JPH0629927B2 - Focusing screen - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a focusing screen for focus detection used in an optical device such as a single-lens reflex camera, and more particularly to a so-called split image matching type focusing screen.

(Background of the Invention) Conventionally, as a focusing screen of a single-lens reflex camera, a pair of wedge prisms arranged at the center on the focal plane has been used in order to improve focusing accuracy. As a result, the subject image is separated in the case of out-of-focus, so that it is possible to focus the subject with considerable accuracy. Such a split image matching type focusing screen 10 is provided with a pair of wedge prisms 20a and 20b at the center of the focal plane formed on the matte surface, as shown in the perspective view of FIG. 20, for example.
The wedge prisms 20a and 20b are semicircular and are arranged so as to deflect light rays in mutually opposite directions, and a circular focus detection unit is configured by them. FIG. 21 is an optical path diagram showing the principle of focus detection by this focusing plate, and light rays I and II focused from the objective lens 30 to the center of the focusing plate 10 (on the optical axis) at an angle ω.
Is refracted by the pair of wedge prisms 20a and 20b at the center of the focusing screen 10 and reaches the eyepiece lens 40 along the optical axis. Then, the observing eye 50 detects the in-focus state depending on whether or not the subject image in the focus detecting section is separated by the two wedge prisms. That is, when the subject is a linear object, the field of view of the focus detection unit when the focus is not matched is, for example, as shown in FIG. 22A, and the division line S corresponding to the boundary between the two wedge prisms is used. As a boundary, a statue separated into left and right
Ia and Ib are formed. Further, when the focus is on, as shown in FIG. 22B, the subject image is formed above and below the dividing line S as one straight line without being separated. Therefore, it is possible to perform focus detection with considerably high accuracy depending on whether or not the subject image is separated above and below the dividing line.

However, in such a split image matching type focusing screen, there is a drawback in that when a diaphragm is narrowed down or a dark lens having a large F number, the prism surface darkens and focus detection becomes difficult. . Further, there is a contradictory relationship between improving the accuracy of focus detection and preventing darkening of the prism surface, and it is difficult to satisfy both at the same time, and various ideas have been proposed for this problem since ancient times.

As an example thereof, Japanese Patent Publication No. 37-9531 discloses that the surface of a split prism is made into a fine grain surface, and the light scattering phenomenon by this prevents darkening in the case of a small aperture. However, in this case, when the image is out of focus, the image of the split prism part causes blurring similar to that of the surrounding matte surface, so that focusing is performed by the blurring rather than by the displacement of the image, and the precision of the split prism is high. Focusing was difficult.
In this case, the scattered light on the surface of the split prism is isotropic and is generated in all directions, so that there is much waste, and the focus detection section becomes dark and it is difficult to focus.

Further, examples of a focusing screen having a diffraction grating structure formed on a split prism surface are disclosed in JP-A-54-626 and JP-A-5-626.
No. 6-67822. These configurations are considerably better than the previous ones,
Due to the diffraction grating structure, as in the field of view of the focus detection unit shown in FIG. 22A and FIG. 22B, a vertical line (m,
m ') is conspicuous and obtrusive, and due to the periodic structure of the diffraction grating, the dispersion direction of light becomes discrete, and the subject image in the case of defocus becomes multi-line blurring, which is not always good-looking. It was Further, if the subject image has a periodic structure, there is a problem that moire fringes occur and the appearance becomes worse. Further, due to the action of the diffraction grating, there is a drawback that a blurred image is colored when the diaphragm is made small.

Then, instead of the split prism, a focus detection unit is configured only by a diffraction grating, and each element of the grating is blazed and the blazed angle is set to be plural, thereby diffracting light in multiple directions and preventing a darkening phenomenon. , Japanese Examined Sho 39-291
No. 23, and the above-mentioned Japanese Patent Laid-Open No. 56-67822. However, these ones have the characteristics peculiar to the diffraction grating more strongly than the ones in which the diffraction grating is formed on the split prism surface, so that the above-mentioned drawbacks are emphasized and a blurred image of the subject is obtained in the case of narrowing down. The drawbacks that result in significant coloration are unavoidable.

(Object of the Invention) It is an object of the present invention to maintain excellent focus detection accuracy without darkening the split prism portion for focus detection even when a diaphragm is narrowed down even for a dark lens. An object of the present invention is to provide a split image type focusing screen in which the focus detection unit looks good both in focus and out of focus.

Further, an object of the present invention is to provide a split image type focusing screen in which a blurred image in a focus detection unit is not a multi-line blurred image but is smoothly blurred, less moire fringes are generated, and the blurred image is less colored. Especially.

(Summary of the Invention) A focusing screen according to the present invention is such that a displacement of a blurred image by a wedge prism is formed on a surface of a split prism having a pair of wedge prisms each having an inclined surface which is inclined in a reverse direction at a predetermined angle with respect to the focal plane. A first-direction ridge line group and a second-direction ridge line group that extend along a first direction and a second direction that are symmetrical with respect to a line perpendicular to the direction are formed. And the first
Each ridge line forming the first ridge line group along the direction is formed by a first slope and a second slope along the first direction, and a second slope along the second direction.
Each of the ridge lines forming the ridge line group is formed of a first slope and a second slope along the second direction, and the first ridge line and the second ridge line group are formed on the wedge prism surface by the first ridge line and the second ridge line. A plurality of quadrangular pyramid-shaped depressions each having a side parallel to the second direction and having a parallelogram as a bottom extending in a direction perpendicular to the displacement direction of the subject image by the wedge prism are formed. Specifically, the two adjacent to each other in the first ridge line group along the first direction
The first ridgeline and the two ridgelines adjacent to each other in the second ridgeline group along the second direction have sides parallel to each other in the first and second directions in plan view, and are formed by the wedge prism. A parallelogram extending in the direction perpendicular to the displacement direction of the blurred image is formed. Three-dimensionally, in this parallelogram, the parallelogram is defined as the bottom surface by the four slopes of the first and second slopes in the first direction and the first and second slopes in the second direction. A quadrangular pyramid-shaped depression is formed.
Among the slopes forming the side surfaces of such a quadrangular pyramid-shaped depression, the first-direction first slopes and the first-direction second slopes are slopes forming mutually adjacent first-direction ridgelines, respectively. The two-direction first slopes and the second-direction second slopes are slopes that respectively form adjacent second-direction ridges.

As described above, by providing the ridge line groups along the first and second directions which are symmetrical to each other, a large number of grooves and troughs are not conspicuous as stripe patterns due to peeling unlike the conventional art, and the split prism portion becomes clear. It is possible to improve the appearance.

Then, it is possible to form the two-dimensional diffraction grating by making the intervals of the respective ridgelines of the first and second ridgeline groups all equal, and at least the intervals of the respective ridgelines of the first and second direction ridgeline groups. It is also possible to arrange these aperiodically as two types. In particular, when each ridge line group is composed of ridge lines that are randomly arranged in a non-periodic manner, it is possible to prevent multi-line blurring when out of focus, obtain a smoother blurred image, and further improve the coloring of the blurred image. It is possible to prevent it.

Here, the inclination angle of each wedge prism constituting the split prism with respect to the focal plane should be set within the range of 6 ° to 12 °. That is, 6 ° or more is required to maintain the distance measurement accuracy sufficiently high, while if it exceeds 12 °, the focus detection unit is likely to darken with respect to a dark lens or when the diaphragm is narrowed down. Harder to get.

The first direction and the second direction in which the first ridge line group and the second ridge line group extend are the angle α formed with respect to the displacement direction of the blurred image by the split prism, specifically, the direction perpendicular to the split line of the split prism. Are in the range of 5 to 20 °, respectively, so that the angle formed by the ridgelines in the two directions is 10 °.
It is desirable that the range is -40 °. When the direction of each ridge line group is smaller than 5 ° with respect to the direction perpendicular to the split line of the split prism, the striped pattern in the field of view of the focus detection section is still conspicuous, while the direction of each ridge line group is When it is close to parallel to the dividing line, the distribution of the scattering intensity of the light rays by each ridge line group increases in the direction perpendicular to the dividing line, which reduces the scattering effect in the dividing line direction required as a split prism, In particular, when the upper limit of 20 ° is exceeded, the effect of preventing darkness of the focus detection unit becomes small. Further, the interval between the ridge lines forming each ridge line group is 5 to 20 μm, and the angle β formed by the first and second slopes forming each ridge line with respect to the slope of the split prism is:
It is desirable that each is in the range of 2 to 8 °. Also,
It is desirable that the first and second slopes forming each ridge line have the same angle with the slope of the split prism in the above angle range.

(Example) Hereinafter, the present invention will be described based on illustrated examples.

FIG. 1 is a schematic perspective view of a split prism portion provided in a central portion of a split image matching type focusing screen according to the present invention, and shows a state in which only a central portion on the focusing plate is cut out. Further, FIG. 2 is a side view showing an outline of one shape of the semicircular wedge prism. One surface of the focusing screen 1 is formed as a matte surface 1a, and two wedge prisms 2a, 2b are provided at the center thereof. Two wedge prisms 2
a and 2b are semicircular shapes with the same prism apex angle θ,
The defocus angles are arranged in opposite directions, and these are combined to form a circular focus detection unit. The boundary surface between the two wedge prisms 2a and 2b corresponds to the diameter of the circular focus detecting portion and constitutes a dividing line in the visual field of the focus detecting portion. Also, a point P where the slopes of both wedge prisms 2a and 2b intersect
Is aligned with the focal plane 1a of the focusing plate 1, and the focusing plate 1 is arranged so that the focusing plane 1a is aligned with the image plane of the objective lens (not shown). On the slope of these wedge prisms,
A ridge line group arranged in two directions is formed, and has a function of further scattering the light beam refracted by the wedge prism.

FIG. 3 is a schematic plan view showing the shape of a ridge line group formed on the inclined surface of the wedge prism of the first embodiment. Only one of the semi-circular wedge prisms 2a is shown, and the other 2b is omitted because it is the same. The intersecting straight line groups in the figure represent the ridge lines that make up each ridge line group. Further, FIG. 4 is a view showing a state of slopes forming each ridge line group in this embodiment,
Corresponding to the partial cross section in the direction perpendicular to the direction of the ridgeline R, A in the figure represents the surface corresponding to the slope of the wedge prism. As shown in the plan view of FIG. 3, on the slope of the wedge prism 2a,
Ridge line groups R _{11 to} R ₁₁₃ are formed along the first direction l ₁ , and ridge line groups R _{21 to} R ₂₁₃ are formed along the _second direction l ₂ and the direction of each ridge line group is formed. Is an angle α = with respect to a perpendicular line N to the dividing line (boundary line) direction S of both wedge prisms.
They form 14 ° and are directions symmetrical to each other with respect to the perpendicular N.

In the first embodiment, the intervals (widths) d of the ridge lines forming each ridge line group are all equal, and the shape of the parallelogram formed by the first direction ridge line group and the second direction ridge line group is that of all sides. It is a diamond with the same length. As shown in the partial side view of FIG. 4, since the angles β formed by the slopes forming the ridgelines with respect to the surface of the wedge prism are all equal, the quadrangular pyramid-shaped depressions are all of the same shape and are blurred by the wedge prism. It is a quadrangular pyramid that extends in a direction perpendicular to the displacement direction of the image. That is, as shown in the enlarged plan view of FIG. 5 and the perspective view of the wedge prism as a whole shown in FIG. 6 and the enlarged perspective view of FIG. 7, each ridgeline R _1i- in the first ridgeline group along the first direction. ₁ , R _1i , R _{1i + 1} etc. are the first
Each ridgeline R in the second ridgeline group formed by the first slope 3a and the second slope 3b along the direction l ₁ and along the second direction
_2i-1 , R _2i , R _{2i + 1,} etc. are the first slopes 4 along the second direction l _2.
It is formed by a and the second slope 4b, and the intersection of these four slopes is formed as the bottom B (top of the recess) of the quadrangular pyramid-shaped recess.

FIG. 6 shows the configuration of the first embodiment in order to facilitate understanding.
FIG. 3 is a perspective view showing an overview of the wedge prism 2a as a whole. Further, FIG. 7 is an enlarged perspective view of a part of the inclined surface of the wedge prism 2a in order to make it easier to understand the shape of the quadrangular pyramid-shaped depression formed by each ridge. The perspective views and the plan views shown in FIGS. 3 and 5 show the intervals between the ridge lines and the heights of the ridge lines forming each ridge line group in order to facilitate understanding of the configuration of the first embodiment. Is exaggerated. In an actual focusing screen, the diameter of the split prism part is about 3 mm and the interval between the ridge lines is 5 to 20 μm as described above,
150 to 600 ridges are formed on one wedge prism, and approximately the same number of quadrangular pyramidal depressions are arranged side by side, and 50 to 200 quadrangular pyramidal depressions in the vertical direction. Are arranged side by side.

Due to the existence of the ridge line groups in such two directions, the light flux incident on each wedge prism of the split prism portion is first deflected by the wedge prism, and then diffracted by the ridge line group in each direction in a direction perpendicular to each of them. It FIG. 8 is a vector diagram for explaining the diffracting directions of these light fluxes by each ridge line group. The diffraction direction by the ridge line group in the first direction l ₁ is perpendicular to it. The diffraction direction by the ridge line group in V ₁ and V ₁ ′ is perpendicular to this.
V ₁ and V ₁ ′, and the diffraction direction by the _second group of l ₂ ridges is represented by V ₂ and V ₂ ′ which are perpendicular thereto. Accordingly, the split prism split line S direction, the resultant vector V 'next' and V ₂ 'V ₁ and the resultant vector V and V ₁ of the and V ₂ and, when the focus detection is the light diffracted by each prism line groups A blurred image due to the combining action in the direction along the dividing line S will be observed.

According to the configuration of the first embodiment as described above, in the case of out-of-focus, the subject image of the split prism portion is clearly separated and observed, and the ridgelines in two directions formed on the slope of the wedge prism are observed. Due to the diffractive effect of the group, the focus detection unit does not darken even when the aperture is narrowed down or when a dark lens is used, and it is difficult to observe annoying fringe patterns on the focus detection unit, resulting in a clear and attractive visual field. Can be obtained.

However, in the first embodiment described above, the two-direction ridge line groups are arranged at a constant period together to form a substantially two-dimensional diffraction grating, and therefore the drawback of multi-line blurring and coloring of a blurred image due to diffracted light still remains. May have. Specifically, as shown in the diffraction pattern of FIG. 9 and the intensity distribution curve of the diffracted light in the direction along the dividing line of the split prism, the diffraction pattern of the focusing screen of the first embodiment has the diffraction order. Clearly separate each. In the intensity distribution curve of the diffracted light shown in the lower part of FIG. 9, the vertical axis represents the intensity I.
The horizontal axis indicates the deflection angle of the light beam, and Δ ₀ is the deflection angle by the wedge prism, and this angle corresponds to the angle of the 0th-order light in the diffracted light by the ridge line group.

As a specific example of the first embodiment, a focusing screen having respective values of θ = 8 ° α = 14 ° β = 5 ° d = 15 μm was formed. FIG. 10 is a schematic plan view thereof, in which an annular microprism portion M is formed around a split prism portion composed of two wedge prisms 2a and 2b. FIG. 11 is a photograph of the diffraction pattern for one wedge prism according to this specific example. From this photograph, it can be seen that a plurality of diffracted lights are clearly separated as shown in the schematic diagram of FIG. In the photograph of the diffraction pattern in FIG. 11, an orthogonal diffraction pattern is formed to the left of the center, but this is the diffracted light by the microprism portion provided around the split prism portion. Therefore, the position where the diffracted light pattern by the micro prism portion intersects indicates the direction in which the light beam incident on the focusing screen goes straight without being deflected by the split prism.

9 and 11 (photographs) show the diffraction phenomenon for monochromatic light, but this tendency remains even for white light that is actually focused. There is a possibility of so-called multi-line blurring which is separated into a plurality of lines, and there is a risk that the blurred image will be colored because the diffraction angle depends on the wavelength.

The second embodiment shown below can solve the drawbacks of the first embodiment.

FIG. 12 is a schematic plan view showing the shape of the ridge line group formed on the inclined surface of the wedge prism in the second embodiment. Again, only one of the semi-circular wedge prisms 2a is shown and the other 2b
Is omitted because it is the same as this. Similar to FIG. 3, the intersecting straight line groups in the figure represent the respective ridge lines. Also,
FIG. 13 is a diagram showing a state of slopes forming each ridgeline R in the second embodiment, which corresponds to a partial cross section taken along a plane perpendicular to the ridgelines, and A in the figure indicates a surface corresponding to the slope of the wedge prism. Represent
Also in the second embodiment, the first direction and the second direction are symmetrical with respect to the direction perpendicular to the split line S of the split prism, and both form the angle α. The slopes forming the ridgelines R all have the same angle β with respect to the slope A of the wedge prism, but there are two types of intervals between the ridgelines, d ₁ and d ₂ .
Then, the ridge line groups R _1i-1 , R _1i , and R _{1i + 1} in the first direction l ₁ are randomly arranged at intervals of these two types without periodicity. Further, the ridge line groups R _2i-1 , R _2i in the second direction l ₂ ,
R _{2i + 1} also has a random arrangement. Therefore, as shown in FIG. 13, there are two types of depressions formed between the ridgelines in depth, and these are randomly present. Further, as shown in the enlarged plan view of FIG. 14 and the perspective view of the entire wedge prism shown in FIG. 15 and the enlarged perspective view of FIG. 16, there are four quadrangular pyramid-shaped depressions formed by each ridge group. There are two types.

That is, firstly, by two ridge lines in the first direction ridge line group arranged at d ₁ with a relatively narrow interval and two ridge lines in the second ridge line group arranged at d _{1 also} having a narrow width. It is a dent that is formed, and is a quadrangular pyramid dent with a diamond-shaped bottom surface.
Further, the first slope 4a and the second slope 4b having a triangle along the first direction l ₁ and the first slope 5a and the second slope 5b having the same triangle along the second direction are provided. An apex B ₁ of a quadrangular pyramidal depression is formed as an intersection. Second,
The first direction ridge line group and the second ridge line array arranged at d ₂ with a relatively wide interval
It is a recess formed between the direction ridge line group and a larger inverted pyramidal recess similar to the above. The height of the vertex B ₂ of this one is d ₂ / d ₁ times that of the first one.

The third depression has a relatively wide spacing within the ridge line group in the first direction.
The ridge line arranged at d ₂ and the ridge line arranged at a relatively narrow interval d ₁ in the ridge line group in the second direction are present at the intersecting positions, and the bottom face is an inverted four-sided parallelogram. It is a pyramidal depression and has a groove Q ₂ along the second direction. Then, the first sloped surface 6a and the second sloped surface 6 of the triangle along the first direction
b, and a trapezoidal first slope 7a and a second slope 7b along the second direction
And have. The fourth depression has a ridge line arranged at a relatively narrow interval d ₁ in the ridge line group in the first direction and a ridge line arranged at a relatively wide space d ₂ in the ridge line group in the second direction. It exists at the position where and intersect. The fourth recess has a trapezoidal first slope 8a and a second slope 8b along the first direction, and a triangular first slope 9a and a second slope 9b along the second direction. It has a groove Q ₁ along it and is symmetrical with the third recess with respect to the plane perpendicular to the parting line.

FIG. 15 is provided in order to facilitate understanding of the configuration of the second embodiment.
FIG. 16 is a perspective view showing an outline of an entire wedge prism 2a,
The figure is an enlarged perspective view of a part of the slope of the wedge prism 2a in order to make it easier to understand the shape of the depression formed by each ridge line group. Further, the perspective view and the plan view shown in FIG. 12 exaggerately show the intervals and heights of the ridge lines forming each ridge line group in order to facilitate understanding of the configuration of the second embodiment. Is. In the actual focus plate, the diameter of the split prism part is about 3 mm and the interval between the ridge lines is 5 to 20 μm as described above.
Therefore, similarly to the first embodiment, 150 to 600 ridge lines are formed in two directions on one wedge prism, and a substantially equal number of quadrangular pyramidal depressions are arranged side by side. 50 vertically
It is composed of ~ 200 quadrangular pyramidal depressions. In addition, it goes without saying that in the second embodiment, four types of quadrangular pyramidal recesses are randomly arranged.

FIG. 17 shows an outline of the diffusion pattern and the intensity distribution curve of diffused light in the focusing screen of the second embodiment. As shown in the figure, the pattern is almost symmetrical about the 0th-order light Δ ₀ , but the diffraction pattern such as the diffraction grating almost disappears and has a widely dispersed distribution. That is, as in the second embodiment, the ridge line group in each direction is randomly arranged at different intervals in a non-periodic manner, thereby having a light amount distribution spread along the dividing line of the split prism,
It is possible to obtain a scattering characteristic close to that of a general diffusion plate. Therefore, if the subject image is out of focus in the field of view of the focus detection unit using such a focusing screen,
Vertical stripes are not conspicuous as in the field of view of the focus detection unit in Fig. 18, and the blurred image does not become multi-line blur as shown in Fig. 22A, which causes smooth blurring and diffusion pattern. Due to the irregularity, there is little possibility that a blurred image will be colored.

As the most preferable specific example of the second embodiment, the apex angle θ of the wedge prism and the ridge lines in two directions formed on the slope of each wedge prism are formed in the direction perpendicular to the dividing line of the split prism. Each angle α, the angle β formed by the slope forming each ridge with the slope of the wedge prism, and the distance between the ridges d ₁
And d ₂ were prepared, and a focusing screen having the following values was prepared.

θ = 8 ° α = 14 ° β = 5 ° d ₁ = 15 μm d ₂ = 20 μm In this focusing screen, in each ridge line group, as shown in FIG.
As shown in Fig. 15, the arrangement of the two types of ridge line intervals was determined by a random number table so that the ridge line array with the same interval was not consecutive three times or more. This further prevents each ridgeline or the groove formed by these from becoming conspicuous as a striped pattern in the visual field of focus detection. A photograph of the diffraction pattern in the split prism portion of this focusing screen is shown in FIG. According to this, although the high-brightness points are distributed with a certain degree of regularity, they are evenly distributed over a wide range and function as a substantial diffusion plate while having left-right symmetry. It is clear that And in practical use, even when the aperture of the lens is narrowed or for dark lenses,
A naturally smooth blurred image was formed, and a focus detection section with an extremely good visual field was obtained with almost no coloring, and the accuracy of focus detection could be improved.

As a concrete example of the above-mentioned second embodiment, in the focusing screen whose photograph of the diffraction pattern is shown in FIG. It can be seen that the increase effect is inherent. That is, in the diffraction pattern by the two ridge line groups along the first direction and the second direction, when the diffracted light is not at equal intervals, the diffracted light distribution is larger due to the combined diffracted light distribution in the direction along the split line of the split prism. Peaks are formed. Therefore, if a ridge line group having such a diffraction pattern is formed on the slope of the wedge prism, a smoother blurred image can be obtained.

Further, in the above-mentioned embodiment, all the ridge lines are formed by the slopes inclined at the same angle with respect to the surface of the wedge prism, but the present invention is not limited to this, and the slopes forming the ridge lines have different slope angles. Then, even when the cross section of each ridge line is an asymmetrical triangle, it is possible to obtain the same effect. Further, the split prism portion is not limited to the two semi-circular wedge prisms illustrated in FIG. 1, and for example, the displacement directions of the blurred images by the four wedge prisms are perpendicular to each other. It goes without saying that it is also possible to combine and configure the above.

(Effect of the Invention) As described above, according to the present invention, excellent focus detection accuracy is maintained without darkening the split prism portion for focus detection even when the diaphragm is narrowed down even for a dark lens. In addition, it is possible to achieve a split image type focusing screen in which the focus detection unit looks good both in focus and out of focus. Furthermore, by configuring the ridge line group with ridge lines arranged at random intervals, the blurred image in the focus detection part is more smooth and not blurred, and moire fringes are less likely to occur, and the blurred image is colored. It is possible to provide a split image type focusing screen having a small number.

[Brief description of drawings]

FIG. 1 is a perspective view of a central portion including a split prism of a focusing screen according to the present invention, FIG. 2 is a side view of a wedge prism which constitutes the split prism, and FIG. 3 is an oblique view of the wedge prism in the first embodiment. Plan view of the provided ridge line group, No. 4
The drawing is a view showing a state of slopes forming each ridge line group in the first embodiment and corresponds to a partial sectional view, FIG. 5 is an enlarged plan view of the ridge line group of the first embodiment, and FIG. 6 is a first embodiment. FIG. 7 is a perspective view showing the whole wedge prism of the example, FIG. 7 is an enlarged perspective view of a part thereof, FIG. 8 is a vector diagram showing a state of scattered light by the focusing screen of the first embodiment, and FIG. FIG. 10 is an explanatory view of a diffraction pattern of a split prism in one embodiment, FIG. 10 is a plan view of a focusing screen according to a concrete example of the first embodiment, and FIG. 11 is a photograph of a diffraction pattern in the concrete example of the first embodiment. FIG. 13 is a plan view of a ridge line group provided on the slope of the wedge prism in the second embodiment, and FIG. 13 is a diagram showing a state of the slope forming each ridge line group in the second embodiment, which corresponds to a partial sectional view. FIG. 14 is an enlarged plan view of the ridge line group of the second embodiment, and FIG. 15 is an oblique view showing the wedge prism of the second embodiment. FIG. 16 is an enlarged perspective view of a part thereof, FIG. 17 is an explanatory view of a diffusion pattern of a split prism in the second embodiment, FIG. 18 is a view of a split prism portion according to the second embodiment, FIG. 19 is a photograph of the diffraction pattern of the split prism part in the specific example of the second embodiment, FIG. 20 is a perspective view of a conventional general split image matching type focusing screen, and FIG. 21 is its general use state. 22A and 22B are view diagrams of a split prism in a known focusing screen showing a defocused state and a focused state, respectively. [Explanation of Signs of Main Parts] 1 ... Focus plate 2a, 2b ... Wedge prism B, B ₁ , B ₂ ... Vertex of micro recess formed by ridge line group Q ₁ , Q ₂ ... Micro recess formed by ridge line group Groove

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Asari Ina 1-17-4 Shimizu, Suginami-ku, Tokyo (56) References JP 57-132130 (JP, A) JP 58-207032 (JP, A) JP-A-52-27634 (JP, A)

Claims (3)

[Claims] 1. A pair of wedge prisms each having an inclined surface inclined with respect to a focal plane and refracting light rays in different directions, and the wedge prisms do not match the subject image with the focal plane. In the focusing screen for detecting the matching state of the focal points by displacing, the first and second directions symmetric with respect to a line perpendicular to the displacement direction of the object image by the wedge prisms on the surfaces of the pair of wedge prisms. A first direction ridge line group and a second direction ridge line group respectively extending along the first direction, and each ridge line forming the first ridge line group extending along the first direction has a first slope and a second slope along the first direction. Formed with a slope and the second
Each ridge line forming a second ridge line group along the direction is formed by a first sloping surface and a second sloping surface along the second direction, and by the first ridge line group and the second ridge line group on the wedge prism surface. , A plurality of quadrangular pyramid-shaped depressions each having a side parallel to the first direction and a direction parallel to the second direction and extending in a direction perpendicular to the displacement direction of the object image by the wedge prism and having a parallelogram as a bottom surface. The first direction ridge line group and the second direction ridge line group each form an angle of 5 ° to 20 ° with respect to a line perpendicular to the displacement direction of the subject image by the wedge prism. Characteristic focusing screen. 2. The first direction ridge line group and the second direction ridge line group each have a structure in which a plurality of ridge lines are periodically arranged at equal intervals. Focus plate. 3. The first direction ridge line group and the second direction ridge line group each have a structure in which a plurality of ridge lines are arranged aperiodically at different intervals. The described focusing screen.