JPS6224223A - Optical filter - Google Patents

Abstract

PURPOSE:To obtain an MTF characteristic with which both removal of a color beat and resolution can be satisfied, by constituting the titled filter so that an incident light is divided into a beam reflected by a half mirror surface, and an optical axis reflected by a mirror surface after transmitting through the half mirror face. CONSTITUTION:An optical filter 1 is constituted geometrically of a mirror surface S1 constituted of a mirror film 4, and a half mirror surface S2 constituted of a half mirror film 3. The half mirror surfaces S2 is parallel to a surface S1a which turns the mirror surface S1 by a small angle alpha centering around a vertical line A against the surface containing an incident light 10 and a reflected light 11b by the mirror surface S1. In this way, this optical filter 1 becomes a trough in a space frequency fV1* as shown by a graph line III, and also it has an ideal MTF characteristic by which the minimum response of the part of this trough is set to about 0.4. Accordingly, by using this optical filter 1, the color beat of a scanning orthogonal direction is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applied to television cameras that multiplex color signals using color stripe filters, and is particularly applicable to optical systems that operate perpendicularly to the scanning direction of a positive picture tube. Regarding filters.

Conventional technology In television cameras that multiplex color signals using color stripe filters, the subject image and the color stripe filter are superimposed and projected, so if the subject image has a specific spatial frequency component, a false signal is generated. Then, a color beat appears on the 1m screen. Optical filters are used to prevent this spurious signal from occurring.

Conventional optical filters are constructed by combining quartz plates, and optical filters that act in a direction perpendicular to the scanning direction of the image pickup tube are also generally composed of quartz plates.

Problems to be Solved by the Invention When an incident light ray passes through a crystal plate, which is an optical filter, it is birefringent and separated into two light rays, and the negative object point of the subject becomes two image points. In this case, the two rays separated by birefringence have equal intensities, that is, the incident rays are separated by 50%, and the brightness of the two separated image points is always equal. Therefore, the MTF curve of an optical filter is a curve in which the response always drops to zero at the given spatial frequency. Note that the spatial frequency at which the response becomes zero is determined by the thickness of the crystal plate.

On the other hand, when we imaged the zone plate and observed the occurrence of color beats, we found that in the direction perpendicular to the scanning line (hereinafter referred to as the scanning vertical direction), 1/2 cycle is between adjacent scanning lines in Fig. 3. Spatial frequency fVl* equal to the distance of
A color beat was occurring near the . This color beat can be removed by using an optical filter whose response is low near the spatial frequency fVI*.

If the optical filter using the above-mentioned crystal plate is made to have a characteristic such that the response becomes zero at the spatial frequency fV+1, as shown by the graph line in Figure 3, the color beat will be completely removed, but Images near the spatial frequency fVIs are blurred and have poor resolution. Therefore, conventionally, as shown by the graph line ■, the MTF characteristic is a curve that passes through the color beat tolerance limit Q (response approximately 0.4), where the color beat is removed to an acceptable degree and the resolution is satisfied to some extent. optical filters were used.

In this case, although the occurrence of color beats is suppressed, the problem remains that the resolution of the image near the spatial frequency fV28, which is higher than the spatial frequency fVI*, deteriorates.

An object of the present invention is to provide an optical filter that solves the above problems.

Means and Effects for Solving the Problems The present invention includes a mirror surface that reflects an incident light beam in a predetermined direction, and a mirror surface that is disposed on the front side of the mirror surface in close proximity to the mirror surface and that reflects the incident light beam in a predetermined direction. It consists of a half-mirror surface that is parallel to a surface slightly rotated around a line perpendicular to the surface containing the reflected ray, and the incident ray is parallel to the ray reflected by the half-mirror surface. The structure is such that the light beam is separated into the transmitted light beam and the reflected light beam on the mirror surface. The inclination angle of the half mirror surface with respect to the mirror surface determines the spatial frequency at which the response is minimum, and the reflectance of the half mirror surface determines the minimum value of the response.

EXAMPLE Next, an example of the optical filter according to the present invention will be described.

As shown in FIGS. 1 and 2, the optical filter 1 has a structure in which a half mirror film 31 is provided on one side of a thin glass plate 2, and a mirror film 4 is provided on the opposite side.
It is stuck on top. Geometrically, the optical filter 1 has a mirror surface S! constituted by the mirror film 4! and a half mirror surface S2 constituted by the half mirror film 3. The half mirror surface S2 is a surface S+ that is obtained by rotating the mirror vinegar S1 by a slight angle α about a line A perpendicular to the plane containing the incident light ray 10 and the reflected light ray 11b by the mirror surface S+.
It is parallel to a.

As shown in FIG. 2, this optical filter 1 is incorporated into an imaging optical system 6 of a television camera. Reference numeral 7 denotes an image pickup tube, which is installed vertically, and the image pickup optical system 6 is shaped like a single character. The X-axis is the scanning direction of the image pickup tube 7, the Y-axis is the scanning direction perpendicular to this, and the optical filter 1
The incident side to the optical filter 1 and the output side from the optical filter 1 are shown separately. 8 is a zoom lens, and 9 is a master lens. The optical filter 1 has a mirror 1104 located between the zoom lens 8 and the master lens 9 at an angle β (-45 degrees) with respect to the incident light beam 10. In other words,
Incident light 1! Opening angle γ between J10 and second reflected light beam 11b
is installed in a 90 degree orientation.

The incident light i*io passes through the zoom lens 8 and is first reflected at the half mirror film 3 at a point B, becoming a first reflected light beam 7a and heading upward, and the rest passes through the half mirror film 3. , travels inside the glass plate 2, is reflected at a point C on the mirror film 4, becomes a second reflected light beam 11b, and heads upward. The light ray 11a is inclined at an angle 2α with respect to the light ray 11b. These two light beams 11a and 11b enter the master lens 9) and are refracted by the camera tube 7! An image is formed on the a image plane 7a at a location spaced apart by a dimension Py in the direction perpendicular to scanning. In other words, the - object point P of the subject is two image points P+ separated by a dimension Py in the direction orthogonal to the scanning direction on the image plane of the image tube.
, Pz. This produces a filter effect in the direction orthogonal to scanning.

For example, when the reflectance of the half mirror is 50%, the above optical filter 1 has M=lcos in the direction perpendicular to scanning.
The MTF characteristic is expressed as πf”Pyl. Here, f”=(1/2
Py), M indicates the minimum value 0. The spatial frequency at which the response is minimum is expressed by the same formula as when the reflectance of the half mirror is 50%, and is determined by the separation dimension Py. In this case, the optical filter 1 is arranged in front of the mask lens 9, and the reflected light beams 11a and 11b pass through the mask lens 9 before reaching the image carrying plane 7a, so the thickness t of the glass plate 2 is The above dimension Py is irrelevant, and the dimension Py is determined by the angle α of the glass plate 2. The above optical filter 1 has a response of the above spatial frequency fV11.
It is determined to be the minimum in .

When manufacturing the optical filter 1, the angle α is set to ti
However, since the thickness t can be determined as appropriate, Japanese Patent Application No. 60-66082, filed earlier by the present applicant,
This is easier to manage than the case where both the thickness and parallelism of the glass plate are managed as in the invention title "optical filter."

The optical filter 1 with the above configuration has variable parameters such as a half mirror in addition to the angle α of the glass plate 2.
There is a reflectance of the film 3. When the reflectance of this half mirror 113 (7) is changed, image points P and P are obtained.

The brightness ratio changes. For example, with a reflectance of 50%
: Sometimes 1:11 When reflectance is 20%, 1:
4. '113160%, 7). Yo. ,2
86°yu. When the brightness ratio of the image points P1 and Pz changes, the filter effect changes. For example, if the ratio is 1=1, the entire brightness of the image points P+, Pz, ie the entire light beam 10, exhibits a filtering effect.

When the ratio is 4:1, out of the brightness 4 of image point P2,
The brightness corresponding to the brightness 1 of the image point P1 exhibits a filter effect with respect to the image point P1, and the remaining brightness does not exhibit a filter effect. That is, 275 of the light amount of the incident light beam 10 has a filter effect, and the remaining 375 has no filter effect. If the ratio is 3:2,
Of the light quantity of the incident light beam 10, 415 will have a filter effect and 115 will have no filter effect. As described above, by appropriately changing the reflectance of the half mirror 123, the ratio of the amount of light that acts as a filter to the amount of incident light 10 can be varied, and as a result, the minimum value of the response can be varied.

The optical filter 1 described above is designed so that the reflectance of the half mirror film 3 is, for example, about 30%, and the minimum response is 0.4.

Furthermore, if there is a shift in the optical axis direction of the image pickup tube between the image points P+ and Pz, the MTF characteristics will deteriorate overall;
Since the optical filter 1 is placed in front of the master lens 9, there is no deviation between the image points P1 and Pz, and the MTF characteristics do not deteriorate due to the deviation.

As a result, the optical filter 1 described above has a valley at the spatial frequency fV19, as shown by the graph line ■ in FIG. 3, and the lowest response of this valley is about 0.4
It has ideal MTF characteristics. Therefore, by using this optical filter 1, the color beat in the direction perpendicular to scanning can be removed.
J(1)'l@F8**'lbltTCm.

Therefore, a television camera with good resolution can be realized.

Note that even if the reflectance of the half mirror [13 is set at approximately 70%, the lowest response is 0.4 as above.
It becomes. Further, instead of providing the mirror surface on the surface of the glass plate 2, it may be provided on the glass surface on the half mirror side.
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IM (A), (B) shows a television camera 12 to which an image carrying optical system 6 is applied. This television camera 12 includes an imaging optical system 6 and a video tape recorder. 13 is integrated, and a
Compared to the case where the picture tube is placed horizontally, the length L is considerably shorter, making it more compact and easier to balance and use when carrying it on the shoulder for imaging.

Further, 14 is a crystal plate which is an optical filter that acts in the scanning direction (direction of the first arrow X), and is disposed between the zoom lens 8 and the optical filter 1.

FIG. 5 shows a modification of the optical filter of the present invention. This optical filter 20 is formed on one surface of the prism 21, and consists of a half mirror film 22, a polar glass plate 23, and a mirror film 24. The reflected light is separated into second reflected light 126a and 26b.

Effects of the Invention As described above, according to the optical filter of the present invention, by changing the gate angle between the half mirror surfaces, the spatial frequency at which the response is minimum can be varied, and furthermore, the reflection of the half mirror surfaces can be varied. By changing the ratio, the minimum response can be varied, and by manipulating the above two parameters, the MTF characteristics can be freely determined. It has the advantage of being able to be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing an embodiment of the optical filter according to the present invention, FIG. 2 is a side view schematically showing a positive image optical system incorporating the optical filter of FIG. 1, and FIG. The figure shows the MTF characteristics that can be obtained by the optical filter of the present invention in correspondence with the MTF characteristics of a conventional optical filter. Figure 4 is a diagram showing an example of a television camera to which the optical filter of the present invention is applied. , 15 are diagrams showing a modification of the optical filter of the present invention. 1.20... Optical filter, 2.23... Glass plate, 3.22... Half mirror film, 4.24... Mirror film, 5... Glass substrate, 6... LA image optical system, 7
. . . Shooting tube, 7a . . . Imaging surface, 8 . Zoom lens, 9 . . . Master lens, 10.25 . , 26
b...Second reflected light beam, 12...Television camera, 13...Video tape recorder 4.14...Crystal plate. Patent applicant Japan Victor Co., Ltd. Seal Figure 5 Parent procedure amendment August 19, 1986 Commissioner of the Patent Office Kuro 1) Akio Yu 1, Indication of the case 1985 Patent application No. 145984 2, Invention Name: Optical filter 3, relationship with the person making the correction Patent applicant address: 3-12 Moriya-cho, Kanayō-ku, Yokohama-shi, Kanagawa 221 Name (432) Victor Japan Co., Ltd. Representative Director and President Kunio Kakiki 4; Agent address: 5-7 Kojimachi, Chiyoda-ku, Tokyo 102 Voluntary amendment 2)
6. Detailed description of the invention in the specification to be amended. 7. Contents of amendment (1) The following sentence is added between page 11, line 6 and line 7 in the specification. [In addition, in Figures 1 and 2, if we look strictly, the incident light 1
ijlIO is refracted when it enters the glass plate 2, reflected by the mirror film 4, and refracted when exiting from the glass plate 2 to become a second reflected light beam 11b. Now, the incident light I! 10
If we consider a mirror film that passes through the intersection of 2 and the second reflected ray 11b and is parallel to the mirror film 4, the incident ray 10 will not be refracted and will enter the glass plate 2, as shown in FIGS. 1 and 2. This is equivalent to a ray of light that enters, is reflected by the mirror film, and exits from the glass plate 2 without being refracted. Therefore, even in actual cases, results similar to those described above are obtained. ” ■ Add the following sentence between lines 12 and 13 on page 11 of the same document. [Also in FIG. 5, the incident ray 25 and the first . The second reflected light beams 26a and 26b are illustrated with their refraction omitted. ”

Claims (1)

[Claims] a mirror surface that reflects an incident ray in a predetermined direction; and a mirror surface that is arranged in front of and close to the mirror surface, and that is perpendicular to a plane that includes the incident ray and the ray reflected by the mirror surface. a half-mirror surface that is parallel to a surface slightly rotated about a central axis, and the incident light beam is reflected by the half-mirror surface and transmitted through the half-mirror surface. An optical filter characterized in that the optical filter is configured to separate into a second reflected light beam reflected by a mirror surface.