JPH09236740A - Photographing lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a practical photographing lens system whose focus deviating image is improved over the wide range of photographing distances from infinity to the closest range. SOLUTION: This lens system is composed, in order from the object side, of a first group Gr1; composed of a first positive meniscus lens L1 whose convex surface confronts the object side, a second positive meniscus lens L2 whose convex surface con-fronts the object side, a third negative meniscus lens L3 whose convex surface confronts the object side, a diaphragm A, an apodization filter F, a fourth lens L4 of biconcave shape and a fifth lens L5 of biconvex shape; and a second group Gr2 composed of a sixth lens L6 of biconvex shape. m1, m2 typically represent the movement of the first group and the second group at the time of focusing from a focusing state at infinity to a focusing state at the closest photographing distance. The photographing lens system performs aberration correction at a close distance by moving the whole system while widening an interval d13 between the first group Gr1 and the second group Gr2 at the time of focusing from the focusing state at infinity to the focusing state at the close range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a taking lens system, and more particularly to a taking lens system having a close distance aberration correction (so-called floating) mechanism suitable as a taking lens of a camera.

[0002]

2. Description of the Related Art Generally, the performance of a taking lens system is evaluated by the image forming performance on the focal plane. For this reason, in the past, many proposals have been made regarding the correction of various aberrations in the taking lens system in order to improve the imaging performance.

However, in the case of a taking lens system used as a taking lens of a camera, not only the image forming performance but also the
The appearance of the out-of-focus image is also very important. For example, in a portrait photograph in which a person is placed in the center of the image, a photograph of a flower photographed in close proximity, etc., the impression of the photograph image greatly depends on the appearance of the defocused image of the background portion other than the main subject. It will be.

As for the appearance of such an out-of-focus image, for example, in the case of hair in a portrait photograph, the hair is widely blurred like spikes of a Japanese pampas grass, 1
Various states are known, such as a state in which the hair of a book is blurred as if it had two hairs (also called two-line blurring), and a state in which the hair is softly blurred while leaving the core of the hair, but the third is shown. It is said that the condition that it is soft and blurring is good.

In particular, when a close-up subject is photographed by using a macro lens having a photographing magnification of about 1/4 to 1/2, the background other than the main subject is out of focus in most cases, and thus the image is out of focus. The appearance of the image is especially important.

As a lens system for improving an out-of-focus image, US Pat. No. 3,843,235 discloses a filter constructed such that the amount of transmitted light gradually decreases as the distance from the center of the optical axis to the direction perpendicular to the optical axis increases. A lens system in which an apodization filter is arranged is proposed, and an example of a triplet lens system including a biconvex lens, a biconcave lens, a diaphragm, an apodization filter, and a biconvex lens is disclosed in this order from the object side. There is. According to the lens system described in this publication, the intensity distribution of the defocused image is modified by the apodization filter (hereinafter, such an effect is referred to as apodization), and the defocused image is improved. I am trying.

[0007]

However, although the lens system described in the above publication proposes the effect of improving an out-of-focus image in an in-focus state at infinity, the lens system has a configuration with an apodization filter. No movement of the lens group during focusing has been proposed.

In view of the above problems, it is an object of the present invention to provide a photographic lens system with an improved defocused image over a wide range of photographic distances from infinity to close proximity.

[0009]

In order to achieve the above object, a taking lens system according to claim 1 has a plurality of lens groups, a diaphragm arranged in any one of the plurality of lens groups, and a vicinity of the diaphragm. A focusing lens system having an apodization filter disposed at, and at the time of focusing from an infinity in-focus state to a close-up focusing distance state, at least one lens group interval is changed to move the entire system. It is characterized in that it is moved to the object side.

A photographic lens system according to a second aspect of the present invention comprises, in order from the object side, a first group and a second group, wherein the first group includes an aperture and an apodic lens disposed near the aperture. A photographing lens system including a zone filter, wherein the whole system is widened while widening the distance between the first group and the second group when focusing from an infinity in-focus state to a close-up focusing distance state. It is characterized in that it is moved to the object side.

A photographic lens system according to a third aspect of the present invention comprises, in order from the object side, a first group, a second group, and a third group. Either the first group or the second group. On the one hand,
A taking lens system including an aperture and an apodization filter arranged in the vicinity of the aperture, wherein the first group and the second group are used for focusing from an infinity in-focus state to a close-up distance focusing state. The distance between the group and the second
The entire system is moved to the object side while widening the distance between the group and the third group.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A photographing lens system embodying the present invention will be described below with reference to the drawings. [Lens Arrangement of Photographic Lens System of Embodiment] FIGS. 1 to 5
6A and 6B correspond to the lens configuration diagrams of the taking lens systems of the first to fifth embodiments and show the lens arrangement in the infinity in-focus state. In each of the taking lens systems of the first to fifth embodiments, at least one apodization filter, which will be described later, is arranged in the lens group and at the time of focusing from an infinity in-focus state to a close-up focusing distance state. Short-range aberration correction that moves the entire system to the object side while changing the lens group spacing,
This is a taking lens system that performs so-called floating. Arrows m1 to m3 shown in FIGS. 1 to 5 schematically show the movement of each lens group when focusing from the infinity in-focus state to the closest focusing distance in-focus state. is there.

The taking lens system of the first embodiment has, in order from the object side, a positive meniscus first lens L1 having a convex surface facing the object side, and a positive meniscus second lens L2 having a convex surface facing the object side. A first lens L3 having a negative meniscus shape having a convex surface directed toward the object side, a diaphragm A, an apodization filter F described later, a biconcave fourth lens L4, and a biconvex fifth lens L5. The lens unit includes a group Gr1 and a second group Gr2 including a biconvex sixth lens L6. The focusing lens system of the first embodiment, when focusing from an infinity in-focus condition to a close-up focusing distance, focuses on the distance between the first group Gr1 and the second group Gr2 (corresponding to the axial upper surface distance d13 in FIG. 1). ) Is widened to move the entire system to the object side to correct short-distance aberration.

The taking lens system of the second embodiment comprises, in order from the object side, a positive meniscus first lens L1 having a convex surface facing the object side, a biconvex second lens L2, and a biconcave object side surface. Is cemented to the image side of the second lens L2, a negative meniscus fourth lens L4 having a convex surface facing the object side, a diaphragm A, an apodization filter F described later, and a concave surface on the object side. The fifth lens L5 having a negative meniscus shape, a first group Gr1 including a biconvex sixth lens L6, and a second group including a biconvex seventh lens L7.
And a group Gr2. The photographic lens system of the second embodiment, when focusing from an infinity in-focus condition to a close-up focusing distance, focuses on the distance between the first group Gr1 and the second group Gr2 (corresponding to the axial upper surface distance d14 in FIG. 2). ) Is widened to move the entire system to the object side to correct short-distance aberration.

The taking lens system of the third embodiment has, in order from the object side, a positive meniscus-shaped first lens L1 having a convex surface facing the object side, and a positive meniscus-shaped second lens L2 having a convex surface facing the object side. , A first group Gr1 including a negative meniscus third lens L3 having a convex surface directed toward the object side, a diaphragm A, an apodization filter F described later, a biconcave fourth lens L4, and a biconvex first lens. It is composed of a second group Gr2 composed of five lenses L5 and a third group Gr3 composed of a biconvex sixth lens L6. The photographic lens system of the third embodiment, when focusing from the infinity in-focus state to the close-up focusing range, focuses on the first group Gr1 and the second group Gr2.
The whole system toward the object side while narrowing the distance (corresponding to the axial upper surface distance d6 in FIG. 3) and widening the distance between the second group Gr2 and the third group Gr3 (corresponding to the axial upper surface distance d13 in FIG. 3). It is moved to correct short-range aberration.

In the taking lens system of the fourth embodiment, in order from the object side, a positive meniscus first lens L1 having a convex surface facing the object side and a positive meniscus second lens L2 having a convex surface facing the object side are provided in this order. , A first group Gr1 including a negative meniscus third lens L3 having a convex surface directed toward the object side, a diaphragm A, an apodization filter F described later, a biconcave fourth lens L4, and a biconvex first lens. A second lens unit Gr2 including a fifth lens L5 and a biconvex sixth lens L6, a biconcave seventh lens L7, a negative meniscus eighth lens L8 having a convex surface facing the object side, and a biconvex first lens L7. The third lens unit Gr3 includes nine lenses L9. The photographic lens system of the fourth embodiment focuses on the first lens unit Gr1 and the second lens unit when focusing from the infinity in-focus state to the close-up distance focusing state.
The whole system is made to be an object while narrowing the distance between the group Gr2 (corresponding to the axial upper surface distance d6 in FIG. 4) and increasing the distance between the second group Gr2 and the third group Gr3 (corresponding to the axial upper surface distance d15 in FIG. 4). It is moved to the side to correct short-range aberration.

In the taking lens system of the fifth embodiment, in order from the object side, a positive meniscus first lens L1 having a convex surface facing the object side and a positive meniscus second lens L2 having a convex surface facing the object side are arranged in this order. A negative meniscus third lens L3 having a convex surface facing the object side, an aperture A, an apodization filter F described later, a biconcave fourth lens L4, a biconvex fifth lens L5, and a biconvex shape. A first group Gr1 including a sixth lens L6, a biconcave seventh lens L7, a negative meniscus eighth lens L8 having a convex surface directed toward the object side,
The second lens unit Gr2 includes a biconvex ninth lens L9. The photographic lens system of the fifth embodiment, when focusing from an infinity in-focus state to a close-up distance focusing state, the distance between the first group Gr1 and the second group Gr2 (corresponding to the axial upper surface distance d15 in FIG. 5). ) Is widened to move the entire system to the object side to correct short-distance aberration.

In each of the above embodiments, an apodization filter is arranged in the taking lens system. The apodization filter is
It is shown as one flat plate. The detailed configuration of this apodization filter will be described later.

In the image-forming state with respect to a close-up subject, the incident height of the axial luminous flux incident on the positive lens group on the image side of the diaphragm becomes high, and the spherical aberration tends to become large under.
Further, since the off-axis light flux passes through a lower position in the vicinity of the optical axis of each lens group than in the infinity focused state, outward coma is generated.

In order to correct various aberrations peculiar to the image formation state for these close-up subjects, it is necessary to correct an appropriate axial upper surface distance and perform floating so as to suppress fluctuations of aberrations occurring at close-up shooting distances. is there.

In the taking lens systems according to the first, second and fifth embodiments, the first group, the second group and the second group are arranged in this order from the object side.
In the taking lens system including an aperture and an apodization filter arranged in the vicinity of the aperture in the first group, in focusing from an infinity in-focus state to a close-up focusing range, A floating mechanism that widens the distance between the first group and the second group is adopted.

By adopting such a floating mechanism, it is possible to satisfactorily correct aberrations occurring at a close-up shooting distance even in a shooting lens system having an apodization filter, and to focus from an infinity in-focus condition. It is possible to realize a practical taking lens system in which an out-of-focus image is improved over a wide range of the close-up distance focusing state.

Further, in the taking lens systems of the third and fourth embodiments, the first group, the second group, and
In a photographing lens system including a third lens group and a diaphragm and an apodization filter arranged near the diaphragm on the most object side of the second lens group, focusing from infinity to a close-up distance At the time of focusing to a focused state, a floating mechanism is employed which narrows the distance between the first group and the second group and widens the distance between the second group and the third group.

By adopting such a floating mechanism, as in the case of each of the previous embodiments, even in a taking lens system having an apodization filter, aberrations occurring at close-up shooting distances can be satisfactorily corrected. Therefore, it is possible to realize a photographic lens system with an improved defocused image over a wide range from the infinity in-focus state to the close-up distance focusing state.

Since the taking lens systems of the third and fourth embodiments have a three-group construction, they are more effective than the taking lens systems of the two-group construction of the first, second and fifth embodiments. It is possible to correct short-range aberration up to a high magnification. Therefore, it can be used in an area where the photographing magnification is larger than in the case of the two-group configuration.

The third and fourth embodiments are embodiments in which the apodization filters are arranged in the second group, but even if the apodization filters are arranged in the first group. , The same effect can be obtained.

[Principle of Defocused Image Improvement Method] Next, the principle of defocused image improvement will be described with reference to the drawings. FIG. 6 is a schematic diagram for explaining an out-of-focus image. In FIG. 6, P indicates a point light source, and L indicates an aberration-free lens system L having an optical axis symmetric circular aperture. The point light source P forms a point image P ′ on a conjugate focal plane by the lens system L. In addition, a surface S that is away from the focal plane by Δ in the optical axis direction
Then, a large defocused image P ″ is formed.

Incidentally, in the image formation relationship during actual photographing, the point image P'on the image plane becomes an out-of-focus image P "due to the change in the distance between the point light source P and the lens system L. In the following description, for simplicity, the position of the point light source P on the optical axis is fixed,
An out-of-focus image P ″ on a plane S parallel to the focal plane containing the point image P ′ will be discussed.

When the transmittance distribution of the aperture of the lens system L is constant, that is, when the transmittance τ (h) is a constant value in the range from the optical axis to the effective radius h1 of the aperture as shown in FIG. In particular, the image P ″ of the point light source P on the image plane S becomes a circle of confusion with uniform intensity.

On the other hand, in the aperture of the lens system L, the transmittance τ (h) decreases as it moves away from the center of the optical axis in the direction perpendicular to the optical axis as shown in FIG. 8, and becomes 0 at the effective radius h1. When absorption is given, the image P ″ of the point light source P on the image surface S becomes a circular image whose intensity distribution is similar to the transmittance distribution. That is, when the transmittance τ (h) has a distribution as shown in FIG. 8, the point light source P
The defocused image P ″ is an image in which the center is bright near the optical axis and the intensity decreases toward the periphery.

Since a general subject is considered to be an aggregate of point light sources having different luminances, the defocused image of the lens system having the distribution of the transmittance τ (h) of the aperture as shown in FIG. 8 has the center at the center. While leaving it, the image becomes softly blurred, and a good defocused image can be obtained. The above is the principle of improving an out-of-focus image by apodization.

A characteristic of apodization is that its effect on an out-of-focus image does not matter with respect to the position of the surface S, the amount of defocus, the amount of defocus before and after defocus, and the like. That is, as is clear from FIG. 6, regardless of the position of the surface S, the defocused image P ″ of the point light source P is in the center near the optical axis as long as it passes through the effective diameter of the lens system L. Is bright and the intensity decreases as you move closer to the periphery.

Further, improvement of an out-of-focus image by apodization will be described using a response function. FIG. 9 shows a case (a) in which the aperture of the lens system has a constant transmittance τ (h) as expressed by the following equation (A),
In the case (b) having a transmittance τ (h) that decreases with increasing distance from the center of the optical axis in the direction perpendicular to the optical axis as represented by the following formula (B), a surface separated by Δ from the focal plane. 8 is a graph showing a response function of a defocused image in FIG. τ (h) = 1 ... (A) τ (h) = 1-h ² ... (B) Further, in the graph of FIG. 9, the horizontal axis is the spatial frequency s, and the vertical axis is the space. The response value is normalized so that the response becomes 1 at the frequency s = 0.

The response function is OTF (optical trans
fer function), which shows the frequency transfer characteristics between the spectrum of the subject and the spectrum of the image.
The response function of the defocused image is calculated by calculating the wavefront aberration due to defocusing in the pupil, obtaining the pupil function, then obtaining the point image intensity distribution from this pupil function, and further Fourier transforming this point image intensity distribution. Derived.

As can be seen from the graph of FIG. 9, the response function in the case where the transmittance of the aperture of the lens system has a constant value is that the spatial frequency s = s1 after abruptly decreasing in the low frequency component of the spatial frequency. A characteristic (a) is shown in which a negative value is once taken in the vicinity, and a positive value is taken in the vicinity of the spatial frequency s = s2.

On the other hand, the response function in the case where the transmittance of the aperture of the lens system decreases as it goes away from the center of the optical axis in the direction perpendicular to the optical axis, the response function gradually decreases monotonically in the low frequency component of the spatial frequency, and the spatial frequency s The characteristic (b) shows a positive value again after taking a slightly negative value in the vicinity of = s2.

Generally, the low frequency component of the spatial frequency has a function of forming a schematic structure of the image, and the high frequency component has a function of correcting the schematic structure of the image formed by the low frequency component. A state in which the response function takes a negative value is called false resolution, and corresponds to a state in which a negative-positive inversion phenomenon occurs in which a black portion becomes white and a white portion becomes black in an actual image.

It is considered that the image based on the characteristic (a), in which the transmissivity is constant, has a large decrease in low-frequency components, and the schematic structure of the image is not reproduced so much. In addition, since the range of negative values near the spatial frequency s = s1 is large, the range of spatial frequencies in the false resolution state is wide. Furthermore, it can be said that a very unnatural image is formed because the vibration of the response function in the high frequency component is remarkable.

On the other hand, in the image based on the characteristic (b), in which the transmittance decreases as the distance from the optical axis increases, the reduction of low frequency components is small, and the schematic structure of the image is more reproduced. Also,
The range of false resolution is also small, and the vibration of the response function at high frequency components is also small.

As described above, in the case of a lens system having an aperture whose transmittance decreases as it goes away from the center of the optical axis in a direction perpendicular to the optical axis, an image with a defocused image is obtained as compared with a lens system having an aperture of constant transmittance. The skeleton of the image is clear, and it can be said that it is naturally blurred. In other words, it can be said that the defocused image of the lens system having the response function (b) has a defocused image while leaving the center at the center.

Thus, from the aspect of the response function as well,
It can be seen that the apodization improves the out-of-focus image.

[Apodization Filter] Next,
The apodization filter will be described. The apodization filters used in the above-described first to fifth embodiments are manufactured using a substance having light absorption (ND glass).

In general, when the light flux passes through the lens, the intensity I of the transmitted light is ignored if the influence of the surface reflection of the lens is ignored.
Is represented by the following formula (C). I = I0 · exp (−αt) (C) where I0: incident light intensity, α: absorption coefficient, t: lens thickness.

In the above equation (C), since the absorption coefficient α is a constant determined by the lens medium, the intensity I of transmitted light with respect to the incident light having a constant intensity is determined only by the thickness of the lens.

By utilizing this characteristic, it is possible to manufacture a lens having absorption such that the transmittance decreases as the distance from the center of the optical axis to the direction perpendicular to the optical axis increases. That is,
As shown in FIG. 10, if a plano-concave lens is manufactured using a lens material having a large absorption coefficient α, the thickness of the lens increases as the lens is separated from the center of the optical axis in the direction perpendicular to the optical axis. The lens has absorption from the center of the lens toward the periphery.

The transmittance distribution of such a plano-concave lens is shown below. In FIG. 10, assuming that the radius of curvature of the concave surface of the lens is r and the thickness of the lens at the height h from the optical axis is t, the thickness t is expressed by the following equation (D) from geometrical calculation. t = r−√ (r ² −h ² ) ... (D) In the above equation, if h is small compared to r and the binomial expansion is performed, the thickness t is calculated by the following equation (E). Can be approximated by. t≈h ² / 2r (E) By substituting this into the equation (C), the following equation (F) is obtained. I (h) = I0 · exp (−α · h ² / 2r) (F) Since the transmittance τ (h) is the ratio of the incident light intensity I0 and the transmitted light intensity I, Equation (G) is obtained. τ (h) = I (h ) / I0 = exp (-α · h 2 / 2r) ····· (G) the formula (G) shows a Gaussian distribution. When a plano-concave lens as shown in FIG. 10 is actually manufactured, since the approximation by the binomial expansion is performed in the above formula (E), the Gaussian distribution is not perfect, and the Gaussian distribution is slightly deviated from the Gaussian distribution. Distribution. That is, it can be seen that if a plano-concave lens as shown in FIG. 10 is made of a medium having an absorption coefficient α, the transmittance τ (h) has a substantially Gaussian distribution.

In FIG. 6, the transmittance τ (h) of the lens system L
Is a substantially Gaussian distribution, the intensity distribution of the defocused image P ″ of the point light source P formed on the surface S is also a substantially Gaussian distribution similar to the transmittance distribution as described above.

By the way, it is known that the Fourier transform of the Gaussian distribution has no negative value. Therefore, the response function obtained by Fourier transforming the point image intensity distribution of the defocused image P ″, which is a Gaussian distribution, has only positive values.

Since the above-mentioned plano-concave lens has a transmittance of approximately Gaussian distribution, in the lens system including this plano-concave lens, the response function of the out-of-focus image takes a large part in a positive value, The spatial frequency range in which false resolution occurs is very small. Moreover, since the response function also monotonically decreases, a natural defocused image can be obtained.

As described above, by using ND glass, it is possible to manufacture a lens which can obtain the effect of apodization. However, (G)
As can be seen from the formula, since the transmittance τ (h) is a function of the radius of curvature of the concave surface of the plano-concave lens, the value of the radius of curvature is limited to obtain the desired transmittance distribution. .
This greatly limits the degree of freedom in designing the optical system and is not preferable.

Therefore, in the first to fifth embodiments, a plano-convex lens having a convex surface with the same radius of curvature as the concave surface of the above-mentioned plano-concave lens is used to join the concave surface and the convex surface to form an apodization filter. There is. As a material of such a plano-convex lens, it is desirable to use glass having the same refractive index and Abbe number as the plano-concave lens but different only in the absorption coefficient. If the plano-concave lens and plano-convex lens have the same refractive index and Abbe number, the light flux will not be refracted at the cemented surface, and the apodization filter should be treated as a flat plate filter that gives only the transmittance distribution. You can

The following table shows examples in which apodization filters were made. Further, FIG. 11 shows a cross-sectional view of the apodization filter of the example. FIG.
The apodization filter has a plano-concave lens 1 and a plano-convex lens 2 cemented together, and has an effective radius of 15.5 m.
m. Furthermore, the graph of the design data of the transmittance τ (h) of the apodization filter of FIG. 12 is shown.

[0053]

[Table 1]

The apodization filter is
In addition to the above configuration, it can also be obtained by vapor-depositing an absorbing substance on a transparent glass flat plate so as to have a predetermined distribution, or by coating a transparent glass flat plate with a photosensitive material and exposing it to a predetermined concentration. You can The apodization filter produced by these methods has the advantage that the thickness of the filter can be reduced. However, the apodization filters produced by these methods have a drawback that the film thickness of the absorbing material and the photosensitive material varies depending on the incident height according to the transmittance distribution, and thus the phase change of the light beam occurs. Further, there is a problem that the light flux is scattered or reflected by the absorbing material and the photosensitive material.

[Conditions to be Satisfied by Photographic Lens System] Next,
Conditions to be satisfied by the taking lens system according to the present invention will be described. 0.1 <φf / φ <2.0 (1) where φf is the refracting power of the first group, and φ is the refracting power of the entire system.

Conditional expression (1) is composed of a first group and a second group in order from the object side. The first group includes an aperture and an apodization filter arranged in the vicinity of the aperture. The first lens group is a condition to be satisfied in a photographing lens system provided with the first lens group and the second lens group, in which the distance between the first lens group and the second lens group is changed to move the entire lens system toward the object side. If the lower limit of conditional expression (1) is exceeded, spherical aberration of the entire system will be undercorrected, which is not desirable. Conversely, conditional expression (1)
When the value exceeds the upper limit of, the spherical aberration of the entire system is overcorrected, which is not desirable.

-0.3 <φb / φ <5.0 (2) where φb is the refractive power of the second group.

Conditional expression (2) is a condition that the second group should satisfy under the condition that the first group satisfies the conditional expression (1). If the lower limit of conditional expression (2) is exceeded, spherical aberration of the entire system will be overcorrected and coma will be undercorrected, which is not desirable. On the other hand, if the upper limit of conditional expression (2) is exceeded, spherical aberration will be undercorrected and coma will be overcorrected, which is not desirable.

1.01 <If / Ib <3.00 (3) where: If: amount of movement of the first lens unit during focusing from the infinity in-focus state to the close-up distance in-focus state , Ib: The amount of movement of the second lens unit during focusing from the infinity in-focus condition to the close-up distance in-focus condition.

Conditional expression (3) is a condition that should be satisfied in order to correct the outward coma aberration of the entire system under the condition that the conditional expressions (1) and (2) are satisfied. When the value goes below the lower limit of the conditional expression (3), the outward coma aberration is insufficiently corrected in the entire system, which is not desirable. On the contrary, when the value exceeds the upper limit of the conditional expression (3), the effect of correcting the outward coma aberration becomes too strong, the balance with respect to the correction of other aberrations is lost, and other aberrations are deteriorated, which is not desirable. If the upper limit of conditional expression (3) is exceeded, the total lens length will become too large, and
The outer diameter of the lens must be increased in order to secure the amount of peripheral light, which is not desirable.

0.5 <φ1 / φ <1.5 (4) where φ1 is the refractive power of the first group.

Conditional expression (4) comprises, in order from the object side, a first group, a second group, and a third group, and one of the first group and the second group has an aperture stop. A photographing lens system including an apodization filter arranged in the vicinity of the diaphragm, wherein the first lens unit and the second lens unit are used for focusing from an infinity in-focus condition to a close-up object focus condition. In the photographic lens system in which the entire system is moved toward the object side while changing the distance between the first lens group and the second lens group and the distance between the second lens group and the third lens group, the first lens group must satisfy the condition. If the lower limit of conditional expression (4) is exceeded, the spherical aberration of the entire system will be overcorrected and the total length of the lens system will be undesirably long. On the other hand, if the upper limit of conditional expression (4) is exceeded, spherical aberration of the entire system will be undercorrected, which is not desirable.

−2.0 <φ2 / φ <1.5 (5) where φ2 is the refracting power of the second group.

Conditional expression (5) is a condition that the second group should satisfy under the condition that the first group satisfies the conditional expression (4). If the lower limit of conditional expression (5) is exceeded, coma will be undercorrected, which is not desirable. On the other hand, if the upper limit of conditional expression (5) is exceeded, coma aberration of the entire system will be overcorrected, and the floating amount will increase and the entire system will become large, which is not desirable.

-0.5 <φ3 / φ <3.0 (6) where φ3 is the refractive power of the third lens unit.

Conditional expression (6) is a condition that must be satisfied in order to correct spherical aberration and coma of the entire system under the conditions that satisfy the conditional expressions (4) and (5). If the lower limit of conditional expression (6) is exceeded, spherical aberration will be overcorrected and coma will be undercorrected, which is not desirable. On the contrary, if the upper limit of conditional expression (6) is exceeded, spherical aberration of the entire system will be undercorrected and coma will be overcorrected, which is not desirable. Further, if the upper limit of conditional expression (6) is exceeded, the floating amount also increases and the entire system becomes large.

1.01 <I1 / I3 <2.50 (7) 1.01 <I2 / I3 <2.50 (8) where I1: infinity of the first group I2: Amount of movement when focusing from a far focus state to a close-up distance focus state, I2: Amount of movement of second lens group from infinity focus state to a close-up distance focus state, I3: First The amount of movement during focusing from the infinity in-focus state of the third group to the close-up distance in-focus state.

The conditional expressions (7) and (8) are satisfied in order to correct the outward coma aberration of the entire system under the conditions that satisfy the conditional expressions (4), (5) and (6). It should be a condition. If the lower limits of conditional expressions (7) and (8) are exceeded, the external coma aberration is insufficiently corrected in the entire system, which is not desirable. On the contrary, if the upper limits of the conditional expressions (7) and (8) are exceeded, the effect of correcting the outward coma aberration becomes too strong, and the balance with respect to the correction of other aberrations is lost, which deteriorates other aberrations, which is not desirable. . If the upper limits of conditional expressions (7) and (8) are exceeded, the total lens length becomes too large, which is not desirable.

0.5 <(ra−rb) / (ra + rb) <15.0 (9) where ra: the image side of the apodization filter is a biconcave lens, a positive lens, or a positive lens. The radius of curvature of the object side surface of the biconcave lens when configured, rb: The radius of curvature of the image side surface of the biconcave lens when the image side of the apodization filter is composed of a biconcave lens, a positive lens, and a positive lens .

Conditional expression (9) is a shape factor of a biconcave lens when the image side of the apodization filter is composed of a biconcave lens, a positive lens, and a positive lens in a taking lens system having an apodization filter.
It is. When the value goes below the lower limit of conditional expression (9), spherical aberration and field curvature of the entire system are overcorrected, and it becomes difficult to correct them. On the other hand, if the upper limit is exceeded, strong downward coma will occur, making correction difficult.

By the way, in order to exert the effect of apodization on the off-axis light flux, it is necessary to reduce the vignetting of the off-axis light flux of the entire system as much as possible. In order to prevent vignetting of the off-axis light beam, it is desirable that the apodization filter is arranged near the diaphragm. When the apodization filter is arranged away from the diaphragm, part of the off-axis light beam having a large angle of view is vignetted by the apodization filter and reaches the image plane. The defocused image of the light flux partially vignetted by the apodization filter is good on the non-eclipsed side due to the effect of the apodization, but the vignetting side behaves in the same manner as in the past. As a result, an asymmetric defocused image is formed, which is very unnatural.

Further, in a taking lens system having an apodization filter, the image height y ', the maximum image height Ymax
When y '= 0.5Ymax, the image plane illuminance is 8
It is necessary to satisfy 0% or more. y '= 0.5Yma
At x, if the image plane illuminance is less than 80%, not only the effect of effective apodization on the off-axis light beam cannot be obtained, but also an unnatural defocused image is generated, which is not desirable.

[0073]

EXAMPLES The taking lens system according to the present invention will be described more concretely with reference to construction data, aberration diagrams and the like. Note that Examples 1 to 5 listed below correspond to the above-described first to fifth embodiments, respectively.
The lens arrangement diagram representing the fifth embodiment shows the corresponding lens configurations of Examples 1 to 5, respectively.

In each embodiment, ri (i = 1,2,3 ...) is the radius of curvature of the i-th surface counted from the object side, and di (i = 1,2,3 ...) is the object. It shows the i-th axial upper surface distance counted from the side, and Ni (i = 1,2,
3 ...), νi (i = 1,2,3 ...) indicates the refractive index and Abbe number of the i-th lens or filter for the d-line counted from the object side.

[0075]

[Table 2]

[0076]

[Table 3]

[0077]

[Table 4]

[0078]

[Table 5]

[0079]

[Table 6]

Further, in the following table, in each embodiment, when focusing from an infinity in-focus state to a close-up distance in-focus state, a change in the axial upper surface distance between the lens groups and an amount of movement to the object side. Is shown as floating data. The closest magnification β is β = 1/4 in Examples 1 and 2, and Example 3 is
For ~ 5, β = 1/2.

[0081]

[Table 7]

Further, the following table shows the refracting powers of the lens groups of the respective examples.

[0083]

[Table 8]

13 to 17 show the first embodiment.
It is an aberration diagram corresponding to ~ 5. In each figure, the upper figure shows the aberration in the infinity focus state, the lower figure shows the aberration in the close-up distance focus state,
Each aberration diagram corresponds to spherical aberration, astigmatism, and distortion in order from the left. In the spherical aberration diagram, the solid line d represents the spherical aberration for the d line, and the dotted line SC represents the sine condition. Also,
In the astigmatism diagram, a dotted line DM and a solid line DS represent astigmatism on the meridional surface and the sagittal surface, respectively.

The first, second, and fifth embodiments have conditional expressions (1) to
(3) and Examples 3 and 4 satisfy the conditional expressions (4) to (8), respectively. Furthermore, Examples 1 and 3 also satisfy the conditional expression (9). The following table shows the value of each conditional expression.

[0086]

[Table 9]

[0087]

As described above, according to the photographing lens system of the present invention, practical photographing in which an out-of-focus image is improved over a wide range from the infinity in-focus state to the close-up distance focusing state. A lens system can be realized.

Therefore, for example, when the taking lens system according to the present invention is applied as a taking lens of a camera, it is possible to provide a photographic image with a beautiful defocused image.

[Brief description of drawings]

FIG. 1 is a lens arrangement diagram of a taking lens system of Example 1 in an in-focus state at infinity.

FIG. 2 is a lens arrangement diagram of a taking lens system of Example 2 in an in-focus state at infinity.

FIG. 3 is a lens arrangement diagram of a taking lens system of Example 3 in an in-focus state at infinity.

FIG. 4 is a lens arrangement diagram of a taking lens system of Example 4 in an in-focus state at infinity.

FIG. 5 is a lens arrangement diagram of a taking lens system of Example 5 in an in-focus state at infinity.

FIG. 6 is a schematic diagram illustrating improvement of an out-of-focus image.

FIG. 7 is a graph showing a transmittance distribution of a normal optical system.

FIG. 8 is a graph showing a transmittance distribution of an apodization optical system.

FIG. 9 is a graph of a response function of a normal optical system and an apodization optical system.

FIG. 10 is a cross-sectional view illustrating a configuration of an apodization filter.

FIG. 11 is a sectional view showing an example of an apodization filter.

FIG. 12 is a graph showing an example of the transmittance of an apodization filter.

13 is an aberration diagram of the taking lens system of Example 1. FIG.

14 is an aberration diagram of the taking lens system of Example 2. FIG.

15 is an aberration diagram of the taking lens system of Example 3. FIG.

16 is an aberration diagram of the taking lens system of Example 4. FIG.

17 is an aberration diagram of the taking lens system of Example 5. FIG.

[Explanation of symbols]

 Gr1: 1st group Gr2: 2nd group Gr3: 3rd group A: Aperture F: Apodization filter

Claims (3)

[Claims] 1. A photographing lens system having a plurality of lens groups, an aperture arranged in any one of the plurality of lens groups, and an apodization filter arranged in the vicinity of the aperture, wherein A photographing lens system characterized by moving the entire system toward the object side while changing the distance between at least one lens group when focusing from a far focus state to a close-up distance focus state. 2. A first group, a second group, in order from the object side,
The first lens unit is a photographic lens system having a diaphragm and an apodization filter arranged in the vicinity of the diaphragm, wherein the first lens group is focused from an infinity focusing state to a close-up focusing distance state. A photographing lens system, wherein the whole system is moved to the object side while widening the distance between the first group and the second group. 3. A first group, a second group, in order from the object side,
A photographing lens system comprising a third lens group, wherein either one of the first lens group or the second lens group includes a diaphragm and an apodization filter arranged in the vicinity of the diaphragm. At the time of focusing from the in-focus state to the close-up object focusing state, the entire system is controlled by narrowing the distance between the first group and the second group and widening the distance between the second group and the third group. A shooting lens system characterized by being moved to the side.