JPH1115042A - Diaphragm device for photographic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of diffraction by a transparent part being very small in an intermediate aperture in the process of reaching a small aperture. SOLUTION: This diaphragm device is provided with two aperture blades 3 and 4 and an ND filter holding member 5 to which a first ND filter 22 is attached. The ND filter holding member 5 is provided to move in the same direction as that of one aperture blade 3 located to hold the other aperture blade 4, in the direction of an optical axis x-x. Then, a second ND filter 23 is attached to one aperture blade 3, to cover a part of the aperture diameter forming notch 14 of the aperture blade 3, so that the area covering an aperture 30 of the first ND filter 22 is made different from that of the second ND filter 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel photographic lens aperture device. More specifically, the present invention relates to an aperture device for a photographic lens that uses a plurality of aperture blades that travel straight in opposite directions to each other, and that prevents image pickup near the image sensor due to deterioration of image quality due to diffraction and an increase in the depth of focus by an ND filter. The present invention relates to a technique for reducing the influence of diffraction caused by a transparent portion that has been minimized in an intermediate diaphragm up to a small diaphragm.

[0002]

2. Description of the Related Art A diaphragm device for a photographing lens of a video camera or the like is provided with a so-called "iris diaphragm" in which a plurality of diaphragm blades are rotated around an optical axis to adjust the diaphragm diameter. 2. Description of the Related Art An aperture device for a photographing lens, which uses two aperture blades moving in opposite directions to reduce the size, weight, and cost, has been used.

However, if the aperture diameter is too small when the subject is bright, deterioration in image quality due to diffraction and reflection of dust due to an increase in the depth of focus poses a problem.

Therefore, an ND filter is attached to one of the aperture blades so that the ND filter protrudes into a notch for forming the aperture diameter of the aperture blade to prevent an extremely small aperture. There is.

FIG. 6 shows an example of a conventional photographic lens aperture device a.

The aperture device a is composed of two aperture blades b and c and a driving means d for driving the aperture blades b and c.

One of the diaphragm blades b has a notch e for forming a diaphragm diameter at a lower edge thereof, and a guided slit f, which extends vertically, is provided at a position near the right edge of the diaphragm blade b.
f is formed vertically. A guided slit g extending in the vertical direction is also formed at a position near the left edge.

[0008] A left and right long connecting slot h is provided immediately above a guided slit f formed on the right of the diaphragm blade b.
Are formed.

A guide pin provided on a housing (not shown) having a light passage hole is slidably engaged with each of the guided slits f, f, and g. The body is slidably supported in the vertical direction.

The other diaphragm blade c has a notch i for forming an aperture diameter formed at an upper edge thereof, and an ND filter j is attached so as to cover a lower end of the notch i for forming an aperture diameter. Guide slits k, k extending in the vertical direction are formed vertically at positions near the left edge of the aperture blade c. A guided slit 1 extending in the vertical direction is also formed at a position near the right edge. The ND filter j has a transmittance of 10%.

A left and right connecting slot m is provided immediately above a guided slit k formed on the upper left of the diaphragm blade c.
Are formed.

A guide pin provided on the casing (not shown) is slidably engaged with each of the guided slits k, k, and l, whereby the diaphragm blade c slides vertically on the casing. It is movably supported.

The drive means d has a drive motor n attached to the upper part of the above-mentioned casing (not shown) and an operation arm o fixed to a rotating shaft of the drive motor n.

The operation arm o is substantially elongated in the left-right direction. The center of the operation arm o is fixed to the rotating shaft of the drive motor n, and connecting pins p, p are protruded from both left and right ends thereof.

The connecting pin p on the right side of the operating arm o
Is connected to the connection elongated hole h of the aperture blade b and the left connection pin p
Are slidably engaged with the connection elongated holes m of the aperture blade c.

Therefore, when the drive arm n is rotated by driving the drive motor n, the connecting pins p and p move in the opposite directions, respectively, so that the aperture blades b and c connected to these move. Will move up and down and in the opposite direction. As a result, the aperture diameter (aperture opening) q defined by the aperture diameter notches e and i of the two aperture blades b and c changes.

FIG. 7 shows a diaphragm device a constructed as described above.
By moving the aperture blades b and c of FIG.
7A illustrates the shape of the aperture when the aperture is sequentially reduced from the small aperture (FIG. 7G) and how the ND filter j covers the aperture.

[0018]

By the way, in the above-described diaphragm device a, as shown in FIG. 7 (e), in the middle of the process down to the small aperture (FIG. 7 (g)), There is a problem that the transparent portion r, which cannot be covered by the ND filter j over the entire surface of the aperture opening q, has an effect like a small aperture, and the image quality is deteriorated.

FIG. 8 is a graph showing the result of measuring the change in contrast in the vertical direction due to the change in the aperture opening q. In FIG. 8, (a) to (g) on the horizontal axis correspond to FIG.
The vertical axis represents the contrast at a certain frequency calculated from the output of the image sensor.

As can be seen in FIG.
As the aperture opening q is reduced from (a)), the contrast gradually decreases. When the state shown in FIG. 7E is reached, the minimum value of the contrast is measured. This is because the shape of the transparent portion r where the ND filter j does not cover the entire surface of the aperture opening q becomes a flat shape (triangle) in the vertical direction, and the light beam passing through the transparent portion r in the small aperture state is diffracted. The light flux passing through the ND filter j forms an image without the influence of diffraction because the F-number is brighter than the transparent portion r, but the light flux passing through the ND filter j is formed, but the transmittance of the ND filter j is low (10 %), As a whole, the light flux passing through the transparent portion r becomes dominant in the image quality, and it is considered that the contrast is thereby reduced. That is, the transparent portion r and ND
Since the difference in transmittance with the filter j is large, the transparent portion r
Is similar to the small aperture state.

From the state shown in FIG.
, The transparent portion r disappears and the ND filter j
Covers the entire surface of the aperture opening q, so that the influence of diffraction is eliminated and the contrast is restored again (FIG. 7F).

When the aperture opening q is further reduced from the state shown in FIG. 7F, the aperture diameter becomes extremely small, so that the contrast is reduced again as a small aperture diffraction (FIG. 7).
(G)).

As described above, in the above-mentioned conventional diaphragm device a, the contrast becomes the minimum value before the small aperture (the aperture diameter is the minimum value) (FIG. 7G) (FIG. 7E). ), There is a problem that image quality is deteriorated.

Accordingly, it is an object of the present invention to reduce the influence of diffraction caused by a transparent portion which has been minimized in an intermediate stop until reaching a small stop.

[0025]

In order to solve the above-mentioned problems, the present invention provides an aperture device for a photographing lens, comprising at least two aperture blades and an ND filter holding member to which a first ND filter is attached. The ND filter holding member is provided so as to move in the optical axis direction in the same direction as the other diaphragm blade located with one diaphragm blade interposed therebetween. A second ND filter was attached so as to cover a part of the notch so that the area where the first ND filter covers the aperture and the area where the second ND filter covers the aperture are different. Things.

Therefore, in the aperture device of the photographic lens according to the present invention, the transmittance is low in a portion where the ND filters appear to overlap when viewed from the optical axis direction, and relatively low in a portion where only one ND filter is visible. The transmittance can be increased, so that the difference in transmittance between the transparent portion and the portion where only one of the ND filters can be seen is not extremely different. Even if it is minimized, the effect of diffraction by the transparent portion can be reduced, and deterioration of image quality can be reduced.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a photographic lens diaphragm apparatus according to an embodiment of the present invention.

FIGS. 1 to 5 show a first embodiment of a diaphragm device for a photographing lens according to the present invention.

An aperture device 1 for a photographing lens includes a thin casing 2, two aperture blades 3 and 4 housed vertically in the casing 2, and an ND filter to which an ND filter described later is attached. A filter holding member 5, an aperture blade 3,
4 and a drive mechanism 6 for moving the ND filter holding member 5.

FIG. 3 shows an example of an optical system 7 in which such a diaphragm device 1 is used.

The optical system 7 has, for example, lenses L1 to L6 and an image sensor 8, and the diaphragm device 1 is disposed between the lenses L4 and L5.

The casing 2 of the squeezing device 1 comprises a flat plate-shaped main portion 9 having an open front surface, and a cover plate 10 for closing the front surface of the main portion 9. In this specification, when indicating a direction, the direction toward the diagonally lower left in FIG. 1 is the front side, and the direction toward the diagonally upper right is the rear side. Further, a direction heading diagonally upward and left is defined as a left side, and a direction heading diagonally downward and right is defined as a right side. Further, an upward direction in the figure is defined as an upper side, and a downward direction is defined as a lower side. In the following description, the direction is indicated by this direction.

The main portion 9 has a rectangular flat back wall 11 which is long in the vertical direction, a small front and rear width peripheral wall 12 which protrudes forward so as to extend along the peripheral edge of the rear wall 11, and a rear wall 11. Small supporting pins 13, 13 and 1 protruding forward by two each from the left and right side edges of the front surface of
3 ', 13' and a frame portion 11b having a small front-rear width protruding rearward from a peripheral portion of an opening 11a formed in a little more than a quarter of the upper end side of the back wall 11 are integrally formed of synthetic resin. A light passing hole 11c having a circular shape is formed at a substantially central portion between the lower end of the back wall 11 and the opening 11a.

The cover plate 10 has a flat plate shape having the same shape as that of the main portion 9 as viewed from the front and rear direction, and is attached to the main portion 9 so as to close the front surface thereof. A box-shaped casing 2 is formed.

A light passage hole 10a is formed in the cover plate 10 at a position facing the light passage hole 11c of the main portion 9, and the light passage hole 10a and the above 11c have the same size. They are arranged so that their positions match each other.

Such a casing 2 is placed in an outer casing (not shown) so that the optical axis xx of the optical system 7 disposed therethrough passes through the centers of the light passing holes 10a and 11c. On the side, the cover plate 10 is arranged in a direction facing the image (imaging element 8).

The diaphragm blades 3 and 4 and the ND filter holding member 5 are formed of a resin film having a relatively strong stiffness, and sandwich one diaphragm blade 4 with the other diaphragm blade 3 and ND.
The filter holding member 5 is located in the casing 2 so that the diaphragm blade 3 is on the object side and the ND filter holding member 5 is on the image side.

The diaphragm blade 3 and the ND filter holding member 5 form a pair, and simultaneously move in the same direction at the same speed (displacement amount). Then, the diaphragm blade 4 moves in a direction opposite to the moving direction of the diaphragm blade 3 and the ND filter holding member 5.

The diaphragm blade 3 has a substantially J-shape, and a large semicircular notch 14 for forming a large diaphragm diameter is formed on the upper edge of the lower part thereof.
The radius of the main portion 14a excluding the lower end of the notch 14 is formed to be almost the same as or slightly larger than the radius of the light passing holes 10a and 11c. The lower end 14b of the aperture diameter forming notch 14 is formed in a substantially triangular shape.

At the position near the right edge of the aperture blade 3, guided slits 15a, 15
In addition, a guided slit 16 extending in the vertical direction is formed at a position closer to the left end edge.

Guided slit 15a on the upper side of diaphragm blade 3
A connection elongated hole 17 extending in the left-right direction is formed at a position immediately above.

Thus, the right guided slit 15a,
15b, two right support pins 1 of casing 2
3 and 13 are separately provided and support pins 13 ′ located on the left guided slit 16 on the lower left side of the casing 2.
The diaphragm blades 3 are slidably engaged with each other, so that the diaphragm blades 3 are supported by the casing 2 so as to be movable in the vertical direction.

The ND filter holding member 5 includes the diaphragm blade 3
It has almost the same shape and also has a function as an aperture blade. The aperture blade means a notch for forming an aperture opening.

That is, the ND filter holding member 5 has a substantially J-shape, and a large semicircular notch 18 is formed at the upper edge of the lower part thereof, and the lower end 18 of the notch 18 is formed.
b is formed in a substantially triangular shape, guided slits 19a and 19b are formed at positions near the right edge, and guided slits 20 are formed at positions near the left edge, respectively.
Further, a connection elongated hole 21 extending in the left-right direction is formed at a position immediately above the upper guided slit 19a.

The notch 18, guided slits 19a, 19b, 20 and connecting elongated hole 21 of the ND filter holding member 5 are respectively provided with the notch 14 for forming the aperture diameter of the diaphragm blade 3, and the guided slits 15a, 15b, 16 Alternatively, they are formed in the positions corresponding to the respective connection elongated holes 17 with the same size.

Thus, when the diaphragm blade 3 and the ND filter holding member 5 are overlapped, the guided slits 15a and
a, 15b and 19b, 16 and 20 respectively match,
In addition, the connection slot 17 and the connection slot 21 also match.

Thus, the right guided slit 19a,
19b, two right support pins 1 of the casing 2
3 and 13 are separately provided and a support pin 13 ′ located on the left guided slit 20 on the lower left side of the casing 2.
However, the ND filter holding member 5 is also slidably engaged with the casing 2 so as to be vertically movable.

The diaphragm blade 3 of the ND filter holding member 5
A first ND filter 22 is attached to a surface (front surface) opposite to the side opposite to the first ND filter 22 so as to cover the lower end portion 18b of the notch 18 and the lower half of the main portion 18a. The lower end 14 of the notch 14 for forming the aperture diameter is formed on the surface (rear surface) opposite to the side facing the ND filter holding member 5.
A second ND filter 23 is attached so as to cover b.

Thus, when the diaphragm blade 3 and the ND filter holding member 5 are overlapped, the lower end portions 14 of the notches 14 and 18
b, 18b, the two ND filters 22 and 23 appear to overlap, and the lower ends 14 of the notches 14, 18
The lower half of the portion excluding b and 18b is covered by the first ND filter 22.

The transmittance of each of the ND filters 22 and 23 is 32%.
The luminous flux passing only through the first ND filter 22 is 3
The luminous flux transmitting 2% and passing through the portion where the ND filters 22 and 23 overlap is about 10% (0.32 × 0.3
2 = 0.1024) is transmitted.

A substantially semicircular aperture diameter notch 24 is formed at the lower edge of the aperture blade 4 sandwiched between the aperture blade 3 and the ND filter holding member 5 in the optical axis direction.
The radius of the main portion 24a excluding the upper end of the notch 24 is formed to be equal to or slightly larger than the radius of the light passing holes 10a and 11c. The upper end 24b of the cutout 24 is further cut out in a substantially triangular shape.

Guided slits 25a and 25b are formed at the position near the left edge of the diaphragm blade 4 and are formed so as to be divided vertically and extend in the vertical direction, respectively. A guided slit 26 extending in the direction is formed. Further, the guided slit 25 on the left side
A long connection long hole 27 is formed on the upper side of a.

The diaphragm blade 4 is provided in the guided slits 25a and 25b on the left side 2
The support pins 13 ', 13' and the lower support pins 13, 13 on the right side of the casing 2 are slidably engaged with the guided slit 26, respectively. It is supported to be movable in the direction.

The drive mechanism 6 of the photographic lens aperture device 1 includes:
It comprises a motor 28 and a rotating arm 29 driven by the motor 28.

The motor 28 is fixed to the frame portion 11b formed on the rear wall 11 of the casing 2 so that the rear end of the case 28a is closed from the rear side. The front end of the shaft 28c is located approximately at the center of the opening 11a of the rear wall 11.

The rotating arm 29 has a central portion fixed to a rotating shaft 28c of the motor 28. A connecting pin 29a is provided at the right end of the rotating arm 29, and a connecting pin 29b is provided at the left end thereof. The connecting pins 29a and 29b are connected to the right connecting pin 29a. This is formed at a position farther from the rotating shaft 28c of the motor 28.

The connection pin 29a located at the right end is connected to the connection slot 17 of the aperture blade 3 and the connection slot 21 of the ND filter holding member 5, and the connection pin 29b at the left end is connected to the connection slot 27 of the aperture blade 4. Are slidably engaged with each other.

Accordingly, when the rotating arm 29 is rotated, the connecting pins 29a and 29b are displaced in the directions opposite to each other up and down, whereby the diaphragm blade 3, the ND filter holding member 5 and the diaphragm blade 4 are connected. They are moved in opposite directions. Also, the aperture blade 3 and the N which move in the same direction
Since the D filter holding member 5 is connected to the same connection pin 29a, the D filter holding member 5 is moved at the same displacement amount, that is, at the same speed, whereas the diaphragm blade 4 is moved to the position of the connection pin 29b to which it is connected. Is protruded at a position closer to the rotary shaft 28c than the connecting pin 29a, so that it is displaced by a smaller amount than the diaphragm blade 3 and the ND filter holding member 5.

When the diaphragm blades 3 and 4 move in the directions opposite to each other in the up and down direction, the apertures formed by the respective aperture diameter forming notches 14 and 24 overlap each other, that is, the size of the diaphragm opening 30. When the diaphragm blade 3 and the ND filter holding member 5 are located at the upper end of the moving range and the diaphragm blade 4 is located at the lower end of the moving range, the aperture opening 30 becomes the smallest small diaphragm. When the ND filter holding member 5 is located at the lower end of the moving range and the diaphragm blade 4 is located at the upper end of the moving range, the aperture opening 30 becomes the largest open aperture. It should be noted that the aperture opening 30 in the open aperture state is notch 14 for forming the aperture diameter.
The size of the light passage holes 10a and 11c of the casing 2 is not caused by the overlap between the light transmission holes 24 and 24.

FIG. 4 is a schematic diagram showing the change of the aperture 30 from the open stop (FIG. 4A) to the small stop (FIG. 4G).

FIG. 4A shows an open aperture state, in which the aperture blades 3 and the notches 14 and 18 of the ND filter holding member 5 are located opposite the light passage holes 10a and 11c of the casing 2, and the light passage In a state where the aperture blade 3 and the ND filter holding member 5 do not cover the holes 10a and 11c, the second ND
The filter 23 slightly covers the lower side of the light passage holes 10a and 11c, and the first ND filter 22 is
In a state in which it extends over approximately 1/3 of the lower side of a and 11c, the transparent portion 31 is approximately 2/3 of the upper side of the light passage holes 10a and 11c.

From this state, the aperture blades 3, 4 and N
When the D filter holding member 5 is moved to squeeze the aperture 30, as shown in FIG.
/ 2 is covered by the first ND filter 22, and approximately 下 of the lower side is covered by the two ND filters 22 and 23.

From the state shown in FIG.
4 and the ND filter holding member 5 are moved to narrow the aperture 30, and in FIG. 4C, the first aperture is left (as the transparent portion 31), leaving approximately 1/10 above the aperture 30. The ND filter 22 covers the remaining approximately 9/10,
Approximately 2/3 of the lower side will be covered by the second ND filter 23 as well. In this state, the transparent portion 31 has a small and flat triangle shape. However, since the difference in transmittance between the transparent portion 31 and the first ND filter 22 is smaller than that in the related art, deterioration of an image due to diffraction is small. It is reduced.

When the diaphragm blades 3 and 4 and the ND filter holding member 5 are further moved to narrow the diaphragm opening 30, the diaphragm opening 30 is further reduced as a whole in FIG. It will be covered by the ND filters 22 and 23.

From the state shown in FIG.
4 and the ND filter holding member 5 are moved to squeeze the aperture 30. As shown in FIG. 4E, approximately 1/10 of the upper side of the aperture 30 is covered by only the first ND filter 22, The remaining approximately 9/10 is covered by two overlapping ND filters 22,23. In this state, approximately 1/10 of the upper part of the aperture opening 30 presents a small and flat triangle. However, the transmittance due to the first ND filter 22 and the transmittance due to the overlap of the ND filters 22 and 23 are different. Since there is not much difference, image deterioration due to diffraction is reduced.

When the diaphragm blades 3, 4 and the ND filter holding member 5 are further moved to narrow the diaphragm opening 30, the diaphragm opening 30 is further reduced as a whole in FIG. It will be covered by the ND filters 22 and 23.

Further, when the diaphragm blades 3 and 4 and the ND filter holding member 5 are moved to narrow the diaphragm opening 30, the diaphragm opening 30 becomes the smallest in FIG. It will be covered by the filters 22 and 23. In the small aperture state (FIG. 4 (g)), the center of the aperture 30 coincides with the optical axis xx.

FIG. 5 is a graph showing the result of measuring the change in the contrast in the vertical direction due to the change of the aperture 30 in the same manner as the graph of FIG. (A)-(g) are the opening shapes (a)-
The vertical axis represents the contrast at a certain frequency calculated from the output of the image sensor.

As can be seen in FIG.
When the aperture 30 of the aperture device 1 is reduced from (a)), the contrast gradually decreases, and when the state shown in FIG. 5C is reached, the contrast shows a minimum value. This is because, similarly to the case described in the conventional example, in the state shown in FIG. 5 (c), the transparent portion is affected by diffraction by exhibiting a very small triangle, but the transparent portion 31 and the first ND filter are not affected. Since the difference in transmittance from that of No. 22 is small, the decrease in contrast is not so large as compared with the related art.

Then, from the state shown in FIG.
As the aperture is reduced to 0, the contrast is restored, and FIG.
In the state, the maximum value is shown. This is because the transparent portion 31 having a very small triangle is eliminated, the influence of the diffraction is eliminated, and the upper half of the aperture 30 is connected to the first ND filter 2.
2, because the lower half is in a state covered by the two ND filters 22, 23.

Further, from the state shown in FIG.
As the aperture value is reduced to 0, the contrast gradually decreases.
When the state (e) is reached, the contrast again shows the minimum value. This is because only the first ND filter 22 has an extremely small triangle at the portion covering the aperture 30 and is affected by the diffraction. However, in such a state, there is little difference between the transmittance by the first ND filter 22 and the transmittance by the overlap of the two ND filters 22 and 23, and therefore, the decrease in contrast does not become large.

The state shown in FIG.
As the aperture is reduced, the contrast gradually recovers, and FIG.
In the state of (f), it shows the maximum value again. This is because the first ND filter 22 having a very small triangle disappears, the effect of the diffraction disappears, and the light beam passes through the two ND filters 22 and 23.

When the stop device 1 is further stopped down from the state shown in FIG. 5 (f), the aperture diameter becomes extremely small, so that the contrast is reduced again as a small stop diffraction (FIG. 5).
(G)).

In the above embodiment, the shape of the ND filter holding member 5 is the same as that of the diaphragm blade 3 to which the second ND filter 23 is attached. The aperture device 1 is not limited to this, and the notch 18 of the ND filter holding member may be formed larger than the aperture diameter forming notch 14 of the aperture blade 3. In short, the aperture opening 30 is formed by the aperture diameter forming cutouts 14 and 24 formed in the two aperture blades 3 and 4, so that the ND filter 22 attached to the ND filter holding member 5 is connected to the aperture opening 30. The area that covers the aperture opening 30 and the area that covers the aperture opening 30 by the ND filter 23 attached to the aperture blade 3 may be different. Also, N
Move the D filter holding member 5 to the front side (image side) of the diaphragm blades 3 and 4
However, the ND filter holding member 5 may be arranged on the rear side (object side) of the diaphragm blades 3 and 4.

In the above embodiment, the amount of displacement of the diaphragm blade 3 and the ND filter holding member 5 to which the ND filters 22 and 23 are respectively attached due to the rotation of the rotation arm 29 is determined by the diaphragm Since it is larger than the blade 4, the area occupied by the transparent portion 31 can be increased at the time of full aperture.
The light amount loss due to the filters 22 and 23 can be reduced (see FIG. 4A), and the center of the aperture 30 can be made coincident with the optical axis xx when the aperture is small (FIG. 4G). reference). The present invention is not limited to this, and it goes without saying that the amount of displacement between the diaphragm blade 3 and the ND filter holding member 5 and the diaphragm blade 4 may be made equal.

In the above-described embodiment, the diaphragm blade 3 having the two ND filters 22 and 23 respectively attached thereto.
And the amount of displacement between the ND filter holding member 5 and the
The present invention is not limited to this, and the amount of displacement of each ND filter may be different. For example, a diaphragm blade having an ND filter with a small area is attached to an ND filter with a large area.
If the ND filter is moved faster than the ND filter holding member having the filter attached thereto, only one (larger area) ND filter can be applied to the aperture opening 30 at the time of the open aperture. The light amount loss due to the filter can be further reduced.

In order to make the speed (displacement amount) between the diaphragm blade having the ND filter attached thereto and the ND filter holding member different, for example, Japanese Patent Application No. Hei.
As disclosed in JP-A-123894, it is conceivable to provide two connecting pins of the rotating arm in the same direction from the center and at different distances from the center, and to connect the aperture blades separately to these.

The larger one 22 of the two ND filters 22 and 23 is attached to the ND filter holding member 5 located on the image side, and the smaller one 23 is attached to the diaphragm blade 3 located on the object side.
, Two ND filters 22 in the optical system 7,
23, the ND filter 22 or 2
Ghosts generated between the camera 3 and the image sensor 8 are not increased.

That is, since anti-reflection processing cannot be performed on the image pickup device and the ND filter, there is a problem that ghost occurs due to mutual reflection between the image pickup device and the ND filter. When two ND filters are arranged in an optical system as in the present invention, they are arranged so as to be parallel to each other. However, since the ND filters are made of a relatively flexible material, the parallelism is lost. Warpage may occur, and in such a case, a ghost generated by the ND filter and the imaging device is reduced by two.
It is conceivable that the ghost becomes more conspicuous as compared with the related art using one ND filter.

Therefore, by making the first ND filter 22 on the image side larger than the second ND filter 23 on the object side as in the above embodiment, the second ND filter 23 with a small area and the The luminous flux causing a ghost with the element 8 passes through the first ND filter 22 having a large area twice, so that its intensity is attenuated, and the ghost that should become two can be seen as one. Only a ghost almost equal to that using one ND filter will occur.

In the above embodiment, ND
Although the edge on the side of the filter that is notched has been described as being linear, the present invention is not limited to this, and a notch may be formed at the center. In such a case, the flat triangle generated when the stop aperture 30 is narrowed can be a polygon, for example, a rhombus, thereby reducing the influence of diffraction by the flat triangle close to the slit shape. it can.

In the above embodiment, two N
Although the D filters used have both transmittances of 32%, the present invention is not limited to this, and ND filters having different transmittances can be used.

[0083]

As is apparent from the above description, the iris diaphragm device of the present invention has at least two diaphragm blades and an ND filter holding member to which the first ND filter is attached. The ND filter holding member is provided so as to move in the optical axis direction in the same direction as the other diaphragm blade located with one diaphragm blade interposed therebetween, and the other diaphragm blade is provided with one notch for forming the diaphragm diameter. Second to cover the part
The area where the first ND filter covers the aperture opening is different from the area where the second ND filter covers the aperture opening, so that the ND filter is viewed from the optical axis direction. The transmittance can be relatively low in the portion where the ND filter can be seen, and the transmittance can be relatively increased in the portion where only one ND filter is visible.
Since the difference in transmittance between the transparent portion and the portion where only one of the ND filters can be seen does not become extremely different, even if the transparent portion becomes small in the intermediate diaphragm up to the small diaphragm, the diffraction by the transparent portion becomes small. Can be reduced, and deterioration of image quality can be reduced.

According to the second aspect of the present invention, the displacement of the diaphragm blade with the ND filter attached is larger than the displacement of the diaphragm blade without the ND filter attached. Therefore, the area occupied by the transparent portion can be made larger at the time of the open aperture, so that the light amount loss due to the ND filter at the time of the open aperture can be reduced.

According to the third and fourth aspects of the present invention, the ND located at the object side is provided.
Since the area of the filter covering the aperture diameter forming notch is smaller than the area of the ND filter located on the image side covering the aperture diameter forming notch, the luminous flux causing a ghost between the ND filter having a small area and the image pickup device, Since the light passes through the ND filter having a large area twice, its intensity is attenuated.
You can see the two ghosts as one,
Only a ghost almost equal to the one using one conventional ND filter is generated, and the ghost can be prevented from increasing.

The shapes and structures of the respective parts shown in the above-described embodiments are merely examples of the specific embodiments to be carried out when carrying out the present invention, and the technical scope of the present invention is thereby reduced. It should not be interpreted restrictively.

[Brief description of the drawings]

FIG. 1 shows an embodiment of an aperture device for a photographic lens according to the present invention, together with FIGS. 2 to 5, which is an exploded perspective view.

FIG. 2 is a front view partially cut away.

FIG. 3 is an explanatory diagram showing an outline of an optical system.

FIG. 4 is a schematic diagram showing the shape of an aperture opening in order from an open aperture (a) to a small aperture (g).

FIG. 5 is a graph showing the relationship between the shape of the aperture opening and the contrast.

FIG. 6 is a perspective view of the conventional photographing lens aperture device together with FIGS. 7 and 8, which is an exploded perspective view thereof.

FIG. 7 is a schematic diagram showing the shape of an aperture opening in order from an open aperture (a) to a small aperture (g).

FIG. 8 is a graph showing the relationship between the shape of the aperture opening and the contrast.

[Explanation of symbols]

Reference numeral 1 denotes an aperture device for a photographing lens, 3 denotes the other aperture blade, 4 ...
One of the aperture blades, 5: ND filter holding member, 14: Notch for forming aperture diameter, 22: first ND filter, 23: second ND filter, 30: aperture opening, xx: optical axis

Claims (4)

[Claims] An aperture device for a photographing lens in which an aperture is formed by moving aperture blades on a plane orthogonal to an optical axis in a direction in which the aperture blades are separated from each other, wherein at least two aperture blades and a first ND filter And an ND filter holding member having the ND filter holding member attached thereto, the ND filter holding member being provided so as to move in the optical axis direction in the same direction as the other diaphragm blade located with the one diaphragm blade interposed therebetween. A second ND filter is attached to the aperture blade so as to cover a part of the aperture diameter forming notch, and an area where the first ND filter covers the aperture opening,
Wherein the area of the ND filter covering the aperture is different. 2. The photographing apparatus according to claim 1, wherein the displacement of the diaphragm blade to which the second ND filter is attached is larger than the displacement of the diaphragm blade to which no ND filter is attached. Lens aperture device. 3. The method according to claim 1, wherein an area of the ND filter located on the object side covering the notch for forming the aperture diameter is smaller than an area of the ND filter located on the image side covering the notch for forming the aperture diameter. Item 2. An aperture device for a photographing lens according to item 1. 4. The method according to claim 1, wherein an area of the ND filter located on the object side covering the aperture diameter notch is smaller than an area of the ND filter located on the image side covering the aperture diameter notch. Item 3. An aperture device for a photographing lens according to item 2.