JP6743398B2 - Observation optics and prism - Google Patents

Description

The present invention is an observation optical device having an observation optical system including at least one lens and a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90°, and an object image is inverted vertically and horizontally to be converted into an erect image. To a prism, especially a roof prism.

The roof prism used in observation optical equipment such as microscopes, telescopes, binoculars, single-lens reflex cameras, single-lens reflex digital cameras, and surveying instruments divides the pupil of the observation optical system by the ridges of a pair of reflecting surfaces that intersect at a nominal surface angle of 90°. Therefore, high processing accuracy is required, but since the prism can be made smaller than other erecting prisms such as Porro prism, there is an advantage that the optical device can be made smaller and lighter.

On the other hand, it is known that when a light beam is reflected by a reflecting surface, a phase difference occurs between the s-polarized component and the p-polarized component of a light wave that are orthogonal to each other before and after that surface. In an optical system where the pupil is divided by ridges like the roof prism, the polarization state of the light emitted from the roof prism differs between one side and the other side of the divided pupil, causing wavefront aberrations and the imaging performance of the observed image. Deteriorate. The larger the phase difference that occurs on the reflecting surface, the larger the difference in the polarization state that occurs, and as in the case where the processing accuracy of the surface angle is low, a double image is observed or the contrast decreases.

In order to reduce the phase difference generated on the reflecting surface of the roof prism, conventionally, a metal film of aluminum or silver has been formed on the reflecting surface. However, as the processing accuracy of the roof prism is improved, it has been pointed out that the effect of reducing the phase difference in question is insufficient with the metal film.

Japanese Patent Laid-Open No. 11-326781 discloses a dielectric film having a refractive index of M1, M2 and M3 (however, 2.0<M1<2.1, 1.35<M2<1.4 and 1.45<M3<1.5) on a roof surface of a roof prism. ) Is disclosed to be effective in reducing the phase difference of visible wavelength light with respect to a roof prism made of a base material having a refractive index of 1.46 to 1.6. .. That is, the phase difference reduction multilayer film described in Patent Document 1 suppresses the change in the phase difference between the s-polarized light and the p-polarized light before and after the reflection of the light beam incident on the pair of reflecting surfaces of the roof prism, and suppresses the deterioration of the wavefront aberration. This has the effect of improving the performance of the observed image.

However, the retardation-reducing multilayer film described in Patent Document 1 is effective for a roof prism having a refractive index of less than 1.6, but is applied to a roof prism having a higher refractive index of 1.6 or more. In that case, an insufficient phase difference reduction effect cannot be obtained, and when the incident angle of the light flux on the reflecting surface changes, the phase difference change amount of visible wavelength light exceeds 90° (±45°). However, there is a problem that the image quality difference (contrast, difference in color tone, etc.) between the left and right and peripheral portions of the observed image becomes remarkable. Therefore, even if the retardation-reducing multilayer film described in Patent Document 1 is applied to a roof prism made of a base material having a high refractive index (refractive index of 1.6 or more), an observation optical device having sufficient practical performance can be obtained. Can not.

When a base material having a refractive index of 1.6 or higher than that of the conventional one is used, there is an advantage that it is possible to totally reflect a light ray having a smaller incident angle. That is, when the refractive index of the base material of the roof prism is M0, the critical angle θc is θc=Arcsin(1/M0)
Since the critical angle is 43.2° when M0=1.46, the critical angle when M0=1.6 is 38.7°, and the Dach prism made of a base material with a high refractive index allows incident light to be totally reflected. It can be seen that the angular range is wide. When a base material with a refractive index M0 higher than 1.6 is used, the critical angle θc becomes smaller, so total reflection occurs in a wide range (38.7° or more) of the incident angle to the roof reflective surface, and from the roof reflective surface The image of is very bright with a neutral color tone over a wide screen range.

Therefore, even in such a roof prism made of a substrate having a high refractive index of 1.6 or more, it is possible to sufficiently suppress the change in the phase difference between the s-polarized light and the p-polarized light and the incident angle dependency, and to use such a substrate in a wide range. There is a demand for the development of a technology that can be used for observation optical equipment (for example, a penta roof prism of a single-lens reflex camera).

JP 11-326781 A

Therefore, the object of the present invention is to suppress the change of the phase difference between the s-polarized light and the p-polarized light of the light beam incident on the roof surface of the roof prism made of the base material having the refractive index of 1.6 or more, as well as the base material having the refractive index of 1.6 or less. It is to provide a multilayer film.

As a result of intensive research in view of the above objects, the present inventors have found that a high refractive index film having a refractive index of 2.15 or more and a low refractive index film having a refractive index of 1.3 to 1.7 are alternately laminated on a substrate having a refractive index of 1.6 or more. The inventors have found that the change of the phase difference between the s-polarized light and the p-polarized light of the light flux can be suppressed by forming such a dielectric multilayer film, and have arrived at the present invention.

The development history of the present invention will be described in detail.

When a light flux that travels inside the substrate enters the interface (reflection surface) with air at an angle of incidence that exceeds the critical angle, the light flux is totally reflected, so both s-polarized light and p-polarized light show a reflectance of 100%. Only the phase difference between polarized light and p-polarized light changes. Therefore, by setting the incident angle of the reflecting surface of the roof prism to be equal to or greater than the critical angle, the phase difference between the s-polarized light and the p-polarized light can be controlled without considering the reflectance change depending on the incident angle. Here, the phase difference between the s-polarized light and the p-polarized light can be controlled by providing a dielectric multilayer film on the base material.

As a result of investigating the wavelength dependence of the phase difference between s-polarized light and p-polarized light by forming a single-layer film of film materials with different refractive indexes on a substrate with a refractive index of 1.6 or higher, a relatively high refractive index of 2.15 or higher. A film material (such as TiO ₂ ) having a large effect has a large effect of bringing the phase difference close to 0°, but a film material having a relatively low refractive index (MgF ₂ , SiO ₂ etc.) has an effect of bringing the phase difference close to 0°. It has been found that the effect of reducing the phase difference is not so different even if the refractive index of the film material is slightly changed. As a result of studying based on this idea, for substrates with a refractive index of 1.6 or more, by forming a laminated film of at least two layers using two kinds of materials with different refractive indexes, It was found that the amount of change in the phase difference between s-polarized light and p-polarized light in the visible light region can be set within 90°, and even within 20°.

Regarding the incident angle dependency, it is known from the theory of interference of optical thin films that the smaller the number of layers and the smaller the total optical film thickness, the smaller the difference in reflectance or phase difference between s-polarized light and p-polarized light. From this idea, the number of layers is made smaller than that of the 9-layer film described in Patent Document 1, and by designing a phase difference reduction film having a smaller total optical film thickness, the incident angle dependence on the phase difference between s-polarized light and p-polarized light It was found that the property can be reduced.

Based on the above consideration, the inventors have achieved the invention described below. That is, the observation optical instrument of the present invention is an observation optical instrument having an observation optical system including at least one lens and a prism having a pair of reflecting surfaces intersecting at a nominal surface angle of 90°, and the prism is The ridges of the pair of reflecting surfaces are arranged so as to divide the pupil of the observation optical system, and the pair of reflecting surfaces has a high refractive index film with a refractive index of 2.15 or more and a low refractive index film with a refractive index of 1.3 to 1.7. And a dielectric multilayer film in which and are alternately laminated.

The high refractive index film preferably includes at least one ultra-high refractive index film having a refractive index of 2.3 to 2.5.

The total optical film thickness of the dielectric multilayer film is preferably 200 to 950 nm.

The total optical film thickness of the low refractive index film is preferably 50 to 450 nm.

The sum of the optical film thicknesses of the high refractive index film is preferably 100 to 600 nm.

The high refractive index film is made of any one of Ta ₂ O ₅ film, Nb ₂ O ₅ film, CeO ₂ film, TiO ₂ film and (TiO ₂ +ZrO ₂ ) mixed film, and the low refractive index film is Al ₂ O. _It is preferably composed of any one of a _three film, a SiO ₂ film, a MgF ₂ film and a (Al ₂ O ₃ +SiO ₂ ) mixed film.

The dielectric multilayer film is a two-layer film in which a first layer and a second layer are sequentially stacked from the base material side,
It is preferable that the first layer is a low refractive index film having an optical film thickness of 65 to 145 nm, and the second layer is a high refractive index film having an optical film thickness of 75 to 160 nm.

The dielectric multilayer film is a three-layer film in which the first layer to the third layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical film thickness of 5 to 80 nm,
It is preferable that the second layer is a low refractive index film having an optical film thickness of 70 to 160 nm, and the third layer is a high refractive index film having an optical film thickness of 100 to 190 nm.

The dielectric multilayer film is a four-layer film in which the first to fourth layers are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 10 to 70 nm,
The second layer is a high refractive index film having an optical film thickness of 25 to 135 nm,
It is preferable that the third layer is a low refractive index film having an optical film thickness of 30 to 200 nm, and the fourth layer is a high refractive index film having an optical film thickness of 100 to 245 nm.

The dielectric multilayer film is a five-layer film in which the first to fifth layers are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 30 to 100 nm,
The second layer is a low refractive index film having an optical film thickness of 30 to 100 nm,
The third layer is a high refractive index film having an optical thickness of 60 to 140 nm,
It is preferable that the fourth layer is a low refractive index film having an optical film thickness of 110 to 200 nm, and the fifth layer is a high refractive index film having an optical film thickness of 110 to 200 nm.

The dielectric multilayer film is a six-layer film in which the first layer to the sixth layer are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 20 to 80 nm,
The second layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The third layer is a low refractive index film having an optical thickness of 40 to 120 nm,
The fourth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
It is preferable that the fifth layer is a low refractive index film having an optical film thickness of 70 to 155 nm, and the sixth layer is a high refractive index film having an optical film thickness of 155 to 255 nm.

The dielectric multilayer film is a 7-layer film in which the first layer to the seventh layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
It is preferable that the sixth layer is a low refractive index film having an optical film thickness of 30 to 210 nm, and the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm.

The dielectric multilayer film is an 8-layer film in which the first layer to the eighth layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
The sixth layer is a low refractive index film having an optical thickness of 30 to 210 nm,
It is preferable that the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm, and the eighth layer is a low refractive index film having an optical film thickness of 5 to 100 nm.

The prism of the present invention has a pair of reflecting surfaces that intersect at a nominal surface angle of 90°, and a high refractive index film having a refractive index of 2.15 or more and a low refractive index film having a refractive index of 1.3 to 1.7 are alternately arranged on the pair of reflecting surfaces. Is provided with a dielectric multi-layered film.

In the prism, the high refractive index film preferably includes at least one ultra-high refractive index film having a refractive index of 2.3 to 2.5.

The prism is preferably a penta roof prism.

The prism is preferably a Peshan prism.

The prism is preferably an Amity prism.

Since the roof prism provided in the observation optical apparatus of the present invention is provided with a multilayer film capable of suppressing the change in the phase difference between the s-polarized light and the p-polarized light of the incident light flux even if the substrate has a refractive index of 1.6 or more. A wide incident angle range capable of totally reflected light, a very bright neutral tone in a wide screen range, and an observation image in which deterioration of wavefront aberration is suppressed can be obtained. Such a roof prism having a refractive index of 1.6 or more, a wide incident angle range capable of totally reflected light, and suppressed deterioration of wavefront aberration can be used in various observation optical devices.

FIG. 6 is a schematic diagram for explaining a change in the phase difference between s-polarized light and p-polarized light when a light beam from the inside of the base material is reflected on the surface (interface with air). 6 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside of the base material is reflected on the surface. It is a schematic diagram which shows the optical path of the light beam which injected into the Pechan prism. It is a schematic diagram which shows the optical path of the light beam which injected into the pentaprism. It is a schematic diagram which shows the optical path of the light beam which injected into the Amichi prism. 7 is a graph showing the wavelength dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a single-layer film. 9 is a graph showing the wavelength dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of the base material provided with the multilayer film shown in Design Example 1 and Design Example 2. 7 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of a conventional technique (comparative example). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 1). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a multilayer film of an example (design example 2). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 3). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 4). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 5). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a multilayer film of an example (design example 6). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light flux from the inside is reflected on the surface of a base material provided with a multilayer film of an example (Design Example 7). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 8). 13 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 9). 9 is a graph showing the incident angle dependence of the phase difference between s-polarized light and p-polarized light when a light beam from the inside is reflected on the surface of a base material provided with a multilayer film of Example (Design Example 10).

An embodiment of the present invention will be described. The present invention is achieved by providing a novel dielectric multilayer film described below on a prism having at least one lens and a pair of reflecting surfaces intersecting at a nominal surface angle of 90°, that is, a roof surface of a roof prism. It is a thing.

[1] Observation optical instrument The observation optical instrument of the present invention has an observation optical system including at least one lens and a prism having a pair of reflecting surfaces intersecting at a nominal surface angle of 90°, and the prism is The ridges of a pair of reflecting surfaces are arranged so as to divide the pupil of the observation optical system, and the pair of reflecting surfaces has a high refractive index film with a refractive index of 2.15 or more and a low refractive index film with a refractive index of 1.3 to 1.7. Is provided alternately with a dielectric multilayer film.

Optimum interference by forming a dielectric multi-layered film on the surface of the base material (prism) by alternately laminating a high refractive index film with a refractive index of 2.15 or more and a low refractive index film with a refractive index of 1.3 to 1.7. The effect can be obtained, and the change in the phase difference between the s-polarized light and the p-polarized light when the light flux propagating in the base material is reflected at the interface with air can be reduced. The dielectric multilayer film may have at least one high refractive index film and at least one low refractive index film. That is, a two-layer film consisting of the high-refractive index film and the low-refractive index film exerts the effect of reducing the phase difference, and the two-layer film is formed on the roof surface of the roof prism made of a base material having a refractive index of 1.6 or more. By forming the observation optical device, it is possible to provide an observation optical device capable of obtaining an observation image having a neutral color tone in a wide screen range and being very bright and suppressing deterioration of wavefront aberration. The high refractive index film preferably includes at least one ultra-high refractive index film having a refractive index of 2.3 to 2.5.

The number of layers of the dielectric multilayer film is preferably 8 or less. It is possible to obtain a multilayer film that exhibits the effect of reducing the phase difference even with 9 or more layers, but as the number of layers increases, the number of manufacturing processes increases and the total optical film thickness increases. The incident angle dependency of the phase difference becomes large, and the color tone change in the peripheral portion of the observed image becomes large. The number of layers of the dielectric multilayer film is more preferably 4 layers or 7 layers, and most preferably 7 layers.

The total optical film thickness of the dielectric multilayer film is preferably 200 to 950 nm, the total optical film thickness of the high refractive index film is preferably 100 to 600 nm, and the total optical film thickness of the low refractive index film is It is preferably 50 to 450 nm. By optimizing the optical film thickness of each layer as a film structure having such a film thickness, a dielectric multilayer film having a 2-layer to 8-layer structure in which the interference effect as described below is optimized can be obtained. By forming these dielectric multilayer films on a substrate with a refractive index of 1.6 or more, the fluctuation of the phase difference between s-polarized light and p-polarized light at an incident center angle of ±5° is kept within 90° (±45°). be able to. Further, as compared with the phase difference reduction film described in Patent Document 1 (dielectric multilayer film having a total optical film thickness of about 1000 nm with a nine-layer structure made of three types of dielectric materials), the number of layers (2 to 8 layers) and It can be seen that the number of types of dielectric materials (at least two types) is small and the total optical film thickness is thin, which is easy to manufacture and advantageous in terms of cost.

In the two-layer dielectric multilayer film, the first layer and the second layer are sequentially stacked from the base material side,
It is preferable that the first layer is a low refractive index film having an optical film thickness of 65 to 145 nm, and the second layer is a high refractive index film having an optical film thickness of 75 to 160 nm.

In the three-layer dielectric multilayer film, the first layer to the third layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical film thickness of 5 to 80 nm,
It is preferable that the second layer is a low refractive index film having an optical film thickness of 70 to 160 nm, and the third layer is a high refractive index film having an optical film thickness of 100 to 190 nm.

In the four-layer dielectric multilayer film, the first layer to the fourth layer are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 10 to 70 nm,
The second layer is a high refractive index film having an optical film thickness of 25 to 135 nm,
It is preferable that the third layer is a low refractive index film having an optical film thickness of 30 to 200 nm, and the fourth layer is a high refractive index film having an optical film thickness of 100 to 245 nm.

In the five-layer dielectric multilayer film, the first layer to the fifth layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 30 to 100 nm,
The second layer is a low refractive index film having an optical film thickness of 30 to 100 nm,
The third layer is a high refractive index film having an optical thickness of 60 to 140 nm,
It is preferable that the fourth layer is a low refractive index film having an optical film thickness of 110 to 200 nm, and the fifth layer is a high refractive index film having an optical film thickness of 110 to 200 nm.

In the 6-layer dielectric multilayer film, the first layer to the sixth layer are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 20 to 80 nm,
The second layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The third layer is a low refractive index film having an optical thickness of 40 to 120 nm,
The fourth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
It is preferable that the fifth layer is a low refractive index film having an optical film thickness of 70 to 155 nm, and the sixth layer is a high refractive index film having an optical film thickness of 155 to 255 nm.

In the 7-layer dielectric multilayer film, the first layer to the seventh layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
It is preferable that the sixth layer is a low refractive index film having an optical film thickness of 30 to 210 nm, and the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm.

In the 8-layer dielectric multilayer film, the first layer to the eighth layer are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
The sixth layer film has a low refractive index of an optical film thickness of 30 to 210 nm,
It is preferable that the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm, and the eighth layer is a low refractive index film having an optical film thickness of 5 to 100 nm.

The high refractive index film is preferably made of any material of Ta ₂ O ₅ film, Nb ₂ O ₅ film, CeO ₂ film, TiO ₂ film and (TiO ₂ +ZrO ₂ ) mixed film, and the low refractive index film The film is preferably made of any material of Al ₂ O ₃ film, SiO ₂ film, MgF ₂ film, and (Al ₂ O ₃ +SiO ₂ ) mixed film. High-refractive index films and low-refractive index films made of these materials are formed by vacuum vapor deposition, sputtering, physical vapor deposition such as ion plating, chemical vapor deposition such as thermal CVD, plasma CVD, or photo CVD. be able to

[2] Prism The prism of the present invention has a pair of reflecting surfaces that intersect at a nominal surface angle of 90°, and the pair of reflecting surfaces has a high refractive index film with a refractive index of 2.15 or more and a low refractive index of 1.3 to 1.7. It is characterized in that a dielectric multi-layered film in which rate films are alternately laminated is provided. The high refractive index film, the low refractive index film and the dielectric multilayer film are the same as those provided on the reflecting surface of the prism of the observation optical device described above.

When the dielectric multilayer film is formed on the pair of reflecting surfaces of the prism, it is desirable to form the same multilayer film on both of the pair of reflecting surfaces. When a difference occurs in the multilayer film formed on the reflecting surface, a difference also occurs in the phase difference between the s-polarized light and the p-polarized light on both surfaces, which deteriorates the imaging performance near the ridge. Therefore, it is desirable that the dielectric multilayer film formed on the pair of reflecting surfaces of the prism is a phase difference reducing film having high film forming stability. That is, a dielectric multilayer film having a small number of layers, a small number of types of film materials, and a small total optical film thickness is desirable as a phase difference reducing film because it reduces error factors and increases stability.

The prism of the present invention is preferably used as a roof prism, and examples of such roof prism include the Peshan prism shown in FIG. 3, the penta roof prism (penta prism) shown in FIG. 4, and the Amichi prism shown in FIG. In these figures, the angle of incidence of the ray indicated by the broken line arrow on the roof surface is 48° (Fig. 3) for the Peshan prism, 49° (Fig. 4) for the penta roof prism, and 60° (Fig. 5) for the Amichi prism. .. Examples of optical equipment in which the Penta-Dach prism is used as an observation optical system include a single-lens reflex camera and a single-lens reflex digital camera, and examples of optical equipment in which the Amichi prism is used as an observation optical system include a microscope and a surveying instrument. As the optical equipment in which the Peshan prism is used as an observation optical system, there are binoculars, a telescope, and the like.

The present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

(1) Incident angle dependence of the phase difference between s-polarized light and p-polarized light
Regarding the phase difference between s-polarized light and p-polarized light, the coordinates are defined as shown in FIG. The incident ray 1 and the outgoing ray 2 are parallel to the paper surface, the ray direction is the z axis, the direction parallel to the paper surface and perpendicular to the z axis is the x axis, and the direction perpendicular to the paper surface and out of the paper surface is the y axis. In this case, the y-axis corresponds to s-polarized light and the x-axis corresponds to p-polarized light. The ray incident angle θi and the exit angle θo are equal from the definition of reflection. According to the definition of the phase difference, the phase difference between the s-polarized light and the p-polarized light at the interface 3 between the non-film-forming substrate and air is 0° until the incident light beam reaches the Brewster angle, and from the Brewster angle to the critical angle. At 180° and above the critical angle, the value depends on the angle. FIG. 2 shows the incident angle dependence of the phase difference between s-polarized light and p-polarized light at a wavelength of 550 nm when S-LAH66 (made by OHARA INC.) having a refractive index nd=1.7725 is used as a substrate. In Figure 2, the Brewster angle is 29.4° and the critical angle is 34.3°.

(2) As a dielectric single-layer film roof prism, the pentadah prism used in the viewfinder optical system of a single-lens reflex camera is taken as an example to explain in detail the effect of reducing the phase difference between s-polarized light and p-polarized light by the dielectric film. To do. In this case, the light flux diverging from the focusing plate of the single-lens reflex camera is incident on the roof surface of the penta roof prism as a light flux centered at an incident angle of 49°. When S-LAH66 (nd=1.7725, critical angle θ=34.3°) is used as the base material of the penta roof prism, all the regular rays are totally reflected (reflectance 100%), and the phase difference between s-polarized light and p-polarized light Is 120°. A single layer film of MgF ₂ (nd=1.388), SiO ₂ (nd=1.468), Al ₂ O ₃ (nd=1.635), ZrO ₂ (nd=2.038) and TiO ₂ (nd=2.304) is formed on this reflective surface. FIG. 6 shows the phase difference between the s-polarized light and the p-polarized light with respect to the wavelength of the incident angle of 49° when the optical film thickness is 137.5 nm, which is a quarter wavelength film thickness of 550 nm.

From FIG. 6, it can be inferred that the phase difference between the s-polarized light and the p-polarized light can be efficiently approached to 0° by using the film TiO ₂ having a high refractive index. Further, in the film having a low refractive index, both MgF ₂ and SiO ₂ have the same retardation, and it can be presumed that there is no great difference in the effect of bringing the retardation close to 0°, regardless of which material is used. Therefore, in a substrate having a refractive index lower than 1.6, a high refractive index film having a refractive index M1 (2.0<M1<2.1) and a refractive index M2 (1.35<M2<1.4) like the multilayer film described in Patent Document 1. ) Is a low refractive index film and three types of film materials of the refractive index M3 (1.45 <M3 <1.5) intermediate refractive index film is effective to bring the phase difference between s-polarized light and p-polarized light close to 0°, For substrates such as S-LAH66 with a refractive index larger than 1.6, it is presumed that it is not necessary to distinguish between MgF ₂ that corresponds to the low refractive index film and SiO ₂ that corresponds to the intermediate refractive index film. it can.

(3) Dielectric multilayer film design examples 1 and 2
From such study results, the optimized design as the phase difference approaches 0 ° the high refractive s-polarized light by the index visible wavelength 400 to 700 nm with TiO ₂ and MgF ₂ having a low refractive index of the p-polarized light went. As a result, Design Example 1 in which a 4-layer film as shown in Table 1 and Design Example 2 in which a 7-layer film as shown in Table 2 were formed on the S-LAH66 (nd=1.7725) substrate were obtained. FIG. 7 shows the wavelength dependence (wavelength 400 to 700 nm) of the phase difference between the s-polarized light and the p-polarized light at the incident angle of 49°, which was obtained for Design Example 1 and Design Example 2. The incident angle of 49° is based on the assumption of a penta roof prism used in a single-lens reflex camera. From Tables 1 and 2 and FIG. 7, s-polarized light at a wavelength of 400 to 700 nm with fewer kinds of materials (two kinds) and a smaller number of layers (four layers and seven layers) than the multilayer film described in Patent Document 1 It was confirmed that a dielectric multilayer film in which the width of the phase difference between the p-polarized light and the p-polarized light was in the range of 20° (±10°) was obtained.

Next, the incident angle dependency will be considered. According to the theory of interference of optical thin films, when the wavelength is λ, the optical film thickness qf, the incident angle θf inside the film, and the refractive index nf, the phase term of the reflection amplitude of each layer is common to both s-polarized light and p-polarized light. π·qf·cos θf/λ]. The reflection amplitude of each layer can be described by an almost common calculation formula by considering it as a film having a refractive index of [nf·cos θf] for s-polarized light and a refractive index of [nf/cos θf] for p-polarized light. Therefore, if simply considered, the smaller the total number of layers and the smaller total optical film thickness, the smaller the difference in reflectance or phase difference between the s-polarized light and the p-polarized light.

Comparative Example As a comparative example, a 9-layer film shown in Table 3 was formed on a base material of BK7 (equivalent to S-BSL7 manufactured by OHARA CORPORATION nd=1.516). This 9-layer film is equivalent to the conventional dielectric multilayer film described in Example 1 of Patent Document 1.

For Comparative Example, Design Example 1 and Design Example 2, the phase difference between s-polarized light and p-polarized light at incident angles of 44°, 49° and 54° at wavelengths of 400 to 700 nm is shown in FIGS. 8, 9 and 10, respectively. .. From these results, the maximum phase difference between s-polarized light and p-polarized light in the wavelength range of 400 to 700 nm obtained in the dielectric multilayer films of Design Example 1, Design Example 2 and Comparative Example was obtained in the incident angle range of 44 to 54°. Table 4 shows the values, minimum values and their widths. It can be seen from Table 4 that the design examples 1 and 2 have the phase difference in the target range of 90° (0±45°), but the comparative example is largely outside the target range.

Design example 3
Assuming an Amichi prism (Dach surface incidence angle 60°), change the base material to TAFD40 (HOYA Co., Ltd., nd=2.001) and configure a 7-layer dielectric multilayer film as in design example 2 Then, design example 3 of the film constitution shown in Table 5 was obtained. FIG. 11 shows the wavelength dependence (wavelength 400 to 700 nm) of the phase difference between the s-polarized light and the p-polarized light at incident angles of 55°, 60°, and 65°, which was obtained for the seven-layer film of Design Example 3. It can be seen from FIG. 11 that the retardation of the dielectric multilayer film of design example 3 is within the target range of 90° (0±45°).

Design example 4
Assuming a Peshan prism (incident angle of the roof of 48°), the substrate is changed to S-LAL7 (Ohara Co., Ltd., nd=1.678), and a 7-layer dielectric multilayer film is constructed as in Design Example 2. Then, optimization was performed to obtain Design Example 4 of the film configuration shown in Table 6. FIG. 12 shows the wavelength dependence (wavelength 400 to 700 nm) of the phase difference between the s-polarized light and the p-polarized light at incident angles of 43°, 48° and 53°, which was obtained for the seven-layer film of Design Example 4. From FIG. 12, it can be seen that the dielectric multilayer film of Design Example 4 has a phase difference within the target range of 90° (0±45°).

Design examples 5-10
Further, as design examples 5 to 10, on a S-LAH66 (nd=1.7725) substrate, the two-layer structure shown in Table 7, the three-layer structure shown in Table 8, the five-layer structure shown in Table 9, and the six-layer structure shown in Table 10 were used. A dielectric multilayer film having a layer structure, an 8-layer structure shown in Table 11 and a 10-layer structure shown in Table 12 was designed and optimized. The wavelength dependence (wavelength 400 to 700 nm) of the phase difference between the s-polarized light and the p-polarized light at the incident angles of 44°, 49°, and 54°, which were obtained for the dielectric multilayer films of these design examples 5 to 10, were obtained. It is shown in FIGS. From FIGS. 13 to 18, the dielectric multilayer films of Design Examples 5 to 10 show that the phase difference is 90° (0±45°), which is the target, in the incident angle range of 44 to 54° at the wavelength of 400 to 700 nm. You can see that it is in the range.

1... Incident ray 2... Exit ray 3... Interface

Claims (18)

An observation optical apparatus having an observation optical system including at least one lens and a prism having a refractive index of 1.6 or more having a pair of reflecting surfaces intersecting at a nominal surface angle of 90°,
The prism is arranged so that the ridges of the pair of reflecting surfaces divide the pupil of the observation optical system,
Observation optics characterized in that the pair of reflecting surfaces is provided with a dielectric multilayer film in which high refractive index films having a refractive index of 2.15 or more and low refractive index films having a refractive index of 1.3 to 1.7 are alternately laminated. machine. The observation optical apparatus according to claim 1, wherein the high refractive index film includes at least one ultra-high refractive index film having a refractive index of 2.3 to 2.5. In the observation optical apparatus according to claim 1 or 2, wherein the total optical thickness of the dielectric multilayer films Ri from 200 to 950 nm der observation optical device number of layers and wherein the 2-8 Sodea Rukoto .. The observation optical instrument according to any one of claims 1 to 3, wherein a sum of optical film thicknesses of the low refractive index films is 50 to 450 nm. The observation optical device according to any one of claims 1 to 4, wherein the sum of the optical film thicknesses of the high refractive index films is 100 to 600 nm. The observation optical instrument according to claim 1, wherein the high refractive index film is a Ta ₂ O ₅ film, a Nb ₂ O ₅ film, a CeO ₂ film, a TiO ₂ film, and a (TiO ₂ +ZrO ₂ ) mixture. made from any one of the film layer, the low refractive index film is an Al ₂ O ₃ film, SiO ₂ film, from either one of the film of MgF ₂ film and _{(Al 2 O 3 + SiO 2} ) mixed film An observation optical instrument characterized by: In the observation optical device according to any one of claims 1 to 6, the dielectric multilayer film is a two-layer film in which a first layer and a second layer are sequentially stacked from the base material side,
An observation optical apparatus, wherein the first layer is a low refractive index film having an optical film thickness of 65 to 145 nm, and the second layer is a high refractive index film having an optical film thickness of 75 to 160 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is a three-layer film in which first to third layers are sequentially stacked from a base material side,
The first layer is a high refractive index film having an optical film thickness of 5 to 80 nm,
An observation optical apparatus, wherein the second layer is a low refractive index film having an optical film thickness of 70 to 160 nm, and the third layer is a high refractive index film having an optical film thickness of 100 to 190 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is a four-layer film in which first to fourth layers are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 10 to 70 nm,
The second layer is a high refractive index film having an optical film thickness of 25 to 135 nm,
An observation optical instrument, wherein the third layer is a low refractive index film having an optical film thickness of 30 to 200 nm, and the fourth layer is a high refractive index film having an optical film thickness of 100 to 245 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is a five-layer film in which first to fifth layers are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 30 to 100 nm,
The second layer is a low refractive index film having an optical film thickness of 30 to 100 nm,
The third layer is a high refractive index film having an optical thickness of 60 to 140 nm,
An observation optical apparatus, wherein the fourth layer is a low refractive index film having an optical film thickness of 110 to 200 nm, and the fifth layer is a high refractive index film having an optical film thickness of 110 to 200 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is a 6-layer film in which first to sixth layers are sequentially stacked from the base material side,
The first layer is a low refractive index film having an optical film thickness of 20 to 80 nm,
The second layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The third layer is a low refractive index film having an optical thickness of 40 to 120 nm,
The fourth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
An observation optical instrument, wherein the fifth layer is a low refractive index film having an optical film thickness of 70 to 155 nm, and the sixth layer is a high refractive index film having an optical film thickness of 155 to 255 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is a seven-layer film in which first to seventh layers are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
An observation optical apparatus, wherein the sixth layer is a low refractive index film having an optical film thickness of 30 to 210 nm, and the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm. The observation optical device according to any one of claims 1 to 6, wherein the dielectric multilayer film is an 8-layer film in which first to eighth layers are sequentially stacked from the base material side,
The first layer is a high refractive index film having an optical thickness of 20 to 80 nm,
The second layer is a low refractive index film having an optical film thickness of 20 to 125 nm,
The third layer is a high refractive index film having an optical thickness of 80 to 155 nm,
The fourth layer is a low refractive index film having an optical film thickness of 15 to 80 nm,
The fifth layer is a high refractive index film having an optical thickness of 70 to 155 nm,
The sixth layer is a low refractive index film having an optical thickness of 30 to 210 nm,
An observation optical apparatus, wherein the seventh layer is a high refractive index film having an optical film thickness of 70 to 210 nm, and the eighth layer is a low refractive index film having an optical film thickness of 5 to 100 nm. A prism with a refractive index of 1.6 or more having a pair of reflecting surfaces that intersect at a nominal surface angle of 90°,
A prism, wherein a pair of reflecting surfaces is provided with a dielectric multilayer film in which a high refractive index film having a refractive index of 2.15 or more and a low refractive index film having a refractive index of 1.3 to 1.7 are alternately laminated. 15. The prism according to claim 14, wherein the high refractive index film includes at least one ultra-high refractive index film having a refractive index of 2.3 to 2.5. 16. The prism according to claim 14 or 15 is a penta roof prism. 16. The prism according to claim 14 or 15, which is a Peshan prism. 16. The prism according to claim 14 or 15, which is an Amity prism.

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