JPH11337709A - Light shielding plate and lens system having this plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light shielding plate, which is superior in characteristics to drive reflected light in each part of an optical system to the outside of the optical axis and which has improved flare, and to provide a lens system having this plate. SOLUTION: This light shielding plate 5 is annular to have a center part, where an aperture spread around an optical axis is formed, and intercepts light in the peripheral area on the outside of the optical axis; and the aperture peripheral edge of the light shielding plate consists of a front plate 11 inclined so as to project to the object side and of a rear plate 13 inclined so as to project to the image side. Since the light shielding surface is not right-angled but inclined to the optical axis, the light shielding plate is superior in characteristics to drive unnecessary reflected light to the outside of the optical axis and can reduce flare of an image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-shielding plate suitable for being mounted on a lens system of a camera, a video camera or the like. Further, the present invention relates to a lens system having such a light shielding plate. In particular, the present invention relates to a light-shielding plate which has excellent characteristics of driving reflected light from various parts of the optical system to outside the optical axis, and is improved so as to improve flare, and a lens system having the same.

[0002]

2. Description of the Related Art In a lens system, light in an outer peripheral area of an optical axis is blocked, and the Fno.
Is arranged. FIG. 3 is a diagram for explaining light rays of a light shielding plate in a conventional lens system and its problems.

FIG. 3A shows a concave lens 31 and a light shielding plate 33 arranged on the image side thereof. Light shield 33
Is a ring-shaped thin plate having an opening 35 in the center,
It is arranged perpendicular to the optical axis. The light shielding plate 33 is black in order to absorb reflected light as much as possible. However, the reflected light cannot be completely eliminated. For example, the light beam L11 in the figure passes through the central portion of the concave lens 31, is reflected on the front surface (object side surface) of the light shielding plate 33, and then reflected by the concave lens 31. The light is reflected on the rear surface, and the opening 3 of the light shielding 33 is formed.
5 to the image side. Such reflected light reaching the image side is not preferable because it causes flare.

The light shielding plate 41 shown in FIG. 3B is obtained by making the light shielding plate 33 shown in FIG. 3A thick and processing the inner edge surface 41a of the light shielding plate 33 into a jagged shape. The jagged edges absorb and scatter light rays that strike the inner edge surface 41a. However, same side 41a
Is also leaked to the image side.

FIG. 3B shows an example in which a light shielding plate 51 is arranged on the object side of a convex lens 53. Here, the ray L1
Numeral 3 reflects on the front surface of the convex lens 53, then reflects on the rear surface of the light shielding plate 51, further reflects on the inner peripheral surface 55 of the lens barrel, and returns to the image side.

As described above, the conventional light-shielding plate has insufficient performance of blocking or capturing reflected light, and cannot sufficiently reduce flare of an image. The present invention has been made in view of such a problem, and has an excellent characteristic of driving reflected light from various parts of an optical system to outside the optical axis, and an improved light-shielding plate capable of improving flare and a lens having the same. It is intended to provide a system.

[0007]

In order to solve the above-mentioned problems, a light-shielding plate according to the present invention comprises a ring-shaped light-shielding plate in which an opening extending around an optical axis is formed at a central portion, and a light in an outer peripheral area of the optical axis. A light-shielding plate for blocking light, wherein a peripheral edge of an opening of the light-shielding plate includes a front plate inclined to project toward the object side and a rear plate inclined to project toward the image side. .

[0008] The lens system of the present invention is a lens system comprising a concave lens, a convex lens, and a light-shielding plate disposed between the two lenses to shield light in an outer peripheral area of an optical axis;
The light-shielding plate is formed of a ring-shaped light-shielding plate having an opening extending around the optical axis formed at the center, and the opening peripheral portion of the light-shielding plate is
It is characterized by comprising a front plate inclined to project toward the concave lens side and a rear plate inclined to project toward the convex lens side.

In the present invention, since the light-shielding surface is inclined not at right angles to the optical axis but obliquely, it is excellent in the property of driving unnecessary reflected light off-axis and flare of an image can be reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a configuration of a lens system according to one embodiment of the present invention. This example is an optical system of a small digital camera. The lens system 1 includes a concave lens 3, a light blocking plate 5, a convex lens 7,
An R filter 9 is provided. In this example, the concave lens 3 is a meniscus lens having a negative convergence with the convex surface facing the object side. The convex lens 7 is a meniscus lens having a positive converging power with a concave surface facing the object side. The IR filter 9 is a filter that cuts infrared light.

The details of the light-shielding plate 5 are shown in FIG. 1 (B). The light-shielding plate 5 has a structure in which two ring-shaped plates, a front plate 11 and a rear plate 13, are overlapped with each other, and has a Y-shaped cross section. ing. Front plate 1
The portion near the inner periphery of 1 is a front plate inclined portion 11a that is inclined so as to project toward the object side. A right angle portion 11b and a circumferential portion 11c ahead of the right angle portion 11b are connected to the outer peripheral side of the same portion 11a. The right angle portion 11b is joined to the right angle portion 13b of the rear plate 13. The object-side end of the circumferential portion 11c is connected to the concave lens 3, and the light shielding plate 5 is positioned.

The rear plate 13 has a rear plate inclined portion 13a inclined so as to protrude toward the image side, and a right angle portion 1 on the outer peripheral side of the rear plate inclined portion 13a.
3b. The right angle portion 13b is joined to the right angle portion 11b of the front plate 11 as described above. An inner peripheral portion between the front plate 11 and the rear plate 13 is a wedge-shaped recess 15.

Next, the operation of each part of the light shielding plate 5 will be described with reference to FIG. As shown in FIG. 2A, the front plate 11 is formed such that the angle θ ₁ formed by the front plate inclined portion 11a and the axis perpendicular to the optical axis is smaller than the right angle. Also, the rear plate 13
As shown in FIG. 2B, the angle θ ₂ formed by the rear plate inclined portion 13b and the axis perpendicular to the optical axis is formed to be deeper than the right angle.

Next, referring to FIG. 1 again, the overall light shielding performance of the light shielding plate 5 will be described. The light ray L1 out of the visual field passes through the concave lens 3 and the front plate inclined portion 11a of the front plate 11 of the light shielding plate 5
And is reflected outward. The reflected light beam strikes the circumferential portion 11c of the front plate 11 and is reflected off the optical axis. The light ray L2 outside the field of view passes through the concave lens 3 and passes through the rear plate 13 of the light shielding plate 5.
And hits the inner surface of the rear plate inclined portion 13a where the wedge-shaped concave portion 15 is formed, and is reflected. The reflected light beam hits the inner surface of the front plate inclined portion 11a forming the wedge shape of the front plate 11, and is further reflected in the wedge-shaped concave portion 15 and absorbed. Ray L out of sight
Numeral 3 passes through the opening of the concave lens 3 and the light shielding plate 5, hits a portion outside the pupil of the convex lens 7, and is reflected. The reflected light beam hits the outer surface of the rear plate inclined portion 13a of the rear plate 13 of the light shielding plate 5 and is reflected. Further, reflections outside the pupil of the convex lens 7 and the rear plate inclined portion 13a are repeated, and finally reflected outside the optical axis. As described above, the flare light is reduced by emitting or absorbing the light rays outside the visual field as much as possible off the optical axis.

The angles θ ₁ and θ ₂ are angles at which the totally reflected light does not return within the optical axis. In the case of the lens system shown in FIG. 1, 10 <θ ₁ <
30, 10 <θ ₂ <30 is preferred. Further, the inner diameters of the front plate inclined portion 11a and the rear plate inclined portion 13b of the light shielding plate 5 define the aperture of the lens system. Is determined to be obtained.

The mechanical position of the light shielding plate is shown in FIG.
As shown in (C), by integrating the front plate 11 and the rear plate 13, more accurate positioning can be achieved. Further, it is preferable to form a wedge-shaped recess 15 between the front plate 11 and the rear plate 13,
As shown in FIG. 2 (D), the above effect is not sufficiently exerted in the simple ring portion 17 in which the wedge-shaped concave portion is filled. That is, the light beam incident on the inner edge surface of the ring portion 17 may be reflected on the inner edge surface into the pupil of the convex lens 7 and become flare light.

FIG. 4 is a sectional view showing the structure of a lens system according to another embodiment of the present invention and the prior art. In the lens system of this embodiment, a concave lens 63, a light shielding plate, and a convex lens 67 are arranged in order from the object side to the image side. Conventionally, when light is shielded at one place, as shown in FIG.
A flat light-shielding plate 65 is arranged at an intermediate position between the concave lens 63 and the convex lens 67. When light is to be shielded at two places, as shown in FIG. 2B, the concave lens 63 abuts on a flange 69 protruding inside the lens barrel, and further, a light shielding plate is provided on the image side of the flange 69. The convex lens 67 is arranged on the image side of the light shielding plate 65. At this time, the object-side inner end surface of the flange portion 69 forms a sharp edge, and functions as a light shielding portion.

FIG. 4C shows an arrangement in which light is shielded at two places by using the light-shielding plate of the present invention. The light blocking plate 75 is arranged between the concave lens 63 and the convex lens 67. In this case, light can be shielded at two places of the front plate inclined portion 71a and the rear plate inclined portion 73a of the light shielding plate 75. At this time,
By adjusting the angles and lengths of the front plate inclined portion 71a and the rear plate inclined portion 73a, flare light can be minimized, and reliable light shielding can be performed. In addition, there is no need to perform processing such as providing a flange on the lens barrel, and high-performance design with a large degree of freedom and space saving is possible.

[0019]

As is apparent from the above description, according to the present invention, the peripheral light quantity is determined by keeping the necessary light rays by the light shielding plate, and unnecessary light rays are more reliably cut than in the conventional art. Can be secured. That is, by making the light-shielding surface not perpendicular to the optical axis but making the concave side shallow and the convex side deep, excellent characteristics of driving unnecessary reflected light off-axis are obtained, and image flare can be reduced. Accordingly, the present invention provides a lens plate for a camera, a video camera, or the like, which has an excellent property of driving reflected light from each part of the optical system to be off the optical axis, and is improved so as to improve flare and a lens having the same. A system can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a lens system according to an embodiment of the present invention. This example is an optical system of a small digital camera.

FIG. 2 is a diagram illustrating an operation of a light shielding plate according to the embodiment of FIG.

FIG. 3 is a view for explaining light rays of a light shielding plate in a conventional lens system and its problems.

FIG. 4 is a sectional view showing a configuration of a lens according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lens system, 3 ... concave lens, 5 ... light shielding plate, 7 ... convex lens, 9 ... IR filter, 11 ... front plate, 11a ... front plate inclined part, 11b ... right angle part, 11c ... circumferential part, 13 ... rear plate , 1
3a: rear plate inclined portion, 13b: right angle portion, 15: wedge-shaped concave portion,
17: ring portion, 31: concave lens, 33: light shielding plate, 35
... opening, 41 ... light shield plate, 41a ... inner edge surface, 51 light shield plate,
53: convex lens, 55: light shielding plate, 63: concave lens, 65
... Shield plate, 67. Convex lens, 69. Flange, 71a
... Front plate inclined portion, 73a Rear plate inclined portion, 75 light shielding plate.

Claims (3)

[Claims] 1. A light-shielding plate, comprising a ring-shaped light-shielding plate having an opening extending around the optical axis formed in a central portion, for shielding light in an outer peripheral area of the optical axis, wherein the peripheral edge of the opening of the light-shielding plate is A light-shielding plate comprising a front plate inclined so as to project toward the object side and a rear plate inclined so as to project toward the image side. 2. The light-shielding plate according to claim 1, wherein a concave portion is provided between the front plate and the rear plate, the concave portion being depressed in the outer peripheral direction of the optical axis. 3. A lens system comprising a concave lens, a convex lens, and a light-shielding plate disposed between the two lenses for shielding light in an outer peripheral area of the optical axis; wherein the light-shielding plate has an opening extending around the optical axis. It is formed of a ring-shaped light shielding plate formed at the center, and has a front plate inclined so that the opening peripheral edge of the light shielding plate projects toward the concave lens side, and a rear plate inclined so as to project toward the convex lens side. A lens system characterized by the following.