JP3610989B2 - Shielding structure of photographic lens - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a light-shielding structure of a photographing lens, and more particularly to a light-shielding structure of a photographing lens that removes a ghost image due to incidence of harmful light rays from outside the photographing angle of view.
[0002]
[Prior art]
In a conventional camera, for example, a first lens group, a second lens group, a third lens group, and a fourth lens group are arranged in this order in a lens barrel, and between the third lens group and the fourth lens group. A diaphragm is arranged on the lens, and the light passing through each lens group and the diaphragm is imaged on an imaging surface such as a CCD.
[0003]
By the way, when extremely strong light such as the sun or illumination light enters from outside the shooting angle of view of a conventional taking lens, the light is reflected by the aperture opening end face or the inner surface of the lens barrel and reaches the imaging surface, so that the ghost appears on the shooting screen. There is a problem that occurs.
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 reduced in the conventional photographing lens (see FIG. 2B).
[0004]
[Problems to be solved by the invention]
However, if the aperture diameter of the stop and the aperture diameter of the lens frame are reduced as in the conventional photographing lens, a part other than the harmful light passage area, that is, a part of the light flux passage area necessary for photographing is widely shielded. There is a problem. This unnecessarily reduces the effective aperture of the lens, and there is a problem that the F-number when the aperture is opened is increased.
[0005]
The present invention has been made in view of such circumstances, and an object thereof is to provide a light-shielding structure for a photographing lens that prevents the occurrence of ghosts caused by harmful rays incident from outside the photographing field angle without reducing the effective aperture. And
[0006]
[Means for solving the problems]
In order to achieve the above object, the present invention provides a light-shielding unit that shields only a part of the lower side of an optical path having a circular cross section when the diaphragm is opened in a photographic lens having a plurality of lenses and a diaphragm in a lens barrel. Is provided in the optical path near the stop.
[0007]
[Action]
According to the present invention, it has been confirmed by experiments that when the photographing lens is close to a telephoto, a ghost of a brownish color like a curtain is generated at the bottom of the screen, that is, harmful rays pass through the lower part of the stop. In view of this, harmful light is removed by providing a light-shielding means at this portion, thereby preventing the occurrence of ghost.
[0008]
That is, according to the present invention, the vicinity where the diaphragm is disposed is a portion through which a substantially parallel light beam passes in terms of optical design, and harmful light incident from above outside the shooting angle of view is near the diaphragm. It 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 aperture is open. Thereby, generation | occurrence | production of a ghost can be prevented.
[0009]
In addition, since the light-shielded area is a small portion from the entire aperture stop, most of the light flux necessary for photographing can be passed. That is, the influence on the effective area of the lens is small, and the change in the F number due to light shielding can be ignored in practice.
Further, as the light shielding means, a harmful member can be shielded with a simple structure by directly attaching a mask member to the lower side of the lens near the stop. In addition, harmful light can be removed with a simple configuration by forming the light shielding unit integrally with the base plate of the diaphragm, the lens frame, or the lens barrel.
[0010]
【Example】
A preferred embodiment of a light-shielding structure for a photographing lens according to the present invention will be described in detail below with reference to the accompanying 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. The light-shielding structure of the photographic lens shown in FIG. 1 includes a first lens group 11, a second lens group 12, a third lens group 13, and a fourth lens group 14 arranged in order from the front along the optical axis L. A diaphragm unit 16 is disposed between the group 12 and the third lens group 13, and a lens frame 18 is disposed between the third lens group 13 and the fourth lens group 14.
[0011]
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 aperture unit 16.
The light that has passed through the lens groups 11, 12, 13, 14 and the aperture unit 16 is imaged on the imaging surface of the CCD 24.
In the diaphragm unit 16, two diaphragm blades (not shown) are arranged opposite to each other on a base plate 26 in which a light transmitting hole 26A is formed, and the galvanometer 28 moves the left and right diaphragm blades toward or away from each other. It moves to expand and contract the aperture. The aperture format is not limited to this, and other formats may be used.
[0012]
2A to 2C are views for explaining the state of the opening when the aperture is fully opened. (A) is a figure in case the mask member 20 is not provided, and the area | region 30 shown in the figure represents the passage area of the harmful light which causes ghost generation. The harmful light is usually strong light that enters from the upper outside of the shooting angle of view, such as sunlight or indoor illumination light, and passes through the lower part of the aperture opening 26A in the vicinity of the aperture unit 16.
[0013]
Conventionally, as shown in FIG. 2B, the aperture diameter d is reduced to block the passage of harmful light. However, when the aperture diameter d is reduced, there is a problem that the effective aperture is reduced as described above.
Therefore, in the light-shielding structure of the photographing lens shown in FIG. 1, a mask member 20 as shown in the figure is attached to a part of the lower side of the third lens group 13, and the mask member 20 passes through the lower part of the opening 26A. Light to be shielded (see FIG. 2C). In this way, by masking a part of the lower side of the third lens group 13, strictly speaking, a part of the effective light beam is blocked. Since the area to be masked is an extremely small area when viewed from the whole, the change in the F number is almost negligible in practice.
[0014]
Next, the operation of the light shielding structure of the photographic lens configured as described above will be described. The vicinity where the diaphragm unit 16 is provided is a portion (substantially afocal part) through which a substantially parallel light beam passes due to optical design, and harmful light incident from above outside the shooting angle of view is near the diaphragm unit 16. Then, it passes through the lower part of the aperture opening 26A. Therefore, the harmful light can be effectively removed by arranging the mask member 20 in that portion.
[0015]
In addition, since the masked area is a small area from the entire aperture stop, almost all the light flux necessary for photographing incident within the photographing field angle can pass therethrough. Thereby, generation | occurrence | production of a ghost can be prevented, without changing F number practically.
FIG. 3 is an assembly diagram for explaining the configuration of the second embodiment of the light-shielding structure of the photographing lens according to the present invention. In the embodiment of FIG. 3, instead of sticking 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 aperture unit 16, and the embodiment of FIG. The same or similar members are denoted by the same reference numerals, and description thereof is omitted.
[0016]
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, thereby blocking harmful light passing below the diaphragm opening 36A, The ghost is removed (see FIG. 2C).
Further, instead of integrally configuring the mask portion 38 with the base plate 36 of the diaphragm 16, it is also possible to configure the mask portion 38 integrally with the lens frame 18.
[0017]
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 the lens barrel 40 behind the aperture unit 16. As a result, harmful light passing under the diaphragm aperture is shielded. 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.
[0018]
In the above embodiment, the mask member 20 and the mask portions 38 and 38 'have been described as having a shape as shown in FIG. 2C. However, the shape of the mask is not limited to this, and other shapes may be used. For example, shapes as shown in FIGS. 5A and 5B are conceivable. If the mask members or mask portions 42 and 43 having a shape as shown in the figure are used, it is possible to sufficiently shield harmful rays incident not only from directly above the shooting angle of view but also from obliquely above. It is more effective.
[0019]
In the above-described embodiment, the case where the present invention is applied to a video camera including an image sensor such as the CCD 24 has been described. However, the present invention is not limited to this and may be applied to a still camera.
[0020]
【The invention's effect】
As described above, according to the light-shielding structure of the photographing lens according to the present invention, since only a part of the lower side of the optical path near the stop is shielded with a small area, the light beam necessary for photographing is almost shielded. In addition, it is possible to block only harmful rays incident from above the imaging field angle. Thereby, the change of the F number can be suppressed to a level that can be almost ignored in practical use, and the occurrence of ghost can be prevented.
[0021]
In addition, the ghost can be generated with a simple configuration by directly fixing the mask member to the lower side of the lens in the vicinity of the stop, or by integrally forming the mask member on the base plate, lens frame, or lens barrel of the stop. Can be prevented, and a good image can be obtained.
[Brief description of the drawings]
FIG. 1 is an assembly diagram for explaining the configuration of a first embodiment of a light-shielding structure of a photographic lens according to the present invention. FIGS. 2 (A) to 2 (C) illustrate the state of an aperture opening. FIG. 3 is an assembly diagram for explaining the configuration of the second embodiment of the light-shielding structure of the photographing lens according to the present invention. FIG. 4 is a diagram in the case where the mask portion is configured integrally with the lens barrel. FIG. 5A and FIG. 5B are diagrams showing examples of other shapes of light shielding masks.
DESCRIPTION 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 plates 26A, 36A ... translucent hole 30 ... harmful light passage region 40 ... lens barrel

Claims (5)

In a photographic lens having a plurality of lenses and an aperture in a lens barrel, a light shielding means for shielding only a part of the lower side of the optical path having a circular cross section when the aperture is opened is provided in the optical path near the aperture. A light-shielding structure for a photographic lens. 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 disposed in the vicinity of the stop. 2. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is formed integrally with the base plate of the diaphragm. 2. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is constructed integrally with a lens frame disposed in the vicinity of the stop. 2. The light-shielding structure for a photographing lens according to claim 1, wherein the light-shielding means is constructed integrally with the lens barrel.

Images