JPH08234072A - Light shielding structure of photographic lens - Google Patents

Abstract

PURPOSE: To provide a light shielding structure of a photographic lens which prevents the generation of ghosts by harmful rays entering from outside a photographing angle of view without making an effective diaphragm smaller. CONSTITUTION: The neighborhood of a part provided with a diaphragm unit 16 is a part (approximately focal part) where approximately parallel luminous fluxes pass in optical design and the harmful light entering from the upper side outside the photographing angle of view passes the lower part of a diaphragm aperture 26A near the diaphragm unit 16. A mask member 20 is, thereupon, stuck directly to the lower side of a third lens group 13 arranged near the diaphragm unit 16 to shut off the harmful light. As a result, the generation of the ghosts of the image pickup plane of a CCD 24 is prevented. In addition, the masked area is a part smaller than the entire part of the diaphragm aperture and, therefore, the change in F-number is substantially negligible. The mask member may be constituted integrally with the base plate 26 or lens frame 18 of the diaphragm unit 16 and may be constituted integrally with a lens barrel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-shielding structure for a photographic lens, and more particularly to a light-shielding structure for a photographic lens for removing a ghost image due to incidence of harmful rays from outside the photographic field angle.

[0002]

2. Description of the Related Art A taking lens of a conventional camera has, for example, a first lens group, a second lens group, a third lens group and a fourth lens group, which are sequentially arranged in a lens barrel, and a third lens group and a third lens group. A diaphragm is arranged between the four lens groups, and the light passing through each lens group and the diaphragm is focused on an image pickup surface such as a CCD.

By the way, when very strong light such as the sun or illumination light enters from outside the angle of view of the conventional taking lens, the light is reflected by the end face of the aperture opening or the inner surface of the lens barrel and reaches the image pickup surface, so that the image is taken. There is a problem that a ghost appears on the screen. In order to prevent harmful rays that cause such ghosts from entering the imaging surface, the aperture diameter of the diaphragm and the aperture diameter of the lens frame are made small in the conventional taking lens (FIG. 2).
(B)).

[0004]

However, when the aperture diameter of the diaphragm or the aperture diameter of the lens frame is reduced like the conventional taking lens, the area other than the harmful light passage area, that is, the light flux passage area required for photographing is reduced. There is a problem that even a part of it is shielded widely. This unnecessarily reduces the effective aperture of the lens, and there is a problem in that the F number when the diaphragm is open becomes large.

The present invention has been made in view of the above circumstances, and provides a light-shielding structure for a photographing lens that prevents the generation of ghosts due to harmful rays incident from outside the photographing angle of view without reducing the effective aperture. The purpose is to

[0006]

In order to achieve the above-mentioned object, the present invention relates to a photographing lens having a plurality of lenses and a diaphragm in a lens barrel, the lower side of an optical path having a circular cross section when the diaphragm is opened. It is characterized in that a light blocking means for blocking only a part of the above is provided in the optical path near the diaphragm.

[0007]

According to the present invention, it is confirmed by experiments that a ghostly ghost like a curtain occurs under the screen when the taking lens is close to the telephoto, that is, harmful rays pass through the lower part of the diaphragm. Focusing on this, the harmful light is removed and a ghost is prevented by providing a light shielding means in this portion.

That is, according to the present invention, the vicinity of the stop is a portion through which a substantially parallel light beam passes due to the optical design, and the harmful light incident from above outside the photographing field angle is
In the vicinity of this diaphragm, the light is concentrated in the lower part of the optical path having a circular cross section. Therefore, harmful light is removed by providing a light shielding means in this portion when the diaphragm is opened. This can prevent the generation of ghosts.

Moreover, since the light-shielded area is a small portion from the entire aperture of the diaphragm, most of the light flux necessary for photographing can pass through. That is, the influence on the effective area of the lens is small, and the change in the F number due to the light shielding can be practically ignored. Further, as the light shielding means, a mask member is directly attached to the lower side of the lens in the vicinity of the diaphragm, so that harmful light can be shielded with a simple structure. Besides, by configuring the light shielding means integrally with the base plate of the diaphragm, the lens frame, or the lens barrel, harmful light can be removed with a simple configuration.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the light-shielding structure of a photographing lens according to the present invention will be described in detail below with reference to the accompanying drawings. FIG.
FIG. 3 is an assembly diagram for explaining the configuration of the first embodiment of the light-shielding structure for a taking lens according to the present invention. The light-shielding structure of the taking lens shown in the figure has a first lens group 11, a second lens group 12, a third lens group 13, and a fourth lens group from the front along the optical axis L.
The lens groups 14 are arranged in order, and the second lens group 12 and the third lens group 14 are arranged.
A diaphragm unit 16 is arranged between the lens groups 13, and a lens frame 18 is arranged between the third lens group 13 and the fourth lens group 14.

A mask member 20 having a shape as shown in FIG. 2C is attached to a part of the lower side of the third lens group 13 behind the diaphragm unit 16. The light passing through the lens groups 11, 12, 13, 14 and the diaphragm unit 16 is imaged on the image pickup surface of the CCD 24. The diaphragm unit 16 is provided with two diaphragm blades (not shown) facing each other on the base plate 26 having a light transmitting hole 26A. The galvanometer 28 moves the diaphragm blades left and right in a direction to move them closer to each other or to a direction away from each other. It moves to expand or contract the aperture. The diaphragm format is not limited to this, and other formats may be used.

FIGS. 2A to 2C are views for explaining the state of the opening when the diaphragm is fully opened. (A) is a diagram when the mask member 20 is not provided, and shows an area 3 shown in the diagram.
0 represents a harmful light passage region that causes a ghost. The harmful light is usually strong light such as sunlight or indoor illumination light that is incident from above and outside the photographing field angle, and passes near the diaphragm unit 16 and below the diaphragm aperture 26A.

Conventionally, as shown in FIG. 2B, the aperture diameter d has been reduced to block the passage of harmful light. However, when the aperture diameter d is reduced, there is a problem that the effective diaphragm becomes smaller as described above. Therefore, in the light-shielding structure of the photographing lens of FIG. 1, a mask member 20 as shown in the drawing is attached to a part of the lower side of the third lens group 13, and the mask member 20 passes through the lower side of the opening 26A. The light is blocked (see FIG. 2C). As described above, since a part of the lower side of the third lens group 13 is masked, strictly speaking, a part of the effective light flux is blocked, so that F at the time of opening is
Although the number is large, the masked area is extremely small when viewed from the entire aperture of the diaphragm, so that the change in the F number can be practically ignored.

Next, the operation of the light blocking structure of the taking lens constructed as described above will be described. Due to the optical design, the vicinity where the diaphragm unit 16 is provided is a portion through which a substantially parallel light flux passes (a substantially afocal portion), and harmful light incident from above outside the shooting angle of view is near the diaphragm unit 16. Then, the light passes through the lower portion of the aperture opening 26A. Therefore,
By disposing the mask member 20 in that portion, harmful light can be effectively removed.

Moreover, since the masked area is a small area in view of the entire aperture of the diaphragm, most of the light flux necessary for photographing that is incident within the photographing angle of view can pass through. As a result, it is possible to prevent the occurrence of a ghost without changing the F number practically. FIG. 3 is an assembly diagram for explaining the configuration of the second embodiment of the light-shielding structure of the taking lens according to the present invention. In the embodiment of FIG. 3, instead of adhering the mask member 20 to the third lens group 13 of FIG. 1, a mask portion 38 is integrally formed on the base plate 36 of the diaphragm unit 16, and the embodiment of FIG. The same or similar members are given the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 3, the base plate 36 of the diaphragm unit 16 has a mask portion 38 integrally formed below the opening 36A thereof, so that harmful light passing under the diaphragm opening 36A can be prevented. The light is shielded and the ghost is removed (see FIG. 2C). Further, instead of integrally forming the mask portion 38 with the base plate 36 of the diaphragm 16, the lens frame 18
It is also possible to configure integrally with.

FIG. 4 is a view for explaining a state in which the mask portion 38 is molded integrally with the lens barrel 40. A mask portion 38 is provided integrally with a lens barrel 40 behind the diaphragm unit 16. As a result, harmful light passing under the aperture is blocked. The arrangement of the diaphragm unit 16 and the mask member 20 is not limited to this, and the diaphragm unit 16 'and the mask portion 38' may be arranged behind the third lens group 13.

In the above embodiment, the mask member 20 and the mask portions 38, 38 'are described as having the shape as shown in FIG. 2C, but the shape of the mask is not limited to this and other shapes may be used. For example, the shapes shown in FIGS. 5A and 5B are conceivable. By using the mask members or the mask portions 42 and 43 having the shapes as shown in the figure, not only just above the photographing angle of view, but also harmful rays incident from obliquely above can be sufficiently shielded, and in order to prevent ghosts. More effective.

Further, in the above-mentioned embodiment, the case where the present invention is applied to the video camera provided with the image pickup device such as the CCD 24 has been described, but the present invention is not limited to this and may be applied to a still camera.

[0020]

As described above, according to the light-shielding structure of the photographing lens of the present invention, only a part of the lower side of the optical path near the diaphragm is shielded with a small area, which is necessary for photographing. It is possible to block only harmful rays that enter from outside the shooting angle of view without blocking the light flux. As a result, the change in the F number can be suppressed to a practically negligible amount, and the occurrence of ghost can be prevented.

Further, by directly fixing the mask member to the lower side of the lens near the diaphragm, or by the base plate of the diaphragm,
By forming the mask member integrally with the lens frame or the lens barrel, it is possible to prevent a ghost with a simple structure and obtain a good image.

[Brief description of drawings]

FIG. 1 is an assembly diagram for explaining the configuration of a first embodiment of a light-shielding structure for a photographing lens according to the present invention.

FIGS. 2A to 2C are views for explaining the state of the aperture opening.

FIG. 3 is an assembly diagram for explaining the configuration of the second embodiment of the light-shielding structure for a taking lens according to the present invention.

FIG. 4 is a view for explaining a state in which a mask portion 38 is integrally formed with a lens barrel 40.

5A and 5B are views showing examples of other shapes of the light shielding mask.

[Explanation of symbols]

 11 ... 1st lens group 12 ... 2nd lens group 13 ... 3rd lens group 14 ... 4th lens group 16 ... Aperture unit 18 ... Lens frame 20 ... Mask member 38 ... Mask part 24 ... CCD 26, 36 ... Base plate 26A , 36A ... Translucent hole 30 ... Harmful light passage area 40 ... Lens barrel

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuyuki Shirie, Inventor No.324 Uetakecho, Omiya City, Saitama Prefecture Fuji Photo Koki Co., Ltd.

Claims (5)

[Claims] 1. In a photographing lens having a plurality of lenses and a diaphragm in a lens barrel, a light shielding means for shielding only a part of a lower side of an optical path having a circular cross section when the diaphragm is opened is provided near the diaphragm. A light-shielding structure for a taking lens, which is provided in the optical path. 2. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is a mask member attached to a lens arranged near the diaphragm. 3. The light-shielding structure for a taking lens according to claim 1, wherein the light-shielding means is integrally formed with a base plate of the diaphragm. 4. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is integrally formed with a lens frame arranged near the diaphragm. 5. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is integrally formed with the lens barrel.