JPS61243402A - Half mirror - Google Patents

Abstract

PURPOSE:To obtain the mirror suitable to use for a main mirror of a single lens reflex camera by alternately laminating a transparent dielectric having a high refractive index and a dielectric having a low refractive index at a visible wavelength region respectively. CONSTITUTION:The titled mirror comprises a substrate plate G, an air layer Air and a translucency mirror part H. The translucency mirror part H is constituted by the first layer 1, the second layer 2, the third layer 3...the sixth layer 6 and the seventh layer 7 in order from the air side to the substrate side. The first-fourth layers belong to the A group A, and the fifth...seventh layers belong to the B group B. The max. optical film thickness among those of the A group is smaller than the min. optical film thickness among those of the B group. The first, third, fifth and seventh layers 1, 3, 5, and 7 are the dielectric layers having the higher refractive index than that of the substrate G. While, the second, fourth and sixth layers 2, 4, 6 are the dielectric layers having the lower refractive index than that of the substrate G. The titled mirror is prepared by alternately laminating the dielectric layers having the high refractive index and the low refractive index respectively on the substrate G.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semi-transparent mirror for splitting incident light into transmitted light and reflected light, and more particularly to a semi-transparent mirror suitable for the main mirror of a 7-rex camera.

Lost! 11 Conventionally, it is known that a light receiving element is arranged under a mirror box in a 7-lens camera to perform exposure control and photometry for focus detection.

In such a case, the main mirror of the 7-lens camera must be a semi-transparent mirror.

Conditions suitable for such a semi-transparent mirror include that the finder image can be observed as brightly as possible, and that a sufficient amount of light must be provided to the light receiving element for exposure control and focus detection. FIG. 9 is a cross-sectional view showing the configuration of the -m7rex camera. In the figure, light transmitted through a photographic lens (2) is reflected by a main mirror (4) consisting of a semi-transparent mirror and enters a finder system having a focus plate (6), a pentaprism (8) and an eyepiece (10). The light passes through the main mirror (4) and passes through the 1st mirror (12). The light is reflected by the light beam and is split into light that passes through the lens (14) to the light receiving element (16). Here, conventional semi-transparent mirrors include those using metal and those using dielectric. However, semi-transparent mirrors made of metal have the disadvantage of poor efficiency because the metal absorbs light. On the other hand, a semi-transparent mirror using a dielectric material is very efficient if the dielectric material itself has no absorption in the visible range.

Therefore, a semi-transparent mirror made of multi-layered dielectric material is used, but in general, the sensitivity to the brightness of the eye is lower than that of the light receiving element (16), so the reflectance of the semi-transparent mirror of the main mirror (4) is It is better to make it larger than the transmittance. However, if the reflectance is increased too much, the amount of light incident on the light-receiving element (16) will decrease, the number of layers of the semi-transparent mirror will increase, which will increase the cost, and manufacturing errors will accumulate, resulting in a spectral spectrum close to the design value. It becomes difficult to obtain the characteristics. Furthermore, there is a problem that cracks are more likely to occur when the number of layers increases.

For example, Japanese Patent Application Laid-Open No. 53-110541 discloses a semi-transparent mirror having the configuration shown in Table 1.

Table 1 However, "ON" indicates the design wavelength.

However, as is clear from FIG. 10, which shows the spectral reflectance characteristics, with the configuration 2, although almost flat spectral characteristics can be obtained over the entire visible range, approximately 5
Only a reflectance of 0% can be obtained, making it unsuitable for use as the main mirror of a 7-lens camera.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semi-transparent mirror that does not suffer from the above-mentioned drawbacks and is suitable for the main mirror of a 7-lens camera.

In order to solve the problem and achieve the above object, the present inventors first determined that a semi-transparent mirror to be used as the main mirror of a 7-lens camera has a diameter of about 55 to 88 mm over the entire visible range.
It has been discovered that it is good to have a reflectance of about 0%.

This is because if the reflectance is less than 55%, the 7-eye image will be too dark, and if it is more than 80%, the amount of light incident on the light receiving element will be too small.

Based on this discovery, the present inventors developed a semi-transparent mirror in which a high refractive index dielectric material and a low refractive index dielectric material that are transparent in the visible wavelength range are alternately laminated on a substrate, with a total number of layers of 7. It consists of ~10 layers, and from the air side to the substrate side, the first layer, the second layer, etc. If the total number of layers is even, the layer from the air side to the L/2N is A. Group, the layers closer to the substrate are divided into Group B, and if the total number of layers is odd, the layers from the air side (
It is separated from the LB group, and is characterized in that the optical thickness of the layer with the largest optical thickness in the A group is smaller than the optical thickness of the layer with the smallest optical thickness in the B group. The semi-transparent mirror has a reflectance of about 55% to 80% over the entire visible range,
We also found that its spectral characteristics were flat.

Therefore, the gist of the present invention is to provide a semi-transparent mirror in which a high refractive index dielectric transparent in the visible wavelength range and a low refractive index dielectric are alternately laminated on a substrate, and the total number of layers is from 7 to 10 layers. At the same time, from the air side to the substrate side, the first layer, second layer, etc.
・When the total number of layers is an even number, the air side to the L/2nd layer is divided into group A, and the layer closer to the substrate is divided into group B. If the total number of layers is odd, the air No. (L+1)72 from the side
The layers up to the substrate are divided into group A, and the layers on the substrate side are group B, and the optical thickness of the layer with the largest optical thickness in group A is the optical thickness of the layer with the smallest optical thickness in group B. The reason is that it is smaller than the optical thickness of the layer.

That is, in the present invention, if the layer on the air side is made thinner and the substrate is mathematically expressed, then when the layer on the air side is thinned and the layers are bound in order from the air side to the substrate side, the first layer, the second layer, etc. If the optical thickness of the layer is Ni, then max[N1tN2* ' *
, n ] < min[Nk+19Nk+24
@ e NLI However, k=L/2 (
When L is an even number) k=(L+1)/2 (When L is an odd number).

to JLfL Examples of the present invention will be described below.

K benign 1 FIG. 1 is a sectional view showing the configuration of Example 1 of the present invention.

In the figure, (G) indicates the substrate, (Air) indicates the air layer, and the semi-transparent mirror section (H) is arranged in order from the air side to the substrate side.
Layer (1), second layer (2), #IJ31 (3), fourth layer (
4), 5th layer (5), 6th layer (6) and 7th layer (7)
It consists of seven layers, with the first layer (1) to the fourth layer (4) being A.
Group (A), the fifth layer (5) to the seventh layer (7) are group B (B). The 1.3.5.7 layer is a high refractive index dielectric layer made of a dielectric material having a higher refractive index than the substrate (G);
．． Layer 4.6 is a low refractive index dielectric layer made of a dielectric having a lower refractive index than the substrate (G).

Table 2 shows the refractive index and optical thickness of each layer.

Table 2 Here, the design wavelength λ is 550 na+, and the incidence 9 on the semi-transparent mirror portion (H) is 45°. In this example,
The high refractive index dielectric layer contains Z r O2 or Z r O
A mixture of 2 and TiO2 is applied, and MgF2 is applied for the low index dielectric layer. Then, it is manufactured by alternately stacking high refractive index dielectric layers and low refractive index dielectric layers on the substrate (G).

The spectral reflectance characteristics of this example are shown in FIG. 2 by (I).

As is clear from FIG. 2, according to this embodiment, 400
It is possible to obtain a reflectance of 72 over the entire visible range from n- to 700 nm, and an average reflectance of 60% or more.

K19 In this example, in the seven-layer structure of Example 1, the low refractive index dielectric layer is made of Sin with a refractive index of 1.47, and the high refractive index dielectric layer is made of Ti0z with a refractive index of 2.3. , the optical thickness of each layer is adjusted by #l accordingly. The configuration of Example 2 is shown in Table 3.

Table 3 Refractive index Optical film thickness Air 1.0 1st layer (1) 2.3 0,159λA 2nd layer (2)
1.47 0.219 people 3rd layer (3) 2,3 0.
231 people 4th layer (4) 1,47 0,244λken em, /e
＼9＾Q12QIQ 22, the design wavelength λ is 550 nm, and the angle of incidence on the semi-transparent mirror portion (H) is 45°. The spectral reflectance characteristics of this example are shown in FIG. 2 by line (II). As is clear from Figure 2,
In this example as well, the spectral characteristics are 7 lats and an average reflectance of about 60% can be obtained.

In this embodiment, as shown in the cross-sectional view of FIG. 3, the first layer (1), the second layer (2), and the third layer (
3), a fourth layer (4), a fifth layer (5), a sixth layer (6), a seventh layer (7), and an eighth layer (8). The first layer (1) closest to the air is made of a high refractive index dielectric. In this example, the high refractive index dielectric layer (1)
(3), (5), and (7) are each made of TiO2, and each of low refractive index dielectric layers (2>(4) and (608) is 5i0
Consists of 2. Table 4 shows the configuration of this embodiment.

Table 4 Here, the design wavelength λ is 550 ns+, and the angle of incidence on the semi-transparent mirror portion (H) is 45°. The spectral reflectance characteristics of this example are shown by line (1) in FIG. As is clear from Figure 4,
In this example as well, the spectral characteristics are 7 lats and an average reflectance of about 60% can be obtained.

In this example, the low refractive index dielectric layer and the high refractive index dielectric layer of Example 3 are reversed, and the optical thickness of each layer is adjusted accordingly. The configuration of Example 4 is shown in Table 5.

Table 5 Here, the design wavelength λ is 550 nm, and the angle of incidence on the semi-transparent mirror portion (H) is 45°. The spectral reflectance characteristics of this example are shown in FIG. 4 by the line (ff). As is clear from FIG.
In this example as well, the spectral characteristics are 7 lats and an average reflectance of about 60% can be obtained.

In this embodiment, as shown in Fig. 5, the first layer (1), the second layer (2), the third layer (3), and the fourth layer (4
), 5th layer (5), 6th layer (6), 7th layer (7), 8th layer
This is an example of a nine-layer structure including layer (8) and V-9th layer (9). In this example, high refractive index dielectric layers (1) (3) (5)
(7) and (9) are made of Z r O2, and the low refractive index dielectric layers (2), (4), (6), and (8) are made of MgF2. Table 6 shows the specific configuration of this embodiment.

The angle of incidence on Table 6 is 45°. The spectral reflectance characteristics of this example are shown by line (V) in FIG. As is clear from FIG.
% average reflectance can be obtained.

In this example, ZrO was used as the high refractive index dielectric material.
A mixture of ZrO2 and T i O2 may be used instead of □.

In this example, the low refractive index dielectric layer and the high refractive index dielectric layer of Example 5 are reversed, and the optical thickness of each layer is adjusted accordingly. The configuration of Example 6 is shown in Table 7.

Table 7 Refractive index Optical film thickness Air 1.0 1st layer (1) 1,385 0,009λA 2nd layer (
2) 2.12 0,214λ 3rd layer (3) 1.3
85 0.246λ 4th layer (4) 2,12 0.222
The design wavelength λ is 550nII, and the angle of incidence on the semi-transparent mirror part (H) is 45°.The spectral reflectance of this example is The characteristics are shown by the line (Vl) in Figure 6. As is clear from Figure 6, in this example, the spectral characteristics are 7 lats, which is about 60%.
It is possible to obtain an average reflectance of .

In this example, the high refractive index dielectric layer is made of ZrO.
2 or a mixture of ZrO2 and T i O2, and MgF2 is used for the low refractive index dielectric layer.

In this embodiment, as shown in FIG. 7, the first layer (1), second layer (2), third layer (3), and fourth layer (4
), 5th layer (5), 6th layer (6), 7th layer (7), 8th layer
10 of layer (8), 9th layer (9) and 10th layer (10)
This is an example of layer structure. In this example, the high refractive index dielectric layer (1) (3) (5) (7) (9) is made of CeO2 or a mixture of ZrO2 and TiO2, and the low refractive index dielectric layer (2 >(4)<6)(8)(10) is Mg
Consists of F2. The specific configuration of this embodiment is shown in Table 8.

Table 8 Here, the design wavelength λ is 550 ns1, and the angle of incidence on the semi-transparent mirror portion (H) is 45°. The spectral reflectance characteristics of this example are shown in FIG. 8 by the line (■). As is clear from Figure 8,
In this example, the spectral characteristics are 7 lats, and an average reflectance of about 70% can be obtained.

Here, the high refractive index dielectric layer includes TiO□, Z r
O2, CeOz, ZnS or a mixture thereof can be applied, and the low refractive index dielectric layer can include MgF, 5iO
z etc. are applicable.

Illustrated IL example.

As detailed above, the present invention provides a semi-transparent mirror in which a high refractive index dielectric material and a low refractive index dielectric material that are transparent in the visible wavelength range are alternately laminated on a substrate, and the total number of layers is 7 to 7. Consisting of 10 layers, from the air side to the substrate side, the first layer, second layer,
..., if the total number of layers is even, the layers from the air side to the L/2nd layer are divided into group A, and the layers closer to the substrate are group B, and if the total number of layers is odd, In this case, the number (L +
1) Divide up to 72 layers into group A and the layers closer to the substrate into group B, and the optical thickness of the layer with the largest optical thickness in group A is the optical thickness of group B. is characterized by being smaller than the optical thickness of the smallest layer + ^
Toni I4 Pusshi + T book? Yuto -
も The F emissivity characteristic is almost flat throughout the visible range,
and can obtain an average reflectance of about 55% to 80%,
- It is possible to obtain a semi-transparent mirror suitable as the main mirror of a 7-rex camera.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the membrane structure of Examples 1 and 2 of the present invention;
FIG. 2 is a graph showing its spectral reflectance characteristics, FIG. 3 is a cross-sectional view showing the film structure of Examples 3 and 4 of the present invention, FIG. 4 is a graph showing its spectral reflectance characteristics, and FIG. 5 is a graph showing its spectral reflectance characteristics. A sectional view showing the film structure of Invention Examples 5 and 6, FIG. 6 is a graph showing the spectral reflectance characteristics, #IJ7 is a sectional view showing the film structure of Invention Example 7, and FIG. 8 is its spectral FIG. 9 is a sectional view showing the optical system of a single-lens 7-rex camera, and FIG. 10 is a graph showing the spectral reflectance characteristics of a conventional example. (1) (2) -------; 11 layers, 2nd layer, ... (A
); Group A (B); Group B and above Applicant Minolta Camera Co., Ltd. Figure 1 q Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Wave length Figure 7 Figure 8

Claims (1)

[Claims] A semi-transparent mirror in which a high refractive index dielectric material and a low refractive index dielectric material transparent in the visible wavelength range are alternately laminated on a substrate, wherein the total number of layers L is 7 to 10 layers, and , from the air side to the substrate side, the first layer, the second layer, etc. If the total number of layers L is an even number, from the air side to the L/2nd layer is A.
group, the layers closer to the substrate are divided into group B, and if the total number of layers L is an odd number, the layers from the air side to the (L+1)/2nd layer are divided into group A, and the layers closer to the substrate are divided into group B. The optical thickness of the layer with the largest optical thickness in group A is B
A semi-transparent mirror characterized in that its optical thickness is smaller than the optical thickness of the smallest layer in the group.