Patent Application
20200319376
The present invention relates to a projection lens.
In recent years, imaging performance required for a projection lens has been increased as the number of pixels of a projected image increases, and the number of constituent lenses tends to increase. Regarding this tendency, in a case of a conventional projection lens including 15 lenses each having four antireflective films formed on a surface of a lens substrate having, for example, a refractive index of 1.52, a light reflection loss of about 5% in the entire projection lens is generated on average in a visible light wavelength range. Furthermore, in a case of a projection lens including 30 lenses, there is a concern that a light reflection loss of about 10% is generated, and brightness of an image projected on a projection plane is largely reduced. Therefore, in order to suppress a decrease in the transmittance of the whole system of a projection lens in response to an increase in the number of constituent lenses, an antireflective film with a lower reflectance and a smaller loss of light is required for a lens substrate. An example of conventional technology related to suppressing the decrease in the transmittance is disclosed in Patent Literature 1.
In an antireflective film described in Patent Literature 1, in order from a substrate side, a first layer is formed of a material having a refractive index lower than that of the substrate, second, fourth, sixth, and eighth layers are formed of a high refractive index material, third, fifth, seventh, and ninth layers are formed of a low refractive index material, and the optical film thickness of each of the layers is individually set to a predetermined value related to a design wavelength. This prevents reflection in a wide wavelength band from an ultraviolet region to an infrared region.
However, according to the conventional technology described in Patent Literature 1, even in an embodiment having the lowest maximum reflectance in a visible light wavelength range (for example, 420 nm to 690 nm), the maximum reflectance is about 0.5%, which is relatively high. As a result, a projection lens is insufficient for application to a recent increase in the number of pixels of an image.
One or more embodiments of the presents invention provide a projection lens capable of effectively suppressing a decrease in the transmittance of the whole system and capable of coping with an increase in the number of constituent lenses.
One or more embodiments of the present invention provide a projection lens for projecting an image onto a projection plane, including: a lens substrate; and an antireflective film constituted by at least eight layers, formed on a surface of the lens substrate, characterized in that, in the antireflective film, in order from an air side, a first layer is formed of MgF2, each of a second layer, a fourth layer, a sixth layer, and an eighth layer has a refractive index of 2.0 to 2.3, each of a third layer, a fifth layer, and a seventh layer is formed of SiO2, and quarter wave optical thicknesses Q1 to Q8 for the first layer to the eighth layer with respect to a refractive index ns of the lens substrate at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8).
Q
1=0.05×ns+A1(0.79≤A1≤0.91) Formula (1)
Q
2=0.09×ns+A2(1.64≤A2≤1.79) Formula (2)
Q
3=0.10×ns+A3(1.65≤A3≤1.90) Formula (3)
Q
4=−0.31×ns+A4(1.01≤A4≤1.23) Formula (4)
Q
5
=A5(0.10≤A5≤0.35) Formula (5)
Q
6=0.79×ns+A6(−1.64≤A6≤0.01) Formula (6)
Q
7=−0.64×ns+A7(1.26≤A7≤1.55) Formula (7)
Q
8=0.32×ns+A8(−0.38≤A8≤0.19) Formula (8)
In addition, the projection lens having the above configuration is characterized in that each of the second layer, the fourth layer, the sixth layer, and the eighth layer is formed of any one of Ta2O5, LaTiO3, a mixture of Ti2O3 and ZrO2, and a mixture of ZrTiO4 and ZrO2.
In addition, the projection lens having the above configuration is characterized in that the antireflective film has a maximum reflectance of 0.2% or less in a wavelength range of 430 nm to 670 nm.
In addition, the projection lens having the above configuration is characterized in that three or more types of glass materials among glass materials classified into five types satisfying the following formulas (9) to (13) regarding a refractive index ns are used as the lens substrate.
1.45≤ns<1.55 Formula (9)
1.55≤ns<1.65 Formula (10)
1.65≤ns<1.75 Formula (11)
1.75≤ns<1.85 Formula (12)
1.85≤ns<1.95 Formula (13)
According to one or more embodiments of the present invention, it is possible to form an antireflective film with a low reflectance and a small loss of light corresponding to lens substrates having various refractive indices. That is, it is possible to form an antireflective film using a high refractive index material which has been relatively difficult to use conventionally, and it is possible to expand the degree of freedom of the configuration of a projection lens. As a result, it is possible to effectively suppress a decrease in the transmittance of the whole system of a projection lens, and it is possible to flexibly cope with an increase in the number of constituent lenses.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the configuration of a projection lens according to one or more embodiments of the present invention will be described with reference to
The projection lens LN is constituted by, for example, 30 lens components as a whole as illustrated in
Next, the detailed configuration of a single lens used for the projection lens LN will be described with reference to
A lens 1 used for the projection lens LN includes a lens substrate 10 and an antireflective film 20 illustrated in
The antireflective film 20 includes, in order from an air side, a first layer 21, a second layer 22, a third layer 23, a fourth layer 24, a fifth layer 25, a sixth layer 26, a seventh layer 27, and an eighth layer 28. The first layer 21 is formed of MgF2. Each of the second layer 22, the fourth layer 24, the sixth layer 26, and the eighth layer 28 is formed of a so-called high refractive index material having a refractive index of 2.0 to 2.3. Each of the third layer 23, the fifth layer 25, and the seventh layer 27 is formed of SiO2.
The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8).
Q
1=0.05×ns+A1(0.79≤A1≤0.91) Formula(1)
Q
2=0.09×ns+A2(1.64≤A2≤1.79) Formula (2)
Q
3=0.10×ns+A3(1.65≤A3≤1.90) Formula (3)
Q
4=−0.31×ns+A4(1.01≤A4≤1.23) Formula (4)
Q
5
=A5(0.10≤A5≤0.35) Formula (5)
Q
6=0.79×ns+A6(−1.64≤A6≤0.01) Formula (6)
Q
7=−0.64×ns+A7(1.26≤A7≤1.55) Formula (7)
Q
8=0.32×ns+A8(−0.38≤A8≤0.19) Formula (8)
Each of the layers of the antireflective film 20 is formed by a vacuum deposition method under heating, for example, at 300° C. Particularly, the second layer 22 to the eighth layer 28 are formed by a vacuum deposition method using ion assist. Ion-assisted vapor deposition may be used in order to reduce a change in film density of the antireflective film 20 and the roughness of a film surface due to variation of the degree of vacuum and the like in the vacuum deposition method. This makes it possible to suppress occurrence of color unevenness and deterioration of characteristic reproducibility caused by a change in film density, that is, a change in refractive index of a film. When ion-assisted vapor deposition is used for forming the antireflective film 20, it is possible to use a high refractive index material which has been relatively difficult to use conventionally for the layers constituting the antireflective film 20.
According to the above configuration, the antireflective film 20 has a maximum reflectance of 0.2% or less in a wavelength range of 430 nm to 670 nm.
Note that each of the second layer 22, the fourth layer 24, the sixth layer 26, and the eighth layer 28 in the antireflective film 20 may be formed of any one of Ta2O5, LaTiO3, a mixture of Ti2O3 and ZrO2, and a mixture of ZrTiO4 and ZrO2.
In each of the 30 lenses of the projection lens LN, three or more types of glass materials having different refractive indexes ns are used as the lens substrate 10. Specifically, three or more types of glass materials among glass materials classified into five types satisfying the following formulas (9) to (13) regarding a refractive index ns are used as the lens substrate 10.
1.45≤ns<1.55 Formula (9)
1.55≤ns<1.65 Formula (10)
1.65≤ns<1.75 Formula (11)
1.75≤ns<1.85 Formula (12)
1.85≤ns<1.95 Formula (13)
Subsequently, in one or more embodiments, evaluation of light reflectance of a lens substrate and an antireflective film in each of Examples and a lens substrate and an antireflective film in Comparative Example will be described with reference to
Conditions of a glass substrate and an antireflective film in Comparative Example are illustrated in Table 1. In Comparative Example, a general antireflective film constituted by four layers was formed on a surface of a glass lens substrate having a refractive index ns=1.52 at a design main wavelength of λ0=550 nm. Each layer of the antireflective film was formed by a vacuum deposition method under heating at 300° C.
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 1 are illustrated in Table 2. In Example 1, the antireflective film 20 constituted by eight layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.52 at a design main wavelength of λ0=550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.52 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 2 are illustrated in Table 3. In Example 2, the antireflective film 20 constituted by eight layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.62 at a design main wavelength of λ0=550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.62 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
[Table 3]
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 3 are illustrated in Table 4. In Example 3, the antireflective film 20 constituted by eight layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.72 at a design main wavelength of λ0=550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.72 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 4 are illustrated in Table 5. In Example 4, the antireflective film 20 constituted by eight layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.82 at a design main wavelength of λ0=550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.82 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 5 are illustrated in Table 6. In Example 5, the antireflective film 20 constituted by eight layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.92 at a design main wavelength of =550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.92 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
According to
Conditions of the glass substrate 10 and the antireflective film 20 in Example 6 are illustrated in Table 7. In Example 6, the antireflective film 20 constituted by nine layers was formed on a surface of the glass lens substrate 10 having a refractive index ns=1.62 at a design main wavelength of λ0=550 nm. The quarter wave optical thicknesses (QWOT) Q1 to Q8 of the first layer 21 to the eighth layer 28 with respect to a refractive index ns=1.62 of the lens substrate 10 at a design main wavelength of λ0=550 nm satisfy the following formulas (1) to (8). Each layer of the antireflective film 20 was formed by a vacuum deposition method under heating at 300° C. Particularly, the second layer 22 to the eighth layer 28 were formed by a vacuum deposition method using ion assist.
According to
In this way, according to the configuration of one or more embodiments, it is possible to form the antireflective film 20 with a low reflectance and a small loss of light corresponding to the lens substrates 10 having various refractive indices. That is, it is possible to form the antireflective film 20 using a high refractive index material which has been relatively difficult to use conventionally, and it is possible to expand the degree of freedom of the configuration of the projection lens LN. As a result, it is possible to effectively suppress a decrease in the transmittance of the whole system of the projection lens LN, and it is possible to flexibly cope with an increase in the number of constituent lenses.
Furthermore, in the antireflective film 20, each of the second layer 22, the fourth layer 24, the sixth layer 26, and the eighth layer 28 is formed of any one of Ta2O5, LaTiO3, a mixture of Ti2O3 and ZrO2, and a mixture of ZrTiO4 and ZrO2. Therefore, it is possible to form the antireflective film 20 with a small loss of light by a vacuum deposition method under a relatively high temperature environment of, for example, 300° C. There is a risk that practical strength may be lowered in a case where MgF2 used in the first layer 21 is formed in a low temperature environment. Therefore, according to the configuration of one or more embodiments, it is possible to increase the strength of the first layer 21.
The antireflective film 20 may have a maximum reflectance of 0.2% or less in a wavelength range of 430 nm to 670 nm. This makes it possible to obtain the antireflective film 20 sufficient for application to a recent increase in the number of pixels of an image in the projection lens LN.
In addition, three or more types of glass materials among glass materials classified into five types satisfying the above formulas (9) to (13) regarding a refractive index ns are used as the lens substrate 10. Therefore, even with the projection lens LN obtained by combining the lens substrates 10 formed of various glass materials for thirty lenses, it is possible to form the antireflective film 20 with a low reflectance and a small loss of light. This makes it possible to further widen the degree of freedom of the configuration of the projection lens LN.
Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.
The present invention can be used in a projection lens.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-105391 | May 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/018922 | 5/19/2017 | WO | 00 |
