JPH11231209A - Photographic lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens system, with which high performance can be achieved even when an apodization filter to be used has power, by keeping a sufficient air gap between front and rear groups, arranging the apodization filter at the air gap and satisfying specified conditions. SOLUTION: This system is composed of a front group Gr1 and a rear group Gr2 successively from the side of an object, the sufficient air gap is kept between the front and rare groups Gr1 and Gr2, an apodization filter AF is arranged at that air gap and further, the conditional expression of 0.0001<|ϕF/ϕR|×|ϕAF/ϕT|<0.5 is satisfied. In this expression, ϕF expresses the power of the front group Gr1, ϕR expresses the power of the rear group Gr2, ϕAF expresses the power of the apodization filter AF, and ϕT expressed the power of the entire system. In this case, a flat convex lens L5 of the apodization filter AF is a first optical member composed of ND glass, and a flat convex lens L5 is a second optical member composed of glass having a refraction factor close to that of ND glass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photographic lens system, and more particularly, to a photographic lens system suitable for a photographic lens of a camera.

[0002]

2. Description of the Related Art Generally, the performance of a photographic lens system is evaluated by the imaging performance on a focal plane. For this reason, many proposals regarding aberration correction for the purpose of improving imaging performance have been made conventionally. However, the photographic lens system used in the camera has not only the imaging performance but also the out-of-focus image.
The appearance of (before and after blur) is also very important. For example, in a portrait photograph in which a person is arranged at the center of an image or a photograph of a flower taken in close proximity, a portion other than the main subject is
The appearance of an out-of-focus image (for example, a background portion) greatly affects the impression of a photographic image. Above all, when shooting close-up subjects using a macro lens with a shooting magnification of about 1/4 to 1/2, the background other than the main subject is almost always out of focus, so the out-of-focus image can be seen. Is particularly important.

[0003] Various appearances of an out-of-focus image are known. Taking the appearance of an out-of-focus image of the hair in a portrait photograph as an example, the following states (1) to (2) are the main appearances of the out-of-focus image. Among these, the state that the whole is softly blurred is considered to be good in appearance. : Hair is wide and blurred like ears of pampas grass. : A state in which two hairs are blurred as if they had two hairs (also referred to as two-line blur). : The whole is soft and blurred while leaving the core of the hair.

A lens system provided with an apodization filter is known as a lens system aiming at improving an out-of-focus image in a state of appearance (Japanese Patent Publication No. Sho 47).
-6982, U.S. Pat. No. 3,843,235, JP-A-9-236740). The apodization filter is a filter configured such that the amount of transmitted light gradually decreases as the distance from the center of the optical axis increases in the direction perpendicular to the optical axis. Due to the modification of the intensity distribution of the out-of-focus image performed by the apodization filter. Hereinafter, such an effect is referred to as apodization. }, The out-of-focus image improves the appearance of the state.

[0005]

An apodization filter used in a photographing lens system is a flat plate having no power in consideration of the ease of handling, the degree of freedom in optical design, the influence on the performance of the entire optical system, and the like. Desirably a filter. The apodization filter exemplified in Japanese Patent Application Laid-Open No. 9-236740 is ND
This is why a plano-concave lens made of (neutral density) glass is joined to a plano-convex lens made of glass having the same refractive index as ND glass. Although only a plano-concave lens made of ND glass functions as an apodization filter, the power of a plano-concave lens alone is so strong that it is necessary to correct aberrations as part of the lens system. ), Assembling accuracy (surface inclination, etc.), refractive index accuracy, etc. are required. In other words, the fact that the apodization filter has power causes the performance of the lens system to deteriorate.

However, even if a plano-convex lens is bonded to a plano-concave lens made of ND glass to form a flat apodization filter, it is practically impossible to reduce the combined power to zero as long as generally available optical materials are used. Is impossible. This is because the refractive index values of commonly available ND glass and optical glass used for ordinary lenses do not completely match. As a result, since the plano-convex lens is formed of optical glass having a refractive index close to that of the ND glass but not completely matched, the apodization filter has power.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a photographic lens system capable of achieving high performance even when an apodization filter to be used has power.

[0008]

In order to achieve the above object, a photographic lens system according to a first aspect of the present invention is a photographic lens system comprising a front group and a rear group in order from the object side. An air gap between the rear group is sufficiently provided, an apodization filter is arranged in the air gap, and the following conditional expression is further satisfied. 0.0001 <| φF / φR | × | φAF / φT | <0.5, where φF: power of the front group, φR: power of the rear group, φAF: power of the apodization filter, and φT: power of the whole system.

According to a second aspect of the present invention, in the imaging lens system according to the first aspect, the apodization filter includes a first optical member made of ND glass and a second optical member made of glass having a refractive index close to that of the ND glass. And an optical member, and satisfies the following conditional expression. 0.0001 <| ndND−ndB | <0.05, where ndND is the refractive index of the ND glass constituting the first optical member with respect to the d line, and ndB is the refractive index of the glass constituting the second optical member with respect to the d line. It is.

A photographic lens system according to a third aspect of the present invention is characterized in that, in the configuration of the first aspect, the following conditional expression is further satisfied: 0.00001 <| φAF / φT | <0.5.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A photographic lens system embodying the present invention will be described below with reference to the drawings. 1 and 3 are lens configuration diagrams respectively corresponding to the photographing lens systems of the first and second embodiments, and show the lens arrangement in an infinity in-focus state [A]. Ri (i = 1,2,
The surface marked with (3, ...) is the i-th surface counted from the object side, and di (i = 1,2,3, ...) is the i-th axial top surface distance counted from the object side. It is. Also, arrows (m1, m2) in each lens configuration diagram
Is from infinity in focus [A] to close focus distance in focus [B]
The front group (Gr1) and the rear group (Gr1)
2) etc. are schematically shown.

Each of the first and second embodiments is a taking lens system composed of a front group (Gr1) and a rear group (Gr2) in order from the object side, and includes a front group (Gr1) and a rear group (Gr2). )) Is a single focal length telephoto lens in which an aperture (AS) and an apodization filter (AF) are arranged in the air space with a sufficient air space. Also, in focusing from infinity in-focus condition [A] to close-distance focusing distance in-focus condition [B], by moving at least one lens unit interval (d7), the entire system is moved to the object side. A method of performing short-range aberration correction (so-called floating) is adopted. Such floating can prevent performance degradation until the nearest neighbor. In any of the embodiments, the aperture (AS) and the apodization filter (AF) move in focus together with the rear group (Gr2).

In the first embodiment, the front group (Gr1) and the rear group
(Gr2) also has a positive power. In addition, the front group (Gr1),
The apodization filter (AF) and the rear group (Gr2) are configured as follows in order from the object side. Front group (Gr1)
Is a plano-convex lens (L1) convex on the object side, a negative meniscus lens (L2) concave on the image side, and a positive meniscus lens (L3) convex on the object side
And a negative meniscus lens (L
4) Consists of Apodization filter (AF)
Consists of a cemented lens of a plano-concave lens (L5) concave on the image side and a plano-convex lens (L6) convex on the object side. In the apodization filter (AF), the plano-concave lens (L5) is a first optical member made of ND glass, and the plano-convex lens (L6) is a second optical member made of glass having a refractive index close to that of ND glass. The rear unit (Gr2) includes a biconvex positive lens (L7) and a negative meniscus lens (L8) concave on the object side. In the first embodiment, the distance between the front group (Gr1) and the aperture (AS) (d
7) Floating to expand is adopted.

In the second embodiment, the front group (Gr1) has a positive power, and the rear group (Gr2) has a negative power. In addition, the front group (Gr1), the apodization filter (AF), the rear group (Gr1)
2) is configured as follows in order from the object side. The front group (Gr1) includes a biconvex lens (L1), a cemented lens composed of a negative meniscus lens (L2) concave on the image side and a positive meniscus lens (L3) convex on the object side, and a negative meniscus lens concave on the image side. (L4). The apodization filter (AF)
A plano-concave lens (L5) concave on the image side and a plano-convex lens (L
6) and made of cemented lens. In the apodization filter (AF), the plano-concave lens (L5) is a first optical member made of ND glass, and the plano-convex lens (L6) is a second optical member made of glass having a refractive index close to that of ND glass. The rear unit (Gr2) includes a biconvex positive lens (L7) and a negative meniscus lens (L8) concave on the object side. The second
In the embodiment, the distance between the front group (Gr1) and the aperture (AS) (d7)
The floating that spreads is adopted.

As described above, it is actually impossible to reduce the power of the apodization filter (AF) to zero, and the apodization filter (AF) used in the first and second embodiments is also impossible. Has weak power. This power is applied to the first optical member (L5) which is a plano-concave lens.
And the second optical member (L6) as a plano-convex lens, the refractive index of the ND glass forming the plano-concave lens (L5) and the refractive index of the glass forming the plano-convex lens (L6) Is different from the above. The conditions for enabling high performance (i.e., high delineation performance at the focus position and improved defocusing image blur performance) even when the apodization filter (AF) has power are described below. Conditional expressions (1) to (3).

The first and second embodiments use the following conditional expressions:
It is configured to satisfy (1). 0.0001 <| φF / φR | × | φAF / φT | <0.5 (1) where φF: power of the front group (Gr1), φR: power of the rear group (Gr2), φAF: power of the apodization filter (AF) , ΦT: power of the whole system.

Conditional expression (1) defines a desirable relationship between the power ratio of the front / rear group and the power ratio of the apodization filter (AF) to the entire system. If conditional expression (1) is satisfied, the apodization filter (AF), the front group (Gr1),
The power of the rear group (Gr2) is appropriately balanced to improve the depiction performance at the focus position, and at the same time, it is possible to achieve smooth blurring with little vignetting to the periphery of the screen. Although the power of the apodization filter (AF) is preferably as small as possible, it is actually very difficult to exceed the lower limit of the conditional expression (1) as described above.
If the upper limit of conditional expression (1) is exceeded, the effect of the power of the apodization filter (AF) on the performance of the entire optical system becomes too large, and the apodization filter (AF)
High precision is required for processing / mounting and refractive index of
The result is reduced performance.

The first and second embodiments use the following conditional expressions:
It is configured to satisfy (2). 0.0001 <| ndND−ndB | <0.05 (2) where ndND is the refractive index of the ND glass constituting the first optical member (L5) with respect to the d-line, and ndB is the second optical member (L6). Is the refractive index of the glass at d-line.

Conditional expression (2) defines a desirable difference in refractive index between the two lenses (L5, L6) constituting the apodization filter (AF). If conditional expression (2) is satisfied, the plano-concave lens that constitutes the apodization filter (AF)
The refractive index difference between (L5) and plano-convex lens (L6) will be appropriate, and the delineation performance at the focus position will be good, and at the same time, it will be possible to achieve smooth blurring with little vignetting to the periphery of the screen . The smaller the refractive index difference, the better, but it is actually very difficult to exceed the lower limit of conditional expression (2), as described above. If the upper limit of conditional expression (2) is exceeded, the effect of the power of the apodization filter (AF) on the performance of the entire optical system becomes too large, and high precision is required for the processing and installation of the apodization filter (AF) and the refractive index. And performance will be reduced as a result. Not only the refractive index but also the Abbe number, if the difference is large, causes the same problem as described above. Further, the optical material constituting the first and second optical members (L5, L6) is not limited to glass, and it is desirable that the optical material such as plastic also satisfy conditional expression (2). .

The first and second embodiments use the following conditional expressions:
It is configured to satisfy (3). 0.00001 <| φAF / φT | <0.5… (3)

Condition (3) defines a desirable power ratio for the entire system of the apodization filter (AF). If conditional expression (3) is satisfied, the power of the entire system of the apodization filter (AF) is properly balanced,
This makes it possible to improve the depiction performance at the focus position, and at the same time, achieve smooth blurring with little vignetting up to the periphery of the screen. Apodization filter
Although the power of (AF) is preferably as small as possible, it is actually very difficult to exceed the lower limit of conditional expression (3) as described above. If the upper limit of conditional expression (3) is exceeded, the effect of the power of the apodization filter (AF) on the performance of the entire optical system becomes too large, and high precision is required for the processing and installation of the apodization filter (AF) and the refractive index. And performance will be reduced as a result.

As in the first and second embodiments, in a taking lens system composed of a front unit (Gr1) and a rear unit (Gr2) in order from the object side, a front unit (Gr1) and a rear unit (Gr1) Gr2) and the apodization filter can be arranged in the air space by making the air space enough.
Since (AF) is located near the aperture (AS), vignetting is reduced. Therefore, a configuration in which the apodization filter (AF) is arranged in a large space secured between the front and rear groups is effective in achieving smooth blurring to the outermost periphery of the screen.

As described above, in order to ensure a sufficient air gap between the front group (Gr1) and the rear group (Gr2) and to dispose the apodization filter (AF) in the air gap, the following conditional expression is required.
It is desirable to satisfy (4). 0.1 <(a + tAF + b) / Σd <0.8 (4) where, a: from the apodization filter (AF) to the front group (Gr
Air spacing up to 1), tAF: On-axis spacing of apodization filter (AF), b: Rear group (Gr) from apodization filter (AF)
Air spacing up to 2), Σd: axial spacing from the first surface to the final surface of the taking lens system.

If the lower limit of conditional expression (4) is exceeded, it will be difficult to arrange an apodization filter (AF) due to its configuration. If the upper limit of conditional expression (4) is exceeded, the space for arranging the apodization filter (AF) becomes too large, and it becomes difficult to correct aberration using a plurality of lenses.
In addition, an increase in the size in the lens radial direction is inevitable.

Although the apodization filter (AF) used in the first and second embodiments has a flat surface on both the entrance and exit surfaces, the conditional expression (1), and preferably the conditional expression (1) If 2) and (3) are satisfied, the entrance surface and the exit surface can be configured by curved surfaces. Further, the apodization filter (AF) used in the first and second embodiments is configured by joining a first optical member (L5) and a second optical member (L6). (1) Preferably, if conditional expressions (2) and (3) are further satisfied, the first optical member
It is also possible to form an air lens by leaving a gap between (L5) and the second optical member (L6).

<< Principle of Improvement of Out-of-Focus Image >> Here, the principle of improvement of an out-of-focus image performed by an apodization filter (AF) will be described. FIG. 5 is a schematic diagram for explaining improvement of an out-of-focus image. In FIG. 5, P indicates a point light source, and L indicates an aberration-free lens system L having a circular aperture symmetrical to the optical axis (AX). The lens system L forms a point image P ′ at a focal plane conjugate with the point light source P, and moves the optical axis from the focal plane.
A large out-of-focus image P ″ is formed on the surface S separated by Δ in the (AX) direction.
By changing the distance between the point light source P and the lens system L,
Although the point image P ′ on the image plane becomes an out-of-focus image P ″, in the following description, for the sake of simplicity, the position of the point light source P on the optical axis (AX) is fixed, and the focus including the point image P ′ The defocused image P ″ on a plane S parallel to the plane will be discussed.

When the transmittance distribution of the aperture of the lens system L is constant, that is, as shown in FIG. 6, the transmittance τ (h) is constant within the range from the optical axis (AX) to the effective radius h1 of the aperture. In the case of, the image P ″ of the point light source P on the surface S is a circle of confusion with uniform intensity. On the other hand, the aperture of the lens system L is inserted from the optical axis center as shown in FIG. If the transmittance τ (h) decreases as the distance increases in the direction perpendicular to (AX), and absorption is given such that the effective radius h1 becomes 0, the image P ″ of the point light source P on the surface S has an intensity distribution Is a circular image similar to the transmittance distribution. That is, when the transmittance τ (h) has a distribution as shown in FIG. 7, an out-of-focus image P ″ of the point light source P is an image in which the center near the optical axis (AX) is bright and the intensity decreases toward the periphery. Becomes

Since a general subject is considered to be an aggregate of point light sources having different luminances, according to a lens system having a distribution of aperture transmittance τ (h) as shown in FIG. It will softly blur while leaving the core. Therefore, a good out-of-focus image as in the above-described state can be obtained. The above is the principle of improvement of an out-of-focus image by apodization.

The feature of the apodization is that its effect on the out-of-focus image does not depend on the position of the surface S, the defocus amount, the front blur, the back blur, and the like. That is, as is clear from FIG. 5, the out-of-focus image P ″ of the point light source P is close to the optical axis (AX) as long as it passes through the effective diameter of the lens system L, regardless of the position of the surface S. Is bright, and the intensity decreases toward the periphery.

Further, the improvement of an out-of-focus image by apodization will be described using a response function. The response function is also called an OTF (optical transfer function) and indicates a frequency transfer characteristic between the spectrum of the subject and the spectrum of the image. The response function of the out-of-focus image is calculated by calculating the wavefront aberration due to defocus at the pupil, obtaining the pupil function, obtaining the point image intensity distribution from the pupil function, and further performing the Fourier transform on the point image intensity distribution. Derived.

FIG. 8 shows that the aperture of the lens system is expressed by the following equation (A).
(A) has a constant transmittance τ (h) as expressed by
And the optical axis (A) from the optical axis center represented by the following equation (B).
X) The transmittance τ (h) that decreases as the distance increases in the direction perpendicular to X)
14B is a graph illustrating a response function of an out-of-focus image on a plane separated by Δ from the focal plane when (b) is included. In the graph of FIG. 8, the horizontal axis is the spatial frequency s.
The vertical axis represents the response value normalized so that the response becomes 1 at the spatial frequency s = 0. τ (h) = 1 (A) τ (h) = 1−h ² (B)

As can be seen from the graph of FIG. 8, when the transmittance τ (h) of the aperture of the lens system is a constant value, the response function (a) sharply decreases in the low frequency component of the spatial frequency. After that, it shows a characteristic in which it temporarily takes a negative value near the spatial frequency s = s1, and takes a positive value near the spatial frequency s = s2. On the other hand, when the transmittance τ (h) of the lens system aperture decreases as the distance from the optical axis center in the direction perpendicular to the optical axis (AX) decreases, the response function of (b) gradually decreases in the low-frequency component of the spatial frequency. It shows a characteristic that monotonously decreases, takes a slightly negative value near the spatial frequency s = s2, and then becomes a positive value again.

In general, the low frequency components of the spatial frequency form the schematic structure of the image, and the high frequency components have the effect of modifying the schematic structure of the image formed by the low frequency components. A state in which the response function takes a negative value is called false resolution. In an actual image, a black-to-white portion becomes white and a white portion becomes black.
Line blur).

It is considered that the image based on the characteristic (a) in which the transmittance τ (h) is constant has a large reduction in low-frequency components, and the schematic structure of the image is not reproduced very much. Further, since the range of negative values near the spatial frequency s = s1 is large, the range of the spatial frequency in which the pseudo-resolution state is obtained is wide. Furthermore, since the oscillation of the response function in the high frequency component is remarkable, it can be said that a very unnatural image is formed.
On the other hand, when the transmittance τ (h) decreases as the distance from the optical axis (AX) increases, the image based on the characteristics in (b) has a small decrease in low-frequency components, and is considered to reproduce the schematic structure of the image more. Can be Further, the range of the spurious resolution is small, and the oscillation of the response function in the high frequency component is also small.

As described above, the optical axis (A
In the case of a lens system having an aperture such that the transmittance τ (h) decreases as the distance from the lens in the direction perpendicular to the direction X) increases, an out-of-focus image is obtained compared to a lens system having an aperture having a constant transmittance τ (h). It can be said that the frame of the image is clear and that the image is naturally blurred. In other words, the out-of-focus image of the lens system having the characteristic of the response function (b) is in a state where the image is softly blurred while leaving the center at the center (the state described above).
)You can say that. Thus, it can be seen that the out-of-focus image is improved by the apodization also from the viewpoint of the response function.

<< Apodization filter >>
The apodization filter will be described. As described above, the apodization filter (AF) uses a first optical member (L5) made of a substance having light absorption (ND glass), and the apodization filter (AF) includes the first optical member (AF). L5) from the optical axis center to the optical axis (A
X) The transmittance τ (h) is configured to decrease as the distance increases in the vertical direction.

In general, when a light beam is transmitted through a lens, the transmitted light intensity I
Is represented by the following equation (C). I = I0 · exp (−αt) (C) where I0: incident light intensity, α: absorption coefficient, t: lens thickness.

In the above equation (C), the absorption coefficient α is a constant determined by the lens medium, so that the transmitted light intensity I with respect to the incident light of a constant intensity is determined only by the thickness of the lens. Using this characteristic, the transmittance τ (h) increases as the distance from the center of the optical axis increases in the direction perpendicular to the optical axis (AX).
A lens can be made that has an absorption such that is reduced. That is, as shown in FIG. 9, when a plano-concave lens is manufactured using a lens material having a large absorption coefficient α, the thickness of the lens increases as the distance from the center of the optical axis to the direction perpendicular to the optical axis (AX) increases. Increases, so that the absorption increases from the center of the lens toward the periphery.

Hereinafter, the transmittance distribution of such a plano-concave lens will be described. In FIG. 9, if the radius of curvature of the concave surface of the lens is r, and the thickness of the lens at a height h from the optical axis (AX) is t, the thickness t is expressed by the following formula (D) from a geometric calculation. Is done. In the formula (D), if the binomial expansion is performed assuming that h is smaller than r, the thickness t can be approximated to the following formula (E). Then, when the equation (E) is substituted into the equation (C), the following equation (F) is obtained. t = r−√ (r ² −h ² )… (D) t ≒ h ² / 2r… (E) I (h) = I0 · exp (−α · h ² / 2r)… (F)

Since the transmittance τ (h) is the ratio between the intensity of the incident light I0 and the intensity of the transmitted light I (h), the following equation (G) is obtained. formula
(G) shows a Gaussian distribution. When a plano-concave lens as shown in FIG. 9 is actually produced, since the approximation by binomial expansion is performed in the above equation (E), the Gaussian distribution is not completely Gaussian, but is substantially Gaussian slightly deviated from the Gaussian distribution. Becomes That is, if the plano-concave lens as shown in FIG. 9 is made of a medium having an absorption coefficient α, the transmittance τ (h) has a substantially Gaussian distribution. In FIG. 5, when the transmittance τ (h) of the lens system L has a substantially Gaussian distribution, the intensity distribution of the out-of-focus image P ″ of the point light source P formed on the surface S is also the same as the transmittance distribution. Τ (h) = I (h) / I0 = exp (−α · h ² / 2r)… (G)

By the way, the Fourier transform of the Gaussian distribution is
It is known that it has no negative value. Therefore, the response function obtained by Fourier-transforming the point image intensity distribution of the out-of-focus image P ″, which is a Gaussian distribution, has only positive values.
(h), in the lens system including this plano-concave lens, the out-of-focus image response function mostly takes a positive value, and the range of the spatial frequency at which spurious resolution occurs is extremely large. Become smaller. In addition, since the response function also decreases monotonously, a natural defocused image can be obtained.

As described above, if ND glass is used,
A lens that can achieve the effect of apodization can be manufactured. However, as can be seen from equation (G), 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 required to obtain a desired transmittance distribution. You will be restricted. This undesirably greatly limits the design freedom of the optical system. Therefore, in the above-described embodiment, an apodization filter (AF) is obtained by joining a concave surface and a convex surface using a plano-convex lens having a convex surface having the same radius of curvature as the concave surface of the plano-concave lens. Ideally, the material of such a plano-convex lens is glass having the same refractive index and Abbe number as the plano-concave lens, but only having a different absorption coefficient α. If the plano-concave lens and the plano-convex lens have the same refractive index and Abbe number, the luminous flux will not be refracted at the joint surface of the two, so that the apodization filter can be treated as a flat filter that gives only the transmittance distribution.

Here, an example of the apodization filter is shown by construction data, and the sectional structure is shown in FIG. In the construction data, Ri (i = 1,2,3) indicates the radius of curvature of the i-th surface counted from the object side, and Ti (i = 1,2) indicates the i-th axial top surface distance counted from the object side. Ni (i = 1,2) and νi (i = 1,2) indicate the refractive index and Abbe number of the i-th lens from the object side with respect to the d-line. FIG. 11 shows a graph of design data of the transmittance τ (h) of the apodization filter. This apodization filter is formed by joining a plano-concave lens 1 and a plano-convex lens 2 and has an effective radius of 15.5 mm.

[0044]

The apodization filter is
Not limited to the above-described configuration, by depositing an absorbing substance so as to have a predetermined distribution on a transparent glass flat plate, or by applying a photosensitive material to a transparent glass flat plate and exposing it to a predetermined density. Can also be obtained. The apodization filter manufactured by these methods has an advantage that the thickness of the filter can be reduced. However, the apodization filters manufactured by these methods have a problem that a phase change of the light beam occurs because the film thickness of the absorbing material or the photosensitive material varies depending on the transmittance distribution (that is, the incident height).
Further, there is a problem that the light beam is scattered or reflected by the absorbing substance or the photosensitive material.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a photographic lens system embodying the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Example 1 given here as an example
Reference numeral 2 corresponds to the first and second embodiments, respectively, and is a lens configuration diagram showing the first and second embodiments.
(FIGS. 1 and 3) show the corresponding lens configurations of Examples 1 and 2, respectively.

In the construction data of 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,. ..) indicates the i-th axial top surface distance counted from the object side, and Ni (i = 1,2,3, ...), νi (i = 1,2,
3, ...) is d of the i-th optical element counted from the object side
The refractive index and Abbe number for the line are shown. In addition, the shaft upper surface interval (variable interval) that changes during focusing is
This is the axial top surface distance between the moving units in the infinity in-focus condition [A] to the close-up shooting distance in-focus condition [B]. Also, the focal length of the whole system
(f), F number (FNO), proximity magnification (β) in state [B],
N used for apodization filter (AF)
Absorption coefficient (α) of D glass; front group in focusing
The ratio (M1) of the movement amount (M1) of (Gr1) and the movement amount (M2) of the aperture (AS), the apodization filter (AF), and the rear group (Gr2)
/ M2); The value corresponding to the conditional expression and its related data are also shown.

Example 1 f = 135.0, FNO = 2.83, β = −1 / 4, α = 0.55 M1 / M2 = 1.11 / 1 φF = 0.00370, φR = 0.00671, φAF = −0.000267, φT = 0.00740 a + tAF + b = (d7 + d8) + (d9 + d10) + d11 = 42.78, Σd = d1 + d2 ... + d14 = 93.86 Conditional expression (1): | φF / φR | × | φAF / φT | = 0.02 Conditional expression (2 ): | NdND−ndB | = 0.00553 Conditional expression (3): | φAF / φT | = 0.036 Conditional expression (4): (a + tAF + b) /Σd=0.46 [curvature radius] [axis top surface interval] [refractive index] [abbe Number] · front group (Gr1)… r1 = 75.063 (L1)… d1 = 9.000 N1 = 1.60311 ν1 = 60.74 r2 = ∞ d2 = 0.250 r3 = 37.102 (L2)… d3 = 3.000 N2 = 1.72342 ν2 = 37.99 r4 = 26.475 (L3)… d4 = 16.000 N3 = 1.51680 ν3 = 64.20 r5 = 104.186 d5 = 2.050 r6 = 678.979 (L4)… d6 = 2.000 N4 = 1.61293 ν4 = 36.96 r7 = 30.584 d7 = 14.397-18.198 ・ Aperture (AS)… r8 = ∞ d8 = 1.500 ・ Apodization filter (AF)… r9 = ∞ (L5)… d9 = 0.300 N5 = 1.50690 ν5 = 58.94 r10 = 20.731 (L6)… d10 = 9.330 N6 = 1.50137 ν6 = 56.46 r11 = ∞ d11 = 17.250・ Rear group (Gr2)… r12 = 97.643 (L7)… d12 = 7.500 N7 = 1.58913 ν7 = 61.11 r13 = -47.530 d13 = 9.500 r14 = -41.707 (L8)… d14 = 1.800 N8 = 1.62041 ν8 = 60.29 r15 = -923.182

Example 2 f = 135.0, FNO = 2.83, β = −1 / 4, α = 0.55 M1 / M2 = 0.97 / 1 φF = 0.00760, φR = −0.00302, φAF = −0.000267, φT = 0.00740 a + tAF + b = (d7 + d8) + (d9 + d10) + d11 = 39.099, Σd = d1 + d2 ... + d14 = 82.70 Conditional expression (1): | φF / φR | × | φAF / φT | = 0.091 Conditional expression ( 2): | ndND−ndB | = 0.00553 Conditional expression (3): | φAF / φT | = 0.036 Conditional expression (4): (a + tAF + b) /Σd=0.47 [curvature radius] [axis top surface interval] [refractive index] [ Abbe number] · front group (Gr1)… r1 = 136.245 (L1)… d1 = 7.799 N1 = 1.62041 ν1 = 60.29 r2 = -2351.337 d2 = 0.250 r3 = 37.142 (L2)… d3 = 2.802 N2 = 1.75000 ν2 = 25.14 r4 = 30.487 (L3)… d4 = 13.000 N3 = 1.51680 ν3 = 64.20 r5 = 138.452 d5 = 1.450 r6 = 698.983 (L4)… d6 = 1.999 N4 = 1.67339 ν4 = 29.25 r7 = 66.753 d7 = 12.00 to 10.983 ・ Aperture (AS) … R8 = ∞ d8 = 1.500 ・ Apodization filter (AF)… r9 = ∞ (L5)… d9 = 0.300 N5 = 1.50690 ν5 = 58.94 r10 = 20.731 (L6)… d10 = 9.300 N6 = 1.50137 ν6 = 56.46 r11 = ∞ d11 = 15.999 ・ after (Gr2) ... r12 = 155.942 (L7) ... d12 = 5.000 N7 = 1.62588 ν7 = 35.70 r13 = -83.733 d13 = 9.500 r14 = -33.259 (L8) ... d14 = 1.801 N8 = 1.61272 ν8 = 58.52 r15 = -256.843

FIG. 2 is an aberration diagram for the first embodiment, and FIG. 4 is an aberration diagram for the second embodiment. 2 and 4, [A] is an infinity in-focus condition, and [B] is a close-up focusing distance in-focus condition.
(From left to right, spherical aberration, astigmatism, distortion; Y ': image height)
Are respectively shown. In the spherical aberration diagram, the solid line (d)
Represents the spherical aberration with respect to the d-line, and the broken line (SC) represents the sine condition. In the astigmatism diagram, a broken line
(DM) and the solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

[0051]

As described above, according to the present invention, even if the apodization filter used has power, high performance (that is, high depiction performance at the focus position and blurring performance with improved out-of-focus image) can be obtained. A achievable photographic lens system can be realized. If the photographing lens system according to the present invention is used in a camera, a photographic image with a beautiful out-of-focus image can be provided.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment (Example 1).

FIG. 2 is an aberration diagram of the first embodiment.

FIG. 3 is a lens configuration diagram of a second embodiment (Example 2).

FIG. 4 is an aberration diagram of the second embodiment.

FIG. 5 is a schematic diagram for explaining improvement of an out-of-focus image.

FIG. 6 is a graph showing a transmittance distribution of a normal optical system.

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

FIG. 8 is a graph showing response functions of a normal optical system and an apodization optical system.

FIG. 9 is a cross-sectional view illustrating a configuration of an apodization filter.

FIG. 10 is a sectional view showing an example of an apodization filter.

FIG. 11 is a graph showing the transmittance of the apodization filter of FIG. 10;

[Explanation of symbols]

 Gr1 ... front group Gr2 ... rear group AS ... stop AF ... apodization filter L5 ... plano-concave lens (first optical member) L6 ... plano-convex lens (second optical member) AX ... optical axis

Claims (3)

[Claims] 1. A photographing lens system comprising a front group and a rear group in order from the object side, wherein an air gap between the front group and the rear group is sufficiently provided, and an apodization filter is arranged at the air gap. 0.0001 <| φF / φR | × | φAF / φT | <0.5, where φF: power of the front group, φR: power of the rear group, φAF : Power of the apodization filter, φT: Power of the whole system. 2. The apodization filter according to claim 2, wherein
A first optical member made of ND glass;
2. The taking lens system according to claim 1, wherein the second optical member is made of glass close to glass, and satisfies the following conditional expression: 0.0001 <| ndND-ndB | <0.05. ndND: Refractive index for d-line of the ND glass constituting the first optical member, and ndB: Refractive index for d-line of the glass constituting the second optical member. 3. The photographing lens system according to claim 1, further satisfying the following conditional expression: 0.00001 <| φAF / φT | <0.5.