JP3473232B2 - Imaging lens system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel image pickup lens system. More specifically, the present invention mainly relates to a downsized imaging lens system used as a zoom lens of a video camera.

[0002]

2. Description of the Related Art In recent years, a so-called zoom lens is often used as an imaging lens system of a video camera, and in addition, downsizing of the video camera is an essential requirement.

However, the zoom lens has a characteristic that its volume is relatively larger than that of a general lens.

Therefore, in order to reduce the size of the zoom lens, for example, Japanese Patent Laid-Open Nos. 4-242707 and 5-2000.
As disclosed in Japanese Patent Application Laid-Open No. -60974 and Japanese Patent Application Laid-Open No. 5-297275, the third lens group is a positive lens and a negative lens in a zoom lens having a four-group configuration having positive, negative, positive, and positive refractive powers. There is an example of a so-called telephoto type in which the total length is shortened to reduce the size.

[0005]

However, in the one disclosed in Japanese Unexamined Patent Publication No. 4-242707,
Since the object-side surface of the negative lens forming the third lens group has a tight curvature, there is a problem that the optical performance is largely deteriorated due to decentering in the third lens group.

Further, in the one disclosed in JP-A-5-60974, the curvature of the object-side surface of the negative lens forming the third lens group is a strong convex surface, so that a negative lens following this is used. There is a problem that spherical aberration and coma cannot be corrected and optical performance is degraded.

Further, even in the one disclosed in Japanese Unexamined Patent Publication No. 5-297275, since the curvature of the object side surface of the negative lens forming the third lens group is a relatively tight convex surface, it is a negative lens. There is a problem in that the spherical aberration and the coma aberration cannot be corrected and the optical performance deteriorates.

As described above, conventionally, it has been difficult to obtain a zoom lens which is downsized and has good optical performance.

[0009]

The image pickup lens system of the present invention comprises:
In order to solve the above problems, 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, and a positive refractive power are provided. Fourth
The zoom lens is composed of four lens units, and at the time of zooming from the wide-angle end to the telephoto end, at least the second lens unit moves from the object side to the image surface side, and the fourth lens unit changes its image surface during zooming. In the imaging lens system configured to move so as to correct the movement of the first lens group, the first lens group includes two lenses arranged in order from the object side, the negative lens and the positive lens, and the second lens group Is a negative lens from the object side, a negative lens,
It consists of three lenses arranged in order of positive lens,
The third lens group is composed of two lenses arranged in order from the object side, a positive lens and a negative lens, and R31:
The radius of curvature of the object-side surface of the positive lens of the third lens group, R3
2: radius of curvature of the image-side surface of the positive lens of the third lens group,
R33: radius of curvature of the object side surface of the negative lens of the third lens group, R34: radius of curvature of the image side surface of the negative lens of the third lens group, ΣD3: of the object side of the positive lens of the third lens group Surface to the image-side surface of the negative lens, fW: focal length at the wide-angle end of the entire lens system, ν3P: Abbe number of the positive lens of the third lens group, ν3N: Abbe of the negative lens of the third lens group , R31 / R32 | <0.
4, −0.5 <R34 / R33 ≦ −0.235, ΣD3
/FW>1.2 and v3P-v3N> 10 are satisfied.

Therefore, in the image pickup lens system of the present invention,
By arranging the third lens group with two lenses, a positive lens and a negative lens, which are arranged in order from the object side to the image plane side, and by disposing optimal positive and negative lenses satisfying various conditions, It is possible to shorten the distance from the third lens group to the image plane to shorten the entire length of the entire lens system, and at the same time, to obtain a good image pickup lens in which chromatic aberration and the like are well corrected and the optical performance is not deteriorated. The system can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the imaging lens system of the present invention will be described below with reference to the illustrated first and second embodiments 1 and 1A in which the imaging lens system of the present invention is applied to a zoom lens for a video camera. To do.

The zoom lenses 1 and 1A are shown in FIGS.
, The first lens group GR having a positive refractive power
1, a second lens group GR2 having a negative refracting power, a third lens group GR3 having a positive refracting power, and a fourth lens group GR4 having a positive refracting power. During zooming, the second lens group GR2 moves from the object side to the image plane 2 side in the lens barrel, and at the same time, at least the fourth lens group GR4 corrects the movement of the image plane 2 due to zooming. It is designed to move like you do.

A glass block FL acting as an optical low pass filter is arranged between the fourth lens group GR4 and the image plane 2, and a glass block FL is arranged between the second lens group GR2 and the third lens group GR3. A diaphragm IR is arranged.

Then, the first lens group is moved from the object side to the image plane 2
The negative lens 3 and the positive lens 4 are arranged in this order in the order of the two lenses.

The second lens group GR2 is composed of three lenses, a negative lens 5, a negative lens 6 and a positive lens 7, which are arranged in order from the object side to the image plane 2 side.

Further, in order to shorten the overall length of the zoom lenses 1 and 1A, the third lens group GR3 is a telephoto type in which two lenses, a positive lens 8 and a negative lens 9, are sequentially arranged from the object side. There is.

That is, in order to reduce the overall length of the zoom lenses 1 and 1A to reduce the size thereof, the movement amount of the second lens group GR2 is reduced, or the distance from the third lens group GR3 to the image plane 2 is reduced. However, if the moving amount of the second lens group GR2 is reduced, the second lens group G
Since the power of R2 becomes large and the optical performance deteriorates, the telephoto type is adopted to shorten the distance from the third lens group GR3 to the image plane 2 as described above.

The third lens group GR3 includes "R3
1 ”is the radius of curvature of the object side surface of the positive lens 8,“ R32 ”
Is the radius of curvature of the surface of the positive lens 8 on the image plane 2 side, |
R31 / R32 | <0.4 (hereinafter, referred to as “conditional expression (1)”), and “R33” is a negative radius of curvature of the object-side surface of the lens 9, and “R34” is a negative value. If the radius of curvature of the surface of the lens 9 on the image plane 2 side is -0.5 <R
34 / R33 ≦ −0.235 (hereinafter, “conditional expression (2)”
Say. In addition, “ΣD3” is the distance from the object side surface of the positive lens 8 to the image surface 2 side surface of the negative lens 9, and “fW” is the focal length at the wide angle end of the entire lens system. Then, ΣD3 / fW> 1.2 (hereinafter, referred to as “conditional expression (3)”), and further, “ν3
“P” is the Abbe number of the positive lens 8 and “ν3N” is the negative lens 9
The Abbe number of is, ν3P-ν3N> 10 (hereinafter,
It is called “conditional expression (4)”. ) Is to be.

Now, the above conditional expressions will be described.

First, in conditional expression (1), | R31 /
When the value of R32 | is larger than 0.4, the principal point of the positive lens 8 is arranged on the image plane side, and the spherical aberration due to the surface of the positive lens 8 on the image plane 2 side becomes large.

Next, in the conditional expression (2), R34 / R
When the value of 33 is −0.5 or less, the power of the surface of the negative lens 9 on the object side becomes too large, and the amount of negative spherical aberration and coma generated becomes large, so that the positive lens 8 and the negative lens 9 are processed. The accuracy and assembly accuracy will be severe. Further, since the power of the object-side surface of the negative lens 9, that is, the surface close to the positive lens 8, becomes large, it becomes impossible to effectively configure the telephoto type.

Contrary to the above, if the value of R34 / R33 is smaller than 0 but larger than −0.235, the object side surface of the negative lens 9 becomes a too gentle concave surface. aberrations, it becomes impossible to correct the coma aberration in the negative lens 9, the optical performance deteriorates.

Then, in conditional expression (3), ΣD3 /
When the value of fw becomes smaller than 1.2, the third lens group G
It becomes difficult to place the principal point position of R3 on the object side,
Therefore, it becomes difficult to reduce the total length of the entire lens system.

Finally, regarding the conditional expression (4),
This shows the condition for properly correcting the chromatic aberration in the third lens group GR3. That is, by setting the Abbe numbers of the positive lens 8 and the negative lens 9 so as to satisfy the conditional expression (4), it is possible to reduce the burden of correcting the chromatic aberration of the third lens group GR 3 , and thus , For facilitating correction of chromatic aberration of the entire lens system.

The first and second embodiments will be specifically described below.

In the following description and tables, "r"
Is the radius of curvature of the surface, “d” is the distance between two adjacent surfaces, “N” is the refractive index at the d line (wavelength 587.6 nm), “ν” is the Abbe number, and “f” is the entire lens system. , FNO is the F number of the entire lens system, and ω is the half angle of view.

Therefore, "r_i] Is from the object side to the image plane 2 side
To the i-th surface (i = 1, 2, 3, ... 28)
Indicates the radius of curvature, "d_iIs the i-th face and the (i + 1) -th face
The distance between the eye planes is shown, and "N_i"as well as
"Ν_iIs the medium between the i-th surface and the (i + 1) -th surface
Refractive index of quality for the above d-line And To indicate the Abbe number
To do.

The lens in each embodiment is a lens.
The one in which the surface has an aspherical shape is also included. Therefore, the non-sphere
The surface shape shall be defined by the following equation. Xa = c · y² / [1 + √ (1-c²・ Y²)] + Σ (A
_2i・ Y²ⁱ) Here, “Xa” is the coordinate of the aspherical surface in the optical axis X direction, and “c”
Is the paraxial curvature (1 / r), and “A” is the 2i-th order aspherical surface
The number “y” indicates the distance from the optical axis X.

1 to 4 show a first embodiment.

In the zoom lens 1 according to the first embodiment, the first lens group GR1 includes the negative lens 3 and the positive lens 4.
The second lens group GR2 has three negative lenses 5, the negative lens 6 and the positive lens 7, the third lens group has two positive lenses 8 and 9, and the fourth lens group has two four groups 10. It is composed of a single lens.

Table 1 shows each value of the lenses constituting the zoom lens 1.

[0032]

[Table 1]

The 13th surface from the object side (the surface on the image surface 2 side of the positive lens 8 of the third lens group GR3) and the 18th surface are aspherical. Table 2 shows the fourth-order, sixth-order and eighth-order aspherical surface coefficients A ₄ , A ₆ and A ₈ .

[0034]

[Table 2]

Incidentally, "e" in Table 2 means exponential expression with base 10 (the same applies to Table 5).

Further, d ₅ (first lens group GR1 and second lens group G) when f changes to 1.000, 2.4587, 9.5730 with zooming operation of the zoom lens 1
Distance between R2), d ₁₀ (distance between the IR diaphragm and the second lens group GR2), and d ₁₅ (third lens group GR3 fourth
Table 3 shows the values of the distance between the lens group GR4) and d ₁₈ (the distance between the fourth lens group GR4 and the glass block FL).

[0037]

[Table 3]

2 to 4 show a spherical aberration diagram, an astigmatism diagram and a distortion diagram of the zoom lens 1. 2 shows the above aberration charts at the wide-angle end, FIG. 3 shows the standard view, and FIG. 4 shows the above-mentioned aberration charts at the telephoto end. Also, in the spherical aberration chart, the solid line is the d line, and the broken line is the g line (wavelength 435.8 nm). And further,
In the astigmatism diagram, the solid line shows the values on the sagittal image plane, and the broken line shows the values on the meridional image plane.

5 to 8 show the second embodiment.

In the zoom lens 1A of the second embodiment, the first lens group GR1 is composed of five lenses including the negative lens 3 and the positive lens 4, and the second lens group GR2 is composed of the negative lens 5, the negative lens 6 and the positive lens 7. The third lens group is composed of two lenses, that is, the positive lens 8 and the negative lens 9, and the fourth lens group is composed of two lenses in four groups and twelve lenses.

In the zoom lens 1A, the negative lens 3 of the first lens group GR1 has a surface on the image surface 2 side that is a composite aspherical surface in which a resin layer is adhered onto a spherical glass surface, which causes distortion. It is designed to make corrections.

A prism PR is disposed as a reflecting member between the most object-side negative lens 3 of the first lens group GR1 and the following positive lens 4, and the optical axis X is provided at this portion.
Is bent, and the negative lens 3 and the positive lens 4 constitute an afocal system. The reflecting member is not limited to the prism PR, and a mirror or the like may be used instead.

Table 4 shows each value of the lenses constituting the zoom lens 1A.

[0044]

[Table 4]

The third, 21st and 26th surfaces from the object side are aspherical. 4 in Table 5
Next, the 6th and 8th order aspherical surface coefficients A ₄ , A ₆ and A ₈ are shown.

[0046]

[Table 5]

Further, d ₁₃ (distance between the first lens group GR1 and the second lens group GR2) when f changes to 1.000, 2.4499, and 9.5812 with zooming operation of the zoom lens 1A. ), D ₁₈ (the distance between the second lens group GR2 and the aperture stop IR), d ₂₃ (the distance between the third lens group GR3 and the fourth lens group GR4) and d ₂₆ (the fourth lens group GR4). Table 6 shows each value of (distance between the glass blocks FL).

[0048]

[Table 6]

6 to 8 are a spherical aberration diagram, an astigmatism diagram and a distortion diagram of the zoom lens 1A. FIG. 6 shows the above aberration diagrams at the wide-angle end, FIG. 7 shows the standard, and FIG. 8 shows the above-mentioned aberration diagrams at the telephoto end. In the spherical aberration diagram, the solid line is the d line, and the broken line is the g line (wavelength 435.8 nm). Further, in the astigmatism diagram, the solid line shows the value on the sagittal image plane, and the broken line shows the value on the meridional image plane.

Finally, f and FNO in each of the above embodiments
Table 7 shows the respective values of 1 and 2ω, and Table 8 shows the respective values in the conditional expressions (1) to (4).

[0051]

[Table 7]

[0052]

[Table 8]

[0053]

As is apparent from the above description, the image pickup lens system of the present invention has the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the positive refractive power. And a fourth lens unit having a positive refracting power, and at least the second lens unit from the object side to the image plane when zooming from the wide-angle end to the telephoto end. In the image pickup lens system in which the fourth lens group moves so as to correct the movement of the image plane due to zooming, the first lens group includes a negative lens and a positive lens from the object side. The second lens group has a negative lens from the object side,
The third lens group is composed of three lenses arranged in order of a negative lens and a positive lens, the third lens group is composed of two lenses arranged in order of a positive lens and a negative lens from the object side, and R31 is a third lens. R32: the radius of curvature of the object-side surface of the positive lens of the third lens group, R32: the radius of curvature of the image-side surface of the positive lens of the third lens group, R33: the radius of curvature of the object-side surface of the negative lens of the third lens group, R34: radius of curvature of the image side surface of the negative lens of the third lens group, ΣD3: distance from the object side surface of the positive lens of the third lens group to the image surface side of the negative lens,
fw: focal length at the wide-angle end of the entire lens system, ν3P:
When the Abbe number of the positive lens of the third lens group is ν3N: Abbe number of the negative lens of the third lens group, | R31 / R
32 | <0.4, -0.5 <R34 / R33 <-0.2
35, ΣD3 / fW> 1.2, ν3P-ν3N> 10,
It is characterized by satisfying each condition of.

Therefore, in the image pickup lens system of the present invention,
By arranging the third lens group with two lenses, a positive lens and a negative lens, which are arranged in order from the object side to the image plane side, and by disposing optimal positive and negative lenses satisfying various conditions, It is possible to shorten the distance from the third lens group to the image plane to shorten the entire length of the entire lens system, and at the same time, to obtain a good image pickup lens in which chromatic aberration and the like are well corrected and the optical performance is not deteriorated. The system can be obtained.

It should be noted that the specific shapes and structures shown in the above embodiments are merely examples of the implementation in carrying out the present invention, and the technical scope of the present invention is limited by these. Is not to be interpreted.

[Brief description of drawings]

1 shows a first embodiment of the image pickup lens system of the present invention, together with FIGS. 2 to 4, and is a schematic diagram showing the configuration.

FIG. 2 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of zooming.

FIG. 3 is a diagram showing spherical aberration, astigmatism, and distortion in a standard state of zooming.

FIG. 4 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of zooming.

FIG. 5 is a second part of the imaging lens system of the present invention, together with FIGS.
FIG. 3 is a schematic diagram showing the configuration of the present invention.

FIG. 6 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of zooming.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and distortion in a standard state of zooming.

FIG. 8 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of zooming.

[Explanation of symbols]

1 Imaging lens system 1A imaging lens system GR1 first lens group GR2 Second lens group GR3 3rd lens group GR4 4th lens group 2 image plane 3 negative lens 4 Positive lens 5 negative lens 6 negative lens 7 Positive lens 8 positive lens 9 negative lens PR reflective member

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Claims (4)

(57) [Claims] 1. 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, and a fourth lens having a positive refractive power. Group 4
At the time of zooming from the wide-angle end to the telephoto end, at least the second lens group moves from the object side to the image plane side and the fourth lens group moves the image plane due to zooming. In the imaging lens system that is configured to move so as to correct, the first lens group includes two lenses arranged in order from the object side, a negative lens and a positive lens, and the second lens group includes The negative lens, the negative lens, and the positive lens are arranged in this order from the object side, and the third lens group is composed of two lenses in which the positive lens and the negative lens are arranged in this order from the object side. An imaging lens system characterized by satisfying the following conditions. | R31 / R32 | <0.4 −0.5 <R34 / R33 ≦ −0.235 ΣD3 / fW> 1.2 ν3P−ν3N> 10 However, R31: a surface of the positive lens of the third lens group on the object side. R32: radius of curvature of image-side surface of positive lens of third lens group, R33: radius of curvature of object side surface of negative lens of third lens group, R34: negative lens of third lens group Radius of curvature of the image-side surface of ΣD3: distance from the object-side surface of the positive lens of the third lens group to the image-side surface of the negative lens, fW: focal length at wide-angle end of the entire lens system, ν3P Is the Abbe number of the positive lens of the third lens group, and ν3N is the Abbe number of the negative lens of the third lens group. 2. The image pickup lens system according to claim 1, wherein the negative lens and the positive lens of the first lens group form an afocal system. 3. A reflecting member is arranged between the negative lens and the positive lens of the first lens group, and the reflecting member bends the optical axis from the object side and the optical axis at the image plane. The imaging lens system according to claim 1. 4. A reflecting member is arranged between the negative lens and the positive lens of the first lens group, and the optical axis from the object side and the optical axis on the image plane are bent by the reflecting member. The imaging lens system according to claim 2.