JP6679963B2 - Optical element having half mirror surface and optical device using the same - Google Patents

Description

  The present invention relates to an optical element having a half mirror surface for separating one optical path into two optical paths or for coupling two optical paths into one optical path, and an optical device using the same.

  The optical viewfinder of a single-lens reflex camera that allows direct observation of an image of a subject formed by a taking lens uses optical elements having half mirror surfaces at various places.

  As an example of an optical element with a half mirror surface used in the optical path of the optical viewfinder of a conventionally known single-lens reflex digital camera, the light flux that has passed through the imaging lens is split by a half mirror in which a dielectric multilayer film is laminated. Then, there is a half mirror called "main mirror" that guides one light flux to an image pickup element which is an image pickup surface and the other light flux to a finder optical system. The dielectric multilayer film has almost flat spectral reflection characteristics (or spectral characteristics) with respect to the components in the visible region (wavelength 380 to 780 nm) of the light beam incident on the half mirror surface at an incident angle of 45 ° from an air medium with a refractive index of 1.000. It is designed to obtain a transmission characteristic).

  Japanese Patent Laid-Open No. 2014-32331 (Patent Document 1) is provided with a 13-layer multilayer film for the purpose of suppressing a change in color tone due to the polarization property of a transmitted light flux of a finder, and includes a first layer, a third layer, and a fifth layer. , The seventh layer, the eleventh layer and the thirteenth layer are low refractive index films having a refractive index of 1.36 to 1.7, and the fourth layer, the sixth layer, the eighth layer, the tenth layer and the twelfth layer have a refractive index of 2 to The high refractive index film has a refractive index of 2.5, the second layer has a refractive index of 1.65 to 2.25, which is smaller than the refractive index of the high refractive index film by 0.2 to 0.6, and the ninth layer has a refractive index of 1.36 to 1.85. It is 0.07 to 0.22 larger than the refractive index of the low refractive index film, the optical thickness of the first layer is 230 to 305 nm, the optical thickness of the second layer is 140 to 245 nm, and the optical film of the third layer is The thickness is 165 to 255 nm, the optical thickness of the fourth layer is 160 to 230 nm, the optical thickness of the fifth layer is 130 to 240 nm, and the optical thickness of the sixth layer is 125 to 220 nm. nm, the optical thickness of the seventh layer is 140 to 255 nm, and the optical thickness of the eighth layer is The optical film thickness is 45 to 160 nm, the optical film thickness of the ninth layer is 80 to 165 nm, the optical film thickness of the tenth layer is 55 to 140 nm, and the optical film thickness of the eleventh layer is 95 nm. Disclosed is a half mirror in which the optical thickness of the 12th layer is 15 to 160 nm and the optical thickness of the 13th layer is 220 to 290 nm.

Further, Japanese Patent Laid-Open No. 2014-119629 (Patent Document 2) discloses a pentaprism having a half mirror surface in which high refractive index layers and low refractive index layers are alternately laminated. Particularly, in Comparative Example 3 of Japanese Patent Laid-Open No. 2014-119629, a half mirror surface made of a multilayer film made of TiO ₂ (refractive index 2.347) and SiO ₂ (refractive index 1.469) is formed on a BK7 (refractive index 1.518) glass substrate with a pentagonal mirror surface. Formed on the reflecting surface of a prism, a light flux with an incident angle of 19.5 ° from the inside of glass (exit angle to the air medium calculated based on Snell's law is about 30.4 °) is almost flat spectral reflection at a wavelength of 400 to 700 nm. A half mirror surface having characteristics is disclosed.

JP 2014-32331 JP JP-A-2014-119629

  However, in the half mirrors and the pentaprisms of these patent documents, the incident angle (or the emission angle) of the light ray from the air medium (or the emission angle to the air medium) is wide, particularly in the range of 20 to 70 °. However, there is a problem that the spectral reflection characteristics change greatly with respect to the ray. In general, single-lens reflex cameras form images with different incident angles at the center and periphery of the subject image in the optical viewfinder field.Therefore, when these half mirrors and pentaprisms are used in single-lens reflex cameras, the subject image in the optical viewfinder field is Color tone is different between the center and the periphery.

  Therefore, an object of the present invention is to provide an optical element having a half mirror surface in which a change in spectral reflection characteristics is small with respect to a wide ray angle in a visible light region.

  Another object of the present invention is to provide an optical device including an optical element having such a half mirror surface.

  As a result of earnest research in view of the above object, the present inventors have found that a high-refractive index film having a refractive index of 2.00 to 2.55 and a refractive index of 2.00 to 2.55 are formed on a half mirror surface of a base material having a refractive index of 1.43 to 2.05 with respect to a d-line having a wavelength of 587.56 nm. A multilayer film of at least 18 layers formed by alternately stacking low refractive index films of 1.35 to 1.7 is formed, and the total optical film thickness of the multilayer film is 2,350 to 2,800 nm, and the average optical film thickness is 135 to 155 nm. By including 1 to 4 thin layers with an optical film thickness of 10 to 70 nm and 2 to 4 thin layers with an optical film thickness of 200 nm or more, it is possible to disperse into a wide light angle in the visible light range. The inventors have found that an optical element having a half mirror surface with a small change in reflection characteristic can be obtained, and conceived the present invention.

That is, an optical element having a half mirror surface of the present invention is formed on a base material having a refractive index of 1.43 to 2.05 for a d-line having a wavelength of 587.56 nm and a half mirror surface of the base material, and has a high refractive index of 2.00 to 2.55. It has a multilayer film of at least 18 layers formed by alternately laminating a refractive index film and a low refractive index film having a refractive index of 1.35 to 1.7, and the total optical film thickness of the multilayer film is 2,350 to 2,800 nm. The average optical film thickness of the film is 135 to 155 nm, the multilayer film includes 1 to 4 thin layers having an optical film thickness of 10 to 70 nm, and 2 to 4 thick layers having an optical film thickness of 200 nm or more. , The angle of incidence from the air medium to the half mirror surface or the angle of exit from the half mirror surface to the air medium is in the range of 20 to 70 °, and is determined based on the spectral reflection characteristics of the light rays having the respective angles of incidence or exit. The maximum difference in CIE chromaticity coordinates is 0.015 or less .

  It is preferable that the thin layer is arranged so as to be biased to either the substrate side or the medium side of the multilayer film. Further, it is preferable that the thin layers are all arranged on the medium side of the multilayer film, and the thick layers are all arranged on the substrate side of the multilayer film.

  In an optical element having a half mirror surface, which is an embodiment of the present invention, the multilayer film is composed of 18 layers, the first layer has an optical film thickness of 30 to 75 nm from the substrate side, and the second layer has an optical film thickness. Is 40 to 145 nm, the optical thickness of the third layer is 55 to 135 nm, the optical thickness of the fourth layer is 25 to 90 nm, the optical thickness of the fifth layer is 85 to 135 nm, and the optical thickness of the sixth layer is Thickness 125-175 nm, optical thickness of 7th layer is 75-125 nm, optical thickness of 8th layer is 100-140 nm, optical thickness of 9th layer is 95-145 nm, 10th layer Optical thickness of 130 to 215 nm, the 11th layer has an optical thickness of 70 to 165 nm, the 12th layer has an optical thickness of 140 to 205 nm, and the 13th layer has an optical thickness of 155 to 185 nm. The 14th layer has an optical thickness of 175 to 220 nm, the 15th layer has an optical thickness of 160 to 190 nm, the 16th layer has an optical thickness of 175 to 220 nm, and the 17th layer has an optical thickness of 175 to 195 nm. , The optical thickness of the 18th layer is 75 to 120 nm.

  In an optical element having a half mirror surface which is another embodiment of the present invention, the multilayer film comprises 18 layers, the first layer has an optical film thickness of 170 to 290 nm from the substrate side, and the second layer has an optical film. The thickness is 110 to 250 nm, the optical thickness of the third layer is 100 to 270 nm, the optical thickness of the fourth layer is 110 to 240 nm, the optical thickness of the fifth layer is 130 to 310 nm, and the optical thickness of the sixth layer is Optical thickness of 70-250 nm, optical thickness of 7th layer is 120-240 nm, optical thickness of 8th layer is 70-210 nm, optical thickness of 9th layer is 80-240 nm, 10th The optical thickness of the layer is 10 to 190 nm, the optical thickness of the 11th layer is 60 to 250 nm, the optical thickness of the 12th layer is 10 to 180 nm, the optical thickness of the 13th layer is 80 to 230 nm, The optical thickness of the 14th layer is 10 to 170 nm, the optical thickness of the 15th layer is 10 to 160 nm, the optical thickness of the 16th layer is 10 to 160 nm, and the optical thickness of the 17th layer is 40 to 230 nm. nm, the optical thickness of the 18th layer is 10 to 120 nm.

  In an optical element having a half mirror surface which is still another embodiment of the present invention, the multilayer film is composed of 19 layers, the optical film thickness of the first layer is 150 to 270 nm from the base material side, and the optical film of the second layer is optical. The film thickness is 170 to 290 nm, the optical thickness of the third layer is 110 to 250 nm, the optical thickness of the fourth layer is 100 to 270 nm, the optical thickness of the fifth layer is 110 to 240 nm, and the sixth layer. Has an optical film thickness of 130 to 310 nm, the seventh layer has an optical film thickness of 70 to 250 nm, the eighth layer has an optical film thickness of 120 to 240 nm, and the ninth layer has an optical film thickness of 70 to 210 nm. Optical thickness of 10 layers is 80-240 nm, optical thickness of 11th layer is 10-190 nm, optical thickness of 12th layer is 60-250 nm, optical thickness of 13th layer is 10-180 nm , The optical thickness of the 14th layer is 80 to 230 nm, the optical thickness of the 15th layer is 10 to 170 nm, the optical thickness of the 16th layer is 10 to 160 nm, the optical thickness of the 17th layer is 10 to The optical thickness of 160 nm, the 18th layer is 40 to 230 nm, and the optical thickness of the 19th layer is 10 to 120 nm.

The high refractive index film is selected from the group consisting of ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CeO ₂ , TiO ₂ , a mixed film of TiO ₂ and ZrO _{2 and} a mixed film of TiO ₂ and Nb ₂ O _5. It is preferable that the low refractive index film is made of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , MgF ₂ and a mixed film of Al ₂ O ₃ and SiO ₂ . Is preferred.

  The optical device of the present invention is characterized by using an optical element having such a half mirror surface.

  According to the present invention, a high-refractive index film having a refractive index of 2.00 to 2.55 and a low refractive index film having a refractive index of 1.35 to 1.7 are formed on a half mirror surface of a substrate having a refractive index of 1.43 to 2.05 with respect to a d-line having a wavelength of 587.56 nm. Forming a multilayer film of at least 18 layers alternately laminated, the total optical film thickness of the multilayer film is 2,350 ~ 2,800 nm, the average optical film thickness is 135 ~ 155 nm, the optical film thickness 10 ~ 70 Since it includes 1 to 4 thin layers with a thickness of 200 nm and 2 to 4 thick layers with an optical thickness of 200 nm or more, a half mirror surface with a small change in spectral reflection characteristics with respect to a wide ray angle in the visible light range is provided. An optical element having the same can be provided.

FIG. 3 is a cross-sectional view showing a half mirror according to an embodiment of the present invention. FIG. 3 is a cross-sectional view showing a penta prism according to an embodiment of the present invention. 1 is a schematic diagram showing a single-lens reflex digital camera according to an embodiment of the present invention. 4 is a table showing basic data of the half mirror of Example 1. 3 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 1. FIG. 6 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 5. 9 is a table showing basic data of the half mirror of Example 2. 9 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 2. FIG. 9 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 8. 9 is a table showing basic data of the half mirror of Example 3. 9 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 3. FIG. 12 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 9 is a table showing basic data of the half mirror of Example 4. 9 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 4. FIG. 15 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle in FIG. 13 is a table showing basic data of the half mirror of Example 5. 13 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 5. FIG. 18 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 13 is a table showing basic data of the half mirror of Example 6. 17 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 6. FIG. 21 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle in FIG. 16 is a table showing basic data of the half mirror of Example 7. 9 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Example 7. FIG. 24 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 9 is a table showing basic data of a half mirror of Comparative Example 1. 7 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Comparative Example 1. 27 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristic at each incident angle in FIG. 26. FIG. 9 is a table showing basic data of a half mirror of Comparative Example 2. 9 is a graph showing the spectral reflection characteristics (Rm) of light incident at 20 °, 30 °, 45 °, and 70 ° on the half mirror of Comparative Example 2. 30 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle in FIG. 16 is a graph showing the spectral transmission characteristics (Tm) when the light incident on the half mirror at 30 °, 45 °, and 60 ° in the optical device of Example 8 passes through the finder. FIG. 32 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral transmission characteristics at each incident angle in FIG. 6 is a graph showing spectral reflection characteristics (Rm) of light incident at 34 °, 49 °, and 64 ° on a roof-side reflecting surface (silver rear surface mirror) of a pentaprism. FIG. 34 A CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle in FIG. 13 is a graph showing a spectral transmission characteristic (Tm) when the light incident on the half mirror at 30 °, 45 °, and 60 ° in the optical device of Comparative Example 3 passes through the finder. FIG. 32 is a CIE chromaticity diagram showing CIE chromaticity coordinates calculated based on the spectral transmission characteristics at each incident angle in FIG.

  The optical element of the present invention having a half mirror surface that reflects a part of incident visible light and transmits a part of the visible light is a base material having a refractive index of 1.43 to 2.05 with respect to a d-line having a wavelength of 587.56 nm, and the base material. Formed on the half mirror surface, having a multilayer film of at least 18 layers formed by alternately stacking a high refractive index film having a refractive index of 2.00 to 2.55 and a low refractive index film having a refractive index of 1.35 to 1.7. The total optical film thickness is 2,350 to 2,800 nm, the average optical film thickness of the multilayer film is 135 to 155 nm, and the multilayer film includes 1 to 4 thin layers having an optical film thickness of 10 to 70 nm. It has a structure including 2 to 4 thick layers having a thickness of 200 nm or more. The features of the present invention described above will be described in detail below with reference to the drawings.

  The optical element having a half mirror surface of the present invention is an optical element having a half mirror surface that separates one optical path into two optical paths, or combines two optical paths into one optical path, Examples include a half mirror, a prism having a half mirror surface, and a beam splitter.

[1] Half Mirror FIG. 1 shows a half mirror according to an embodiment of the present invention. The half mirror 10 shown in FIG. 1 has a base material 11 and a multilayer film 4 provided on the half mirror surface 11 a of the base material 11.

  The refractive index nd of the substrate 11 with respect to light having a wavelength of 587.56 nm is 1.43 to 2.05. The material of the base material 11 is not particularly limited, and examples thereof include glass, plastic, and ceramics. Specifically, S-BSL7 (Ohara Corporation, refractive index nd = 1.516), soda lime glass (refractive index nd = 1.512), white plate glass (refractive index nd = 1.523), D263 (Shot Nippon KK, refraction) The index nd = 1.524), synthetic quartz (refractive index nd = 1.459) and the like are preferably used.

  In order to prevent light from being reflected by the emission surface that is the surface opposite to the half mirror surface 11a of the base material 11, an antireflection film is provided on the surface opposite to the half mirror surface 11a of the base material 11. Antireflection treatment may be applied.

  The multilayer film 4 comprises a high-refractive index film having a refractive index nd of 2.00 to 2.55 and a low refractive index film having a refractive index nd of 1.35 to 1.7 on the half-mirror surface 11a of the substrate 11 at least 18. The layers are alternately laminated. The layer in contact with the half mirror surface 11a and the outermost layer on the medium side may be a high refractive index film or a low refractive index film. Further, the refractive index nd of the high refractive index film is preferably 2.03 to 2.46, and the refractive index nd of the low refractive index film is preferably 1.38 to 1.66.

  The total optical film thickness of the multilayer film 4 is 2,350 to 2,800 nm, and the average optical film thickness is 135 to 155 nm. Here, a layer having an optical film thickness of less than 10 nm does not particularly affect the optical characteristics of the multilayer film 4, and may be ignored. That is, the “total optical film thickness” means the sum of the optical film thicknesses of the layers having an optical film thickness of 10 nm or more among the layers constituting the multilayer film 4, and the “average optical film thickness” constitutes the multilayer film 4. It means the average value of the optical film thickness of a layer having an optical film thickness of 10 nm or more among the layers. When the total optical film thickness of the multilayer film 4 is 2,350 to 2,800 nm and the average optical film thickness is 135 to 155 nm, it has excellent characteristics as a half mirror, while suppressing the manufacturing cost and in the visible light range. It is possible to realize flattening of the spectral reflection characteristic for a wide ray angle.

  The multilayer film 4 includes 1 to 4 thin layers having an optical film thickness of 10 to 70 nm and 2 to 4 thin layers having an optical film thickness of 200 nm or more. By providing such a thin layer and a thick layer in the multilayer film having the above optical film thickness, a wide light ray angle, particularly an incident angle from an air medium, can be obtained in a visible light region (especially in a wavelength range of 350 to 800 nm). Changes in the spectral reflection characteristics can be reduced for light rays in the range of 20 to 70 °. The thick layer having an optical film thickness of 200 nm or more preferably has an optical film thickness in the range of 200 to 310 nm, more preferably 200 to 250 nm.

  CIE chromaticity coordinates representing the color of the reflected light of each incident angle can be obtained from the spectral reflection characteristics obtained when a randomly polarized light beam of each incident angle is incident. In the CIE chromaticity coordinates, the coordinates of perfect white are x = 0.333 and y = 0.333, and the color is recognized as the distance from this coordinate increases. When the distance between the CIE chromaticity coordinates of the reflected light of each incident angle is large, the chromaticity is different because the spectral reflection characteristics change greatly depending on the incident angle of light. Therefore, especially in a single-lens reflex camera, there occurs a problem that the color tone changes between the center and the periphery of the subject image in the optical viewfinder field. Therefore, the optical element having a half mirror surface of the present invention, in the visible light region, a wide ray angle, particularly even in the case of a large ray with an incident angle from the air medium of 20 to 70 °, the CIE chromaticity for each ray. It is desirable that the difference between the coordinates is small, that is, the change in the spectral reflection characteristic due to the ray angle is small.

In the half mirror 10, the range of incidence angles of 20 to 70 ° from the air medium to the multilayer film 4, the maximum difference in CIE chromaticity coordinates for rays having respective incident angles is 0.015 or less. The “maximum difference in CIE chromaticity coordinates” means the maximum distance among the CIE chromaticity coordinates calculated based on the spectral reflection characteristics of randomly polarized light rays having respective incident angles. When the maximum difference of CIE chromaticity coordinates is within this range, the color difference due to the incident angle of light is small, and it is possible to solve the problem that the color tone changes especially in the center and the periphery of the subject image in the optical viewfinder field in a single-lens reflex digital camera. The maximum difference in CIE chromaticity coordinates is preferably 0.001 to 0.010.

  It is preferable that the thin layer having an optical film thickness of 10 to 70 nm is arranged so as to be biased to either the substrate side or the medium side of the multilayer film 4. In particular, all thin layers having an optical film thickness of 10 to 70 nm are arranged on the medium side of the multilayer film 4, and all thin layers having an optical film thickness of 200 nm or more are arranged on the base material side of the multilayer film 4. Is preferred. By arranging the thin layer and the thick layer so as to be biased toward the base material side and the medium side in this way, it is possible to further enhance the flatness of the spectral reflection characteristic for a wide ray angle in the visible light region. Here, the "base material side" and the "medium side" are, for example, when the multilayer film 4 is composed of 18 layers, the first to ninth layers are the base material side layers from the base material side, and the base material side It means that the 10th to 18th layers are layers on the medium side. When the multilayer film 4 is composed of 19 layers, the first to ninth layers from the base material side are layers on the base material side, and the eleventh to nineteenth layers from the base material side are layers on the medium side, The tenth layer from the base material side is not included in either. The same applies even if the number of layers is increased.

The high refractive index film is selected from the group consisting of ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CeO ₂ , TiO ₂ , a mixed film of TiO ₂ and ZrO _{2 and} a mixed film of TiO ₂ and Nb ₂ O _5. It is preferable that the low refractive index film is made of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , MgF ₂ and a mixed film of Al ₂ O ₃ and SiO ₂ . Is preferred. However, the materials for the high refractive index film and the low refractive index film are not limited to those described above, and can be appropriately selected as long as the characteristics of the optical element having the half mirror surface of the present invention can be obtained.

  The half mirror 10 is preferably a 45 ° incidence half mirror that splits a light beam having an incident angle of 45 °. When the designed incident angle is 45 °, even if the actual incident light is incident in a wide range (especially 20 to 70 °) centered around the designed incident angle of 45 °, it is possible to suppress the change in the spectral reflection characteristic to be small. Since the half mirror 10 of the present invention has a small change in spectral reflection characteristics with respect to a wide incident angle, when the half mirror 10 is used in a single-lens reflex digital camera, the difference in color tone between the center and the periphery of the subject image in the optical viewfinder field. Can be kept small. Therefore, the half mirror 10 of the present invention can be suitably used particularly as a main mirror of a single-lens reflex digital camera.

  An example of a preferable layer structure of the multilayer film 4 is an 18-layer film, and the optical film thickness of the first layer is 30 to 75 nm, the optical film thickness of the second layer is 40 to 145 nm, and the optical film thickness of the third layer is from the base material side. Optical thickness 55-135 nm, 4th layer optical thickness 25-90 nm, 5th layer optical thickness 85-135 nm, 6th layer optical thickness 125-175 nm, 7th layer The optical thickness of the layer is 75 to 125 nm, the optical thickness of the eighth layer is 100 to 140 nm, the optical thickness of the ninth layer is 95 to 145 nm, the optical thickness of the tenth layer is 130 to 215 nm, The optical thickness of the 11th layer is 70 to 165 nm, the optical thickness of the 12th layer is 140 to 205 nm, the optical thickness of the 13th layer is 155 to 185 nm, the optical thickness of the 14th layer is 175 to 220 nm. , the optical thickness of the 15th layer is 160 to 190 nm, the optical thickness of the 16th layer is 175 to 220 nm, the optical thickness of the 17th layer is 175 to 195 nm, and the optical thickness of the 18th layer is 75 nm. ~ 120 nm.

  Another example of a preferable layer structure of the multilayer film 4 is an 18-layer film, and the optical film thickness of the first layer is 170 to 290 nm, the optical film thickness of the second layer is 110 to 250 nm, and the third film is formed from the base material side. The optical thickness of the layer is 100 to 270 nm, the optical thickness of the fourth layer is 110 to 240 nm, the optical thickness of the fifth layer is 130 to 310 nm, the optical thickness of the sixth layer is 70 to 250 nm, The optical thickness of the seventh layer is 120 to 240 nm, the optical thickness of the eighth layer is 70 to 210 nm, the optical thickness of the ninth layer is 80 to 240 nm, and the optical thickness of the tenth layer is 10 to 190. nm, the optical thickness of the 11th layer is 60 to 250 nm, the optical thickness of the 12th layer is 10 to 180 nm, the optical thickness of the 13th layer is 80 to 230 nm, and the optical thickness of the 14th layer is 10 nm. ~ 170 nm, optical thickness of 15th layer is 10-160 nm, optical thickness of 16th layer is 10-160 nm, optical thickness of 17th layer is 40-230 nm, optical thickness of 18th layer Is 10 to 120 nm.

  Yet another example of the preferable layer structure of the multilayer film 4 is a 19-layer film, and the optical film thickness of the first layer is 150 to 270 nm, the optical film thickness of the second layer is 170 to 290 nm, The optical thickness of 3 layers is 110-250 nm, the optical thickness of 4th layer is 100-270 nm, the optical thickness of 5th layer is 110-240 nm, the optical thickness of 6th layer is 130-310 nm. , The optical thickness of the seventh layer is 70 to 250 nm, the optical thickness of the eighth layer is 120 to 240 nm, the optical thickness of the ninth layer is 70 to 210 nm, the optical thickness of the tenth layer is 80 to 240 nm, 11th layer optical thickness 10-190 nm, 12th layer optical thickness 60-250 nm, 13th layer optical thickness 10-180 nm, 14th layer optical thickness 80-230 nm, 15th layer optical thickness 10-170 nm, 16th layer optical thickness 10-160 nm, 17th layer optical thickness 10-160 nm, 18th layer optical film The thickness is 40 to 230 nm, and the optical thickness of the 19th layer is 10 to 120 nm.

  The high refractive index film and the low refractive index film are preferably formed by a physical film forming method. Examples of the physical film forming method include a vacuum vapor deposition method and a sputtering method. Above all, a vacuum deposition method such as a resistance heating method or an electron beam method is preferable in terms of manufacturing cost and processing accuracy.

[2] Penta Prism A penta prism according to another embodiment of the present invention is shown in FIG. The pentaprism 20 shown in FIG. 2 includes a base material 22 having an entrance surface 22a, a roof surface 22b, and a third reflection surface (half mirror surface) 22c, and a multilayer film 6 provided on the third reflection surface 22c of the base material 22. Have and. The pentaprism 20 has a plurality of reflecting surfaces, and reflects the light beam incident from the incident surface 22a on the roof surface 22b and then on the third reflecting surface 22c. The roof surface 22b has a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and the incident light is reflected twice by the roof surface 22b.

  By making the third reflecting surface 22c a half mirror surface, LED light or the like having information such as distance-measuring information is made to enter the penta prism 20 from the third reflecting surface 22c as described later, and at the third reflecting surface 22c. You can superimpose with the reflected rays.

  In the pentaprism 20 according to the present embodiment, as shown in FIG. 2, a light ray is incident on the third reflection surface 22c from the base material 22 side, a part of the incident light ray is reflected, and a part thereof is emitted to the air medium. . That is, it differs from the above-mentioned half mirror 10 in which a light ray is incident from the air medium, in that the light ray is emitted to the air medium (the traveling direction of the light ray is opposite). The optical element having the half mirror surface of the present invention has the same effect whether the light ray is incident from the air medium to the multilayer film or the light ray is emitted from the multilayer film to the air medium. Therefore, the pentaprism 20 according to the present embodiment can also exhibit the same spectral reflection characteristic as that of the half mirror 10. Therefore, the material of the base material 22, the material of the multilayer film 6, and the layer structure may be the same as those of the half mirror 10.

  In the third reflection surface 22c of the pentaprism 20, when the light beam has a designed incident angle such that the emission angle to the air medium is around 45 °, the present invention is such that the change of the spectral reflection characteristic is small for a wide light beam angle. The excellent effect of is obtained. Here, the "designed incident angle" is an ideal incident angle at the third reflection surface 22c when a light ray is vertically incident on the incident surface 22a of the pentaprism 20, and is the shape of the base material 22 of the pentaprism 20. Determined by refractive index. For example, when a light ray having an incident angle of 25 ° is incident on the third reflecting surface 22c from the base material 22 having a refractive index of 1.516, Snell's law [(refractive index of incident medium) × SIN (incident angle) = (refraction of outgoing medium Ratio) × SIN (emission angle)], the emission angle to the air medium is 39.9 °. Further, when a light ray having an incident angle of 25 ° is incident on the third reflecting surface 22c from the base material 22 having a refractive index of 1.7725, the emission angle to the air medium is 48.6 ° according to Snell's law. By such a combination of the refractive index of the base material 22 and the design incident angle of the light beam, when the emission angle of the light beam to the air medium is around 45 °, a wide range around the emission angle of 45 ° (especially 20 to 70 °). It is possible to suppress the change in the spectral reflection characteristic to be small even for the light beam emitted in (1). The designed incident angle of the light ray on the third reflection surface 22c of the pentaprism 20 is preferably a value such that the exit angle of the light ray to the air medium is about 25 to 65 °.

[3] Optical Device An optical device of the present invention is characterized by including an optical element having the half mirror surface. Examples of such optical devices include image pickup devices such as single-lens reflex digital cameras, projectors, measuring devices, digital movie cameras, surveying instruments, binoculars, and telescopes.

  FIG. 3 shows a single-lens reflex digital camera according to an embodiment of the present invention. The single-lens reflex digital camera 1 shown in FIG. 3 includes a camera body 2 and an interchangeable lens 3 that is attachable to and detachable from the camera body 2. The light flux from the subject enters the camera body 2 through the taking lens 31 in the interchangeable lens 3 and is incident on the pentaprism 20 by the main mirror (half mirror) 10 in which the multilayer film 4 is formed on the half mirror surface. The part is reflected. Therefore, a part of the light flux passes through the main mirror 10, is reflected downward by the sub-mirror 12 provided on the back surface of the main mirror 10, and is incident on the automatic focus detection module 13.

  The automatic focus detection module 13 detects the focus state of the subject and outputs a signal according to the detection result to the body CPU 14. The body CPU 14 performs defocus calculation based on the signal input from the automatic focus detection module 13, and adjusts the focus of the taking lens 31 based on the defocus amount obtained by the calculation. Note that, in the drawing, electrical connection of each block is omitted for convenience of simplifying the drawing.

  When a release switch (not shown) is pressed, the body CPU 14 raises the main mirror 10 only between the front curtain running start and the rear curtain running end of the focal plane shutter (not shown) to raise the main mirror 10. The main mirror 10 is retracted from the optical path parallel to the optical axis AX 31. The sub-mirror 12 is configured to mechanically interlock with the main mirror 10, and retracts from the optical path when the main mirror 10 is moved up. Therefore, the subject light flux is imaged on the imaging surface of the image sensor 15 after passing through the taking lens 31. The image sensor 15 is, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and accumulates the optical image combined at each pixel on the imaging surface as a charge according to the amount of light to obtain an imaging signal. Convert to. The converted image pickup signal is processed so that it can be displayed on a monitor by an image processing circuit (not shown). The photographer can visually recognize the photographed image through an LCD (Liquid Crystal Display) monitor (not shown) provided on the back surface of the camera body 2.

  While the main mirror 10 is not retracted from the optical path, the subject light flux reflected by the main mirror 10 is incident on the pentaprism 20 via the diffusion plate 21 as described above. The diffusion plate 21 is arranged at a position optically equivalent to the image pickup surface of the image sensor 15, and the subject light flux that has passed through the photographing lens 31 forms an image.

  The pentaprism 20 has a plurality of reflecting surfaces and forms an erect image by reflecting the object image formed on the diffusing plate 21 and incident on each reflecting surface. More specifically, the pentaprism 20 inverts the light by sequentially reflecting it on the entrance surface 22a, the roof surface 22b, and the third reflection surface 22c, and emits it as an erect image toward the eyepiece lens 23. The eyepiece lens 23 re-images the subject image, which is formed on the diffusion plate 21 and is erected by the pentaprism 20, into a virtual image suitable for observation by a photographer. The photographer can observe the subject image (virtual image) re-formed by the eyepiece lens 23 by looking through the finder window 24.

  The superimposing unit 25 includes a light emitting unit 25a, a mirror 25b, a condenser lens 25c, and a prism 25d. The light emitting unit 25a includes a plurality of LEDs as light emitting elements. Further, the light emitting unit 25a is provided with a mask member corresponding to the superimpose display in front of the LED. The light emission of each LED is controlled by the body CPU 14, and superimpose light corresponding to various superimpose displays is emitted from the light emitting unit 25a. The superimposed information is mainly information for assisting shooting, and examples thereof include information indicating a focus detection point, a focusing state, and a focusing position. Superimposed light emitted from the light emitting unit 25a is reflected by the mirror 25b, condensed by the condenser lens 25c, and incident on the prism 25d.

  A metal film 7 made of silver, aluminum, or the like is formed on the roof surface 22b of the pentaprism 20 to form an internal reflection mirror. Since the light flux that has entered the inner reflection mirror of the roof surface 22b is rapidly attenuated, the influence of the incident angle of the light flux on the reflection characteristics is very small. The multilayer film 6 is formed on the third reflecting surface 22c of the pentaprism 20 and constitutes a half mirror surface.

  The superposed light passes through the third reflecting surface 22c and enters the pentagonal prism 20. The superimposing light incident on the pentaprism 20 advances toward the eyepiece inside the pentaprism 20 in a state of being superposed on the erect image reflected by the third reflecting surface 22c and guided to the eyepiece 23. The viewfinder window 24 is reached via the eyepiece lens 23. Thereby, the photographer can observe the subject image in which the distance measuring points and the like are superimposed through the finder window 24.

  The subject light flux entering the main mirror 10 and the pentaprism 20 of the single-lens reflex digital camera 1 has an incident angle range of about 30 to 60 ° from the air medium to the half mirror surface 11a of the main mirror 10, and the pentaprism. The range of the incident angle from the base material 22 side to the third reflection surface 22c of 20 is about 19 to 35 °. When S-BSL7 (Ohara Co., Ltd., refractive index 1.516) is used as the base material 22 of the pentaprism 20, the incident angle of 19 to 35 ° with respect to the pentaprism base material is about 30 to 50 ° according to Snell's law. This corresponds to the case of incidence from an air medium at an incidence angle of. When S-LAH66 (Ohara Co., Ltd., refractive index 1.7725) is used as the base material 22 of the pentaprism 20, the incident angle of 19 to 35 ° with respect to the pentaprism base material is about 35 to 58.5 according to Snell's law. It corresponds to the case of incident from an air medium at an incident angle of °. Therefore, in order to prevent the color tone change between the center and the periphery of the subject image, the incident angle from the air medium (or the emission angle to the air medium) is 30 with respect to the half mirror surfaces of the main mirror 10 and the pentaprism 20. It is desirable that the change in the spectral reflection characteristics for light rays in the range of -60 ° is small. In particular, if the change in the spectral reflection characteristic with respect to a light ray in the range of 20 to 70 ° is small, an excellent effect of preventing a change in color tone can be obtained.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1
The half-mirror surface 11a of the substrate 11 made of S-BSL7 (refractive index nd = 1.516, manufactured by OHARA INC.) Was formed with a multilayer film 4 having an 18-layer structure shown in FIG. The half mirror 10 which aimed at was created. Three thin layers with an optical thickness of 10 to 70 nm are arranged on the substrate side from the center (boundary between the ninth and tenth layers), and a thick layer with an optical thickness of 200 to 250 nm is located on the medium side from the center. The layers are arranged.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristics (Rm) in this case were measured using a Hitachi spectrophotometer U-4000 type. The obtained measurement result is shown in FIG. FIG. 6 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 1 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Example 2
The half-mirror surface 11a of the substrate 11 made of TAFD40 (refractive index nd = 2.001, manufactured by HOYA Co., Ltd.) is formed with a multilayer film 4 having an 18-layer structure shown in FIG. 7 by a sputtering method, and a reflectance of 80% is targeted. I made a half mirror 10. One thin layer having an optical film thickness of 10 to 70 nm is arranged on the substrate side from the center, and two thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement result is shown in FIG. FIG. 9 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 2 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Example 3
A multilayer film 4 having an 18-layer structure shown in FIG. 10 is formed on a half mirror surface 11a of a substrate 11 made of S-FPL53 (refractive index nd = 1.439, manufactured by OHARA CORPORATION) by a vacuum deposition method, and the reflectance is 70%. The half mirror 10 which aimed at was created. Three thin layers having an optical film thickness of 10 to 70 nm are arranged on the substrate side from the center, and two thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement results are shown in FIG. FIG. 12 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 3 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Example 4
A half-mirror surface 11a of a base material 11 made of S-BSL7 (refractive index nd = 1.516, manufactured by OHARA CORPORATION) is formed by a sputtering method with a multilayer film 4 having an 18-layer structure shown in FIG. The target half mirror 10 was created. Two thin layers having an optical film thickness of 10 to 70 nm are arranged on the substrate side from the center, and four thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement results are shown in FIG. FIG. 15 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 4 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Example 5
On the half mirror surface 11a of the substrate 11 made of TAFD40 (refractive index nd = 2.001, manufactured by HOYA Co., Ltd.), a multilayer film 4 having an 18-layer structure shown in FIG. 16 is formed by a sputtering method, and a reflectance of 85% is targeted. I made a half mirror 10. Three thin layers having an optical film thickness of 10 to 70 nm are arranged on the substrate side from the center, and two thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement results are shown in FIG. FIG. 18 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 5 shows the CIE chromaticity coordinates (x coordinate and y coordinate) and the average value (average Rm) of the spectral reflection characteristics (Rm) at each incident angle.

Example 6
A multilayer film 4 having an 18-layer structure shown in FIG. 19 is formed on a half mirror surface 11a of a base material 11 made of S-LAH66 (refractive index nd = 1.7725, manufactured by OHARA CORPORATION) by a vacuum deposition method, and a reflectance of 85%. The half mirror 10 which aimed at was created. Two thin layers having an optical film thickness of 10 to 70 nm are arranged on the substrate side from the center, and two thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement result is shown in FIG. FIG. 21 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 6 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Example 7
The half-mirror surface 11a of the base material 11 made of S-BSL7 (refractive index nd = 1.516, manufactured by OHARA CORPORATION) is formed by a vacuum deposition method with a multilayer film 4 having a 19-layer structure shown in FIG. 22 and a reflectance of 80%. The half mirror 10 which aimed at was created. Three thin layers having an optical film thickness of 10 to 70 nm are arranged on the substrate side from the center (10th layer), and three thick layers having an optical film thickness of 200 to 250 nm are arranged on the medium side from the center.

  Randomly polarized light rays in the wavelength range of 350 to 800 nm are incident on the half mirror surface 11a of the half mirror 10 on which the multilayer film 4 is formed at an incident angle of 20 °, 30 °, 45 ° and 70 ° from the air medium. The spectral reflection characteristic (Rm) in the case of performing was measured in the same manner as in Example 1. The obtained measurement result is shown in FIG. FIG. 24 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 7 shows the CIE chromaticity coordinates (x coordinate and y coordinate) and the average value (average Rm) of the spectral reflection characteristics (Rm) at each incident angle.

Comparative Example 1
A multilayer film having a 13-layer structure similar to that of Example 1 of JP-A-2014-32331 shown in FIG. 25 is formed on the incident surface of a substrate made of S-BSL7 (refractive index nd = 1.516, manufactured by OHARA CORPORATION) by a vacuum deposition method. To form a half mirror.

  The spectrum of randomly polarized rays with wavelengths in the 350 to 800 nm range from the air medium at the incident angles of 20 °, 30 °, 45 °, and 70 ° is incident on the incident surface on which the multilayer film of this half mirror is formed. The reflection characteristic (Rm) was measured as in Example 1. The obtained measurement result is shown in FIG. FIG. 27 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 8 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

Comparative Example 2
A multilayer film having a 20-layer structure similar to that of Comparative Example 3 of JP-A-2014-119629 shown in FIG. 28 is formed on the incident surface of a substrate made of S-BSL7 (refractive index nd = 1.516, manufactured by OHARA CORPORATION) by a vacuum deposition method. To form a half mirror. The S-BSL7 corresponds to BK7 manufactured by Shot Japan Co., Ltd.

  The spectrum of randomly polarized rays with wavelengths in the 350 to 800 nm range from the air medium at the incident angles of 20 °, 30 °, 45 °, and 70 ° is incident on the incident surface on which the multilayer film of this half mirror is formed. The reflection characteristic (Rm) was measured as in Example 1. The obtained measurement result is shown in FIG. FIG. 30 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. Table 9 shows the average value (average Rm) of the CIE chromaticity coordinates (x coordinate and y coordinate) and the spectral reflection characteristic (Rm) at each incident angle.

  For Examples 1 to 7 and Comparative Examples 1 and 2, the maximum value of the distance between the CIE chromaticity coordinates of each incident angle (the maximum difference in the CIE chromaticity coordinates) and the maximum difference between the averages Rm of the respective incident angles (the average). The maximum difference in Rm) is shown in Table 10.

  As can be seen from Table 10 and FIGS. 4 to 30, the half mirrors of Examples 1 to 7 of the present invention have a visible range at an incident angle of 20 to 70 ° as compared with the half mirrors of Comparative Examples 1 and 2 which are conventional examples. The change in spectral reflection characteristics was small, and the maximum difference in CIE chromaticity coordinates was also small. In the half mirror of Comparative Example 1, the number of layers is as small as 13 layers, and the number of layers having an optical film thickness of 200 nm or more is as large as 6 layers. Therefore, the maximum difference in the average value (average Rm) of the spectral reflection characteristics (Rm) is 5.0%. However, the maximum difference in CIE chromaticity coordinates was 0.0463, which was very large, and the change in spectral reflection characteristics was large for different ray angles. The half mirror of Comparative Example 2 has a small average optical film thickness of 133.1 mm and only one layer having an optical film thickness of 200 nm or more, which is one layer. Therefore, the maximum difference in CIE chromaticity coordinates and the average spectral reflection characteristic (Rm) are obtained. The maximum difference in the values (mean Rm) was large in all cases. The half mirrors of Examples 1 to 7 have a smaller maximum difference in CIE chromaticity coordinates than the half mirrors of Comparative Examples 1 and 2, and also have a sufficient maximum difference in the average value (average Rm) of the spectral reflection characteristics (Rm). Since it is suppressed, it can be suitably used especially for a single-lens reflex digital camera.

Example 8
In the single-lens reflex digital camera 1 shown in FIG. 3, the multilayer film 4 of Example 7 is formed on the half mirror surface 11a of the main mirror 10, the silver mirror is formed on the roof surface 22b of the pentaprism 20, and the third reflecting surface 22c is formed. Then, the multilayer film 5 of Example 1 was formed. When a randomly polarized light beam with a wavelength range of 350 to 800 nm is incident on the main mirror 10 at incident angles of 30 °, 45 °, and 60 °, it is reflected by the main mirror 10 and then passes through the pentaprism 20. 23, the spectral transmission characteristics (Tm) of light transmitted through the finder window 24 were obtained by simulation. At this time, the transmittances of the diffuser plate 21, the pentaprism 20, the eyepiece lens 23, and the finder window 24 have a small effect on the color tone, and are ignored. The obtained results are shown in FIG. FIG. 32 shows a CIE chromaticity diagram in which CIE chromaticity coordinates calculated based on the spectral transmission characteristic (Tm) at each incident angle and white CIE chromaticity coordinates are plotted. When light rays are incident on the main mirror 10 at incident angles of 30 °, 45 °, and 60 °, the emission angle of the light rays emitted from the third reflecting surface 22c of the pentaprism 20 to the air medium is defined by the light rays perpendicular to the incident surface 22a. When the incident angle and the outgoing angle when considering only the angle change in the ridge direction of the roof surface 22b when incident on 20 ° and the incident angle and the outgoing angle at the third reflecting surface 22c were calculated as 25 °, respectively, It was about 25 °, about 40 ° and about 55 °.

  Further, when light rays are incident on the main mirror 10 at incident angles of 30 °, 45 ° and 60 °, the incident angle and the outgoing angle at each reflecting surface of the roof surface 22b of the pentaprism 20 are about 34 ° and about 49 °, respectively. And about 64 °. Spectral reflection characteristics of randomly polarized light rays with wavelengths of 350 to 800 nm incident on the reflecting surface (silver backside mirror) of the roof surface 22b at the incident angles of 34 °, 49 ° and 64 ° from the substrate side were obtained by simulation. It was The obtained results are shown in FIG. FIG. 34 shows a CIE chromaticity diagram in which the CIE chromaticity coordinates calculated based on the spectral reflection characteristics at each incident angle and the white CIE chromaticity coordinates are plotted. As can be seen from FIGS. 33 and 34, the spectral reflection characteristic of the reflecting surface (silver rear surface mirror) of the roof surface 22b of the pentaprism 20 is 350 to 800 nm regardless of the incident angle of the light ray incident on the main mirror 10. Has a high reflectance in the range. Therefore, it has almost no effect on the above-mentioned spectral transmission characteristics (Tm).

Comparative Example 3
In the single lens reflex digital camera 1 shown in FIG. 3, the multilayer film of Comparative Example 1 is formed on the half mirror surface 11a of the main mirror 10, the silver mirror is formed on the roof surface 22b of the pentaprism 20, and the third reflecting surface 22c is formed. A multilayer film of Comparative Example 2 was formed. As in the case of Example 8, the spectral transmission characteristics of the light transmitted through the finder window 24 when a randomly polarized light beam having a wavelength range of 350 to 800 nm is incident on the main mirror 10 at incident angles of 30 °, 45 ° and 60 °. (Tm) was calculated by simulation. The obtained results are shown in FIG. FIG. 36 shows a CIE chromaticity diagram in which CIE chromaticity coordinates calculated based on the spectral transmission characteristic (Tm) at each incident angle and white CIE chromaticity coordinates are plotted.

  As can be seen from FIGS. 31, 32, 35, and 36, in the finder transmittance of Example 8, the plot position variation of the CIE chromaticity coordinates is very small as compared with Comparative Example 3. Therefore, the single-lens reflex digital camera including the main mirror 10 and the pentaprism 20 according to the embodiment of the present invention can flatten the color tone at the center and the periphery of the finder subject image.

10 ... Half mirror
11 ... Substrate
11a ・ ・ ・ Half mirror surface 4 ・ ・ ・ Multilayer film
20 ・ ・ ・ Penta prism
22 ... Substrate
22a: Incident surface
22b ... Dach
22c ... third reflective surface 5 ... multilayer film

Claims (8)

An optical element having a half mirror surface,
A base material having a refractive index of 1.43 to 2.05 with respect to a d-line having a wavelength of 587.56 nm, and a high refractive index film having a refractive index of 2.00 to 2.55 and a low refractive index film having a refractive index of 1.35 to 1.7 formed on the half mirror surface of the base material. And a multilayer film of at least 18 layers formed by alternately laminating,
The total optical film thickness of the multilayer film is 2,350 to 2,800 nm, the average optical film thickness of the multilayer film is 135 to 155 nm,
The multilayer film comprises a thin layer of optical thickness 10 to 70 nm 1 to 4 layers, the above thickness layer optical thickness 200 nm observed 2-4 So含,
In the range of the incident angle from the air medium to the multilayer film or the emission angle from the multilayer film to the air medium in the range of 20 to 70 °, the CIE color obtained based on the spectral reflection characteristics of the light beam having each incident angle or emission angle. An optical element having a half mirror surface, wherein the maximum difference in degree coordinates is 0.015 or less . The optical element having a half mirror surface according to claim 1 , wherein the thin layer is arranged so as to be biased to one of a base material side and a medium side of the multilayer film. 2. The half mirror surface according to claim 1 , wherein the thin layers are all arranged on the medium side of the multilayer film, and the thick layers are all arranged on the substrate side of the multilayer film. Optical element. The multilayer film is composed of 18 layers, and the optical film thickness of the first layer from the base material side is 30 to 75 nm, the optical film thickness of the second layer is 40 to 145 nm, and the optical film thickness of the third layer is 55 to 135. nm, the fourth layer has an optical thickness of 25 to 90 nm, the fifth layer has an optical thickness of 85 to 135 nm, the sixth layer has an optical thickness of 125 to 175 nm, and the seventh layer has an optical thickness of 75. ~ 125 nm, optical thickness of 8th layer is 100 ~ 140 nm, optical thickness of 9th layer is 95 ~ 145 nm, optical thickness of 10th layer is 130 ~ 215 nm, optical thickness of 11th layer Is 70 to 165 nm, the optical thickness of the 12th layer is 140 to 205 nm, the optical thickness of the 13th layer is 155 to 185 nm, the optical thickness of the 14th layer is 175 to 220 nm, and the optical thickness of the 15th layer is The film thickness is 160 to 190 nm, the optical thickness of the 16th layer is 175 to 220 nm, the optical thickness of the 17th layer is 175 to 195 nm, and the optical thickness of the 18th layer is 75 to 120 nm. An optical element having a half mirror surface according to claim 1 or 2 . The multilayer film is composed of 18 layers, and the optical thickness of the first layer is 170 to 290 nm, the optical thickness of the second layer is 110 to 250 nm, and the optical thickness of the third layer is 100 to 270 from the substrate side. nm, the fourth layer has an optical thickness of 110 to 240 nm, the fifth layer has an optical thickness of 130 to 310 nm, the sixth layer has an optical thickness of 70 to 250 nm, and the seventh layer has an optical thickness of 120. 〜240 nm, optical thickness of 8th layer is 70-210 nm, optical thickness of 9th layer is 80-240 nm, optical thickness of 10th layer is 10-190 nm, optical thickness of 11th layer Is 60 to 250 nm, the optical thickness of the 12th layer is 10 to 180 nm, the optical thickness of the 13th layer is 80 to 230 nm, the optical thickness of the 14th layer is 10 to 170 nm, and the optical thickness of the 15th layer is The optical thickness of the 16th layer is 10-160 nm, the optical thickness of the 16th layer is 10-160 nm, the optical thickness of the 17th layer is 40-230 nm, and the optical thickness of the 18th layer is 10-120 nm. An optical element having a half mirror surface according to claim 1 or 3 . The multilayer film is composed of 19 layers, and the optical thickness of the first layer is 150 to 270 nm, the optical thickness of the second layer is 170 to 290 nm, and the optical thickness of the third layer is 110 to 250 from the base material side. nm, the fourth layer has an optical thickness of 100 to 270 nm, the fifth layer has an optical thickness of 110 to 240 nm, the sixth layer has an optical thickness of 130 to 310 nm, and the seventh layer has an optical thickness of 70. ~ 250 nm, optical thickness of 8th layer is 120-240 nm, optical thickness of 9th layer is 70-210 nm, optical thickness of 10th layer is 80-240 nm, optical thickness of 11th layer Is 10 to 190 nm, the optical thickness of the 12th layer is 60 to 250 nm, the optical thickness of the 13th layer is 10 to 180 nm, the optical thickness of the 14th layer is 80 to 230 nm, and the optical thickness of the 15th layer is Thickness 10-170 nm, 16th layer optical thickness 10-160 nm, 17th layer optical thickness 10-160 nm, 18th layer optical thickness 40-230 nm, 19th layer The optical film having a half mirror surface according to claim 1 or 3 , wherein the optical film thickness is 10 to 120 nm. The high refractive index film is selected from the group consisting of ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CeO ₂ , TiO ₂ , a mixed film of TiO ₂ and ZrO _{2 and} a mixed film of TiO ₂ and Nb ₂ O _5. And at least one material, and the low refractive index film is made of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , MgF ₂ and a mixed film of Al ₂ O ₃ and SiO _2. an optical element having a half mirror surface according to claim 1-6 to. Optical instrument using an optical element having a half mirror surface according to claim 1-7.

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