JPH07128501A - Imaging optical system - Google Patents

Abstract

PURPOSE:To easily and surely decrease the flares and ghosts generated by the internal reflected light of the optical system to a level substantially negligible in practicable use without a limitation of a design by providing the specific reflection part of the effective diameter of the optical system on the effective coupling part of which detrimental rays are made incident by reflection with an antireflection means. CONSTITUTION:The luminous flux imaged on a CCD image pickup plane 3a is reflected by its surface and while the luminous flux diameter thereof is widened, the luminous flux travels backward in the optical system and is reflected again in the specific reflection part 2. At this time, the luminous flux is converted by the curvature of the subject side face 4a of a combined lens 4 and is made incident as flare light of high intensity again on the CCD image pickup surface 3a. An antireflection film is formed over the entire surface of the subject side face 4a of the combined lens 4 including the specific reflection part 2. Then, the intensity of the reflected light is decreased to <=1/10 and the flare light is suppressed down to the level negligible for practicable use. The light transmitted through the specific reflection part 2 is absorbed by a light shielding mask 1 arranged on the subject side of the combined lens 4, by which trouble is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an image forming optical system including an optical element having a relatively high reflectance such as a CCD or a filter.

[0002]

2. Description of the Related Art Conventionally, as a method for coping with flare light caused by internally reflected light of an optical system, it has been generally known that a lens surface is provided with an antireflection film for reducing internally reflected light. In addition, as described below, a coping method in terms of designing the flare light has been proposed. FIG. 5 shows Japanese Patent Laid-Open No. 64-408.
The optical system described in JP-A-08 is shown. This is designed for a zoom lens optical system so that a good image can be obtained even when strong reflected light returns from the image plane or its vicinity so that the image plane and the lens plane are designed. The re-imaging of the reflected light is configured to form an image on the imaging lens side from the imaging surface. In addition, FIG.
The optical system described in Japanese Patent No. 8716 is shown. this is,
Mainly for videoscopes, in order to reduce the flare light to a level that has no practical effect by repeated reflection between the imaging surface and the filter surface in the telecentric optical system, the flare light intensity is designed to be an acceptable level. The arrangement position of the filter in the lens system is defined so that

Further, for a video camera, as in the optical system described in Japanese Patent Application Laid-Open No. 2-186318 shown in FIG. 7, flare light due to reflection between an image pickup surface and a filter in a photographing lens having a filter. To reduce
It is proposed that the filter surface is curved so that the light flux reflected by the filter surface diverges on the image forming surface.
Further, as a method of using a light-shielding mask, as in the optical system described in Japanese Utility Model Laid-Open No. 2-107111 shown in FIG.
In order to prevent ghost and flare due to the specific reflection surface of the lens, it has been proposed to provide a light-shielding mask for cutting harmful rays outside the screen before the specific reflection surface that causes ghost.

[0004]

Generally, since the yatoys are used when depositing an antireflection film or the like, an edge portion of the coating and an uncoated portion can be formed outside the effective diameter. The edge portion functions as a reflection increasing film, and the uncoated portion has a reflectance of several percent. However, in order to coat the entire surface of all the lenses, a dedicated lens toy is required for each lens, which causes a problem of cost increase. By the way, the above-mentioned Japanese Patent Laid-Open No. 64-408.
08, JP-A-3-78716 and JP-A-2-186.
In the optical system described in each publication of No. 318, there are many restrictions at the time of design because of the design countermeasures, and the design is difficult.
It has a drawback that it takes a lot of time to design.
Further, they have a drawback that they cannot cope with a change in the configuration of the lens system, and thus the applicable range is limited. In the optical system disclosed in Japanese Utility Model Laid-Open No. 2-107111, no consideration is given to reflected light generated within the effective diameter on the image side, and further harmful light and effective light are separated. If not, there is a problem that even effective light is blocked.

In view of the problems of the prior art as described above, the present invention has practically no influence on flare or ghost generated by the internal reflected light of the optical system without any design restrictions. It is an object of the present invention to provide an imaging optical system that can be reduced to a level that does not exist.

[0006]

In order to achieve the above object, an image forming optical system according to the present invention comprises at least one optical element having a property of reflecting a part of a light beam within an effective diameter, and In an optical system in which harmful rays can be incident on the effective image forming portion by reflection of two or more times by the optical element and the specific reflecting portion outside the effective diameter, the specific reflecting portion is provided with antireflection means, The prevention means is realized by providing an antireflection film on the entire surface of the lens including the outside of the effective diameter, and the optical element is a CCD light receiving surface.
The optical element is characterized by being various filters.

[0007]

Therefore, according to the imaging optical system of the present invention, the design period can be shortened because there are no design restrictions as compared with the conventional design method. Further, since the antireflection means is applied only to the specific reflecting portion, it does not adversely affect the effective light ray, and the internal reflected light generated within the effective diameter can be easily and reliably brought to a level at which it is practically unaffected. Can be reduced and can be applied to any lens configuration,
It can be applied in a wide range of fields.

[0008]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a sectional view taken along the optical axis direction when a CCD is used in the image forming optical system according to the first embodiment of the present invention. In the figure, 1 is a light-shielding mask, 2 is a non-coated portion (reflectivity is several percent) provided outside the effective diameter of the object-side surface 4a of the cemented lens 4, or an edge portion of an antireflection film (as a reflection increasing film). Specific reflection part (having a function),
Reference numeral 3 is a CCD arranged on the final surface, and 3a is an image pickup surface of the CCD 3 having a reflectance of several tens of percent. An antireflection film is provided within the effective diameter of each lens surface.

Since the optical diameter of the present embodiment is configured as described above, the light flux imaged on the CCD image pickup surface 3a is reflected by the surface thereof, and as shown in the figure, the light flux is expanded while the light flux diameter is expanded. It goes backward in the system and is reflected again by the specific reflection part 2. At this time, due to the curvature of the object-side surface 4a of the cemented lens 4, the light flux is converged and re-enters the CCD image pickup surface 3a as flare light with high intensity. However, in the optical system of the present embodiment, since the entire surface of the object-side surface 4a of the cemented lens 4 including the specific reflection portion 2 is provided with the antireflection film, the intensity of the reflected light is 1/10 or less. The flare light can be suppressed to a level that has no practical effect. Further, as a result, the light transmitted through the specific reflection portion 2 is absorbed by the light-shielding mask 1 arranged on the object side of the cemented lens 4, and it is possible to prevent the occurrence of defects such as flare due to the transmitted light.

FIG. 2 shows a second embodiment of the present invention, CC
7 is a cross-sectional view of the endoscope objective optical system using D, taken along the optical axis. FIG. In the figure, the light shielding mask 1, the specific reflection portion 2, the CCD 3 and the cemented lens 4 are the same as those shown in the first embodiment. An infrared absorption filter 5 is provided on the front side (subject side) of the CCD 3 and a YAG (yttrium aluminum garnet) cut filter 6 (reflectance is several percent).
It is arranged in the form of being sandwiched between. Further, an antireflection film is provided within the effective diameter of each surface of the YAG cut filter surface 6a excluding the interference film.

Since the optical system of this embodiment is constructed as described above, when the light outside the field of view enters the optical system, it is reflected by the YAG cut filter surface 6a as shown in the drawing and goes backward in the optical system. Then, it is reflected again by the specific reflection portion 2 of the surface 4a of the cemented lens 4 on the object side. At that time, the cemented lens surface 4
Due to the curvature of a, the light flux is converged and re-enters the CCD image pickup surface 3a as flare light having high intensity. However, the flare light can be reduced to a level that has no practical effect by taking the same means as in the first embodiment.

FIG. 3 shows a third embodiment of the present invention, CC
FIG. 7 is a cross-sectional view of the image pickup optical system using D along the optical axis. As shown in the figure, in the optical system of the present embodiment, the CCD 3 is arranged on the final surface, and the field lens 7 is provided on the front part (subject side) of the CCD 3. Reference numeral 2 denotes an uncoated portion (having a reflectance of several percent) or an edge portion of the antireflection film (having a function as a reflection increasing film) provided outside the effective diameter of the object-side surface 7a of the field lens 7. It is a specific reflection part. The CCD image pickup surface 3a has a reflectance of several tens of percent, and unevenness is formed on the surface thereof. An antireflection film is provided within the effective diameter of each lens surface.

Therefore, the image-formed light flux is reflected by the CCD image pickup surface 3
It is diffusely reflected on the surface of a, and as shown in the drawing, it is diffused and is again reflected by the specific reflecting portion 2 of the object side surface 7a of the field lens 7. At that time, due to the curvature of the field lens surface 7a, the light flux is converged toward the center of the optical axis, and again enters the CCD image pickup surface 3a near the optical axis as flare light with high intensity. However, by taking measures similar to those shown in the first embodiment, it is possible to reduce the flare light to a level that has no practical effect.

FIG. 4 is a sectional view taken along the optical axis of the endoscope objective optical system according to the fourth embodiment of the present invention. In the figure, 1 is a light-shielding mask, 2 is a non-coated portion (reflectance is several percent) provided outside the effective diameter of the image-side surface 8a of the second lens 8 or an edge portion of an antireflection film (as a reflection increasing film). Is a specific reflection portion, 9 is a first lens, 9a is a first lens surface, and 10 is a final image forming surface. An antireflection film is provided within the effective diameter of each lens surface except the first lens surface 9a, which has a problem in durability.

Since the optical system of the present embodiment is constructed as described above, as shown in the drawing, when the light outside the visual field is incident, it is reflected by the specific reflecting portion 2 of the image side surface 8a of the second lens 8. . The reflected light travels backward in the optical system, is reflected again by the first lens surface 9a (uncoated), passes through the effective diameter of the optical system, and enters the final image forming surface 10 as flare light. However, by taking the same means as in the first embodiment, the flare light can be reduced to a level that has no practical effect.

Further, as shown in the above-mentioned first to fourth embodiments, as an alternative to the antireflection means such as applying an antireflection film on the entire surface of the optical system constituting member such as a lens,
A method of diffusing flare light to reduce its intensity by forming a rough surface on the specific reflection part 2 or an uncoated part or an edge of coating by applying an antireflection film after depositing a mask on the specific reflection part 2. For example, a method of blocking a portion and absorbing harmful light to prevent its reflection can be considered. As described above, the antireflection means is not limited to the methods shown in the above embodiments.

[0017]

As described above, the imaging optical system of the present invention is
It has an important advantage that flare and ghost due to harmful internal reflection light can be reduced to a level that has no practical effect, and a good image can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view taken along the optical axis of an optical system according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the optical axis of an optical system according to a second embodiment of the present invention.

FIG. 3 is a sectional view taken along the optical axis of an optical system according to a third embodiment of the present invention.

FIG. 4 is a sectional view taken along the optical axis of an optical system according to a fourth embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along the optical axis of a conventional optical system used for a zoom lens.

FIG. 6 is a sectional view along the optical axis of a conventional optical system used for a videoscope.

FIG. 7 is a sectional view along the optical axis of a conventional optical system used for a video camera.

8A and 8B are cross-sectional views taken along the optical axis direction of an optical system using a light-shielding mask according to the related art, respectively.

[Explanation of symbols]

 1 Light-shielding mask 2 Specific reflection part 3 CCD 3a CCD image pickup surface 4 Bonded lens 4a Bonded lens surface 5 Infrared absorption filter 6 YAG cut filter 6a YAG cut coated surface 7 Field lens 7a Field lens surface 8 First lens 8a First lens surface 9 Second lens 9a Second lens surface 10 Final image plane L Optical axis

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Tsurugi 2-34-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Akira Yokota 2-34-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (72) Inventor Tatsuya Orihara 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd.

Claims (4)

[Claims] 1. An at least one optical element having a property of reflecting a part of a light beam within an effective diameter is provided, and a harmful ray is generated by two or more reflections by the optical element and a specific reflection portion outside the effective diameter. An optical system capable of entering an effective image forming section, wherein the specific reflecting section is provided with antireflection means. 2. The image forming optical system according to claim 1, wherein the antireflection means is provided with an antireflection film on the entire lens surface including the outside of the effective diameter. 3. The image forming optical system according to claim 1, wherein the optical element is a CCD light receiving surface. 4. The imaging element according to claim 1, wherein the optical element is various filters.