lens 13 and the fourth lens 14 of the front lens group 10 are brought into contact with each other, and the rear lens group 20 includes the fifth lens 41 and the sixth lens 42. It has a single lens configuration. Otherwise, the lens is the same as the first embodiment shown in FIG. The first lens 11 and the fifth lens 41 are plastic aspheric lenses.

Next, regarding the small zoom lens according to the second embodiment, the radius of curvature ri, interval di,
Second Embodiment A description will be given of a second embodiment in which the refractive index ni and the Abbe number νi are specifically determined and implemented.

[0030]

FIGS. 5 and 6 show spherical aberration, astigmatism, distortion, and the like obtained by the small zoom lens according to the second embodiment.
The chromatic aberration of magnification is shown.

FIG. 7 shows a small zoom lens shown as the third embodiment.
FIG. 2 is an optical system diagram of a lens. The small zoom lens according to this embodiment has a configuration in which the lens diameter of the front lens group 10 is reduced.
It has the same configuration as the embodiment. Also in the present embodiment, the first lens 11 and the fifth lens 41 are plastic aspheric lenses.

Next, regarding the small zoom lens according to the third embodiment, the radius of curvature ri of each lens, the distance di,
Third Embodiment A description will be given of a third embodiment in which the refractive index ni and the Abbe number νi are specifically determined.

[0034]

FIGS. 8 and 9 show the spherical aberration, astigmatism, distortion and chromatic aberration of magnification obtained by the small zoom lens of the third embodiment.

[0036]

As described above, the compact zoom lens according to the present invention has a two-group lens structure with a reduced number of lenses, so that it is suitable for miniaturization and satisfies each conditional expression. As a result, the angle of view at the wide end can be made as wide as about 70 °, a lens performance of about 2.5 times the zoom ratio can be obtained, and a plastic aspherical lens is provided, which reduces costs. A small zoom lens that is advantageous for cost reduction.

[Brief description of the drawings]

FIG. 1 is an optical system diagram of a small zoom lens shown as a first embodiment.

FIG. 2 is a characteristic diagram showing wide aberrations obtained by Example 1 in which the first embodiment is performed.

FIG. 3 is a characteristic diagram similar to FIG. 2, showing each aberration of telephoto.

FIG. 4 is an optical system diagram of a small zoom lens shown as a second embodiment.

FIG. 5 is a characteristic diagram showing wide aberrations obtained by Example 2 in which the second embodiment is performed.

6 is a characteristic diagram similar to FIG. 5, showing each aberration of telephoto.

FIG. 7 is an optical system diagram of a small zoom lens shown as a third embodiment.

FIG. 8 is a characteristic diagram showing wide aberrations obtained by Example 3 in which the third embodiment is performed.

FIG. 9 is a characteristic diagram similar to FIG. 8, showing each aberration of telephoto.

[Explanation of symbols]

 Reference Signs List 10 front group lens 11 first lens 12 second lens 13 third lens 14 fourth lens 20 rear group lens 21 fifth lens 22 sixth lens 23 seventh lens 30 aperture

Continued on the front page F term (reference) 2H087 KA01 PA05 PA06 PA18 PB06 PB07 QA02 QA07 QA12 QA17 QA22 QA25 QA37 QA41 QA45 QA46 RA05 RA12 RA13 RA36 SA06 SA10 SA62 SA63 SB05 SB13 SB14 UA01

Claims (1)

[Claims] 1. A positive or negative power having a convex surface on the object side.
A first lens, a bi-concave second lens, and a bi-convex third and fourth lens arranged in this order from the object side, and a front lens group having a positive power as a whole; At least one fifth lens having positive or negative power, and the sixth lens having negative power having a concave surface on the object side.
A first lens and a fifth lens, wherein the first lens and the fifth lens are plastic lenses having at least one aspherical surface. The focal length f ₁ of the front lens group, the focal length f ₂ of the rear lens group, and the focal length fw at the wide end. The focal length f ₁₂ , the refractive index nd, and the Abbe number νd of the second lens are −2. _{.8 <f 1 / f 12 <} -2.1 1.3 <fw / f 1 <1.6 -1.1 <f 2 / f 1 <-0.8 nd> 1.80 νd> 37.3 A small-sized zoom lens characterized by having a configuration satisfying the following.