JPWO2015105076A1 - Optical element, optical system, and imaging apparatus - Google Patents

Abstract

Provided is an optical element capable of obtaining high intra-pupil transmittance and high resolution while suppressing deterioration of shading performance even when mounted separately from a lens unit. The optical element is formed around the optical axis and is formed around the central region, which is a region having a relative transmittance of 95% or more with respect to a position where the transmittance is the highest, and the transmittance is around the periphery. An intermediate region that decreases toward the intermediate region, and a peripheral region that is formed around the intermediate region and has a transmittance of 0.5% or less. The diameter of the central region is φ1, and the intermediate region And the peripheral area are 1.1 ≦ φ2 / φa ≦ 2.1, where φ is the diameter of the boundary between the center region, the peripheral region, and φa, and the aperture diameter of the optical system is φa. And at least one of 0.1 ≦ φ1 / φa ≦ 1.1 and 0.0 ≦ φ1 / φ2 ≦ 0.95 is satisfied.

Description

  The present invention relates to an optical element that exhibits an apodization effect, an optical system using the optical element, and an imaging apparatus.

  In an optical apparatus such as an imaging apparatus, an optical diaphragm, a neutral density (ND) filter, or the like is used to adjust the amount of incident light incident on a lens or the like. For example, an optical aperture or a neutral density filter is also used in an imaging device mounted on a mobile phone or a mobile terminal (for example, Patent Document 1).

  FIGS. 17A to 17B are explanatory views showing examples of a general optical diaphragm. FIG. 17A is a top view of a diaphragm 910 which is an example of a general optical diaphragm, and FIG. 17B is an example of a light transmittance distribution on the line AA ′ of the diaphragm 910. It is explanatory drawing shown. As shown in FIGS. 17A to 17B, the stop 910 includes an opening 911 that transmits almost 100% of light at the central portion, and a light shielding portion 912 that blocks almost 100% of light at the peripheral portion. ing. Such a diaphragm 910 is formed, for example, by providing an opening 911 in a plate formed using a light shielding material.

  Image pickup devices used for mobile phones and mobile terminals are increasingly required to be smaller and thinner while the number of pixels is increasing. Therefore, it is desired to reduce the size and thickness of optical diaphragms and neutral density filters used in such optical devices. In recent years, an imaging module equipped with a bright lens having a small F value has also been made in order to increase the sensitivity of photographing in a dark place.

  However, in the case of a general optical diaphragm, there is a problem that the influence of the diffraction of light generated around the opening becomes so large that it cannot be ignored, and the resolution deteriorates.

  As an optical aperture that does not deteriorate the resolution, there is a filter having an apodization effect (hereinafter referred to as an apodized filter) (see Patent Document 2). The apodized filter can reduce the influence of diffraction generated around the opening on the projection plane by, for example, converting incident light into a beam having a light intensity with a normal distribution of light intensity. If the influence of diffraction on the projection plane can be suppressed to a negligible range, the resolution can be improved and the depth of field can be increased.

  FIGS. 18A to 18B are explanatory diagrams illustrating an example of an apodized filter. 18A is a top view of an aperture 920 that is an example of an apodized filter, and FIG. 18B is an explanatory diagram showing an example of a light transmittance distribution on the line BB ′ of the aperture 920. FIG. . The diaphragm 920 shown in FIGS. 18A and 18B transmits toward the peripheral region 923 with the peripheral region 923 being a region where the light transmittance is approximately 0% and the transmittance of the central portion being approximately 100%. It consists of an intermediate region 922 that is a region where the rate gradually decreases.

  Ideally, the transmittance distribution of the apodized filter is a normal distribution in terms of improving the resolution. However, when the transmittance distribution is a normal distribution, there are many portions that block light, so that there is a problem that the amount of transmitted light is greatly reduced and the optical system becomes dark. For example, when the transmittance distribution is a normal distribution, the transmittance of light that enters the aperture diameter of the subsequent optical system (hereinafter referred to as intra-pupil transmittance) in a light beam that passes through the apodized filter vertically. It may be around 40%.

  Therefore, the transmittance in the central region of the apodized filter is increased to prevent a decrease in the amount of transmitted light (see, for example, FIGS. 3 and 15 of Patent Document 3). FIGS. 19A and 19B are explanatory diagrams illustrating an example of an apodized filter provided with a central region 921 having a substantially uniform transmittance. FIG. 19A is a top view of an aperture 930 as an example of an apodized filter provided with a central region 921 having a substantially uniform transmittance, and FIG. 19B shows light on the CC ′ line of the aperture 930. It is explanatory drawing which shows an example of the transmittance | permeability distribution.

  In addition, as a technique related to the present invention, Patent Document 4 provides a filter housing provided with a cover wall having a filter characteristic around an image sensor having an image pickup device. The example of the imaging device which has arrange | positioned the lens between is shown.

Japanese Patent Laid-Open No. 11-231209 Japanese Unexamined Patent Publication No. 2011-221120 Japanese Patent No. 4428961 Japanese Unexamined Patent Publication No. 2002-268120

  However, when an apodized filter as shown in FIGS. 18A to 18B and FIGS. 19A to 19B is used for an imaging module of a thin mobile phone or a mobile terminal, There was a problem like this. First, it was difficult to mount due to space problems. For example, when an apodized filter is newly incorporated in a lens unit used in an existing smartphone, the apodized filter has a thickness of about 50 μm to 80 μm in order to reduce the thickness of the imaging module. Must be. However, it is difficult to produce an apodized filter having an accurate transmittance distribution with such an element thickness, and it is difficult to use it for a thin lens unit due to thickness restrictions. Secondly, there is a problem that warpage occurs when a film is used for thinning. Thirdly, adding parts to the lens unit increases the weight and places a burden on the drive mechanism.

  The above problems can be avoided by mounting the apodized filter separately from the lens unit. However, since the apodized filter also has an optical aperture function, when the apodized filter is mounted separately from the lens unit, the apodized filter and the optical system installed in the lens unit are used. As the distance between the optical aperture that determines the F value increases, another problem arises in that the amount of light around the screen decreases due to vignetting, that is, shading deteriorates.

  Note that Patent Document 4 shows an example of an image pickup apparatus provided with a filter housing provided with a lid wall having filter characteristics at a position away from the lens. However, the filter characteristics have an apodization effect. However, it is not shown what kind of transmittance distribution should be used when the filter characteristics are good and how far the distance between the filter and the lens can be separated. When mounting the apodized filter separately from the lens unit, anti-shading measures should be taken in consideration of the effects on the performance that are related to each other, such as the decrease in resolution and the decrease in intra-pupil transmittance due to the effects of diffraction described above. However, Patent Document 4 does not consider such an effect at all. For example, Patent Document 4 discloses a parameter condition in which when the filter characteristic is a filter characteristic that exhibits an apodization effect, high resolution and high intra-pupil transmittance can be obtained while suppressing shading performance deterioration due to vignetting. Etc. are not disclosed at all.

  Therefore, an object of the present invention is to provide an optical element that exhibits an apodization effect and can provide a balanced performance to an optical system even when mounted separately from a lens unit. Another object of the present invention is to provide an optical system and an imaging apparatus that are easy to mount and have a good performance balance.

  An optical element according to the present invention is an optical element that exhibits an apodization effect in an optical system, and is formed around an optical axis, and is a central region having a relative transmittance of 95% or more with respect to a position having the highest transmittance. And an intermediate region which is formed around the central region and whose transmittance decreases toward the periphery, and a peripheral region which is formed around the intermediate region and has a transmittance of 0.5% or less When the diameter of the central region is φ1, the diameter of the boundary between the intermediate region and the peripheral region is φ2, and the aperture diameter of the optical system is φa, the central region, the intermediate region, and the The peripheral region is formed to satisfy at least one of the following formulas (B) and (C) in addition to the following formula (A).

1.1 ≦ φ2 / φa ≦ 2.1 Formula (A)
0.1 ≦ φ1 / φa ≦ 1.1 Formula (B)
0.0 ≦ φ1 / φ2 ≦ 0.95 (formula (C))

  Further, the optical element may have a transmittance of 80% or more for light transmitted through a region having a diameter of φa centered on the optical axis with respect to a light beam perpendicularly incident on the optical element.

  In addition, when the optical element is used in the optical system, the optical element has a light quantity at the screen position when the light quantity at the screen position corresponding to the maximum angle of view when the optical element is not used is 1. May be 0.75 or more.

  The optical element includes a transparent substrate, and a light absorbing portion formed of a material that absorbs part or all of light on the surface of the transparent substrate, and at least the intermediate region and the peripheral region include: The light absorbing portion may be formed, and the thickness of the light absorbing portion formed in the intermediate region may gradually increase from the central region side toward the peripheral region side.

  Moreover, the thickness of the light absorption part formed in the peripheral region may be not less than 10 μm and not more than 30 μm.

  The transparent substrate may be a substrate using chemically tempered glass or sapphire.

  The optical element is a protective glass incorporated in the housing of the imaging device or device in order to protect the assembled lens, and is provided on the surface of the transparent substrate opposite to the surface on which the light absorbing portion is formed. A dirty coating layer may be formed.

  An optical system according to the present invention includes any one of the optical elements described above and a combined lens, and the optical element side surface of the lens arranged closest to the light emitting side of the optical element among the combined lenses, The maximum value at the time of photographing of the distance between the optical element and the surface on the lens group side is 0.1 mm or more and less than 0.4 mm.

  An image pickup apparatus according to the present invention includes an assembled lens and a protective glass incorporated in a housing for protecting the assembled lens, and the protective glass is formed on a transparent substrate and the surface of the transparent substrate. An apodization layer, the apodization layer being formed around the optical axis and having a relative transmittance of 95% or more with respect to a position having the highest transmittance, and a periphery of the central region An intermediate region which is a region where the transmittance decreases toward the periphery, and a peripheral region which is formed around the intermediate region and has a transmittance of 0.5% or less, and the protection The maximum value at the time of photographing of the distance between the group lens side surface of glass and the protective glass side surface of the lens disposed closest to the protection glass among the group lenses is 0.1 mm or more and And less than .4Mm.

  In the imaging device, the protective glass may be any one of the above optical elements including a transparent substrate and the apodization layer formed on the surface of the transparent substrate.

  In the imaging device, the apodization layer may be formed on a surface of the protective glass on the side of the assembled lens.

  ADVANTAGE OF THE INVENTION According to this invention, it is an optical element which has an apodization effect, Comprising: Even if it is a case where it mounts separately from a lens unit, the optical element which can provide a balanced performance to an optical system can be provided. For example, even when mounted separately from the lens unit, it is possible to provide an optical element that can provide high intra-pupil transmittance and high resolution while suppressing deterioration of shading performance.

  Further, according to the present invention, it is possible to provide an optical system and an imaging apparatus that are easy to mount and have a good performance balance. For example, it is possible to provide an imaging apparatus capable of achieving both mounting ease, intra-pupil transmittance, and resolution while suppressing shading performance deterioration.

(A)-(b) is explanatory drawing which shows the example of the optical element of 1st Embodiment. It is a graph which shows the example of the screen periphery light quantity at the time of using a general apodized filter. (A)-(b) is a graph which shows the relationship between the transmittance | permeability in a pupil according to the setting parameter of the optical element 100, and MTF. (A)-(b) is a graph which shows the relationship between the transmittance | permeability in a pupil according to the setting parameter of the optical element 100, and a screen peripheral light quantity. (A) is a graph showing the relationship between the effective diameter ratio and φ1 / φa in the combination of design parameters together with the evaluation results for the performance, and (b) is the graph showing the relationship between the effective diameter ratio and the FT ratio in the combination of design parameters. It is a graph shown with the evaluation result with respect to. It is explanatory drawing which shows the structural example of the optical element 100 of 1st Embodiment. It is a schematic cross section which shows the structural example of the optical element 200 of 2nd Embodiment. It is a schematic cross section which shows the other structural example of the optical element 200 of 2nd Embodiment. It is sectional drawing which shows the example of the assembly to the imaging device of the optical element 200 of 2nd Embodiment. It is explanatory drawing which shows the structural example of the imaging device 400 of 3rd Embodiment. 3 is an explanatory diagram illustrating a configuration example of an optical system 420. FIG. FIG. 11 is an explanatory diagram showing a configuration example of an optical system 520. It is explanatory drawing which shows the transmittance | permeability distribution of the optical element 100 of an Example. (A)-(b) is a graph which shows the screen periphery light quantity at the time of using the optical element 100 of an Example. (A)-(b) is a graph which shows the performance of the optical element 100 of an Example. (A)-(b) is a graph which shows the performance of the optical element 100 of an Example. (A)-(b) is explanatory drawing which shows the example of a general optical aperture stop. (A)-(b) is explanatory drawing which shows the example of an apodized filter. (A)-(b) is explanatory drawing which shows the other example of an apodized filter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter. It is explanatory drawing which shows the example of the model data used for examination of a setting parameter.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1. FIG.
FIGS. 1A to 1B are explanatory views showing examples of the optical element according to the first embodiment of the present invention. 1A is a schematic top view of an optical element 100 that is an example of the optical element of the first embodiment, and FIG. 1B is a light transmittance on the DD ′ line of the optical element 100. It is explanatory drawing which shows distribution. The optical element 100 is a so-called apodized filter. As shown in FIG. 1A, the optical element 100 is formed around the optical axis, and has a central region 21 that has a transmittance of almost 100% with respect to visible light (420 nm or more and 780 nm or less). An intermediate region 22 that is formed around the central region 21 and has a transmittance that decreases toward the periphery, and a peripheral region 23 that is formed around the intermediate region 22 and has a transmittance of approximately 0%. Have. Here, the transmissivity ignores the reflection at the air interface of the transparent substrate and the interface between the material layers constituting the apodized filter, and the transmissivity of light transmitted through the transparent substrate and the light transmitting portion described later is 100. Define to be%.

  In the present embodiment, the central region 21, the intermediate region 22, and the peripheral region 23 are formed concentrically and as continuous regions. In the present embodiment, the central region 21 and the intermediate region 22 are distinguished depending on whether the rate of decrease from the highest transmittance is within 5% or more. On the other hand, the peripheral region 23 and the intermediate region 22 are distinguished depending on whether the transmittance is 0.5% or less or larger. In other words, a region having a relative transmittance of 95% or more with respect to a position having the highest transmittance around the optical axis is referred to as a central region 21, and a region having a transmittance of 0.5% or less is referred to as a peripheral region 23. A region sandwiched between the central region 21 and the peripheral region 23 is referred to as an intermediate region 22.

  The transmittance of the central region 21 does not necessarily have to be uniform. For example, it may be a distribution in which the optical axis has the highest transmittance and the transmittance decreases toward the periphery. Further, the transmittance of the peripheral region 23 may be 0.5% or less, but more preferably 0.1% or less.

  Note that, as illustrated in FIG. 1B, the transmittance distribution may not be continuous at the boundary between the intermediate region 22 and the peripheral region 23. For example, the transmittance at the end of the intermediate region 22 on the peripheral region 23 side may be 5 to 20%.

  Further, the diameter of the central region 21 is φ1, the effective diameter as an apodized filter, that is, the diameter of the boundary between the intermediate region 22 and the peripheral region 23 is φ2, and the lens unit disposed on the light emitting side of the optical element 100 When the optical aperture diameter that determines the F value of the optical system is φa, the optical element 100 includes a central region 21, an intermediate region 22, and a peripheral region 23 with the following formula (1) and the following formula (2): And at least one of the formulas (3).

1.1 ≦ φ2 / φa ≦ 2.1 (1)

0.1 ≦ φ1 / φa ≦ 1.1 Formula (2)

0.0 ≦ φ1 / φ2 ≦ 0.95 (3)

  By satisfying the formula (2) or the formula (3) in addition to the above formula (1), the intra-pupil transmittance can be increased and the MTF (Modulation Transfer Function) value at a predetermined spatial frequency can be increased. Therefore, when the optical element 100 of this embodiment is used for an imaging apparatus such as a camera, an image with better image quality can be taken. Further, the optical element 100 of the present embodiment may be arranged away from the lens of the optical system, and even in such a case, the decrease in the amount of light on the periphery of the screen due to vignetting can be suppressed within an allowable range. Hereinafter, φ2 / φa is referred to as an effective diameter ratio, and φ1 / φ2 is referred to as an FT ratio.

  In general, in an apodized filter, intra-pupil transmittance and MTF are in a trade-off relationship. As described above, it is ideal that the transmittance distribution of the apodized filter is a normal distribution in terms of improving the resolution, but in this case, the portion that blocks light increases, so the amount of transmitted light Is greatly reduced and the optical system becomes dark. For example, in the case of an apodized filter with a normal transmittance distribution, the transmittance in the pupil of light perpendicularly incident on a region corresponding to the aperture diameter φa of the optical system of the apodized filter is about 40%. Become. When the central region 21 occupying the aperture diameter φa of the optical system is increased so as to increase the transmittance in the pupil, the width of the intermediate region 22 is decreased, so that the MTF value is decreased.

  In the imaging optical system, light passing through a circular aperture corresponding to a normal optical aperture is diffracted, and the point image distribution on the imaging surface becomes a concentric bright and dark pattern. There is a bright circular area called an Airy disk in the center of the optical axis, and a concentric ring diffraction pattern called an Airy pattern is generated around the area. Since the intensity of the Airy pattern generated by this diffraction mainly affects the resolution and contrast at low spatial frequencies, the intensity of the Airy pattern, particularly the first bright ring near the Airy disk, should be suppressed. ing. If the apodization effect is used, the strength of the Airy pattern can be reduced. Since the intensity of the Airy pattern is easily affected by the overlap of relatively low spatial frequencies, in this embodiment, whether the resolution is good or bad is determined by looking at the values of 50 MTF / mm and 100 MTF / mm. The imaging optical system is designed so that the resolution is balanced at the center and the periphery of the screen, but the light beam forming the image around the screen is an oblique incident light beam that is off the optical axis. It is difficult in design to increase the resolution around the screen compared to the center of the screen due to aberration of the optical system, and it is preferable that the resolution around the screen is improved by the apodized filter. In addition, since the resolution at the center of the screen already has sufficient performance, in this embodiment, the resolution around the screen is more important than the resolution at the center of the screen. The light rays that form the image around the screen are obliquely incident light rays that deviate from the optical axis, and in general imaging devices, the resolution is inferior to the center of the screen due to aberrations of the optical system. The resolution improvement effect of the apodized filter can also be expected to improve the resolution degradation due to the aberration of the oblique incident light.

  Furthermore, in the present embodiment, in addition to the above-described intra-pupil transmittance and MTF, a screen peripheral light amount is used as an index (hereinafter referred to as a design index) when designing the transmittance distribution in the element plane.

  FIG. 2 is a graph showing an example of the amount of light around the screen when a general apodized filter is used. FIG. 2 is a graph showing an example in which an apodized filter having a normal transmittance distribution as shown in FIGS. 18A to 18B is used. In FIG. 2, the vertical axis indicates the light intensity normalized with the light intensity at the center of the screen, ie, Field angle = 0, being 1, and the horizontal axis indicates the screen position as the incident angle of the principal ray incident on that position. In FIG. 2, the series is divided and displayed according to the distance L between the apodized filter and the first lens of the subsequent optical system.

  In the optical system of FIG. 2, since the first lens is provided with an optical aperture, as shown in FIG. 2, the decrease in the amount of light around the screen due to vignetting increases as the distance L increases. Further, the amount of decrease increases as the distance to the periphery of the screen increases.

  In order to prevent such a decrease in the amount of light around the screen due to vignetting, in the present invention, the diameter φ2 of the boundary between the intermediate region 22 and the peripheral region 23 exceeds the aperture diameter φa of the optical system, as shown in Expression (1). Increase to range.

  The following standardized screen peripheral light quantity is considered as an index for judging the degree of reduction of the screen peripheral light quantity caused by installing the apodized filter. That is, the light amount when the apodized filter is not provided at a certain screen peripheral position is set to 1, and the light amount around the screen at the same position when the apodized filter is installed is standardized. Hereinafter, the screen peripheral light amount normalized with the light amount at the same position when the apodized filter is not provided as 1 is defined as a first normalized peripheral light amount.

  In many imaging modules, correction by image processing is performed to compensate for a decrease in the amount of light around the screen. For this reason, if the amount of decrease in the amount of light when an apodized filter is added is small, correction by image processing is often sufficient. In other words, even if the amount of light around the screen is smaller than the amount of light at the center of the screen, if the first normalized peripheral light amount is greater than or equal to a predetermined value, the shading performance deterioration is suppressed by accompanying correction by image processing. It can be regarded as being. Hereinafter, in order to distinguish from the first normalized peripheral light amount, the light amount around the screen when the light amount at the center of the screen is 1 may be referred to as the second normalized peripheral light amount.

  Based on the above, a combination of φ1 and φ2 with respect to φa is obtained so that the three performance indicators of intra-pupil transmittance, MTF, and screen peripheral light amount satisfy predetermined conditions. In the following, the case where the transmittance of most part of the central region 21 is 100% was examined.

  FIGS. 3A and 3B are graphs showing the relationship between the intra-pupil transmittance and the MTF according to the setting parameters of the optical element 100. FIG. In FIG. 3A, the abscissa indicates the intra-pupil transmittance, and the ordinate indicates the value of 100 MTF / mm when light is incident at 38.5 degrees. In FIG. 3B, the horizontal axis represents the intra-pupil transmittance, and the vertical axis represents the value of 50 MTF / mm when light is incident at 38.5 degrees. Further, the performance shown in FIGS. 3A and 3B is such that the distance L between the optical element 100 and the first lens of the subsequent optical system is 0.3 mm, and the aperture diameter φa of the optical system lens is 1. .64 mm, calculated with a focal length of 3.51 mm and an F value of 2.16. In the optical system of this example, the MTF is evaluated at the maximum angle of view of 38.5 degrees. However, in the case of a different optical system, the MTF at the angle of view near the maximum angle of view may be evaluated. Further, when evaluating the picture quality of a photograph, it may be considered that the image quality of the peripheral area that is a little closer to the center is more important than the image quality of the peripheral area corresponding to the maximum angle of view. In such a case, the MTF at a predetermined angle of view (for example, 30 degrees) smaller than the maximum angle of view may be evaluated.

  Moreover, in FIG. 3A and FIG. 3B, the series is divided according to the effective diameter ratio. A curve F101 in the figure indicates the direction of change in the FT rate within each series. The series of effective diameter ratio = 1 is a comparative example, and is an apodized filter in which the aperture diameter φa of the optical system and the effective diameter (diameter) φ2 of the apodized filter coincide. A part of specific combinations of setting parameters in each marker is shown in FIGS. 20A to 20G.

  As shown in FIGS. 3 (a) and 3 (b), when the effective diameter ratio is the same combination, when the FT ratio is lowered, the MTF is increased but the intra-pupil transmittance is lowered, and when the FT ratio is increased, the pupil is increased. It can be seen that the internal transmittance increases but the MTF decreases. It can also be seen that when the FT rate exceeds a certain value, the MTF rapidly decreases.

  Therefore, for example, when the transmittance in the pupil is 0.80 or more and the value of MTF100 / mm at the incidence of 38.5 degrees is 0.54 or more, the corresponding range on the graph of FIG. May be included in the combination. Further, for example, when the transmittance in the pupil is 0.80 or more and the value of 50 MTF / mm at the incidence of 38.5 degrees is 0.74 or more, the corresponding range on the graph of FIG. May be included in the combination.

  4A and 4B are graphs showing the relationship between the intra-pupil transmittance and the screen peripheral light amount according to the setting parameters of the optical element 100. FIG. In FIG. 4A, the horizontal axis indicates the intra-pupil transmittance, and the vertical axis indicates the first normalized peripheral light amount at the position corresponding to the incident angle of 38.5 degrees, that is, the screen peripheral light amount without the apodized filter. The amount of light around the screen is shown. In FIG. 4B, the horizontal axis represents the second normalized peripheral light amount at the position corresponding to the incident angle of 38.5 degrees, that is, the screen peripheral light amount when the light amount at the screen center is 1, and the vertical axis represents the light. Shows a value of 100 MTF / mm when incident at 38.5 degrees. Further, the distance L, the aperture diameter φa, the focal length, and the F value used in the calculation of the performance shown in FIGS. 4A and 4B are the same as those in FIGS. 3A to 3B. is there.

  In FIG. 4A and FIG. 4B as well, the series is shown separately according to the effective diameter ratio. Curves F101 and F102 in the figure indicate the direction of change in the FT rate within the series. A part of specific combinations of setting parameters in each marker is shown in FIGS. 20A to 20G.

  As shown in FIG. 4A, the amount of light at the periphery of the screen increases as the effective diameter ratio increases, and if the effective diameter ratio is the same, it does not greatly depend on the FT ratio. On the other hand, the intra-pupil transmittance increases as the FT rate increases. Therefore, in order to increase the intra-pupil transmittance and the screen peripheral light amount, the effective diameter rate may be increased and the FT rate may be increased.

  Further, as shown in FIG. 4B, the MTF becomes better as the FT rate is lower. On the other hand, the screen peripheral light amount increases as the effective diameter ratio increases, and takes a minimum value with respect to the change in the FT ratio. Therefore, in order to increase the screen peripheral light amount and improve the MTF, the effective diameter ratio may be increased and the FT ratio may be decreased.

  Therefore, for example, when the intra-pupil transmittance is 0.80 or more and the first normalized peripheral light amount is 0.75 or more, the effective diameter ratio is set to 1.2 or more on the graph of FIG. The FT rate may be set to be included in the range. As shown in FIG. 4B, when the FT ratio is increased, the MTF value tends to decrease, and the amount of light around the screen tends to increase after decreasing once. Reduce the FT rate to the extent that it falls within the range and give priority to the MTF value and the amount of light around the screen, or increase the FT rate to the extent that the MTF value falls within the permissible range and prioritize the improvement in the pupil transmittance and the amount of light around the screen Is also possible.

  FIG. 5A is a graph showing the relationship between the effective diameter ratio and φ1 / φa in the combination of design parameters, together with the evaluation results for performance. FIG. 5B is a graph showing the relationship between the effective diameter ratio and the FT ratio in the combination of the design parameters together with the evaluation result for the performance. The graphs of FIGS. 5A and 5B show that, among the model data used for studying the design parameters, the intra-pupil transmittance is 0.80 or more and the first normalized peripheral light amount is 0.75 or more. In addition, model data in which the value of MTF 50 / mm when incident at 30 degrees is 0.86 or more and the value of MTF 100 / mm when incident at 30 degrees is 0.725 or more is referred to as a Good model. The relationship between the ratio and φ1 / φa and the relationship between the effective diameter ratio and the FT ratio are plotted. In this example, MTF at an angle of view smaller than the maximum angle of view is used for evaluation instead of the maximum angle of view. FIG. 5A shows that the Good model is included in the combination of this example in the range where the effective diameter ratio is 1.1 to 2.1 and φ1 / φa is 0.1 to 1.1. As shown in FIG. 5 (b), when the above range is expressed using the effective diameter ratio and the FT ratio, the effective diameter ratio is 1.1 to 2.1 and the FT ratio is 0.0 to It can be said that the range is 0.95. Note that the above-described determination threshold values for each index are merely examples, and are not limited to these. For example, when the transmittance in the pupil is changed from 0.80 to 0.85, the range in which the Good model is included is that the effective diameter ratio is 1.1 to 1.5 and φ1 / φa is 0.6 to 1.1. Change to range.

20A to 20G calculate various performances assuming that the transmittance distribution in the intermediate region 22 is a distribution according to a Gaussian function, but the transmittance distribution in the intermediate region 22 follows a Gaussian function. It is not limited to distribution. For example, a distribution according to a function proportional to the cosine of the nth power (for example, the second power), a distribution according to exp (x ⁴ ), or a function according to an even power function ^xn may be used. Here, x is the distance from the center in the element plane, that is, the optical axis position.

  FIG. 6 is an explanatory diagram showing a configuration example of the optical element 100 of the present embodiment. As shown in FIG. 6, the optical element 100 of the present embodiment is formed of a transparent substrate 10 formed of a transparent resin material or glass or the like, and a material that absorbs visible light formed on the transparent substrate 10. It has the light absorption part 20 and the light transmission part 30 formed with the material which permeate | transmits visible light. Hereinafter, the layer in which the light absorption part 20 and the light transmission part 30 are formed may be referred to as an apodization layer 40 in the sense of a layer that causes an apodization effect.

  The light absorbing portion 20 is hardly formed in the central region 21, and is formed thick in the peripheral region 23. In the intermediate region 22 between the central region 21 and the peripheral region 23, The thickness is gradually increased from the side toward the peripheral region 23 side.

  Here, when the optical density of the light absorbing material constituting the light absorbing portion 20 is OD and the thickness of the light absorbing portion 20 is t, the transmittance T (%) is expressed by the following equation (4).

T = 100 × 10 ^{(−OD × t)} % (4)

  The optical density OD is represented by the following equation (5) from the transmittance T0 (%) per unit thickness.

OD = -log (T0 / 100) (5)

  Accordingly, in the optical element 100, the transmittance in the central region 21 is a value close to 100% because the thickness of the light absorbing material is almost zero, and transmits almost all of the incident light. Further, the transmittance in the peripheral region 23 is defined by Expression (4). Therefore, for example, in the case of 0.1%, it is necessary to determine the optical density OD and the thickness t of the peripheral region 23 so as to satisfy OD × t = 3.

  When an absorbing material having a large OD, that is, a high absorbing capacity is used, the thickness of the peripheral region 23 can be reduced. However, when a residual film is generated in the central region 21, the transmittance is significantly reduced due to the residual film, which makes manufacturing difficult. On the other hand, when an absorbing material having a small OD, that is, a low absorptivity is used, the thickness of the peripheral region 23 is increased, which is not suitable for an imaging system that requires a reduction in thickness.

  Therefore, the thickness of the peripheral region 23, that is, the height difference between the central region 21 and the peripheral region 23 of the light absorbing portion 20 is preferably about 5 μm to 100 μm, and further about 10 μm to 30 μm can make the optical element thin and stable. This is preferable.

  The transmittance in the intermediate region 22 is formed so that the transmittance gradually decreases from the central region 21 side toward the peripheral region 23 side. For this reason, from the central region 21 side to the peripheral region 23 side. The amount of transmitted light gradually decreases toward the side.

  Since the transmittance of the optical element 100 shown in FIG. 6 varies depending on the thickness of the light-absorbing material, if the thickness of the light-absorbing material can be precisely controlled using, for example, a mold, the reproducibility and accuracy is high. It is excellent in that the transmittance distribution can be easily obtained.

  The configuration of the optical element 100 is not limited to the above. For example, the optical element 100 can be manufactured even by a method using an ink jet recording apparatus as shown in FIG.

  Moreover, the light transmission part 30 is formed so that it may be embedded in the part in which the light absorption part 20 is not formed, and the surface of the light transmission part 30 is substantially flat. For this reason, the thickness of the light transmission part 30 is the thickest in the central region 21, the thinnest in the peripheral region 23, and is formed so as to gradually decrease from the central region 21 toward the peripheral region 23. . Note that in this embodiment, visible light means light having a wavelength of 420 nm or more and 780 nm or less.

  The transparent substrate 10 may be transparent, such as glass or resin, and it is preferable to reduce the thickness of the transparent substrate 10 for applications such as mobile phone cameras that require thinning. The following is preferable.

  Moreover, the light absorption part 20 is formed by what added the absorption material which absorbs light to the transparent resin material which permeate | transmits light. The light absorbing portion 20 may be obtained by curing a liquid light absorbing resin material, which is a liquid in which an absorbing material is added to a transparent resin material, by irradiation with ultraviolet rays or the like.

  Absorbent materials include anthraquinone, phthalocyanine, benzimidazolone, quinacridone, azo chelate, azo, isoindolinone, pyranthrone, indanthrone, anthrapyrimidine, dibromoanthanthrone, flavanthrone , Perylene, perinone, quinophthalone, thioindigo, dioxazine, aniline black, nigrosine black and other organic dyes and pigments, metal nanoparticles using gold, silver, copper, tin, nickel, palladium and their alloys In addition, barium sulfate, zinc white, lead sulfate, yellow lead, bengara, ultramarine, bitumen, chromium oxide, black iron, lead red, zinc sulfide, cadmium yellow, cadmium red, zinc, manganese purple, cobalt, magnetite, carbon black , Carbon nanotube, glass E down, inorganic pigments such as titanium black can be used. In particular, titanium black is preferable because of its excellent dispersibility and high absorption coefficient. Further, when added to the transparent resin material and molded, the addition concentration of titanium black can be lowered, so that the viscosity can be kept low.

  Titanium black is a compound of low-order titanium oxide represented by TiNxOy (0 ≦ x <1.5 and 0.16 <y <2) or (1.0 ≦ x + y <2.0 and 2x <y) The particles can be easily obtained. When used as an optical element, since the haze is preferably small, the average particle size of the titanium black particles used in the present embodiment is preferably 100 nm or less, and more preferably 30 nm or less. Here, the particle size of the dispersion is the number average particle size of 100 particles in a TEM photograph obtained by photographing a 100,000 times enlarged image of titanium black particles contained in an organic solvent with a transmission electron microscope (TEM). Means.

  In the present embodiment, when particles are used, a dispersant may be used, and the same applies to titanium black. The dispersing agent is used for dispersing uniformly in the resin. Dispersants include polymer dispersants (alkyl ammonium and its salts, alkylol ammonium salts of copolymers having acid groups, hydroxyl group-containing carboxylic acid esters, carboxylic acid-containing copolymers, amide group-containing copolymers, pigments Derivatives and silane coupling agents). Further, a functional group or a polymerizable functional group that interacts with the resin may be present in the molecule of the dispersant. Moreover, these may be used independently and may be used in combination of 2 or more types.

  The proportion of titanium black added to the transparent resin material, that is, the proportion of titanium black in the light absorbing portion 20 is preferably 0.3% by mass or more and 15% by mass or less, more preferably 0.5% by mass. To 13% by mass. This corresponds to an optical density at 10 μm of 0.2 or more and 4.0 or less. If the proportion of added titanium black is less than 0.3% by mass, a film thickness of 100 μm or more is required to express the desired transmittance, and molding may be very difficult. On the other hand, if the ratio of added titanium black is greater than 15% by mass, the transmittance per unit film thickness decreases, so that the residual film is required to be almost zero in the central portion. Manufacturing becomes difficult.

  In addition to titanium black, other materials may be added and used. In particular, the transmittance of carbon black monotonously decreases from 800 nm to 380 nm, and exhibits characteristics opposite to those of titanium black. By combining these two, the wavelength dependency of the transmittance can be reduced.

  Transparent resin materials include thermoplastic resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycarbonate (PC), cycloolefin (COP), polyimide (PI), and polyether. Thermosetting resins such as imide (PEI), polyamide (PA), and polyamideimide (PAI), and energy ray curable resins such as acrylic and epoxy can be used. In the case of using a thermosetting resin or an energy beam curable resin, an absorbing material may be added at the stage of a polymerization precursor compound (hereinafter also referred to as a polymerizable compound) such as an oligomer or a monomer, and then cured. Among these, energy beam curable resins are preferably used. Such a polymerizable compound can be used without particular limitation as long as it is a component that is cured by a polymerization reaction to form a cured product. For example, a radical polymerization type curable resin, a cationic polymerization type curable resin, and a radical polymerization type curable compound (monomer) can be used without particular limitation. Among these, a radical polymerization type curable compound (monomer) is preferable from the viewpoint of polymerization rate and moldability. Radical polymerization type curable resins include (meth) acryloyloxy groups, (meth) acryloylamino groups, (meth) acryloyl groups, allyloxy groups, allyl groups, vinyl groups, vinyloxy groups, etc. Examples thereof include a resin having a group having a bond.

  The polymerizable compound is not particularly limited, but ethoxylated o-phenylphenol acrylate, 2- (perfluorohexyl) ethyl methacrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecane (meth) acrylate, Cyclodecane methanol (meth) acrylate, tricyclodecane ethanol (meth) acrylate, 1-adamantyl acrylate, 1-adamantyl methanol acrylate, 1-adamantyl ethanol acrylate, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl Monofunctional compounds such as acrylate, 2-propyl-2-adamantyl acrylate, 9,9-bis [4- (2-acryloyloxyethoxy) phenyl] fluorene, diethylene glycol di (me ) Acrylate, 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, isobornyl di (meth) acrylate, tricyclodecane di (meth) acrylate , Tricyclodecane dimethanol di (meth) acrylate, tricyclodecane diethanol di (meth) acrylate, adamantane diacrylate, adamantane dimethanol diacrylate and other trifunctional compounds such as trimethylolpropane tri (meth) acrylate Compounds, tetrafunctional compounds such as pentaerythritol tetra (meth) acrylate, hexafunctional compounds such as dipentaerythritol hexa (meth) acrylate, and the like. Moreover, the polymeric compound may contain the 1 type (s) or 2 or more types. When only a monofunctional compound is used, cohesive failure may occur at the time of mold release after molding. Therefore, it is preferable to include a bifunctional or higher polyfunctional compound. The polyfunctional compound in the polymerizable compound group is preferably 1% by mass or more and 90% by mass or less, and more preferably 10% by mass or more and 80% by mass or less. When the amount of the polyfunctional compound is less than 1% by mass, the effect of improving the cohesive failure is insufficient, and when it exceeds 90% by mass, shrinkage after polymerization may be a serious problem.

  Moreover, the polymeric compound which raise | generates a ring-opening reaction like an epoxy group other than the functional group which has said carbon-carbon unsaturated double bond can also be used. Although not specifically illustrated, in this case as well, since a monofunctional compound alone may cause cohesive failure at the time of mold release after molding, it is preferable to include a bifunctional or higher polyfunctional compound. The polyfunctional compound in the polymerizable compound group is preferably 1% by mass or more and 90% by mass or less, and more preferably 10% by mass or more and 80% by mass or less. These photocurable absorbing materials may be used alone or in combination for the purpose of reducing the difference in refractive index with the transparent substrate 10 to reduce interface reflection or adjusting the viscosity.

  Moreover, the light transmission part 30 is formed with said transparent resin material. Since there is almost no absorbing material forming the light absorbing portion 20 between the transparent substrate 10 and the light transmitting portion 30, the transmittance in this region can be increased and can be made uniform.

  As described above, according to the present embodiment, even when an optical element that exhibits an apodization effect is mounted separately from the lens unit, high intra-pupil transmittance and high resolution are achieved while suppressing shading performance deterioration. Is obtained. Therefore, a well-balanced performance can be imparted to the subsequent optical system.

Embodiment 2. FIG.
Next, an optical element according to a second embodiment of the present invention will be described. The optical element of the present embodiment is an optical element used as protective glass for an imaging module in an imaging apparatus or the like.

  FIG. 7 is a schematic cross-sectional view showing a configuration example of the optical element 200 of the present embodiment. As shown in FIG. 7, the optical element 200 of the present embodiment includes a transparent substrate 201 formed of a transparent resin material or glass, and an apodization layer 202 formed on one surface of the transparent substrate 201. And at least one transparent layer 203 formed on any surface of the transparent substrate 201. In the example shown in FIG. 7, a transparent layer 203 is formed on the surface of the transparent substrate 201 opposite to the apodization layer 202.

  The transparent substrate 201 may be a substrate using chemically tempered glass or sapphire in addition to the material of the transparent substrate 10 of the first embodiment.

  The apodization layer 202 is a layer that generates an apodization effect, and may be the apodization layer 40 of the optical element 100 of the first embodiment, for example. In addition to the above formula (1), the apodization layer 202 includes a central region 21, an intermediate region 22, and a peripheral region 23 formed so as to satisfy at least one of the formula (2) or the formula (3). If it has, a specific structure is not ask | required.

  The transparent layer 203 may be formed of, for example, an unsaturated polyester-based, urethane-acrylate-based, epoxy-acrylate-based, or polyester-acrylate-based photocurable resin that is cured by irradiation with ultraviolet rays.

  The transparent layer 203 may be a hard coat layer for protecting the surface of the transparent substrate 201 from scratches, for example. In this case, the material forming the hard coat layer is preferably formed of a material harder than the material forming the transparent substrate 201, and pencil hardness (JIS-K-5600 JIS-K-5400). Is preferably H or more. The material for forming the hard coat layer is preferably an acrylic UV curable resin, an acrylic resin in which inorganic fine particles are dispersed, or the like.

  The transparent layer 203 may be an antireflection film (AR coat layer). Specifically, an inorganic multilayer film formed by a vapor deposition method or a sputtering method may be used. Further, it may be an AR film having a high film strength, for example, a high-strength antireflection film (Hard-AR film) having a pencil hardness of 6H or more, which is formed by a technique such as ion-assisted vapor deposition or magnetron sputtering.

  The transparent layer 203 may be an antistatic film (antistatic coating layer). Specifically, it may be a film formed by applying an ion conductive antistatic agent such as a long-chain alkyl compound having a sulfonate group or a polymer having a nitrogen atom ionized in the main chain. Moreover, the film | membrane formed by apply | coating the antistatic agent containing electroconductive materials, such as tin oxide particle | grains and the tin oxide particle | grains which doped indium and antimony, may be sufficient.

  Further, the transparent layer 203 may be an antifouling coating layer such as anti-fingerprint. Specifically, it may be a fluorine coat layer formed by applying or depositing an antifouling agent such as a fluorine compound.

  The transparent layer 203 is applied by a coating method such as spray coating, dipping, roll coating, die coating, spin coating, reverse coating, gravure coating, wire bar coating, or gravure printing, screen printing, offset printing, inkjet printing, etc. After printing by this printing method, it may be formed by ultraviolet irradiation or heating.

  The transparent layer 203 may be a combination of the above hard coat layer, antireflection film, and antifouling coat layer as appropriate. In that case, for example, by forming an antireflection film on the surface of the transparent substrate 201 and forming an antifouling coating layer thereon, the transparent layer 203 having a function of preventing fingerprints and a function of preventing reflection may be used.

  FIG. 8 is a cross-sectional view showing another configuration example of the optical element 200 of the present embodiment. As shown in FIG. 8, the optical element 200 may have an antifouling coating layer 203A, a Hard-AR film 203B, a transparent substrate 201, an apodization layer 202, and an antireflection film 203C in this order from the light incident side. Good.

  FIG. 9 is a cross-sectional view showing an example of incorporating the optical element 200 of the present embodiment into an imaging apparatus. As shown in FIG. 9, the optical element 200 is bonded to the housing 234 via an adhesive 232, for example. At this time, the imaging element (not shown), the combined lens (lens unit), and the optical element 200 may be arranged in this order. In such a case, the light absorbing portion 20 of the optical element 200 may be arranged in a direction facing the assembled lens, which is preferable because it is closer to the optical aperture 231.

  The adhesive 232 may be an ultraviolet curable adhesive such as an acrylic resin, a thermosetting adhesive such as an epoxy resin, a double-sided adhesive tape, or the like, as long as the optical element 200 and the housing 234 can be fixed.

  In the example illustrated in FIG. 9, between the lens surface of the first lens 221 that is disposed closest to the optical element 200 among the combined lenses of the optical system, and the surface of the optical element 200 on the first lens 221 side. The distance on the optical axis corresponds to the distance L described above. Further, when the optical aperture 231 is provided on the light incident side of the first lens 221, the diameter of the optical aperture 231 corresponds to the above-described φa. The optical aperture 231 may be provided between the lenses, and even in such a case, the diameter of the optical aperture 231 corresponds to φa.

  In general, in a camera module provided in a portable terminal such as a smartphone, a protective glass is incorporated in a casing 234 of the portable terminal for the purpose of protecting the camera module, particularly a lens. Therefore, as described above, by providing the protective glass with an apodization effect, it is possible to save the trouble of newly attaching the apodized filter alone to the camera module, and thus it is possible to suppress an increase in the number of parts. Further, when the lens unit has a drive mechanism, the same effect as that of the first embodiment can be obtained without increasing the burden. That is, since high pupil transmittance and high resolution can be obtained while suppressing deterioration of shading performance, by using the optical element 200 of this embodiment, an optical system and an imaging system that are easy to mount and have a good performance balance. Get the equipment.

  Further, in the case of a configuration in which an apodized filter is provided between the protective glass and the first lens as in the prior art, reflected light is generated on the surface of the apodized filter in addition to the surface of the protective glass. Although flare and ghost on the captured image caused by reflection are likely to occur, as described above, by forming the apodization layer 202 on the surface of the protective glass substrate, an increase in the reflection surface can be suppressed.

Embodiment 3. FIG.
Next, a third embodiment will be described. The present embodiment is an imaging apparatus using the optical element of the first or second embodiment. The imaging device in the present embodiment is an imaging device mounted on an electronic device having a portable communication function such as a smartphone or a mobile phone.

  FIG. 10 is an explanatory diagram illustrating a configuration example of the imaging apparatus according to the present embodiment. As shown in FIG. 10, the imaging apparatus 400 of the present embodiment includes an optical element 200, an optical system 420, an autofocus unit 431, an image sensor 432 that is an imaging element, a substrate 433, a flexible substrate 434, and the like. . The optical system 420 is mounted on the autofocus unit 431, and the autofocus unit 431 controls the movement of the optical system 220 to perform an autofocus operation. The image sensor 432 that is an imaging element is formed by a CMOS sensor or the like, and the image sensor 432 detects an image by light incident through the optical system 420.

  FIG. 11 is an explanatory diagram showing a configuration example of the optical system 420. As shown in FIG. 11, the optical system 420 includes a first lens 421, a second lens 422, a third lens 423, a fourth lens 424, and an infrared cut filter 425. Note that the optical system 420 may include the optical element 200 of the second embodiment. Further, the infrared cut filter 425 may be fixed to the image sensor 432 without being included in the optical system 420. Further, the number of lenses is not limited to four, and in order to obtain imaging performance, the lens may be composed of five or six aspheric lenses.

  In the optical system 420, the light incident from the optical element 200 enters the image sensor 432 via the first lens 421, the second lens 422, the third lens 423, the fourth lens 424, and the infrared cut filter 425.

  Note that the optical element 100 of the first embodiment may be provided instead of the optical element 200 of the second embodiment. The optical element 100 according to the first embodiment is not limited to the light incident side of the first lens 421, for example, between the first lens 421 and the second lens 422, or between the second lens 422 and the third lens 423. It may be provided. In any case, it is desirable that the optical element 100 be installed at a position close to the optical diaphragm of the optical system 420, for example, less than 0.4 mm.

  In the configuration including the optical element 200 of the second embodiment, the first lens 221 of the second embodiment may be used as the first lens 421 of the optical system 420, and in that case, the optical element 200 is the second embodiment. It may be a protective glass in the form.

  According to the present embodiment, by including the optical element 100 of the first embodiment or the optical element 200 of the second embodiment, an imaging device that is easy to mount and has a good performance balance can be obtained. More specifically, it is possible to obtain an imaging apparatus that can achieve both mounting ease, intra-pupil transmittance, and resolution while suppressing deterioration in shading performance.

Example 1.
The first example is an example of the optical element 100 used in the optical system 520 shown in FIG. An optical system 520 illustrated in FIG. 12 includes a first lens 521, a second lens 522, a third lens 523, a fourth lens 524, a fifth lens 525, and an infrared cut filter 526. In the image sensor 532, an image by light incident through the optical system 520 is detected. The F value of the optical system 520 is 2.16. The optical aperture of the optical system 520 is determined by the surface of the first lens 521 on the subject side, and the aperture diameter φa is the effective diameter of the first surface of the first lens 521 = 1.64 mm. The distance L between the optical element 100 and the first lens 521 is 0.3 mm at the maximum, and changes to a minimum of 0.05 mm according to the distance of the subject. Hereinafter, the distance L is the longest, that is, the distance between the optical aperture of the optical system 520 and the optical element 100 is the longest, that is, L = 0.3 mm.

  Based on such parameters, the optical element 100 of this example forms the apodization layer 40 so that φ1 = 1.12 mm and φ2 = 2.21 mm. In the optical element 100 of this example, the effective diameter ratio (φ2 / φa) = 1.35, the FT ratio (φ1 / φ2) = 0.51, and φ1 / φa = 0.69.

The transmittance distribution in the intermediate region 22 is a distribution according to a Gaussian function. FIG. 13 shows the transmittance distribution of the optical element including this example. In FIG. 13, the horizontal axis indicates the normalized radius, that is, the distance from the optical axis when the optical axis is 0 and the aperture radius (φa / 2) of the optical system 520 is 1. The vertical axis represents the transmittance. Note that Example 1b shown in FIG. 13 is an example of the optical element 100 in which the transmittance distribution in the central region 21 is uniform and the transmittance distribution in the intermediate region 22 follows a function proportional to the square of cosine. Example 1c is an example of the optical element 100 in the case where the transmittance distribution of the central region 21 is uniform and the transmittance distribution of the intermediate region 22 conforms to exp (x ⁴ ). Example 1d is an example of the optical element 100 when the transmittance distribution of the central region 21 follows exp (x ⁴ ) and the transmittance distribution of the intermediate region 22 follows a Gaussian function.

  When the optical element 100 of this example is used, the transmittance in the pupil is 0.872, the first normalized peripheral light amount (38.5 degrees incident) is 0.807, and the MTF is 50 lines / mm (38.5 degrees incident). The value is 0.777, the MTF is 100 / mm (incident at 38.5 degrees) is 0.580, the MTF is 50 / mm (incident at 30 degrees) is 0.889, and the MTF is 100 / mm (incident at 30 degrees). The value is 0.755. The performance of the optical element 100 of this example is shown as model data of number 50 in the model data group shown in FIGS. 20A to 20G.

Example 2.
The second example is another example of the optical element 100 used in the optical system 520 shown in FIG. The aperture diameter φa of the optical system 520 and the distance L between the optical element 100 and the first lens 521 are the same as in the first example.

  Based on such parameters, the optical element 100 of this example forms the apodization layer 40 so that φ1 = 1.56 mm and φ2 = 2.13 mm. In the optical element 100 of this example, the effective diameter ratio (φ2 / φa) = 1.30, the FT rate (φ1 / φ2) = 0.73, and φ1 / φa = 0.95.

  Further, the transmittance distribution in the intermediate region 22 is a distribution according to a Gaussian function (see FIG. 13).

  When the optical element 100 of this example is used, the transmittance in the pupil is 0.99, the first normalized peripheral light quantity (38.5 degrees incident) is 0.863, and the MTF is 50 lines / mm (38.5 degrees incident). The value is 0.757, the MTF is 100 / mm (incident of 38.5 degrees) is 0.553, the MTF is 50 / mm (incident at 30 degrees) is 0.873, and the MTF is 100 / mm (incident at 30 degrees). The value is 0.727. Note that the performance of the optical element 100 of this example is shown as model data of number 34 in the model data group shown in FIGS. 20A to 20G.

  For reference, FIG. 14A is a graph showing the amount of light around the screen in the optical system 520 when the optical element 100 of the first example is used. FIG. 14B is a graph showing the amount of light around the screen in the optical system 520 when the optical element 100 of the second example is used. 14 (a) and 14 (b), the vertical axis indicates the light intensity normalized with the light intensity at the center as 1, that is, the second normalized peripheral light amount, and the horizontal axis indicates the light incident on the screen position at that position. The incident angle is shown. 14 (a) and 14 (b), the series is divided and displayed according to the distance L.

  15 (a) and 15 (b) are marked with an asterisk in the first example and the second example together with the model data shown in the graphs of FIGS. 3 (a) and 3 (b). It is shown. In addition, FIGS. 16 (a) and 16 (b) are marked with an asterisk in the first and second examples together with the model data shown in the graphs of FIGS. 4 (a) and 4 (b). It is shown.

As described above, the present invention has been described with reference to the respective embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and within the scope described in the claims, Various modifications and changes are possible.
This application is based on Japanese Patent Application No. 2014-002089 filed on Jan. 9, 2014, the contents of which are incorporated herein by reference.

  The present invention can be suitably applied to any optical element, optical system, and apparatus that utilizes the apodization effect.

100, 200 Optical element 21 Central region 22 Intermediate region 23 Peripheral region 10, 201 Transparent substrate 20 Light absorbing portion 30 Light transmitting portion 40, 202 Apodization layer 203 Transparent layer 203A Antifouling coating layer 203B Hard-AR film 203C Antireflection film 232 Adhesive 231 Optical diaphragm 234 Housing 400 Imaging device 420, 520 Optical system 421, 521 First lens 422, 522 Second lens 423, 523 Third lens 424, 524 Fourth lens 525 Fifth lens 425, 526 Infrared cut filter 431 Autofocus unit 432, 532 Image sensor 433 Substrate 434 Flexible substrate

Claims (11)

An optical element having an apodization effect in an optical system,
A central region that is formed around the optical axis and has a relative transmittance of 95% or more with respect to a position having the highest transmittance, and is formed around the central region, and the transmittance decreases toward the periphery. An intermediate region that is a region, and a peripheral region that is formed around the intermediate region and has a transmittance of 0.5% or less,
When the diameter of the central region is φ1, the diameter of the boundary between the intermediate region and the peripheral region is φ2, and the aperture diameter of the optical system is φa, the central region, the intermediate region, and the peripheral region are as follows: In addition to the formula (A), the optical element is formed so as to satisfy at least one of the following formula (B) and formula (C).
1.1 ≦ φ2 / φa ≦ 2.1 Formula (A)
0.1 ≦ φ1 / φa ≦ 1.1 Formula (B)
0.0 ≦ φ1 / φ2 ≦ 0.95 (formula (C)) 2. The optical element according to claim 1, wherein the transmittance of light transmitted through a region having a diameter of φa centered on the optical axis is 80% or more with respect to a light beam perpendicularly incident on the optical element. When the optical element is used in the optical system, the light quantity at the screen position is 0.75 or more when the light quantity at the screen position corresponding to the maximum angle of view when the optical element is not used is 1. The optical element according to claim 2. A transparent substrate;
A light absorbing portion formed of a material that absorbs part or all of the light on the surface of the transparent substrate;
The light absorbing portion is formed at least in the intermediate region and the peripheral region,
The thickness of the light absorption part currently formed in the said intermediate | middle area | region is gradually thickened toward the side of a peripheral region from the said center area | region side. Optical elements. The optical element according to claim 4, wherein a thickness of the light absorption part formed in the peripheral region is 10 μm or more and 30 μm or less. The optical element according to claim 4, wherein the transparent substrate is a substrate using chemically strengthened glass or sapphire. In order to protect the assembled lens, it is a protective glass incorporated in the housing of the imaging device or device,
The optical element according to any one of claims 4 to 6, wherein an antifouling coating layer is formed on the surface of the transparent substrate opposite to the surface on which the light absorbing portion is formed. The optical element according to any one of claims 1 to 7,
With a pair of lenses,
The maximum value at the time of photographing the distance between the optical element side surface of the lens arranged closest to the light emitting side of the optical element and the surface of the optical element in the group lens, An optical system characterized by being 0.1 mm or more and less than 0.4 mm. A pair of lenses,
A protective glass incorporated in the housing to protect the group lens;
The protective glass includes a transparent substrate and an apodization layer formed on the surface of the transparent substrate,
The apodization layer is formed around the optical axis, and is formed around a central region where the relative transmittance with respect to a position having the highest transmittance is 95% or more, and around the central region, and the transmittance is around An intermediate region that is a region that decreases toward the intermediate region, and a peripheral region that is formed around the intermediate region and has a transmittance of 0.5% or less,
The maximum value at the time of photographing of the distance between the surface of the protective glass on the side of the lens group and the surface of the lens of the lens group disposed closest to the protective glass is 0.1 mm or more. And the imaging device characterized by being less than 0.4 mm. The imaging device according to any one of claims 1 to 8, wherein the protective glass includes a transparent substrate and an apodization layer formed on a surface of the transparent substrate. apparatus. The imaging device according to claim 9 or 10, wherein the apodization layer is formed on a surface of the protective glass on a group lens side.

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