JPH1184230A - Compact wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle lend small in size, light in weight, low in cost and also compensative in various aberrations with simple constitution such as four groups and five lenses. SOLUTION: This lens is composed of four groups and five lenses, that is, a 1st lens 1 having negative refractive power, a 2nd lens 2 having positive refractive power, a 3rd lens 3 having the negative refractive power, a 4th lens 4 having a joining part r7 with the 3rd lend 3 and having the positive refractive power and a 5th lens 5 having the positive refractive power and having an aspherical surface where the positive refractive power is weaker and weaker toward a periphery part at least as one surface in order from an object side; and satisfies following conditions defined by (1) to (3). (1) 0.7|r6|<|r8|<1.3|r6|, (2) ν1<ν2, ν3<ν4, ν5>50, (3) |f1,2|>2f3, 4, 5. Provided that r6 is the radius of curvature of the surface of the 3rd lens on the object side, r8 is the radius of curvature of the surface of the 4th lens on an image surface side, νi is the Abbe number of the i-th from the object side, f1, 2 is the synthetic focal distance of the 1st and the 2nd lenses 1 and 2, and f3, 4, 5 is the synthetic focal distance of the 3rd, the 4th and the 5th lenses 3, 4 and 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact wide-angle lens, and more particularly to an electronic still camera capable of obtaining a high resolution within a wide angle of view and having a small size with a simple lens structure of four groups and five lenses. The present invention relates to a high-resolution, high-performance small-sized wide-angle lens suitable for a camera.

[0002]

2. Description of the Related Art Cameras having image pickup means in place of conventional silver halide films have become widespread, for example, as surveillance cameras and other cameras for capturing moving images. Since these surveillance cameras and the like are used for moving image shooting and have a small number of pixels, no particular high performance is required. However, recently, electronic still cameras have become widespread as a form of still image data acquisition means for personal computers, and very high-density imaging means with a large number of pixels are used to support high-resolution displays. As a lens to be used, a lens having sufficient brightness and excellent optical performance while having a small and simple lens configuration has been demanded.

[0003]

However, it is difficult to obtain a lens that satisfies sufficient brightness and excellent optical performance while achieving downsizing, weight reduction, and cost reduction with a simple lens configuration. is there.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and has a simple lens structure that can be reduced in size, weight, and cost while having an F-number of 2 or less. It is an object of the present invention to obtain a small and wide-angle lens having excellent optical performance, having a practically sufficient brightness of about 0.0 to 3.2 and correcting various aberrations. 2. The compact wide-angle lens according to claim 1, wherein, in order from the object side, a first lens 1 having a negative refractive power and a second lens 2 having a positive refractive power.
And a third lens 3 having a negative refractive power, and the third lens 3
Fourth lens 4 having a junction r7 with a positive refractive power
And a fifth group 5 of five lenses 5 having a positive refractive power and at least one surface formed into an aspheric surface having a shape in which the positive refractive power becomes weaker toward the periphery. )
To (3) are satisfied. (1) 0.7 | r6 | <| r8 | <1.3 | r6 | (2) ν1 <ν2, ν3 <ν4, ν5> 50 (3) | f1, |> 2f3,4,5 r6: radius of curvature of the object-side surface of the third lens r8: radius of curvature of the image-side surface of the fourth lens νi: Abbe number of the i-th lens from the object side f1, 2: first lens and second lens F3,4,5: composite focal length of the third, fourth and fifth lenses

According to a second aspect of the present invention, there is provided a small-sized and wide-angle lens according to the first aspect of the present invention, wherein at least one resin lens is included in a lens system.
Further, a small wide-angle lens according to claim 3 is characterized in that the resin lens is at least a fifth lens based on claim 2.

According to the first aspect of the present invention, the third lens and the fourth lens are formed as cemented lenses in accordance with the condition defined in the above (2), so that chromatic aberration which greatly affects high resolution can be satisfactorily corrected. And facilitates lens processing. When this cemented lens is replaced with a single lens, it is necessary to make the Abbe number very large. However, glass that achieves the same performance as this cemented lens is extremely unusual and does not generally exist. It becomes difficult to sufficiently correct chromatic aberration, and it is difficult to achieve high resolution. In addition, when a single lens is used, the curvature of both surfaces of the lens becomes a very close value. As a result, automatic centering cannot be performed in manufacturing, and processing becomes extremely difficult.

Further, by forming one surface of the fifth lens as an aspheric surface having a shape in which the positive refractive power becomes weaker toward the peripheral portion, various aberrations are corrected well. When this lens is formed of a spherical lens, about two more lenses are required to obtain the same aberration correction, and it is difficult to achieve a reduction in size, weight, and cost.

The condition specified in (1) is a condition relating to spherical aberration and coma. If the condition deviates from the condition specified in (1), it becomes difficult to correct spherical aberration and coma.

The condition specified in (2) relates to correction of chromatic aberration, and if this condition is not satisfied, it becomes difficult to correct chromatic aberration.

The condition specified in (3) is a condition relating to distortion and back focus. When the combined focal length of the first lens and the second lens is a negative value, if the condition deviates from the condition defined in (3), the distortion becomes large, and it becomes difficult to correct the distortion. If the combined focal length of the first lens and the second lens deviates from the condition when the value is a positive value, the back focus becomes extremely short, and it becomes difficult to secure a space for inserting a quartz plate or the like.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described with reference to FIG.
A first lens 1 having a negative refractive power, a second lens 2 having a positive refractive power, a third lens 3 having a negative refractive power,
A fourth lens 4 having a junction r7 with the third lens 3 and having a positive refracting power, and a shape having a positive refracting power and having a positive refracting power weaker toward at least one surface toward the peripheral portion. The fifth lens 5 has an aspherical surface and is composed of five elements in four groups, and satisfies the conditions defined in the above (1) to (3). In FIG. 1, r5 denotes an aperture, and 5 denotes a protection member such as a quartz plate.

[0012]

Next, concrete numerical examples will be shown. Table 1 shows a specific first numerical example of the present invention, and FIG. 1 shows an optical axis sectional view of the example shown in Table 1. In the figure, ri (i is 1 to 12) is i from the object side.
In the table, ri indicates the radius of curvature of the surface. In the table, di is i from the object side.
The n-th optical axis upper surface interval, ni indicates the refractive index of the i-th glass from the object side, and νi indicates the Abbe number of the i-th glass from the object side. The aspherical shape of the surface r9 representing the aspherical surface is defined by the following equation (1). FIG. 2 shows the first
It is an aberration diagram of an Example, d is d line, F is F line, C is C
The line and SC indicate the sign condition, respectively.
In the aberration diagram, astigmatism is shown separately in the sagittal direction S and the meridional direction M.

[0013]

[Table 1]

[0014]

(Equation 1)

Next, Table 2 shows a second numerical example, FIG. 3 is a sectional view of the optical axis of the second example, and FIG. 4 is an aberration diagram of the second example. In Tables 2, 3 and 4, r
i, di, ni, and νi are defined as in the first embodiment.
The aspherical shape of the surface r9 representing the aspherical surface is also defined by the above-described formula 1 as in the first embodiment, and each symbol in the aberration diagram is also defined in the same manner.

[0016]

[Table 2]

Table 3 shows a third numerical example, FIG. 5 is a sectional view of the optical axis of the third example, and FIG. 6 is an aberration diagram of the third example. In Tables 3, 5 and 6, r
i, di, ni, and νi are defined as in the first embodiment.
The aspherical shapes of the surfaces r1, r4, and r9 representing the aspherical surface are also defined by the above-described formula 1 as in the first embodiment, and the signs in the aberration diagram are also defined in the same manner. In the third embodiment, the first lens 1, the second lens 2, and the fifth lens 5
Are formed of resin.

[0018]

[Table 3]

Further, Table 4 shows a fourth numerical example, FIG. 7 is a sectional view of the optical axis of the fourth example, and FIG. 8 is an aberration diagram of the fourth example. In Tables 4, 7 and 8, r
i, di, ni, and νi are defined as in the first embodiment.
The aspherical shapes of the surfaces r3 and r9 representing the aspherical surface are also defined by the above-described formula 1 as in the first embodiment, and the respective symbols in the aberration diagram are also defined in the same manner. In the fourth embodiment, the second lens 2 and the fifth lens 5 are formed of resin.

[0020]

[Table 4]

[0021]

As can be seen from the above-described embodiment and the aberration diagram, although it has a simple structure of 5 elements in 4 groups, it has sufficient brightness with an F-number of 2.0 to 3.2 and about 56 degrees. A compact wide-angle lens having a wide angle of view, optimally small, lightweight, and low-cost aberrations can be satisfactorily corrected, such as an electronic still camera.

[Brief description of the drawings]

FIG. 1 is an optical axis sectional view of a first embodiment of the present invention.

FIG. 2 is an aberration diagram for the embodiment shown in FIG.

FIG. 3 is an optical axis sectional view of a second embodiment of the present invention.

FIG. 4 is an aberration diagram for the embodiment shown in FIG.

FIG. 5 is an optical axis sectional view of a third embodiment of the present invention.

6 is an aberration diagram of the embodiment shown in FIG.

FIG. 7 is an optical axis sectional view of a fourth embodiment of the present invention.

FIG. 8 is an aberration diagram for the embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens r6 Object side surface of 3rd lens r8 Image surface side of 4th lens

Claims (3)

[Claims] 1. A junction of a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, and the third lens in order from the object side A fourth lens having a positive refractive power and a fifth lens having a positive refractive power and having at least one surface formed as an aspherical surface having a shape in which the positive refractive power becomes weaker toward the periphery. A small and wide-angle lens comprising a four-group, five-lens structure and satisfying the following conditions (1) to (3). (1) 0.7 | r6 | <| r8 | <1.3 | r6 | (2) ν1 <ν2, ν3 <ν4, ν5> 50 (3) | f1, |> 2f3,4,5 r6: radius of curvature of the object-side surface of the third lens r8: radius of curvature of the image-side surface of the fourth lens νi: Abbe number of the i-th lens from the object side f1, 2: first lens and second lens F3,4,5: composite focal length of the third, fourth and fifth lenses 2. The small wide-angle lens according to claim 1, wherein the lens system includes at least one resin lens. 3. The small wide-angle lens according to claim 2, wherein said resin lens is at least a fifth lens.