JP3311317B2 - Imaging lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens for forming an image of a subject on an image receiving surface.

[0002]

2. Description of the Related Art In a device requiring a high resolution, an imaging lens is required to have a lens having the same imaging performance as a photographing lens for a single-lens reflex camera, for example.

On the other hand, in a device having a relatively low resolution, such as a small-sized videophone, importance is placed on compactness rather than imaging performance, and it is required that the device be made as compact as possible with a minimum number of images. You.

Conventionally, an imaging lens composed of, for example, three spherical glass lenses is generally used for this type of application. In order to obtain a certain imaging performance using a spherical lens, it is difficult to further reduce the number of components.

FIG. 14 shows a conventional imaging lens composed of three lenses 1, 2, 3, and FIG.
Shows the lateral aberration due to this configuration. In addition, the code | symbol 4 in a figure has shown the cover glass.

FIG. 16 shows an example of an imaging lens constituted by one aspherical lens 5 for the purpose of reducing the number of lenses. FIG. 17 shows various aberrations of this lens.

[0007]

The imaging lens of FIG. 14 satisfies the performance of this type of lens, but has a large number of components. On the other hand, the lens shown in FIG. 16 has the minimum number of components, but the performance is significantly deteriorated particularly at the periphery.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an imaging lens capable of securing required performance with a smaller number of components.

[0009]

Means for Solving the Problems] To solve the above problem, an imaging lens according to claim 1, and one piece of imaging lens, and one of the correction lens of aspherical disposed on the image side consists, the paraxial curvature radius of the first surface of the imaging lens r1, the thickness on the axis of the imaging lens as d1, and satisfies the 0.3 <r1 / d1 <1.0 .

According to a second aspect of the present invention, in the imaging lens of the first aspect, the correction lens is a meniscus lens whose both surfaces are convex to the object side in paraxial.

According to a third aspect of the present invention, in the imaging lens of the first aspect, the aspherical displacement direction of the correction lens is opposite to a paraxial radius of curvature of the aspherical surface.

[0012] The imaging lens according to claim 4 is the imaging lens according to claim 1, wherein the imaging lens, wherein at least one surface Ru aspherical der.

According to a fifth aspect of the present invention, in the imaging lens of the first aspect, the focal length of the entire system is set to f,
The aspherical coefficients of order, sixth, eighth, etc. are An, the conic coefficient is K,
Let the curvature (1 / r) of the aspherical vertex be C, and from the paraxial curvature plane on the aspherical surface at a height Y from the optical axis of the object side surface (N = 1) and the image side surface (N = 2) of the correction lens. Deviation ΔX
_{When N} (Y) is defined as in Equation 4, the condition of Equation 3 is satisfied.

[0014]

(Equation 3)

[0015]

(Equation 4)

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

First, various conditions satisfied by the imaging lens according to the embodiment of the present invention will be described.

The focal length of the entire system at the main wavelength is f, the focal length of the imaging lens is f1, and the focal length of the correction lens is f.
2. Assuming that the paraxial radius of curvature of the first surface of the imaging lens is r1 and the axial thickness of the imaging lens is d1, 0.75 <f / f1 <1.0 (1) −0.10 < f / f2 <0 (2) 0.3 <r1 / d1 <1.0 (3)

Equations (1) and (2) are conditions relating to field curvature and astigmatism, and are the lower limit of equation (1) or (2).
When the value exceeds the upper limit of the expression, the sagittal curvature of field becomes excessively large. On the other hand, when the value exceeds the upper limit of the expression (1) or the lower limit of the expression (2), the astigmatic difference increases and the imaging lens and the correction lens have Refractive power becomes excessive and coma aberration occurs.

Equation (3) is a condition relating to field curvature and coma. When the value exceeds the upper limit, the meridional field curvature increases, and when the value falls below the lower limit, coma occurs.

Further, the fourth-order, sixth-order, eighth-order... Aspherical coefficients An and conic coefficients of the lens are K, and the curvature (1/1 /
r) is C, and the deviation ΔX _N (Y) from the paraxial curvature surface on the aspheric surface having a height Y from the optical axis of the object side surface (N = 1) and the image side surface (N = 2) of the correction lens is It is characterized by satisfying the condition of Expression 5 when defined as Expression 6.

[0022]

(Equation 5)

[0023]

(Equation 6)

Equations (4) and (5) are conditions relating to astigmatic difference and distortion. If the lower limit of both equations is exceeded, negative distortion occurs in a low image height range,
Exceeding the upper limit increases the field curvature of the meridional,
Astigmatism increases.

In order for the correction lens to work effectively, the entrance pupil of the correction lens is located in the imaging lens, the distance from the object-side surface of the correction lens to the entrance pupil of the correction lens is d0, and the entire system It is preferable to set the focal length of f to satisfy the condition of -0.4 <d0 / f <-0.2 (6).

Equation (6) is a condition for defining the position of the entrance pupil of the correction lens. If this condition is not satisfied,
Astigmatism increases, and imaging performance deteriorates. (First Embodiment) FIGS. 1 to 3 show a first embodiment of an imaging lens according to the present invention. This imaging lens includes a double-sided aspherical imaging lens 10 and a double-sided aspherical correction lens 20 disposed on the image side. On the image side of the correction lens 20, a sensor (not shown) for reading a signal of an image to be formed is provided.

The sensor is sealed with a cover glass 30 so that the light receiving surface is not directly exposed to moisture, and a space between the light receiving surface and the cover glass is filled with nitrogen gas. The correction lens 20 has a special shape in which both surfaces are convex on the object side when paraxial, and the aspherical displacement direction is opposite to the paraxial radius of curvature of the aspherical surface.
Such an aspherical shape can be easily realized by using a plastic material.

The specific numerical configuration of this lens is as shown in Table 1. The symbols in the table are Fno.
f is the focal length at the main wavelength, m is the magnification, r is the radius of curvature of the surface, d is the lens thickness or air gap, nd is the refractive index of the lens at d-LINE (588 nm), ν is the Abbe number, and ne is the lens's Abbe number. It is a refractive index in e-LINE (546 nm).

In the description of the table, the numerical value in the radius of curvature of the aspherical surface is the radius of curvature of the apex of the aspherical surface. The aspheric surface is
The distance from the tangent plane to the apex of the aspheric surface on the aspheric surface having a height Y from the optical axis is X, the curvature (1 / r) of the aspheric surface apex is C, the conic coefficient is K, and the fourth to tenth order aspheric surfaces Assuming that the coefficients are A _{4 to} A ₁₀ , the conic coefficients and the aspherical coefficients of each surface are as shown in the lower part of Table 1 below. FIG. 2 shows various aberrations due to the configuration of Table 1, and FIG. 3 shows lateral aberrations.

[0030]

(Equation 7)

[0031]

[Table 1]

(Second Embodiment) FIG. 4 shows a second embodiment of the imaging lens according to the present invention. In this example, a correction lens 20 provided on the image side of the imaging lens 10 is used.
Also serves as the sensor cover. The specific numerical configuration of the lens is as shown in Table 2. The symbols in the table are the same as in the first embodiment. FIG. 5 shows various aberrations due to the configuration of Table 2.

[0033]

[Table 2]

(Third Embodiment) FIG. 6 shows a third embodiment of the imaging lens according to the present invention.

This lens comprises an imaging lens 10 and a correction lens 20 as in the first embodiment, and a cover glass 30 of the sensor is provided on the image side.

The specific numerical configuration of this embodiment is shown in Table 3, and various aberrations due to this configuration are as shown in FIG.

In the third, fourth and fifth embodiments, APO (amorphous polyolefin: trade name) is used for the imaging lens 10 and the correction lens 20. PMMA conventionally used as a material for plastic lenses
(Polymethyl methacrylate) has a problem in that the refraction state changes greatly due to changes in temperature and humidity, and the optical performance greatly changes due to changes in the environment. In particular, when there is a change in humidity, not only out of focus but also the wavefront of the light beam is disturbed.

This APO is a low hygroscopic plastic developed by Mitsui Petrochemical Co., Ltd. and has a water absorption of 0.01% or less, which is one digit smaller than that of the conventional one, and therefore is not easily affected by changes in humidity. Therefore, the APO
Is used, the performance of the lens system can be further stabilized.

[0039]

[Table 3]

(Fourth Embodiment) FIG. 8 shows a fourth embodiment of the imaging lens according to the present invention.

This lens comprises an imaging lens 10 and a correction lens 20 as in the first embodiment, and a cover glass 30 of the sensor is provided on the image side.

The specific numerical configuration is shown in Table 4.
Various aberrations due to this configuration are as shown in FIG.

[0043]

[Table 4]

(Fifth Embodiment) FIG. 10 shows a fifth embodiment of the imaging lens according to the present invention.

In this example, as in the second embodiment, the correction lens 20 provided on the image side of the imaging lens 10 also serves as a cover for the sensor, and both lenses are formed of APO.

When a resin having high hygroscopicity such as PMMA is used when the correction lens 20 also functions as a cover glass, moisture permeation may be caused through moisture absorption and discharge, and the sensor performance may be degraded. As in this embodiment, the correction lens is AP
In the case of O, the light receiving surface can be protected from moisture, and a decrease in sensor performance can be prevented.

The specific numerical configuration of the lens is as shown in Table 5, and the various aberrations are as shown in FIG.

[0048]

[Table 5]

(Sixth Embodiment) FIG. 12 shows an imaging lens according to a sixth embodiment of the present invention.

In this embodiment, the correction lens 20 provided on the image side of the imaging lens 10 also serves as a sensor cover, as in the second embodiment.

The specific numerical configuration of the lens is as shown in Table 6, and the various aberrations are as shown in FIG.

[0052]

[Table 6]

The above-described embodiments and conditional expressions (1) to (1)
Table 7 shows the correspondence with (6).

[0054]

[Table 7]

The first to sixth embodiments relate to an imaging lens used for a small camera such as a videophone camera or a door phone camera. In order to meet such demands, the imaging lenses of the first to sixth embodiments have a compact configuration including one imaging lens and one correction lens.

[0056]

As described above, according to the present invention, the required performance can be ensured with a smaller number of components.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of an imaging lens according to the present invention;

FIG. 2 is a diagram illustrating various aberrations of the first example.

FIG. 3 is a lateral aberration diagram of the first example.

FIG. 4 is a sectional view of a lens according to a second embodiment.

FIG. 5 is a diagram illustrating various aberrations of the second example.

FIG. 6 is a sectional view of a lens according to a third embodiment.

FIG. 7 is a diagram illustrating various aberrations of the third example.

FIG. 8 is a sectional view of a lens according to a fourth embodiment.

FIG. 9 is a diagram illustrating various aberrations of the fourth example.

FIG. 10 is a sectional view of a lens according to a fifth embodiment.

FIG. 11 is a diagram illustrating various aberrations of the fifth example.

FIG. 12 is a sectional view of a lens according to a sixth embodiment.

FIG. 13 is a diagram illustrating various aberrations of the sixth example.

FIG. 14 is a sectional view of a conventional three-element imaging lens.

15 is a lateral aberration diagram of the conventional example of FIG.

FIG. 16 is a cross-sectional view of a conventional single-lens imaging lens.

17 is a lateral aberration diagram of the conventional example of FIG.

[Description of Signs] 10 Imaging lens 20 Correction lens 30 Cover glass

Continuation of front page (56) References JP-A-2-289806 (JP, A) JP-A-2-96107 (JP, A) JP-A-61-77819 (JP, A) JP-A-2-250014 (JP) JP-A-62-153811 (JP, A) JP-A-1-209413 (JP, A) JP-A-4-78814 (JP, A) JP-A-4-11209 (JP, A) 4-168408 (JP, A) JP-A-2-124509 (JP, A) JP-A-1-158409 (JP, A) JP-A 1-245211 (JP, A) (58) Fields investigated (Int. Cl ^7, DB name) G02B 9/00 -. 17/08 G02B 21/02 - 21/04 G02B 25/00 - 25/04

Claims (5)

(57) [Claims] 1. A and one imaging lens made up of a single correction lenses having aspherical surfaces disposed on the image side, the paraxial curvature radius of the first surface of the imaging lens r1, sintered An imaging lens characterized by satisfying 0.3 <r1 / d1 <1.0, where d1 is an on-axis thickness of the image lens. 2. The imaging lens according to claim 1, wherein the correction lens is a meniscus lens having both surfaces convex on the object side in paraxial. 3. The aspherical displacement direction of the correction lens is opposite to the paraxial radius of curvature of the aspherical surface.
An imaging lens according to item 1. Wherein said imaging lens, an imaging lens according to claim 1, wherein at least one surface Ru aspherical der. 5. The focal length of the entire system is represented by f, 4th, 6th, 8th,.
Let A be the aspherical coefficient, K be the conic coefficient, and C be the curvature (1 / r) of the vertex of the aspherical surface, and set the object side surface of the correction lens (N = 1).
And when the deviation ΔX _N (Y) from the paraxial curvature surface on the aspheric surface having a height Y from the optical axis of the image side surface (N = 2) is defined as in Expression 2, the condition of Expression 1 is satisfied. The imaging lens according to claim 1, wherein: (Equation 1) (Equation 2)