JPH10307255A - High-resolution image forming lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently compensate distortion aberration, to improve off-axis image forming performance in a low frequency area and to make image side numerical aperture N.A. much larger by providing 1st to 8th lenses in order from an object side and arranging a diaphragm and the respective lenses to be telecentric on an image side. SOLUTION: This system is provided with the positive 1st lens, the positive 2nd lens and the positive 3rd lens whose convex surface faces to the object side in order from the object side. The negative 4th lens is arranged adjacently to the 3rd lens and has shape that the concave surface faces to the image side. Then, the system is provided with the diaphragm. The next negative 5th lens has shape that the concave surface faces to the object side, and the positive 6th lens is arranged adjacently to the 5th lens and has shape that the convex surface faces to the image side. Then, the system is provided with the positive 7nd lens and the positive 8th lens. The diaphragm and the respective lenses are arranged to be telecentric on the image side. By such constitution, the distortion aberration is compensated by the 1st lens and the coma aberration in an off-axis meridional direction is compensated by the 2nd lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Gauss-type imaging lens, and more particularly to an image-side telecentric lens having a numerical aperture N.P. A.
The present invention relates to a high-resolution imaging lens system that requires a resolution determined by (Numerical Aperture).

[0002]

2. Description of the Related Art Conventionally, as a Gaussian type imaging lens, for example, a lens disclosed in Japanese Patent Application Laid-Open No. 3-72310 is known.

[0003]

FIG. 13 shows a lens configuration diagram of a conventional Gaussian type imaging lens. The optical system shown in FIG. 13 has three lenses on the object side and four lenses on the image side with a diaphragm interposed therebetween. In this configuration, the numerical aperture N. A is a telecentric high-resolution lens having an image resolution having a theoretical resolution determined by A. Distortion, off-axis imaging performance in a low frequency region, A. It was difficult and problematic to achieve further expansion of the system at the same time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it has been found that distortion is well corrected, off-axis imaging performance in a low frequency region is improved, and an image-side numerical aperture N.I.
It is an object of the present invention to provide a Gaussian imaging lens in which A is further increased.

[0005]

SUMMARY OF THE INVENTION A high-resolution imaging lens system according to the present invention has, in order from the object side, a first lens which is disposed closest to the object side and has a positive refractive power, and a first lens which has a positive refractive power. Second
A positive third lens having a shape with a convex surface facing the object side;
A lens, a fourth negative lens disposed adjacent to the third lens and having a concave surface facing the image side, an aperture, and a fifth negative lens having a concave surface facing the object side A sixth lens having a shape with a convex surface facing the image side, a seventh lens having a positive refractive power, and an eighth lens having a positive refractive power disposed adjacent to the fifth lens. And a lens, wherein the stop and the lenses are arranged to be telecentric on the image side.

Incidentally, the image side telecentric in the present invention is an image space (a space from the lens surface on the most image side to the image surface).
In which the angle between the principal ray and the optical axis is within ± 2 degrees.

With such a configuration, distortion can be corrected by the first lens, and a lens having high resolution can be achieved. Further, coma in the off-axis meridional direction can be corrected by the second lens, and the angle of view and the numerical aperture can be increased.

In the present invention, in order to make the optical system telecentric on the image side, it is desirable to dispose the stop at the front focal position of the following optical system.

It is preferable that the high-resolution imaging lens system of the present invention satisfies the following condition: 0.26 <(f1 / f) · β <1.0. Here, f1 represents the focal length of the first lens, f represents the focal length of the entire imaging lens system, and β represents the absolute value of the imaging magnification of the entire imaging lens system.

This conditional expression defines a preferable range of the distribution of the refractive power of the first positive lens in the entire lens system at a predetermined imaging magnification. If the lower limit of the conditional expression is not reached, the refractive power of the first positive lens becomes too strong, which leads to deterioration of the imaging performance. Conversely, when the value exceeds the upper limit, the effect of distortion correction is lost, which is not preferable.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIG. 1 is a sectional view of a lens structure according to a first embodiment of the present invention. The optical system according to the first embodiment has a magnification β
= 1/5, numerical aperture NA = 0.2, image size 15m
mφ.

A first convex lens L1 is added to the object side of the Gaussian type imaging lens with a significant air gap, and a second convex lens subsequent to the first convex lens L1 has a meniscus shape convex to the object side. . In order to clarify the difference from the prior art, the first embodiment of the present invention will be described in comparison with the conventional example shown in FIG.

In FIG. 13, the single-convex lens on the most object side has to be shaped as a biconvex lens in order to correct axial spherical aberration and various off-axis aberrations, particularly distortion. For this reason, coma aberration in the meridional direction cannot be sufficiently corrected among the off-axis performances, and an optical MTF (Modulation Transfer) in a low frequency region is not provided.
rFunction), which is a problem.

On the other hand, in the first embodiment of the present invention shown in FIG. 1, since the first convex lens L1 is added, the first convex lens L1 mainly plays a role of correcting distortion. It has become possible. Further, the second convex lens L2 corresponding to the top single convex lens of the conventional example is
This is mainly for correcting coma aberration in the off-axis meridional direction. For this reason, it is possible to correct the optical MTF in all frequency regions to a value close to a theoretical value, together with good correction of distortion.

Table 1 shows the specification values and aberration coefficients of the optical system of the first embodiment, and Table 7 shows the specification values and aberration coefficients of the conventional optical system.
Listed in In Table 1, the surface numbers indicate the order of the lens surfaces from the object side along the traveling direction of the light rays, r indicates the radius of curvature, d indicates the distance between the lens surfaces, and n indicates the g-line (λ = 435.8).
nm). further,
D0 is the object point distance, R is the object-image distance, fb is the rear focal position, β is the imaging magnification, f is the focal length of the entire imaging lens system, and f1 is the focal length of the first lens. Are respectively shown. Hereinafter, the same applies to other tables.

[0016]

[Table 1]

A comparison between the coma aberration coefficient (−0.00324) of the fourth surface among the aberration coefficients in Table 1 and the coma aberration coefficient (−0.17705) of the second surface in the conventional optical system shown in Table 7 is shown below. As is apparent, the coma aberration is greatly reduced in the first embodiment of the present invention. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 2 shows various aberration diagrams of the optical system according to the first embodiment. In the aberration diagram showing the spherical aberration, the solid line indicates the spherical aberration amount, and the broken line indicates the sine condition violation amount. Further, in the aberration diagram showing the curvature of field, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane.

As is clear from the aberration diagrams, not only the on-axis spherical aberration and off-axis various aberrations, especially the distortion, but also the coma of the meridional image plane can be corrected. Therefore, in this embodiment, it is possible to satisfactorily correct the distortion and improve the off-axis imaging performance in the low frequency region.

Further, the values corresponding to the conditions of the first embodiment are shown below.

Imaging magnification β = −0.2 f1 / f = 3.77 (f1 / f) · β = 0.754

The condition corresponding values in the conventional example are shown below for the invention disclosed in Japanese Patent Application Laid-Open No. 50-34823.

Imaging magnification β = −0.1 f1 / f = 2.1 (f1 / f) · β = 0.21

(Second Embodiment) FIG. 3 shows a lens configuration of a second embodiment of the present invention. The second embodiment is an example in which the image size is enlarged, and its specifications are a magnification β = １ ／, a numerical aperture NA = 0.1, and an image size φ = 30 mm.

Table 2 shows the specification values and aberration coefficients of the optical system of the second embodiment.

[0026]

[Table 2]

As is apparent from a comparison between the coma aberration coefficient of the fourth surface among the aberration coefficients in Table 2 and the comatic aberration coefficient of the second surface in the conventional optical system shown in Table 7, the first embodiment of the present invention is evident. In the figure, coma is greatly reduced. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 4 shows various aberration diagrams of the optical system according to the second embodiment. As is clear from the various aberration diagrams, the on-axis spherical aberration and off-axis various aberrations, in particular, the distortion are well corrected,
Furthermore, coma of the meridional image plane can be corrected.
Therefore, in this embodiment, while favorably correcting the distortion,
In addition, it is possible to improve off-axis imaging performance in a low frequency region.

Further, the condition corresponding values of the second embodiment are shown below.

Imaging magnification β = −0.5 f1 / f = 1.62 (f1 / f) · β = 0.81

(Third Embodiment) FIG. 5 shows a lens configuration of a third embodiment of the present invention. The third embodiment is also an example in which the image size is enlarged similarly to the second embodiment, and the specifications are a magnification β = 1/10, a numerical aperture NA = 0.25, and an image size φ = 8.4 mm. .

Table 3 shows the specification values and aberration coefficients of the optical system of the third embodiment.

[0033]

[Table 3]

As is apparent from a comparison between the coma aberration coefficient of the fourth surface among the aberration coefficients shown in Table 3 and the comatic aberration coefficient of the second surface in the conventional optical system shown in Table 7, the third embodiment of the present invention is evident. In the figure, coma is greatly reduced. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 6 shows various aberration diagrams of the optical system according to the third embodiment. As is clear from the various aberration diagrams, the on-axis spherical aberration and off-axis various aberrations, in particular, the distortion are well corrected,
Furthermore, coma of the meridional image plane can be corrected.
Therefore, in this embodiment, while favorably correcting the distortion,
In addition, it is possible to improve off-axis imaging performance in a low frequency region. The condition corresponding values of the third embodiment are shown below.

Imaging magnification β = −0.1 f1 / f = 4.72 (f1 / f) · β = 0.472

(Fourth Embodiment) The fourth to sixth embodiments of the present invention include the contents disclosed in the first to third embodiments, and
In order to enlarge the numerical aperture NA on the image side, a lens L9 having a positive refractive power is added between the two lenses L7 and L8 on the image side.

FIG. 7 shows a lens configuration of a fourth embodiment of the present invention. The specifications are magnification β = 1/5, numerical aperture NA = 0.3
5. The image size φ is 5.6 mm.

Table 4 shows the specification values and aberration coefficients of the optical system of the fourth embodiment.

[0040]

[Table 4]

As is apparent from a comparison between the coma aberration coefficient of the fourth surface among the aberration coefficients in Table 4 and the comatic aberration coefficient of the second surface in the conventional optical system shown in Table 7, the third embodiment of the present invention is evident. In the figure, coma is greatly reduced. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 8 shows various aberration diagrams of the optical system of the fourth embodiment. As is clear from the various aberration diagrams, the on-axis spherical aberration and off-axis various aberrations, in particular, the distortion are well corrected,
Furthermore, coma of the meridional image plane can be corrected.
Therefore, in this embodiment, while favorably correcting the distortion,
In addition, it is possible to improve off-axis imaging performance in a low frequency region. In particular, compared to the first to third embodiments of the present invention,
Further, the optical system becomes brighter, and various aberrations are well corrected over the entire on-axis and off-axis image regions.

Further, the values corresponding to the conditions of the fourth embodiment are shown below.

Imaging magnification β = −0.2 f1 / f = 2.42 (f1 / f) · β = 0.484

(Fifth Embodiment) FIG. 9 shows a lens configuration of a fifth embodiment of the present invention. The specifications are a magnification β = β, a numerical aperture NA = 0.2, and an image size φ = 12.6 mm.

Table 5 shows the specification values and aberration coefficients of the optical system of the fifth embodiment.

[0047]

[Table 5]

As is apparent from a comparison of the coma aberration coefficient of the fourth surface among the aberration coefficients shown in Table 5 with the comatic aberration coefficient of the second surface in the conventional optical system shown in Table 7, the fifth embodiment of the present invention. In the figure, coma is greatly reduced. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 10 shows various aberration diagrams of the optical system according to the fifth embodiment. As is clear from the various aberration diagrams, on-axis spherical aberration and off-axis various aberrations, particularly distortion, are well corrected, and further, coma on the meridional image plane can be corrected. Therefore, in this embodiment, it is possible to satisfactorily correct the distortion and improve the off-axis imaging performance in the low frequency region. In particular, the optical system becomes brighter than in the first to third embodiments of the present invention, and various aberrations are satisfactorily corrected over the entire on-axis and off-axis image regions.

Further, the condition corresponding values of the fifth embodiment are shown below.

Imaging magnification β = −0.5 f1 / f = 1.32 (f1 / f) · β = 0.66

(Sixth Embodiment) FIG. 11 shows a lens configuration of a sixth embodiment of the present invention. Its specifications are magnification β = 1/10,
The numerical aperture NA is 0.4, and the image size φ is 3.0 mm.

Table 6 shows the specification values and aberration coefficients of the optical system of the sixth embodiment.

[0054]

[Table 6]

As is clear from the comparison of the coma aberration coefficient of the fourth surface among the aberration coefficients shown in Table 6 with the comatic aberration coefficient of the second surface in the conventional optical system shown in Table 7, the fifth embodiment of the present invention. In the figure, coma is greatly reduced. This is apparent from the total value of the coma aberration shown in the lowermost column of the third-order aberration coefficient.

FIG. 12 shows various aberration diagrams of the optical system of the sixth embodiment. As is clear from the various aberration diagrams, on-axis spherical aberration and off-axis various aberrations, particularly distortion, are well corrected, and further, coma on the meridional image plane can be corrected. Therefore, in this embodiment, it is possible to satisfactorily correct the distortion and improve the off-axis imaging performance in the low frequency region. In particular, the optical system becomes brighter than in the first to third embodiments of the present invention, and various aberrations are satisfactorily corrected over the entire on-axis and off-axis image regions.

Further, the condition corresponding values of the sixth embodiment are shown below.

Imaging magnification β = −0.1 f1 / f = 3.03 (f1 / f) · β = 0.303

Table 7 shows the specification values and aberration coefficients of the conventional optical system.

[0060]

[Table 7]

According to the above embodiment of the present invention, distortion can be corrected by the first lens, and a lens having high resolution can be achieved. Further, coma in the off-axis meridional direction can be corrected by the second lens, and the angle of view and the numerical aperture can be increased.

[0062]

According to the high-resolution imaging lens system of the present invention,
Distortion aberration is satisfactorily corrected, and off-axis imaging performance in a low frequency region is improved. A can be further increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing a lens configuration of an optical system according to a first example of the present invention.

FIG. 2 is a diagram illustrating various aberrations of the optical system according to the first example.

FIG. 3 is a diagram illustrating a lens configuration of an optical system according to a second example of the present invention.

FIG. 4 is a diagram illustrating various aberrations of the optical system according to Example 2.

FIG. 5 is a diagram showing a lens configuration of an optical system according to Example 3 of the present invention.

FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 3.

FIG. 7 is a diagram illustrating a lens configuration of an optical system according to Example 4 of the present invention.

FIG. 8 is a diagram illustrating various aberrations of the optical system according to Example 4.

FIG. 9 is a diagram showing a lens configuration of an optical system according to Example 5 of the present invention.

FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 5.

FIG. 11 is a diagram showing a lens configuration of an optical system according to Example 6 of the present invention.

FIG. 12 is a diagram illustrating various aberrations of the optical system according to Example 6.

FIG. 13 is a diagram showing a lens configuration of a conventional optical system.

FIG. 14 is a diagram showing various aberrations of a conventional optical system.

[Explanation of symbols]

 L1 first lens L2 second lens L3 third lens L4 fourth lens L5 fifth lens L6 sixth lens L7 seventh lens L8 eighth lens L9 ninth lens

Claims (5)

[Claims] 1. A first lens having a positive refractive power and being disposed closest to an object side, a second lens having a positive refractive power, and a positive lens having a convex surface facing the object side in order from the object side. A third lens disposed adjacent to the third lens and having a shape having a concave surface facing the image side; an aperture; and a negative lens having a shape having a concave surface facing the object side. A fifth lens, a positive sixth lens disposed adjacent to the fifth lens and having a shape with the convex surface facing the image side, a seventh lens having a positive refractive power, and a positive refractive power. A high-resolution imaging lens system, characterized in that the diaphragm and the respective lenses are arranged so as to be telecentric on the image side. 2. When the focal length of the first lens is f1, the focal length of the entire imaging lens system is f, and the absolute value of the imaging magnification of the entire imaging lens system is β, 0.26 <0.26 < 2. The high-resolution imaging lens system according to claim 1, wherein a condition of (f1 / f) .beta. <1.0 is satisfied. 3. The high resolution lens according to claim 1, wherein the second lens has a meniscus shape having a convex surface on the object side in order to improve off-axis imaging performance in a low frequency region. Image forming lens system. 4. A high resolution image as claimed in claim 1, wherein a ninth lens having a positive refractive power is arranged on the image side of said sixth lens in order to increase the image side numerical aperture. Imaging lens system. 5. The high-resolution imaging lens according to claim 1, wherein the image-side lens surface of the lens disposed closest to the image has a concave surface facing the image side. system.