JP2000258686A - Photographing lens system having high-resolution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photographing lens system having high resolution suitable for a photographing lens, etc., for electronic image equipment such as a video camera or a digital still camera. SOLUTION: This lens system is equipped with an aperture diaphragm S, a front lens group GF having negative refractive power and arranged on the object side of the diaphragm S, and a rear lens group GR having positive refractive power and arranged on the image side thereof. The lens group GF has at least a positive lens LA having an aspherical surface formed so that the positive refractive power may be weakened as separating from an optical axis. The lens group GR is provided with at least a negative meniscus lens LU turning a convex surface to the object side and having center thickness larger than maximum image height and a positive lens LB having an aspherical surface formed so that the positive refractive power may be weakened as separating from the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic lens system, and more particularly to a high-resolution photographic lens system for electronic images using a solid-state image sensor such as a CCD.

[0002]

2. Description of the Related Art Conventionally, photographing lenses having a wide angle of view of 60 degrees or more have been disclosed in Japanese Patent Publication No. 57-54767, Japanese Patent Publication No. 1-53765, and Japanese Patent Publication No. 8-205593. . Japanese Patent Publication No. 57-54767 discloses a technique mainly used in an optical system for silver halide photography. In addition, Japanese Patent Publication No. 1-53765 and Japanese Patent Publication No. 8-20593 disclose techniques used in an optical system for ITV and an optical system for electronic images.

[0003]

However, in the prior art disclosed in each of the above-mentioned publications, the resolving power tends to be insufficient for recent miniaturization of the pixels of the image pickup device. In addition, one of the inability to secure a sufficiently long back focus, the inability to keep the exit pupil away from the image plane sufficiently, and the correction of various aberrations, particularly the correction of distortion, is not sufficient. Has two disadvantages. As a result, the taking lens system according to the prior art does not have sufficient resolving power to be applied to a taking lens for a high-resolution electronic imaging system.

The present invention has been made in view of the above-mentioned problems, and has a photographic lens having a sufficient resolution to be applied to a photographic lens for a high-resolution electronic imaging device such as a video camera or a digital still camera. It is intended to provide a system.

[0005]

In order to solve the above-mentioned problems, the present invention provides an aperture stop, a front lens group GF having a negative refractive power and disposed on the object side of the aperture stop, and the aperture stop. A rear lens group GR having a positive refractive power disposed on the image side of the lens, and the front lens group GF has an aspheric surface formed such that the positive refractive power becomes weaker as the distance from the optical axis increases. Having at least a positive lens LA,
The rear lens group GR includes a negative meniscus lens L having a convex surface facing the object side and having a center thickness larger than the maximum image height.
U and a positive lens LB having an aspheric surface formed so that the positive refractive power becomes weaker as the distance from the optical axis increases.

According to a preferred aspect of the present invention, the distance along the optical axis from the most object side surface of the photographic lens system to the image plane is TL, the maximum image height is Y0, and the focus of the photographic lens system is When the distance is f and the distance along the optical axis from the image plane to the exit pupil is EP, 8.0 <TL / Y0 <25.0 (1) -0.5 <f / EP <0.5 The condition of (2) is satisfied.

According to another preferred embodiment of the present invention, the positive lens LA in the front lens group GF is a positive meniscus lens having a convex surface facing the object side, and the positive lens LA in the rear lens group GR. The positive lens LB is a biconvex lens, the focal length of the positive meniscus lens LA is fLA, the focal length of the biconvex lens LB is fLB, and the most image side surface of the positive meniscus lens LA and the biconvex lens LB. DAB is the distance along the optical axis between the most object side surface
When the maximum image height is Y0, the condition of 2.0 <fLA / fLB <30.0 (3) 5.0 <DAB / Y0 <25.0 (4) is satisfied.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, conditions suitable for a photographing lens for an electronic imaging device such as a digital still camera and a video camera will be described. The first condition is that a sufficiently long back focus is secured as described above in order to insert an optical low-pass filter, a color separation prism, and the like. The second condition is that in order to avoid shading, a sufficient amount of peripheral light is secured and the exit pupil is sufficiently away from the image plane.

For this reason, the present invention employs a retrofocus type configuration in which a negative lens group (front lens group GF) is disposed on the object side and a positive lens group (rear lens group GR) is disposed on the image side. I have. By employing this configuration, it is easy to ensure a sufficiently long back focus compared to the focal length of the entire lens system. Also, in order to ensure sufficient telecentricity, it is necessary to dispose an aperture stop near the object-side principal point position of the entire optical system on the image side of the aperture stop. In the present invention, by arranging the aperture stop at an appropriate position in the optical path between the front lens group GF and the rear lens group GR, it is possible to secure sufficient telecentricity while achieving good imaging performance. I found what I could do.

Further, in the present invention, in addition to the above-described structure, a relatively long overall length is employed and an aspherical surface is effectively used, thereby achieving a high resolution. Further, they have found that it is important to use a lens having a large center thickness and to provide an appropriate refractive power distribution to each lens group in order to obtain a high resolution. In addition, by making at least one of the positive lens arranged closest to the object side and the positive lens arranged closest to the image side function as a diffractive optical element having a diffractive action, excellent correction can be made particularly for chromatic aberration. As a result, it has been found that excellent optical performance can be achieved.

Hereinafter, the configuration of the present invention will be described along with the description of the conditional expressions. In the present invention, it is desirable to satisfy the following conditional expressions (1) and (2). 8.0 <TL / Y0 <25.0 (1) -0.5 <f / EP <0.5 (2) where TL is the optical axis from the most object side surface of the taking lens system to the image plane. , And Y0 is the maximum image height. F is the focal length of the taking lens system, and EP is the distance along the optical axis from the image plane to the exit pupil. In addition,
The sign of EP is positive when the exit pupil is on the object side of the image plane, and negative when the exit pupil is behind the image plane.

Conditional expression (1) defines the distance along the optical axis from the first surface (the surface closest to the object) of the taking lens system to the image plane (ie, the total length of the taking lens system) TL with respect to the maximum image height Y0. It specifies an appropriate range for the ratio. In general,
An optical system aimed at high resolution tends to have a longer overall length, but it is extremely important to balance the practical overall length with good imaging performance in terms of the lens configuration.
This is because the pupil position, the magnitude of the back focus, the achievable F-number, the amount of off-axis aberration, and the like greatly change depending on the magnitude of the full length TL. As described above, the overall length TL of the photographing lens system is an important factor because it has a significant effect on the specific configuration and the achieved performance of the finally formed lens system. In the conditional expression (1), the maximum image height Y
A value of 0 is used to standardize the full length TL.

When the value exceeds the upper limit of conditional expression (1), the total length T
Not only does L become too long, making it easy to increase the size,
It is not preferable because the photographing lens system is not suitable for practical use due to an increase in the lens diameter. In addition, high-order field curvature and astigmatism are likely to occur, which tends to cause a decrease in resolution around the screen, which is not preferable. On the other hand, when the value goes below the lower limit of conditional expression (1), the total length TL becomes too short, and it becomes difficult to secure a sufficient back focus. In addition, field curvature and astigmatism are likely to occur, and as a result, the resolution around the screen is likely to decrease, which is not preferable. In order to achieve the effect of the present invention more sufficiently, the upper limit of conditional expression (1) should be set to 20.0.
And the lower limit is preferably set to 10.0.

Conditional expression (2) defines an appropriate range for the ratio of the focal length of the taking lens system to the distance from the image plane to the exit pupil along the optical axis. If the upper limit of conditional expression (2) is exceeded, the exit pupil position will be too far from the image plane, and the optical system behind the aperture stop (ie, the rear lens group GR)
This is not preferable because it causes an increase in diameter. In addition, distortion tends to increase on the negative side, which is not preferable from the viewpoint of imaging performance.

On the other hand, when the value goes below the lower limit of conditional expression (2),
The back focus is too small, and it is difficult to secure a space for disposing a filter, a prism, and the like. Furthermore, the exit pupil is too close to the image plane, which tends to cause shading, which is not preferable. It is desirable that the position of the aperture stop be slightly shifted from the object-side principal point position to the image side in order to avoid an increase in the diameter of the optical system behind the aperture stop. From this viewpoint, in order to more fully exert the effects of the present invention, it is preferable to set the lower limit of conditional expression (2) to 0.03 and the upper limit to 0.25.

In the present invention, the positive lens LA is a positive meniscus lens having a convex surface facing the object side, and the positive lens LB is a biconvex lens, and satisfies the following conditional expressions (3) and (4). It is desirable. 2.0 <fLA / fLB <30.0 (3) 5.0 <DAB / Y0 <25.0 (4) where fLA is the focal length of the positive meniscus lens LA, and fLB is the focal length of the biconvex lens LB. Distance. Also, D
AB is the distance along the optical axis between the most image side surface of the positive meniscus lens LA and the most object side surface of the biconvex lens LB. Further, Y0 is the maximum image height.

Conditional expression (3) indicates that the positive meniscus lens LA
An appropriate range is defined for the ratio between the focal length fLA of the biconvex lens LB and the focal length fLB of the biconvex lens LB. That is, the conditional expression (3) defines an appropriate refractive power distribution for the positive meniscus lens LA and the biconvex lens LB. In the present invention, it has been found that introducing an aspherical surface into the front lens group GF is particularly effective in correcting distortion among various aberrations and correcting coma below the principal ray. In addition, introducing an aspherical surface into the rear lens group GR makes it possible to correct distortion among various aberrations and to achieve coma aberration higher than the principal ray while securing a sufficient back focus and keeping the exit pupil sufficiently away from the image plane. It was also found to be particularly effective in correcting the image. Conditional expression (3) defines an appropriate paraxial refractive power distribution found for the positive meniscus lens LA and the biconvex lens LB both having an aspheric surface.

When the value exceeds the upper limit of conditional expression (3), the focal length fLA of the positive meniscus lens LA becomes too large.
Distortion tends to increase on the negative side, and further, coma tends to occur in light rays below the principal ray.
As a result, the entire aberration balance tends to be lost, which is not preferable. On the other hand, when the value goes below the lower limit of conditional expression (3),
The focal length fLB of the biconvex lens LB becomes too large, so that the distortion is likely to be increased on the positive side, and further, coma is easily generated in the light rays above the principal ray. As a result, the entire aberration balance tends to be lost, which is not preferable. In order to more fully exert the effects of the present invention, it is preferable to set the upper limit of conditional expression (3) to 25.0 and the lower limit to 3.0.

In the present invention, the aspheric surface of the positive meniscus lens LA in the front lens unit GF and the rear lens unit G
It has also been found that both aspherical surfaces of the biconvex lens LB in R are preferably formed such that the positive refracting power becomes weaker as the distance from the optical axis increases. This means that in the aspheric surfaces of both lenses, the local radius of curvature increases as the distance from the optical axis increases. It has also been found that it is most effective to dispose the front lens group GF closest to the object side of the optical system and arrange the rear lens group GR closest to the image side of the optical system. Furthermore, it was also found that if an aspherical surface is not used, it is impossible to achieve a high resolution because the field curvature and coma cannot be sufficiently corrected.

In the positive meniscus lens LA and the biconvex lens LB, only one lens surface may be formed in an aspherical shape, or both lens surfaces may be formed in an aspherical shape. However, when only one lens surface is formed to be aspherical, it is desirable that the image-side surface of the positive meniscus lens LA and the object-side surface of the biconvex lens LB are formed to be aspherical. This is because, due to the mechanical structure of the lens barrel, by directly attaching the aspherical surface to the body, it is possible to adopt a structure that reduces the performance deterioration due to the eccentricity built in.

Conditional expression (4) indicates that the positive meniscus lens LA
It shows an appropriate range for the arrangement of the lens and the biconvex lens LB. Specifically, an appropriate range is defined for a value obtained by standardizing the axial distance DAB between the most image-side surface of the positive meniscus lens LA and the most object-side surface of the biconvex lens LB with the maximum image height Y0. . When the value exceeds the upper limit of conditional expression (4),
Since the on-axis distance DAB is too large, higher-order field curvature and coma aberration are likely to occur, and the entire aberration balance is easily lost, which is not preferable. In addition, the manufacturing tolerance of the aspherical surface tends to be strict, which is not preferable from this viewpoint.

On the other hand, when the value goes below the lower limit of conditional expression (4),
The on-axis distance DAB becomes too small, and the degree of freedom in correcting coma and curvature of field decreases, which is not preferable. In particular,
It is difficult to correct coma aberration below the principal ray, and the Petzval sum tends to be too large on the positive side. As a result, the entire aberration balance tends to be lost, which is not preferable. In order to more fully exert the effects of the present invention, it is preferable to set the upper limit of conditional expression (4) to 13.0 and the lower limit to 8.0.

In the present invention, the front lens group G
F includes a negative meniscus lens LM, a biconcave lens LR, and a biconvex lens LW, and the rear lens group GR includes a cemented lens LS that is made of a cemented negative meniscus lens LU and has a positive refractive power as a whole. It is desirable to satisfy the expressions (5) and (6). 0.5 <dM / Y0 <5.0 (5) 1.5 <dS / Y0 <10.0 (6) where dM is the center thickness of the negative meniscus lens LM, and dS is the center of the cemented lens LS. And Y0 is the maximum image height.

Conditional expression (5) defines an appropriate range for the ratio between the center thickness dM of the negative meniscus lens LM in the front lens group GF and the maximum image height Y0. When the value exceeds the upper limit of conditional expression (5), the center thickness of the negative meniscus lens LM becomes too large, and the lens component itself becomes large.
It is not preferable because it is disadvantageous for reducing the overall size and weight. Further, the Petzval sum shifts excessively to the negative side, and as a result, the field curvature becomes undesirably large to the positive side.
On the other hand, when the value goes below the lower limit value of conditional expression (5), coma aberration lower than the principal ray easily occurs, which is not preferable. Further, the Petzval sum is excessively shifted to the positive side, and as a result, the field curvature becomes undesirably large to the negative side. In order to more fully demonstrate the effects of the present invention,
It is preferable to set the upper limit value of conditional expression (5) to 3.0 and the lower limit value to 0.8.

Conditional expression (6) defines an appropriate range for the ratio between the center thickness dS of the cemented lens LS in the rear lens group GR and the maximum image height Y0. Exceeding the upper limit of conditional expression (6) is not preferable because the center thickness of the cemented lens LS becomes too large, and the lens component itself becomes large, which is disadvantageous in reducing the overall size and weight. Further, the Petzval sum shifts to the negative side, and as a result, the field curvature becomes undesirably large to the positive side. On the other hand, when the value goes below the lower limit value of the conditional expression (6), coma aberration lower than the principal ray easily occurs, which is not preferable. Further, the Petz-Pearl sum shifts to the positive side, and as a result, the field curvature becomes extremely large to the negative side, which is not preferable. In order to achieve the effect of the present invention more sufficiently, the upper limit of conditional expression (6) should be set to 4.0.
And the lower limit is preferably set to 2.3.

In the present invention, it is desirable to satisfy the following conditional expressions (7) and (8). 2.0 <Φ1 / Y0 <12.0 (7) 0.015 <fLB / fLS <2.0 (8) Here, Φ1 is the effective diameter of the most object side surface of the photographing lens system, and Y0 is This is the maximum image height. FLB is the focal length of the positive lens LB, and fLS is the focal length of the cemented lens LS.

Conditional expression (7) defines an appropriate range for the ratio between the effective diameter Φ1 through which light rays on the most object side surface of the taking lens system pass and the maximum image height Y0. Front lens group G
When the positive lens LA of F is disposed closest to the object side,
Φ1 is the effective diameter of the positive lens LA on the object side. Exceeding the upper limit of conditional expression (7) is not preferable because the effective diameter becomes too large and the size of the entire optical system tends to increase. In addition, stray light is likely to be mixed, and as a result, the imaging performance is apt to deteriorate, which is not preferable. On the other hand, when the value goes below the lower limit of conditional expression (7), the effective diameter becomes too small, the peripheral light quantity tends to be insufficient, and the brightness around the screen tends to be insufficient. In order to achieve the effect of the present invention more sufficiently, it is preferable to set the upper limit of conditional expression (7) to 8.0 and the lower limit to 3.0.

Conditional expression (8) is a conditional expression for defining the distribution of refractive power inside the rear lens group GR, and the positive lens LB
An appropriate range is defined for the ratio of the focal length fLB of the cemented lens LS to the focal length fLS of the cemented lens LS. Exceeding the upper limit of conditional expression (8) is not preferable because it is difficult to ensure a sufficient back focus. In addition, the convergence of the positive lens LB becomes too strong, and the overall aberration balance is likely to be lost. In particular, it becomes difficult to correct spherical aberration and coma, which is not preferable. On the other hand, when the value goes below the lower limit of conditional expression (8), the back focus is easily secured, but the deflection angle of the positive lens LB becomes too large, and it becomes difficult to correct coma aberration, which is not preferable. Further, since the Petzval sum tends to shift to the positive side, the curvature of field tends to be excessive to the negative side, which is not preferable from this viewpoint. In addition,
In order to achieve the effect of the present invention more sufficiently, it is preferable to set the upper limit of conditional expression (8) to 1.2 and the lower limit to 0.02.

When the photographic lens system of the present invention is actually constructed, in addition to the above-mentioned conditions, the following conditional expression (9)
It is desirable to satisfy (11). -3.0 <(Rbm + Ram) / (Rbm-Ram) <-0.2 (9) -5.0 <(Rbu + Rau) / (Rbu-Rau) <-1.5 (10) 1.5 <BF / Y0 <10.0 (11) where Ram is the radius of curvature of the most object side surface of the negative meniscus lens LM, and Rbm is the radius of curvature of the most image side surface of the negative meniscus lens LM. Rau is the radius of curvature of the surface closest to the object side of the negative meniscus lens LU.
bu is the radius of curvature of the most image side surface of the negative meniscus lens LU. Further, BF is the back focus of the taking lens system, and Y0 is the maximum image height.

The conditional expressions (9) and (10) define appropriate ranges for the shape factor (shape factor) of the negative meniscus lens LM and the shape factor of the negative meniscus lens LU. That is, conditional expressions (9) and (1)
In (0), the negative meniscus lens LM and the negative meniscus lens LU have shapes that can achieve good imaging performance, and that are favorable in terms of production technology. Exceeding the upper limit of conditional expression (9) is not preferable because the curvature of field becomes too large on the positive side. Further, it is not preferable because the shape becomes difficult to process, and the production technology becomes unreasonable. On the other hand, when the value goes below the lower limit of conditional expression (9), the distortion becomes undesirably large on the negative side. In order to achieve the effect of the present invention more sufficiently, it is preferable to set the upper limit of conditional expression (9) to -1.5 and the lower limit to -2.0.

When the value exceeds the upper limit of conditional expression (10), the spherical aberration becomes excessively large on the positive side, so that it becomes impossible to obtain good image forming performance, which is not preferable. Further, it is not preferable because the shape becomes difficult to process, and the production technology becomes unreasonable. On the other hand, when the value goes below the lower limit of conditional expression (10), not only the distortion becomes excessively large on the negative side, but also a ghost due to surface reflection easily occurs, which is not preferable. In order to achieve the effect of the present invention more fully, conditional expression (1) must be satisfied.
It is preferred that the upper limit of 0) be -2.0 and the lower limit be -3.5.

Conditional expression (11) defines an appropriate range for the magnitude of the back focus with respect to the maximum image height. Exceeding the upper limit of conditional expression (11) is not preferable because the back focus becomes too large and the entire optical system becomes large. Also, the diameter of the rear lens becomes too large, which tends to increase the size of the entire optical system. In addition, distortion tends to increase on the negative side, which is not preferable from the viewpoint of imaging performance. On the other hand, when the value goes below the lower limit of conditional expression (11), the back focus becomes too small, and it becomes difficult to secure a space for disposing a filter, a prism, and the like. Furthermore, the exit pupil is too close to the image plane, which tends to cause shading, which is not preferable. In order to more fully demonstrate the effects of the present invention,
The upper limit of conditional expression (11) is set to 3.5, and the lower limit is set to 2.0.
It is preferable that

When an optical system is actually constructed, it is desirable to satisfy the following conditions in addition to the above conditions. First, in order to sufficiently correct various aberrations, the photographing lens system should be arranged in order from the object side with a positive lens LA, a negative meniscus lens LM, a biconcave lens LR, and a biconvex lens LW.
, An aperture stop, a cemented lens LS, and a positive lens LB.

The positive lens LA not only has an aspheric surface as described above, but also has a positive meniscus shape having a convex surface facing the object side so that its basic shape can have a structure strong against the angle of view. Is desirable. Similarly, it is desirable that the lens LM has a negative meniscus shape with the convex surface facing the object side so that the lens LM can have a strong structure with respect to the angle of view. In addition, it is desirable to use a structure having a large center thickness in order to correct the Petzval sum. Generally, securing a sufficiently large center thickness is preferable from the viewpoint of production technology, because it is easy to process into a desired shape at the time of manufacturing and a manufacturing error hardly occurs.

The lens LR preferably has a biconcave shape for aberration correction (especially for correction of coma aberration of light rays below the principal ray), and the object-side surface has a larger radius of curvature than the image-side surface. It is desirable that the absolute value is large. It is desirable that the center thickness of the biconcave lens LR is smaller than the maximum image height, contrary to the negative meniscus lens LM. The lens LW is used to correct spherical aberration and coma for light rays below the principal ray.
Desirably, it has a biconvex shape, and its refractive index is 1.55.
It is desirable that this is the case. Further, it is preferable to have a center thickness equal to or more than the maximum image height from the viewpoint of imaging performance and the viewpoint of production technology.

As described above, it is desirable that the cemented lens LS be a cemented lens having a positive refractive power, especially for correcting axial chromatic aberration. Specifically, it is desirable that the cemented lens LS be a cemented lens composed of a negative meniscus lens LU having a center thickness larger than the maximum image height and a convex surface facing the object side, and a biconvex lens. This is because the thick negative meniscus lens LU not only allows the Petzval sum to be reduced and appropriately controlled, but also facilitates securing telecentricity due to its strong negative refractive power. The positive lens LB is a biconvex lens having an aspheric surface formed so that the positive refractive power becomes weaker as the distance from the optical axis increases. It is technically preferable. This aspherical shape is particularly effective for correcting coma aberration of a light ray above the principal ray.

Hereinafter, glass (optical material) forming each lens will be described. First, in order to sufficiently correct various aberrations, it is desirable that the lens component on the object side of the aperture stop be made of glass having a refractive index of 1.65 or more and an Abbe number of 45 or more. In particular, the negative meniscus lens L
It is desirable that the refractive index of M is 1.75 or more. On the other hand, on the image side of the aperture stop, it is desirable to have at least one lens component made of low dispersion glass having an Abbe number of 80 or more. Further, the specific position of the aperture stop is determined by satisfying the above-mentioned conditional expression (2) while keeping the front lens group G
It is desirable to arrange in the optical path between F and the rear lens group GR. At the time of focusing (at the time of focusing), the aperture stop may be fixed without moving along the optical axis.

When the rear lens group GR is constituted by three lenses, it is desirable to constitute one negative lens and two positive lenses. More specifically, it is composed of a cemented lens LS having a positive refractive power including a negative meniscus lens LU having a large center thickness with a concave surface having a strong curvature directed to the image side and a biconvex lens, and a biconvex lens LB having an aspheric surface. It is desirable. It is preferable that the cemented lens LS has a divergent cemented surface and satisfies the following conditional expressions (12) and (13). Δν> 35 (12) Δn> 0.25 (13) Here, Δν is the difference between the Abbe numbers of the two lenses sandwiching the cemented surface of the cemented lens LS. Δn is the d-line (λ = 5) of the two lenses sandwiching the cemented surface of the cemented lens LS.
87.6 nm).

In order to further correct various aberrations and further improve the imaging performance, it is also important to distribute the refractive power between the front lens group GF and the rear lens group GR. It is desirable to satisfy −50 <fR / fF <−1.5 (14) where fF and fR are the front lens groups GF, respectively.
And the focal length of the rear lens group GR. As described above, due to the configuration of the retrofocus type lens system, the front lens group GF on the front side of the aperture stop has a negative refractive power, and the rear lens group GR on the rear side has a positive refractive power.
By satisfying conditional expression (14), it is possible to obtain a sufficient back focus and to obtain a good balance between the field curvature and the coma.

Hereinafter, focusing on a short-distance object will be described. First, the focusing method in which the rear lens group GR is moved along the optical axis to perform focusing on a short-distance object has several advantages. First, the rear lens group GR among the lens groups constituting the taking lens system
Can be configured relatively small, it is advantageous from the viewpoint of the mechanical configuration to make the rear lens group GR a focusing lens group, and this focusing method is suitable for, for example, an autofocus mechanism. . In addition, this focusing method is advantageous in terms of imaging performance because aberration fluctuations due to focusing are small and good imaging performance can be obtained even in a short-distance focusing state. At this time, it is desirable that a substantially parallel system is provided between the front lens group GF and the rear lens group GR.

Further, in the case of a focusing system (so-called floating system) in which both the front lens unit GF and the rear lens unit GR are extended while changing the air gap between the front lens unit GF and the rear lens unit GR, the focus around the screen is changed. Focusing can be performed while maintaining an extremely good image performance. Also in this case, it is desirable that the front lens group GF and the rear lens group GR have a substantially parallel system. In addition,
As the size of the photographing magnification increases, the depth on the object field side becomes shallower, so that there is an inconvenience that the subject is likely to be out of focus. However, it is possible to prevent out of focus by combining with an autofocus system.

In the present invention, the rear lens group GR includes:
It has been found that by introducing a lens surface by diffraction (hereinafter, referred to as "diffractive lens surface"), excellent correction can be made, particularly with respect to chromatic aberration, and as a result, further excellent optical performance can be achieved. Hereinafter, this point will be described in detail. In general, three types of action of bending light rays are known: refraction, reflection, and diffraction. In the present invention, the “diffractive lens surface”
It refers to a lens surface capable of obtaining various optical functions by bending a light beam by utilizing a diffraction function as a light wave. Specifically, it is known that the diffractive lens surface has a number of advantages in that it can generate negative dispersion and that it can be easily miniaturized, and that it is particularly capable of excellent correction of chromatic aberration.

The details of the properties of the diffractive optical element and the design method using the high refractive index method are described in "Introduction to the Diffractive Optical Element Supervised by the Japan Society of Applied Physics".
FIG. 7 is a diagram modeling and showing a state in which a diffractive lens surface is formed on the lens surface by the high refractive index method. In FIG. 7, a layer 2 (shown by oblique lines in the figure) made of high refractive index glass is formed on one lens surface of the lens 1. The high-refractive-index glass layer 2 has a predetermined optical path difference distribution from the center of the lens 1 to the periphery thereof, and has a surface formed in an aspherical shape. As described above, a diffractive lens surface formed by the high refractive index method is formed on one lens surface of the lens 1 shown in FIG. In the present invention, it has been found that forming a diffractive lens surface on one of the surfaces of the rear lens group GR is effective for improving the imaging performance.

First, as described above, important conditions for a lens system for an electronic image are to secure a sufficiently large back focus and to keep an exit pupil sufficiently away from an image plane. This indicates that the height of each ray is higher (the distance from the optical axis becomes larger) at the most object side portion or the most image side portion in the electronic image lens system, and the occurrence of aberration is reduced. It means that it is easy to grow. In the present invention, the positive lens LA
Introducing an aspherical surface or a diffractive lens surface into the positive lens LB and the positive lens LB suppresses the occurrence of aberration and enables good aberration correction.
In the present invention, the aspherical surface of the positive lens LB is effective in correcting the upper coma and the curvature of field, and the diffractive lens surface is effective in correcting the chromatic aberration of magnification and the chromatic difference of the coma of the light above the principal ray. It turned out to be. In the present invention, it has been found that arranging a diffractive lens surface in the rear lens group GR is particularly effective for good chromatic aberration correction, and in particular, arranging it on the positive lens LB is effective.

When a diffractive lens surface is used in the imaging optical system, a problem of flare due to higher-order diffracted light has been pointed out. In the case of an electronic image, the DC component of the image signal must be appropriately cut. Thus, a sufficiently practical image can be obtained, so that there is not much problem. Note that the refractive power of the diffractive lens surface is desirably a weak positive refractive power.
This is necessary especially for correcting lateral chromatic aberration. The focal length fd of the diffractive lens surface is
It is preferred that the focal length fR be 50 times or more and 100 times or less the focal length fR of R. Further, in the present invention, the lenses LA and LB originally formed in an aspherical shape as a refraction surface are used.
It has also been found that adding a kinoform having a diffractive action or a multi-level binary layer to the lens surface is preferable in terms of production technology. Hereinafter, this point will be further described.

In general, when an aspheric lens is formed by a glass molding method, a so-called "mold" is formed, and a large number of replicas which transfer the shape of the "mold" are made of glass at low cost and with high precision. Therefore, to form a diffractive lens surface on a lens surface originally formed as an aspherical surface as a refracting surface, it is only necessary to add a kinoform or binary layer to the "mold". This method has a high practical value because it does not significantly increase the cost and the process time. In particular, the method of adding a binary layer to the lens surface is similar to the method of manufacturing a semiconductor chip,
More practical value. FIG. 8 shows a series of flow procedures for obtaining a kinoform from the optical path difference function obtained by the high refractive index method and converting the kinoform into an 8-level binary shape. Note that the lens surface may be formed in a flat or spherical shape, and a thin transparent resin layer may be added to the surface to form a kinoform or a binary shape.

Further, by displacing a part of the lens or lens group of the taking lens system of the present invention in a direction substantially orthogonal to the optical axis, image stabilization (correction of image position blur caused by lens system blur) is performed. ) Can be performed. Further, it is also possible to perform vibration proof by displacing a part or the whole of the rear lens group GR as a vibration proof lens group in a direction substantially orthogonal to the optical axis. At this time, it is preferable that the image stabilizing lens group includes at least one positive lens and at least one negative lens. Further, it goes without saying that better optical performance can be obtained by further using an aspherical lens, a diffractive optical element, a gradient index lens, and the like for each lens constituting the lens system of the present invention.

[0048]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each embodiment, the taking lens system of the present invention includes a front lens group GF having a negative refractive power disposed on the object side of the aperture stop S and a positive refractive power disposed on the image side of the aperture stop S. And the rear lens group GR.

In each embodiment, the height of the aspheric surface in the direction perpendicular to the optical axis is defined as y, and the distance along the optical axis from the tangent plane at the vertex of the aspheric surface to the position on the aspheric surface at height y. When the (sag amount) is x, the vertex radius of curvature is r, the conic constant is κ, and the nth-order aspherical surface coefficient is Cn, it is expressed by the following equation (a). In the third embodiment,
Similarly, the aspheric surface of the diffractive lens surface obtained by the high refractive index method is expressed by the following equation (a).

[Number 1] ^{x = (y 2 / r)} / {1+ (1-κ · y 2 / r 2) 1/2} + C 4 · y 4 + C 6 · y 6 + C 8 · y 8 + C 10 · y 10 (A) In each embodiment, an asterisk is attached to the right side of the surface number on the lens surface formed in an aspherical shape. In the third embodiment, the aspherical surface of the diffractive lens surface has ** on the right side of the surface number.
Marked.

[First Embodiment] FIG. 1 is a diagram showing a lens configuration of a taking lens system according to a first embodiment of the present invention.
In the first embodiment, the present invention is applied to a photographing lens for an electronic imaging device. In the photographing lens system shown in FIG. 1, the front lens group GF includes, in order from the object side, a positive meniscus lens LA having a convex surface facing the object side and an aspheric surface on the image side, and a convex surface facing the object side. Negative meniscus lens LM
, A biconcave lens LR, and a biconvex lens LW.

The rear lens group GR includes, in order from the object side, a cemented positive lens LS formed by bonding a negative meniscus lens LU having a convex surface toward the object side and a biconvex lens;
A biconvex lens LB having an aspherical surface on the object side. An aperture stop S is arranged in the optical path between the front lens group GF and the rear lens group GR, and a parallel plane plate (filter) F is arranged in the optical path between the biconvex lens LB and the image plane. ing. The image-side aspheric surface of the positive meniscus lens LA and the object-side aspheric surface of the biconvex lens LB are formed such that the positive refracting power becomes weaker as the distance from the optical axis increases.

The following Table (1) shows values of specifications of the first embodiment of the present invention. In Table (1), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, and φS represents the aperture stop diameter. The surface number indicates the order of the lens surface from the object side along the traveling direction of the light ray, r indicates the radius of curvature of the lens surface (vertical radius of curvature for an aspheric surface),
d is the distance between the lens surfaces, n (d) and n (g) are the d-line (λ = 587.6 nm) and the g-line (λ = 43, respectively).
5.8 nm), and ν indicates the Abbe number.

[0053]

Table 1 f = 6 FNO = 2.8 2ω = 58.6 ° φS = 4.36 Surface number r dn (d) n (g) ν 1 32.0110 3.3 1.693500 1.709750 53.31 (LA) 2 * 83.0260 0.13 16.3258 6.0 1.772500 1.791920 49.61 (LM) 4 5.0303 1.9 5 -29.4200 1.0 1.696800 1.712350 55.48 (LR) 6 6.9030 4.35 7 14.3630 5.8 1.696800 1.712350 55.48 (LW) 8 -25.8310 1.59 ∞ 2.0 (Aperture stop S) 10 12.2960 6.0 1.846660 1.893900 23.83 (LS) 11 5.3822 3.5 1.497000 1.504510 81.61 12 -29.0400 0.1 13 * 10.2830 3.9 1.516800 1.526670 64.20 (LB) 14 -13.8470 3.4018 15 ∞ 4.4 1.516800 1.526670 64.20 (F) 16 ∞ 2.499 (aspherical data) r κ C ₄ 2 Surface 83.0260 1.00000 -2.20510 × 10 ^-5 C ₆ C ₈ C ₁₀ 1.61130 × 10 ^-7 -1.05 450 × 10 ^-10 -3.31920 × 10 ^-12 r κ C ₄ 13 surface 10.2830 1.00000 -2.80 280 × 10 ^-5 C ₆ C _{8 ^{C 10 8.52130 × 10 -6 -1.95240 ×}} 10 -7 4.60780 × 10 -9 ( values for conditional expressions) TL = 49.75 EP = 38.81 0 = 3.3 fLA = 73.184 fLB = 12.084 DAB = 32.25 dM = 6 dS = 9.5 Φ1 = 19.2 fS = 32.286 BF = 8.802 Δν = 57.78 Δn = 0.34966 fF = -27.041 fR = 11.309 f = 6.0007 (1) TL / Y0 = 15.076 (2) f / EP = 0.548 (3) fLA / fLB = 6.056 ( 4) DAB / Y0 = 9.773 (5) dM / Y0 = 1.818 (6) dS / Y0 = 2.879 (7) Φ1 / Y0 = 5.818 (8) fLB / fLS = 0.374 ( 9) (Rbm + Ram) / (Rbm-Ram) =-1.891 (10) (Rbu + Rau) / (Rbu-Rau) =-2.557 (11) BF / Y0 = 2.667 (12) Δν = 57. 78 (13) Δn = 0.34966 (14) fR / fF = -2.391

FIG. 2 is a diagram showing various aberrations of the first embodiment when focused on an object at infinity. In each aberration diagram, FNO represents the F number, Y represents the image height, and d represents the d-line (λ = 587.6 nm).
And g indicates a g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in the first embodiment,
It can be seen that various aberrations are corrected well and high resolution is achieved.

[Second Embodiment] FIG. 3 is a diagram showing a lens configuration of a taking lens system according to a second embodiment of the present invention.
In the third embodiment, as in the first embodiment, the present invention is applied to a photographic lens for an electronic image device. In the photographing lens system of FIG. 3, the front lens group GF includes, in order from the object side, a positive meniscus lens LA having a convex surface facing the object side and an aspheric surface on the image side, and a convex surface facing the object side. A negative meniscus lens LM, a biconcave lens LR, and a biconvex lens LW.

The rear lens group GR includes, in order from the object side, a cemented positive lens LS formed by bonding a negative meniscus lens LU having a convex surface toward the object side and a biconvex lens,
A biconvex lens LB having an aspherical surface on the object side. An aperture stop S is arranged in the optical path between the front lens group GF and the rear lens group GR, and a parallel plane plate (filter) F is arranged in the optical path between the biconvex lens LB and the image plane. ing. The image-side aspheric surface of the positive meniscus lens LA and the object-side aspheric surface of the biconvex lens LB are formed such that the positive refracting power becomes weaker as the distance from the optical axis increases.

Table 2 below summarizes data values of the second embodiment of the present invention. In Table (2), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, and φS represents the aperture stop diameter. The surface number indicates the order of the lens surface from the object side along the traveling direction of the light ray, r indicates the radius of curvature of the lens surface (vertical radius of curvature for an aspheric surface),
d is the distance between the lens surfaces, n (d) and n (g) are the d-line (λ = 587.6 nm) and the g-line (λ = 43, respectively).
5.8 nm), and ν indicates the Abbe number.

[0058]

Table 2 f = 4.2 FNO = 2.8 2ω = 77.7 ° φS = 4.08 Surface number r dn (d) n (g) ν 1 41.0795 2.7703 1.693500 1.709750 53.31 (LA) 2 * 56.6738 1.0949 3 14.7098 2.8318 1.772500 1.791920 49.61 (LM) 4 4.7992 2.1843 5 -33.2489 0.9103 1.696800 1.712350 55.48 (LR) 6 6.6593 4.4702 7 23.8358 5.8872 1.696800 1.712350 55.48 (LW) 8 -11.7477 5.09 ∞ 2.0738 (Aperture stop S) 10 13.2798 1.846660 1.893900 23.83 (LS) 11 4.6175 3.0731 1.497000 1.504510 81.61 12 173.8022 0.1 13 * 10.4136 3.9175 1.516800 1.526670 64.20 (LB) 14 -7.1885 2.215 ∞ 4.4 1.516800 1.526670 64.20 (F) 16 ∞ 2.499 (aspherical data) r κ C ₄ 2 56.6738 1.00000 -7.02930 × 10 ^-5 C ₆ C ₈ C ₁₀ 4.34330 × 10 ^-7 9.76860 × 10 ^-12 -1.01840 × 10 ^-11 r κ C ₄ 13 10.4136 1.00000 -6.40 200 × 10 ^-4 C ₆ C _{8 ^{C 10 4.10780 × 10 -6 6.25500 ×}} 10 -7 -1.81410 × 10 -8 ( values for conditional expressions) TL = 50. 1 EP = 72.01 Y0 = 3.3 fLA = 200.677 fLB = 8.904 DAB = 34.222 dM = 2.883183 dS = 9.66972 Φ1 = 19.94 fS = 322.617 BF = 7. 601 Δν = 57.78 Δn = 0.3966 fF = −315.193 fR = 11.364 f = 4.200 (1) TL / Y0 = 15.155 (2) f / EP = 0.05833 (3) fLA / fLB = 22.538 (4) DAB / Y0 = 10.370 (5) dM / Y0 = 0.858 (6) dS / Y0 = 2.930 (7) Φ1 / Y0 = 6.042 (8) fLB / fLS = 0.0276 (9) (Rbm + Ram) / (Rbm-Ram) =-2.969 (10) (Rbu + Rau) / (Rbu-Rau) =-2.066 (11) BF / Y0 = 2. 303 (12) Δν = 57.78 (13) Δn = 0 34966 (14) fR / fF = -27.736

FIG. 4 is a diagram showing various aberrations of the second embodiment when focused on an object at infinity. In each aberration diagram, FNO represents the F number, Y represents the image height, and d represents the d-line (λ = 587.6 nm).
And g indicates a g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in the second embodiment,
It can be seen that various aberrations are corrected well and high resolution is achieved.

[Third Embodiment] FIG. 5 is a diagram showing a lens configuration of a taking lens system according to a third embodiment of the present invention.
In the third embodiment, as in the first and second embodiments, the present invention is applied to a photographic lens for an electronic image device. In the photographing lens system shown in FIG.
Are, in order from the object side, a positive meniscus lens LA having a convex surface facing the object side and an image-side surface formed as an aspheric surface, a negative meniscus lens LM having a convex surface facing the object side, and a biconcave lens LR. And a biconvex lens LW.

The rear lens group GR includes, in order from the object side, a cemented positive lens LS formed by bonding a negative meniscus lens LU having a convex surface toward the object side and a biconvex lens,
A biconvex lens LB having an aspherical surface on the object side. The diffractive lens surface (surface number 13) is placed on the object-side aspherical surface (surface number 14) of the biconvex lens LB.
Are formed. This diffractive lens surface is a phase surface having an optical path difference distribution that is rotationally symmetric with respect to the optical axis, and is configured to use + 1st-order diffracted light as the diffraction order. An aperture stop S is arranged in the optical path between the front lens group GF and the rear lens group GR, and a parallel plane plate (filter) F is arranged in the optical path between the biconvex lens LB and the image plane. ing. The image-side aspheric surface of the positive meniscus lens LA and the object-side aspheric surface of the biconvex lens LB are formed such that the positive refracting power becomes weaker as the distance from the optical axis increases.

Table 3 below summarizes the data values of the third embodiment of the present invention. In Table (3), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, and φS represents the aperture stop diameter. The surface number indicates the order of the lens surface from the object side along the traveling direction of the light ray, r indicates the radius of curvature of the lens surface (vertical radius of curvature for an aspheric surface),
d is the distance between the lens surfaces, n (d) and n (g) are the d-line (λ = 587.6 nm) and the g-line (λ = 43, respectively).
5.8 nm), and ν indicates the Abbe number.

[0063]

Table 3 f = 6 FNO = 2.8 2ω = 58.6 ° φS = 4.82 Surface number r dn (d) n (g) ν 1 32.0110 3.3 1.693500 1.709750 53.31 (LA) 2 * 83.0260 0.13 16.3258 6.0 1.772500 1.791920 49.61 (LM) 4 5.0303 1.9 5 -29.4200 1.0 1.696800 1.712350 55.48 (LR) 6 6.9030 4.35 7 14.3630 5.8 1.696800 1.712350 55.48 (LW) 8 -25.8310 2.0 9 ∞ 1.5 (Aperture stop S) 10 10.2441 4.6459 1.846660 1.893900 23.83 (LS) 11 5.1705 3.3775 1.497000 1.504510 81.61 12 -24.8509 1.4448 13 ** 10.2830 0.0 11000.1 74186.853 -3.453 (LB) 14 * 10.28301632932 4.0027 1.516800 1.526670 64.2 15 -21.5219 2.8689 16 ∞ 4.4 1.516800 1.526670 64.2 (F) 17 ∞ 1.8679 ( Aspherical surface data) r κ C ₄ 2 plane 83.0260 1.00000 -2.18383 × 10 ^-5 C ₆ C ₈ C ₁₀ 1.52617 × 10 ^-7 -5.43984 × 10 ^-12 -3.99975 × 10 ^-11 r κ C ₄ 13 plane 10.2830 1.000175- ^{_{2.80281538949 × 10 -4 C 6 C 8}} C 10 8.52082470259 × 10 -4 -1.95163658696 × 10 -5 4.60462084447 10 ^-7 r κ C ₄ 14 faces _{^{10.28301632932 1.00000 -2.80261712703 × 10 -4 C 6}} C 8 C 10 8.52113207536 × 10 -4 -1.95161553107 × 10 -5 4.60452713130 × 10 -7 ( Values for Conditional Expressions) TL = 48.558 EP = 32.059 Y0 = 3.3 fLA = 73.184 fLB = 13.789 DAB = 32.118 dM = 6 dS = 8.02339 Φ1 = 19.95 fS = 22.929 BF = 7.638 Δν = 57.78 Δn = 0.34966 fF = −27.041 fR = 11.239 f = 5.999 fd = 647.55 (1) TL / Y0 = 14.715 (2) f / EP = 0.1871 ( 3) fLA / fLB = 5.307 (4) DAB / Y0 = 9.733 (5) dM / Y0 = 1.818 (6) dS / Y0 = 2.431 (7) Φ1 / Y0 = 6.045 ( 8) fLB / fLS = 0.601 (9) (Rbm + Ram) / (Rbm (Ram) =-1.891 (10) (Rbu + Rau) / (Rbu-Rau) =-3.038 (11) BF / Y0 = 2.315 (12) Δν = 57.78 (13) Δn = 0.3966 (14) fR / fF = -2.406 fd / fR = 57.616

FIG. 6 is a diagram showing various aberrations of the third embodiment when focused on an object at infinity. In each aberration diagram, FNO represents the F number, Y represents the image height, and d represents the d-line (λ = 587.6 nm).
And g indicates a g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in the third embodiment,
It can be seen that various aberrations are satisfactorily corrected and higher resolution is achieved than in the first and second embodiments.

[0065]

As described above, according to the present invention,
A high-resolution shooting lens system suitable for a shooting lens for an electronic imaging device such as a video camera or a digital still camera can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens configuration of a taking lens system according to a first example of the present invention.

FIG. 2 is a diagram illustrating various aberrations of the first embodiment in a focused state at infinity.

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

FIG. 4 is a diagram illustrating various aberrations of the second example in an infinity in-focus condition.

FIG. 5 is a diagram showing a lens configuration of a taking lens system according to a third example of the present invention.

FIG. 6 is a diagram illustrating various aberrations of the third example in an infinity in-focus condition.

FIG. 7 is a diagram modeling and showing a state in which a diffractive lens surface is formed on a lens surface by a high refractive index method.

FIG. 8 shows a series of flow procedures for obtaining a kinoform from an optical path difference function obtained by a high refractive index method and converting the kinoform into an 8-level binary shape.

[Explanation of symbols]

 GF Front lens group GR Rear lens group S Aperture stop F Parallel plane plate (filter) L Each lens component

Claims (12)

[Claims] 1. An aperture stop, a front lens group GF having a negative refractive power disposed on the object side of the aperture stop, and a rear lens group having a positive refractive power disposed on an image side of the aperture stop. GR, wherein the front lens group GF has at least a positive lens LA having an aspherical surface formed so that its positive refractive power becomes weaker as the distance from the optical axis increases. Negative meniscus lens L having a convex surface facing the side and having a center thickness larger than the maximum image height
1. A photographic lens system comprising at least U and a positive lens LB having an aspheric surface formed such that a positive refractive power becomes weaker as the distance from the optical axis increases. 2. The distance along the optical axis from the most object side surface of the taking lens system to the image plane is TL, and the maximum image height is Y.
0, and the focal length of the photographic lens system is f, and the distance from the image plane to the exit pupil along the optical axis is EP: 8.0 <TL / Y0 <25.0 (1) -0. The imaging lens system according to claim 1, wherein the following condition is satisfied: 5 <f / EP <0.5 (2). 3. The positive lens LA in the front lens group GF is a positive meniscus lens having a convex surface facing the object side, the positive lens LB in the rear lens group GR is a biconvex lens, The focal length of the positive meniscus lens LA is fLA, the focal length of the biconvex lens LB is fLB, and the optical axis between the most image-side surface of the positive meniscus lens LA and the most object-side surface of the biconvex lens LB. The distance along is DAB,
2. The condition of 2.0 <fLA / fLB <30.0 (3) 5.0 <DAB / Y0 <25.0 (4) when the maximum image height is Y0. Or the imaging lens system according to 2. 4. The front lens group GF includes a negative meniscus lens LM, a biconcave lens LR, and a biconvex lens LW, and the rear lens group GR includes the negative meniscus lens LU.
And a cemented lens LS having a positive refractive power as a whole. The central thickness of the negative meniscus lens LM is dM, the central thickness of the cemented lens LS is dS, and the maximum image height is Y0. Wherein the condition 0.5 <dM / Y0 <5.0 (5) 1.5 <dS / Y0 <10.0 (6) is satisfied. 2. The taking lens system according to 1. 5. The effective diameter of the most object side surface of the taking lens system is Φ1, the maximum image height is Y0, and the positive lens L
When the focal length of B is fLB and the focal length of the cemented lens LS is fLS, 2.0 <Φ1 / Y0 <12.0 (7) 0.015 <fLB / fLS <2.0 (8) The photographing lens system according to claim 4, wherein a condition is satisfied. 6. The radius of curvature of the most object side surface of the negative meniscus lens LM is defined as Ram, the radius of curvature of the most image side surface of the negative meniscus lens LM is defined as Rbm, and the most object side surface of the negative meniscus lens LU is defined as Rbm. Where Rau is the radius of curvature of the surface of the negative lens, LU is the radius of curvature of the surface closest to the image of the negative meniscus lens LU, BF is the back focus of the photographic lens system, and Y0 is the maximum image height. <(Rbm + Ram) / (Rbm-Ram) <-0.2 (9) -5.0 <(Rbu + Rau) / (Rbu-Rau) <-1.5 (10) 1.5 <BF / Y0 <10. The imaging lens system according to claim 4, wherein the condition 0 (11) is satisfied. 7. The photographing lens system includes:
The positive lens LA, the negative meniscus lens LM,
The biconcave lens LR, the biconvex lens LW, the aperture stop, the cemented lens LS, and the positive lens LB, wherein the biconvex lens LW and the positive lens LB are larger than a maximum image height Y0. 7. The photographic lens system according to claim 4, wherein the photographic lens system has a center thickness. 8. The cemented lens LS has a divergent cemented surface, the difference between the Abbe numbers of two lenses sandwiching the cemented lens LS is Δν, and the cemented lens LS is a cemented lens LS. The condition of Δν> 35 (12) Δn> 0.25 (13) is satisfied assuming that the difference between the refractive indices of the two lenses sandwiched with respect to the d-line is Δn. 2. The photographing lens system according to claim 1. 9. The focal length of the front lens group GF is fF
The condition of −50 <fR / fF <−1.5 (14) is satisfied, where fR is the focal length of the rear lens group GR. 2. The taking lens system according to 1. 10. The rear lens group GR includes a diffractive optical element having a diffractive action.
10. The photographing lens system according to any one of claims 9 to 9. 11. The diffractive optical element, wherein the positive lens L
The imaging lens system according to claim 10, wherein the lens system is a diffractive lens surface formed on the lens surface of B. 12. The positive lens L, wherein:
The photographic lens system according to claim 11, wherein the photographic lens system is formed on an aspheric surface of B.