JPH0516003B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention relates to a detection system for using the light flux incident through the photographing lens of a single-lens reflex camera, video camera, etc. for exposure, focusing control, etc., and a finder for visually confirming the shooting range. This invention relates to a laminated structure of dielectric thin films mainly used in semi-transparent mirrors and the like that divide the system into two parts. Conventional technology and its problems Traditionally, the TTL method, which uses light transmitted through the photographic lens, has been used for exposure control and focal position detection in single-lens reflex cameras because it makes the most of the characteristics of single-lens reflex cameras. There is. FIG. 4 shows the configuration of such a single-lens reflex camera. A part of the light beam incident through the photographing lens 1 is reflected by the main mirror 2 made of a semi-transparent mirror and proceeds to a finder system having a focus plate 3, a pentaprism 4 and an eyepiece lens 5, and the remaining part passes through the main mirror 2. The light is transmitted, reflected by the sub-mirror 6, and guided to the light-receiving element 8 via the lens 7. In addition, since the finder system must clearly capture the subject in a short time, the light receiving element 8
Since the lens has higher sensitivity than the naked eye and does not require a large amount of light, it is generally desirable to configure the main mirror 2 so that 60 to 80% of the light transmitted through the photographic lens 1 is guided to the viewfinder system. For such a main mirror 2, there is a
There are those described in JP-A-110541, JP-A-61-243402, and JP-A-62-39801. These mirrors are constructed by laminating an optical thin film made of dielectric material on a transparent substrate to eliminate loss due to absorption.
It has a reflectance of However, since the reflectance of the mirror described above is near the lower limit of the above-mentioned optimum conditions, it is desirable to increase the reflectance to ensure a brighter field of view for the finder system. Generally speaking, increasing the number of dielectric layers is used to increase the reflectance, but increasing the number of layers narrows the band that exhibits flat spectral reflection characteristics and causes coloration in the visible image, as well as increasing the number of dielectric layers. This increases the total amount of internal distortion, leading to cracks and bending of the circuit board, and is a fatal flaw in the viewfinder system of single-lens reflex cameras that check the focus state. By the way, when performing focus position detection and exposure control using spot photometry using the TTL method, the light used for photometry is only a small portion of the light that has passed through the center of the main mirror 2, and the light that has passed through the other peripheral areas is used for photometry. No light is used. Therefore, if this unused light can be guided to the finder system, almost 100% of the light can be guided to the finder system without increasing the number of dielectric layers to increase the reflectance, and the light receiving element 8 can guide 40-50% of the light in the area covered through lens 6,
Desirable characteristics can be obtained as a main mirror for a single-lens reflex camera. A mirror having such a configuration is disclosed in Japanese Patent Application Laid-Open No. 60-57301. In this disclosed example, the center part is a semi-transparent mirror and the peripheral part is an increased reflection metal mirror, and the vapor deposition process includes a first step of vapor depositing the lower layer of the dielectric semi-transparent film structure on the entire surface of the glass substrate, and a first step in which the central part is vapor-deposited on the entire surface of the glass substrate. The method consists of a second step in which an aluminum layer is deposited using a shielding mask, and a third step in which the mask is removed and an upper layer of the dielectric semi-transparent film structure is deposited. By the way, one step in vacuum evaporation consists of the following steps: cleaning the substrate, placing the substrate in the coating frame, evacuation, vacuum evaporation, taking it out to the atmosphere, and taking out the substrate from the coating frame. Furthermore, if the number of vapor deposition steps increases, not only will the processing time become longer and the unit price of parts will rise, but there will also be more opportunities for chipping and dirt to adhere to the substrate during handling. This will increase. Note that since the surface of the vapor deposited film is very clean, once dirt adheres to it, it cannot be removed by simple cleaning, and these factors contribute to an increase in the unit cost of parts. A composite mirror having a semi-transparent mirror portion and a reflective metal mirror portion can be manufactured in essentially two steps: masking a glass substrate and depositing an aluminum layer, then removing the mask and depositing a dielectric layer. However, while using the conventional laminated structure of dielectric thin films,
When a composite mirror is manufactured by a vapor deposition process, as pointed out in the disclosed example above, a spike-like abnormal transmission band occurs in the spectral reflection characteristics of the reflective metal mirror portion, resulting in coloring. There is.
Note that this phenomenon also occurs for all the film configurations shown in the three disclosed examples above. Therefore, in order to manufacture a composite mirror with satisfactory characteristics using the conventional dielectric film configuration, it is necessary to accept the disadvantages of the increase in the number of steps described above.
I needed to go through a process. Purpose of the Invention The present invention has been made in view of the above-mentioned problems, and provides a dielectric thin film that has flat spectral reflection characteristics in the visible region and does not cause coloring even when a mirror having a metal layer is manufactured in two steps. The purpose is to provide a laminated structure. Means for Solving the Problems In order to achieve the above object, the present invention provides a stack of dielectric thin films formed by stacking dielectric thin films having different refractive indexes on a substrate at least partially provided with a metal layer. In the structure, the dielectric thin film is the first layer and the second layer from the substrate side, and the layer in contact with the light incident medium is the mth layer.
When made into layers, the first layer is a low refractive index n _L layer, the second layer is a high refractive index n _H layer (n _H > n _L ), and the n _L layer and the n _H layer are sequentially stacked repeatedly. The (m-1) layer is an n _H layer, the (m-2) layer is an intermediate refractive index n _M layer, the m-th layer is an intermediate refractive index n _M ' layer, and the optical film of each dielectric thin film is When the thickness is 1/4 of the reference wavelength, when n _M = n _M ′, n _L < n _M < n _H n _L < n _M ′ < n _H , and when n _M ≠ n _M ′, n _L It is characterized by satisfying <n _M ≦n _H n _L ≦n _M ′<n _H. EXAMPLES Hereinafter, the present invention will be explained based on the drawings. [First Embodiment] FIG. 1 shows a first embodiment of a laminated structure of dielectric thin films according to the present invention. The substrate G in this example is a transparent optical glass (refractive index n _G
= 1.52), and has a metal layer A1 in the peripheral part Y except for the central part X of the surface where the dielectric thin film is laminated. In addition, the total number of layers of the dielectric thin film is m = 8, and the 1st, 3rd, and 5th layers counting from the substrate G side, .
is the low refractive index n _L layer, the 2nd, 4th, 7th layer,,
is a high refractive index n _H layer, and the sixth and eighth layers are intermediate refractive index n _M and n _M ' layers. The composition of each layer is shown in Table 1, and here
n _M = n _M ′. The light incident medium is air, and the reference wavelength is 490 nm.
It is said that

【table】

[Second example]

Table 2 on the next page shows the structure of a second embodiment of the laminated structure of dielectric thin films according to the present invention. In this example, the total number of dielectric thin film layers m = 6, counting from the substrate G side, the first and third layers are low refractive index n _L layers, and the second and fifth layers, V are high refractive index layers. n _H
The fourth and sixth layers have an intermediate refractive index n _M ,
n _M ′ layers. Other structures such as the metal layer are the same as those in the first embodiment, so their explanation will be omitted.

【table】

[Table] Figure 3 E shows the reflectance of a composite mirror with this configuration (in Figures 3 E and F, the solid line is the central part X where no metal layer is provided, and the broken line is the periphery where the metal layer is provided) The reflectance of part Y is shown, and the incident angle is 45° in both cases). Although the reflectance itself is lower than in the first embodiment due to the small number of layers, the spectral reflection characteristics in the visible region are flat in both the central portion X and the peripheral portion Y. The reflectance is approximately 40% in the central part X, and approximately 95% in the peripheral part Y, which is higher than the reflectance of A1 alone (90%). Next, one modification of the second embodiment will be mentioned. In this variant, the fourth layer is TiO ₂ (refractive index n _M =
n _H = 2.35), and the sixth layer is MgF ₂ (refractive index n _M ′ =
n _L = 1.38). Since the fourth layer and the fifth layer V have the same refractive index, the optical thickness of the fourth layer is λ/2.
It is equivalent to a five-layer laminated structure. FIG. 3F shows the spectral reflection characteristics of this modification. As can be understood from this figure, the spectral reflection characteristics are even flatter than in the second embodiment, and the bandwidth sufficiently covers the visible region. This concludes the description of the embodiment. In addition, in each of the above examples, the reference wavelength is set for all layers.
Although it is assumed to be 490 nm, since the substrate and the materials of each layer have refractive index dispersion, the actual spectral reflection characteristics generally have a higher reflectance on the shorter wavelength side.
To correct this, it is necessary to slightly change the film thickness of each layer, so the reference wavelength is set to 400 in the visible region.
It will vary within a range of ~700 nm. Effects As explained above, when the laminated structure of dielectric thin films according to the present invention is laminated on a glass substrate to form a semi-transparent mirror, the spectral reflection characteristics in the visible region are flat, and the reflected light is and does not cause coloring in transmitted light. In addition, when laminated on a metal reflective surface such as aluminum, it not only exhibits an increased reflection effect, but also eliminates the spike-like abnormal transmission band that could only be avoided with conventional three-step vapor deposition by using two-step vapor deposition. Since it is possible to obtain a flat high reflectance over the entire visible region, it is possible to reduce the number of steps and suppress an increase in the unit cost of parts. Therefore, if the above laminated structure is laminated on a transparent glass plate with a metal layer on the periphery except for the center of the surface, it will be difficult to use a single-lens reflex camera that uses the TTL method to detect the focus position and control exposure using spot photometry. A composite mirror ideal as a main mirror can be obtained in the shortest process. Further, in this case, since the metal layer, which is easily attacked by oxygen in the atmosphere, is not brought into contact with the atmosphere, the metal layer can be effectively protected. Note that, as is clear from the examples, there is a large degree of freedom in selecting the materials used for the intermediate refractive index n _M and n _M ' layers, so there is also an advantage that there are few restrictions on the materials used and manufacturing is easy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the structure of a first embodiment of a composite mirror using a laminated structure of dielectric thin films according to the present invention. FIG. 2 is a graph showing the spectral reflection characteristics of the composite mirror of the first embodiment and its modified example. FIG. 3 is a graph showing the spectral reflection characteristics of a second embodiment of a composite mirror using a laminated structure of dielectric thin films according to the present invention and a modification thereof. FIG. 4 is a schematic diagram showing the arrangement of optical components of a single-lens reflex camera. {,,V...Low refractive index n _L layer,,,...
...high refractive index n _H layer, ... middle refractive index n _M ,
n _M ′ layer, }Dielectric thin film, G...Glass substrate, A1
...Metal layer.

Claims (1)

[Scope of Claims] 1. A laminated structure of dielectric thin films in which dielectric thin films having different refractive indexes are laminated on a substrate on which at least a portion is provided with a metal layer, wherein the dielectric thin film is laminated from the substrate side. 1st layer, 2nd layer
layer, and the layer in contact with the light incident medium is the m-th layer, the first layer is a low refractive index nL layer, and the second layer is a high refractive index layer.
As an nH layer (n _H > n _L ), the following n _L layer and n _H layer are repeatedly laminated in sequence, the (m-1)th layer is the n _H layer, and the (m-2) layer is the intermediate refractive index n. _M layer, the m-th layer is a layer with an intermediate refractive index n _M ′, and the optical thickness of each dielectric thin film is 1/4 of the reference wavelength, and when n _M = n _M ′, n _L < n A dielectric which satisfies _M < n _H n _L < n _M ′ < n _H , and when n _M ≠ n _M ′, satisfies n _L < n _M ≦n _H n _L ≦ n _M ′ < n _H. Laminated structure of body membranes. 2. The laminated structure of dielectric thin films according to claim 1, wherein the substrate is a transparent glass substrate. 3. The lamination of dielectric thin films according to claim 1, wherein the metal layer is provided in a peripheral part of the surface of the substrate on which the dielectric thin film is laminated, excluding a central part. structure. 4. The laminated structure of dielectric thin films according to any one of claims 1 to 3, wherein the total number of layers of the dielectric thin films is m=8. 5. The laminated structure of dielectric thin films according to any one of claims 1 to 3, wherein the total number of layers of the dielectric thin films is m=6.