DESCRIPTION
OPTICAL FUNCTION DEVICE AND IMAGE-CAPTURING
DEVICE
5 TECHNICAL FIELD
The disclosure of the present application relates
to an optical function device and an image-capturing
device. More particularly, the disclosure of the present
application relates to an optical function device and an
10 image-capturing device including the optical function
device in which multiple reflection is suppressed.
BACKGROUND ART
A single-lens reflex camera is known, in which a
15 single lens is used as both an image-capturing lens and a
finder lens so that incident light from the imagecapturing
lens is reflected by a mirror to allow it to be
seen in a finder. The single-lens reflex camera allows a
photographer to change the lens so as to take photos in
20 accordance with the scenes where photos are taken and in
accordance with the needs of the photographer. The light
incident upon the finder's optical system is obtained by
reflecting the light incident from the lens using the
mirror, and when a photo is taken, the mirror is
25 retracted, and the light incident from the lens reaches
the film as it is. Accordingly, when the single-lens
reflex camera is used, there is an advantage in that it
is possible to take a picture of a subject which is seen
in the finder exactly as the shown image without any
30 parallax.
In order to provide a single-lens reflex camera
with an autofocus sensor, a single-lens reflex camera is
known, in which a mirror is made of a semi-transparent
mirror, and transmission light is passed to an autofocus
sensor using a still another sub-mirror (for example, see
5 Patent Documents 1 and 2). In such single-lens reflex
cameras, autofocus (hereinafter, autofocus is referred to
as AF as necessary) is performed until the shutter is
triggered.
As described above, the single-lens reflex camera
10 changes the position of the movable mirror, thereby
switching which of the finder's optical system and the
film the incident light is passed to. This means that,
at the instance at which a subject is photographed
(exposed), it is impossible to see the subject through
15 the finder. When the semi-transparent mirror and the
sub-mirror is provided in the configuration, it is
necessary to retract both of the semi-transparent mirror
and the sub-mirror to a retraction position, and this
makes it difficult to cause the AF to function normally
20 when continuous shooting is performed.
Accordingly, a configuration to abolish the submirror
and make the semi-transparent mirror as a fixedtype
has been suggested (for example, see Patent Document
3). In the configuration as disclosed in Patent Document
25 3, reflection light from the semi-transparent mirror is
passed on to the AF sensor unit, and transmission light
therefrom is passed on to the image-capturing device.
According to the configuration as disclosed in Patent
Document 3, a subject can be seen at all times even
30 during exposure, and the AF can be performed at all times
However, when the semi-transparent mirror is made
as the fixed-type, multiple reflection occurs within the
semi-transparent mirror, and an image that does not
actually exist (hereinafter referred to as a ghost as
necessary) may appear. This kind of phenomenon also
5 occurs when an infrared (IR) cut filter and an
ultraviolet (W)cu t filter are provided on one surface
of the semi-transparent mirror.
In particular, in a digital camera, it is easy to
enlarge a taken digital image, and the ghost is likely to
10 cause problems.
CITATION LIST
PATENT DOCUMENTS
Patent Document 1: Specification of Patent No. 2801217
15 Patent Document 2: Japanese Patent Application Laid-Open
NO. H8-254751
Patent Document 3: Japanese Patent Application Laid-Open
NO. 2006-197406
20 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
It is an object to provide an optical function
device and an image-capturing device including the
optical function device in which multiple reflection is
25 suppressed.
SOLUTIONS TO PROBLEMS
A preferred embodiment of an optical function
device is as follows.
30 An optical function device includes a base material
layer, a semi-transparent layer formed on a principal
plane of the base material layer, the semi-transparent
layer reflecting light of incident light at a ratio
determined in advance and passing remaining light; and a
reflection prevention layer formed on a principal plane
5 opposite to the principal plane of the base material
layer with respect to the base material layer, the
reflection prevention layer preventing reflection of the
light passing through the base material layer.
A preferred embodiment of an image-capturing device
10 is as follows.
An image-capturing device includes an optical
function device including a base material layer, a semitransparent
layer formed on a principal plane of the base
material layer, the semi-transparent layer reflecting
15 light of incident light at a ratio determined in advance
and passing remaining light, and a reflection prevention
layer formed on a principal plane opposite to the
principal plane of the base material layer with respect
to the base material layer, the reflection prevention
20 layer preventing reflection of the light passing through
the base material layer, the image-capturing device
further includes a first light receiving device for
receiving transmission light from the optical function
device and a second light receiving device for receiving
25 reflection light from the optical function device.
The optical function device has a semi-transparent
layer formed on a principal plane of the base material
layer, and a reflection prevention layer formed on a
principal plane opposite to the surface formed with the
30 semi-transparent layer. The light propagating through
the inside of the base material layer to the reflection
prevention layer is prevented from being reflected to the
inside of the base material layer by the reflection
prevention layer. Therefore, multiple reflections within
the optical function device are suppressed.
5
EFFECTS OF THE INVENTION
According to at least one example, multiple
reflections within the optical function device can be
suppressed, and therefore, an image-capturing device that
10 suppresses the appearance of a ghost can be provided.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic cross sectional view
illustrating an optical function device according to a
15 first embodiment.
Fig. 2A is a schematic cross sectional view
illustrating an example of configuration of a semitransparent
layer. Fig. 2B is a figure illustrating a
simulation result of optical characteristics expected
20 from the layer configuration as illustrated in Fig. 2A.
Fig. 3A is a schematic cross sectional view
illustrating an example of configuration of a reflection
prevention layer formed by stacking an inorganic material
Fig. 3B is a figure illustrating a simulation result of
25 optical characteristics expected from the layer
configuration as illustrated in Fig. 3A.
Fig. 4 is a figure illustrating an effective
reflectance Re [%I with respect to a wavelength h [nml of
incident light when moth-eye is formed on a base material
30 as a reflection prevention layer.
Fig. 5 is a schematic line diagram illustrating
overview of spectroscopy of reflection light.
Figs. 6A and 6B are schematic line diagrams
illustrating a semi-transparent mirror-fixed-type imagecapturing
device, and explain how the AF is affected by
5 warping of the semi-transparent mirror.
Fig. 7A is a schematic cross sectional view
illustrating overview of an image-capturing device
according to a second embodiment. Fig. 7B is a schematic
line diagram enlarging and illustrating a portion close
10 to the optical function device.
Fig. 8 is a figure illustrating an effective
reflectance Re [%] with respect to a wavelength h [nm] of
incident light, concerning sample S1 to sample S5.
Figs. 9A to 9E are figures for explaining images
15 captured by a light source device, concerning sample S1
to sample S5.
Fig. 10A is a schematic cross sectional view
illustrating a schematic configuration of a semitransparent
mirror-fixed-type image-capturing device.
20 Fig. 10B is a schematic line diagram enlarging and
illustrating a portion close to the semi-transparent
mirror.
MODE FOR CARRYING OUT THE INVENTION
25 Hereinafter, embodiments of an optical function
device and an image-capturing device will be explained.
It should be noted that the explanation will be made in
the following order.
cO. Semi-transparent mirror-fixed-type image-capturing
30 device>
(Schematic configuration)
(Multiple reflections within semi-transparent mirror)
el. First embodiment>
[Optical function device]
(Base material layer)
5 (Semi- transparent layer)
(Reflection prevention layer)
(Reduction of warping)
c2. Second embodiment>
[Image-capturing device]
10 (Configuration of image-capturing device)
(Arrangement of optical function device)
[Example]
c3. Modification>
It should be noted that embodiments described below
15 are preferred specific examples of an optical function
device and an image-capturing device. In the explanation
below, various kinds of limitations which are preferred
in terms of techniques are added, but unless it is
specifically indicated that the disclosure of the present
20 application is particularly limited, examples of optical
function devices and image-capturing devices are not
limited to the embodiments described below.
cO. Semi-transparent mirror-fixed-type image-capturing
device>
25 In order to facilitate understanding of the
embodiments, first, a schematic configuration of a semitransparent
mirror-fixed-type image-capturing device will
be explained.
(Schematic configuration)
30 Fig. 10A is a schematic cross sectional view
illustrating a schematic configuration of a semitransparent
mirror-fixed-type image-capturing device.
Fig. 10B is a schematic line diagram enlarging and
illustrating a portion close to the semi-transparent
mirror. As illustrated in Fig. 10A, a replaceable image-
5 capturing optical system 123 is attached to a housing 121
constituting a main body of an image-capturing device 111.
An image-capturing lens 125, a diaphragm, and the like
are arranged in a lens barrel 127, which constitute the
image-capturing optical system 123. The image-capturing
10 lens 125 of the image-capturing optical system 123 is
driven by a focus driving system (not shown), which
enables AF operation.
In the housing 121, the semi-transparent mirror 101
is fixed so that it can be inclined with respect to the
15 optical axis of subject light. Above the semitransparent
mirror 101, an AF module 133 is provided.
The method of the AF is usually a phase difference
detection method. A film 135 is provided at the side
opposite to the image-capturing lens 125 with respect to
20 the semi-transparent mirror 101. In Fig. 10A, the
shutter mechanism is not shown.
The semi-transparent mirror 101 reflects and
transmits the subject light incident into the housing 121
via the image-capturing lens 125. As illustrated in Fig.
25 10B, the semi-transparent mirror 101 uses a resin film
103 having optical transparency as a base material, and
an optical thin film 105 is formed on one principal plane
thereof. The optical thin film 105 is formed on the
principal plane closer to the image-capturing lens 125,
30 and is provided to reflect, with a predetermined
reflectance, the light incident upon the semi-transparent
mirror 101. The light reflected by the semi-transparent
mirror 101 is passed on to the AF module 133, and the
remaining light (transmission light) is passed on to the
film or the image-capturing device. More specifically,
5 the image-capturing device having the configuration of
Fig. 10 uses a portion of the subject light for the AF,
and performs exposure of the film or the image-capturing
device with the remaining light. The image-capturing
device as illustrated in Fig. 10 is an example where the
10 transmission light reaches the film 135.
In the configuration as illustrated in Fig. 10, the
semi-transparent mirror 101 is made as the fixed-type,
and the retraction operation is not performed, and
therefore, a portion of the subject light is incident
15 upon the AF module at all times. Therefore, the AF is
performed at all times. In the configuration as
illustrated in Fig. 10, no optical view finder is
provided, and the light reflected upward by the semitransparent
mirror 101 is passed on to the AF module 133
20 for the AF. However, the optical system may be devised
to provide both of the optical view finder and the AF
module 133 at the upper portion.
(Multiple reflections within semi-transparent mirror)
As illustrated in Fig. 10B, the light transmitting
25 through the semi-transparent mirror 101 includes light
that is reflected within the semi-transparent mirror 101
multiple times and is thereafter output to the film or
the image-capturing device.
In the semi-transparent mirror 101 of Fig. 10B, a
30 surface closer to the image-capturing lens is denoted as
Si, and the surface opposite thereto is denoted as Sp.
In contrast to the subject light B incident upon the
surface Sit lights that transmit through the semitransparent
mirror 101 and go out from the surface Sp to
the outside are denoted as T, (n=O, 1, 2, . . . ) . A
5 portion of the subject light B incident upon the semitransparent
mirror 101 is reflected by the surface Si
with a predetermined ratio, and is made into reflection
light Ro to the AF module. The remaining light advances
inside of the semi-transparent mirror 101, but a portion
10 thereof is reflected by the surface Sp, and returns back
to the inside of the semi-transparent mirror 101. The
light that is not reflected by the surface Sp is emitted
to the outside as To.
The light that returned to the inside of the semi-
15 transparent mirror 101 is reflected by the surface Si,
and a portion thereof is reflected by the surface Sp
again to return back to the inside of the semitransparent
mirror 101, and the remaining light is
emitted to the outside as TI. Thereafter, lights that
20 are repeatedly reflected and emitted to the outside are
denoted as T2, T3, . . . , which are arranged in the
descending order of the number of reflections, and T,
where n is equal to or more than one is denoted as highorder
unwanted light.
25 When the film or the image-capturing device is
exposed by high-order unwanted light, the high-order
unwanted light is recorded as ghost. For example, an
object emitting light such as a fluorescent light is
captured as an image, a mist-like blurred image appears
30 as a ghost around the image of the fluorescent light.
The ghost is generated in a certain direction with
respect to the image of the fluorescent light. When an
illuminating LED (Light-Emitting Diode) and the like are
captured as an image, multiple bright spots arranged in a
row appear close to a portion where the LED emits light.
5 Multiple bright spots become inconspicuous as they grow
away from the light emitting portion of the LED. This is
considered to be because, when n increases, the intensity
of the unwanted light decreases.
The appearance of the ghost as described above does
10 not cause serious problems in a photograph developed from
a film, but causes problems in a case where the semitransparent
mirror-fixed-type image-capturing device is a
digital camera using a CCD (Charge Coupled Device), CMOS
(Complementary Metal Oxide Semiconductor) and the like as
15 an image sensor. This is because the digital image can
be easily enlarged using a personal computer and the like
In the semi-transparent mirror-fixed-type imagecapturing
device, a portion of the subject light is
reflected and used for the AF, and the remaining light is
20 used for exposure. For this reason, such high-order
unwanted light is preferably reduced as much as possible,
and it is preferred that the amount of light used for
image-capturing be made sufficient.
As illustrated in Fig. 10B, a portion of the light
25 reflected by the surface Sp and returned to the inside of
the semi-transparent mirror 101 becomes light R, (m=l,
2, . . . ) that is not reflected by the surface Si but is
emitted to the outside. In the configuration in which an
AF module for phase difference AF is arranged above the
30 semi-transparent mirror 101, the light R, is taken as
noise light, which causes an error in a distance
measuring value. Therefore, it is impossible to obtain a
focused image.
Ghost and displacement of a distance measuring
value may occur even when an IR cut filter and a W cut
5 filter are provided on a surface of the semi-transparent
mirror 101, and therefore, the semi-transparent mirror
used for the semi-transparent mirror-fixed-type imagecapturing
device is preferably configured to suppress
multiple reflection occurring therein.
10 el. First embodiment>
Subsequently, the first embodiment will be
explained. The first embodiment relates to an optical
function device preferably used as a semi-transparent
mirror for a semi-transparent mirror-fixed-type image-
15 capturing device.
[Optical function device]
The optical function device includes a base
material layer, a semi-transparent layer formed on a
principal plane of the base material layer, and a
20 reflection prevention layer formed on a principal plane
opposite to the surface formed with the semi-transparent
layer.
The semi-transparent layer reflects incident light
with a ratio defined in advance, and transmits the
25 remaining light. The reflection prevention layer
prevents the light advancing in the base material layer
from being reflected by an interface between the base
material layer and the reflection prevention layer and
from being returned back to the inside of the base
30 material layer.
Therefore, this can suppress multiple reflection in
the optical function device, and can reduce the highorder
unwanted light emitted from the optical function
device. Moreover, since the semi-transparent layer and
the reflection prevention layer are not formed on the
5 surface of the same side of the base material layer, this
can reduce warping of the optical function device due to
film stress. More specifically, flatness is enhanced as
compared with an optical function device in which optical
function layers such as a semi-transparent layer and a
10 reflection prevention layer are stacked on one surface.
As a result, in particular, the accuracy of the
reflection angle of the reflection light is increased,
and the AF performance is enhanced.
Fig. 1 is a schematic cross sectional view
15 illustrating the optical function device according to the
first embodiment. An optical function device 1 is
configured to include a base material layer 3, a semitransparent
layer 5, and a reflection prevention layer 7,
which are stacked. As illustrated in Fig. 1, the semi-
20 transparent layer 5 is formed on a principal plane of the
base material layer 3. The reflection prevention layer 7
is formed on a principal plane opposite to the surface
formed with the semi-transparent layer 5 with respect to
the base material layer 3. Hereinafter, the base
25 material layer 3, the semi-transparent layer 5, and the
reflection prevention layer 7 will be explained in order.
(Base material layer)
The base material layer 3 serves as a support
substrate for forming the semi-transparent layer 5 and
30 the reflection prevention layer 7. The shape and the
size of the base material layer 3 is not particularly
limited, but when the optical function device 1 is
incorporated into the semi-transparent mirror-fixed-type
image-capturing device, the thickness of the base
material layer 3 is preferably thinner. More
5 specifically, the thickness of the base material layer 3
is preferably equal to or more than 10 pm and equal to or
less than 100 pm. This is because the distance for which
the incident light transmits within the base material
layer 3 can be reduced, and the degradation of the image-
10 focus performance can be reduced. In addition, this is
because the weight of the image-capturing device can be
reduced.
The base material layer 3 is transparent. The base
material layer 3 is preferably highly transparent in a
15 visible light region. This is because, when the optical
function device 1 is incorporated into a semi-transparent
mirror-fixed-type image-capturing device, the sensitivity
characteristics are determined by the design based on
the visible light region. In this case, visible light
20 region (this may be called a sensitivity region of an
image-capturing device including a color filter) means a
wavelength band of 400 nm to 700 nm. The optical
transparency of the base material layer 3 itself is
preferably such that, for example, the haze is 0.9 or
25 less, but is also acceptable if predetermined
transmittance and reflectance are achieved by the optical
function device 1 formed with the semi-transparent layer
5 and the reflection prevention layer 7. The measurement
condition of the haze is based on JIS K 7361 (IS0 13468),
30 JIS K 7136 (IS0 14782), JIS K 7105 or ASTM D 1003.
Hereinafter, a haze measurement device will be shown.
Measurement device: haze meter (NDH 5000 made by
Nippon Denshoku Industries Co., Ltd.)
The base material layer 3 is preferably optically
isotropic concerning the direction within the surface
5 thereof. This is because, as compared with the case
where the base material layer 3 is optically anisotropic
concerning the direction within the surface thereof, the
amount of light loss due to absorption when the light is
incident can be reduced. When the optical function
10 device is incorporated into the optical path of the
image-capturing device, the variation of the
transmittance for each wavelength can be reduced, and
therefore, disruption of white balance can be reduced.
In addition, this can suppress displacement of the image
15 focus position in the oscillation direction of the light,
and can suppress degradation of the image quality
(resolution) .
In this case, I1optically isotropicH means that,
when the refractive indexes in two directions
20 perpendicular to each other within the surface are
denoted as Nx, Ny, the value of AN=Nx-Ny (where Nx>Ny
holds) is less than 0.01. AN can be obtained by emitting
a single wavelength light ray onto a sample, measuring a
phase difference of transmission light, and using the
25 following relationship: (phase difference) = (thickness
of sample) xAN. In this specification, "optically
isotropic" includes not only isotropy strictly in terms
of optics but also a certain level of anisotropy caused
by manufacturing error and measurement error (evaluation
30 error). Hereinafter, a phase difference measurement
device will be shown.
Measurement device: phase difference measurement
device (KOBRA made by Oji Scientific Instruments)
A material of which AN is equal to or more than
0.01 may be used as a material constituting the base
5 material layer 3. In this case, a measurement value of
phase difference is preferably equal to or less than 300
nm. When the phase difference is equal to or less than
300 nm, the degradation of the image quality (resolution)
is not affected even when the optical function device is
10 incorporated into an optical path of the image-capturing
device.
Examples of materials of the base material layer 3
include polycarbonate (PC), cycloolefin Polymer (COP),
polyethyleneterephtalate (PET), polyethersulphone (PES),
15 polyethylenenaphthalate (PEN), triacetylcellulose (TAC),
polyimide, aramid (aromatic polyamide) . The material of
the base material layer 3 is not limited to resin.
Alternatively, glass and the like may be used. In terms
of being optically isotropic, PC which is amorphous
20 plastic, polyimide, or COP is preferably selected.
Alternatively, glass is preferably selected.
For example, acrylic resin-attached film may be
used as the base material layer 3. A material which is
transparent within the visible light region and having a
25 desired optical transparency is to be selected.
(Semi-transparent layer)
The semi-transparent layer 5 is formed on a
principal plane of the base material layer 3. The semitransparent
layer 5 is provided so that the optical
30 function device 1 has predetermined reflectance and
transmittance. For example, the semi-transparent layer
is designed so that the optical function device 1 has
reflection characteristics (light transmission
characteristics) that have the reflectance of 30+10%
(transmittance of 70f10%) in the visible light region.
5 For example, the semi-transparent layer 5 is a
stacked body including a high refractive index material
and a low refractive index material. A layer made of a
high refractive index material (hereinafter referred to
as a high refractive index layer) and a layer made of a
10 low refractive index material (hereinafter referred to as
a low refractive index layer) stacked alternately can be
treated as the semi-transparent layer 3. The high
refractive index material constituting the high
refractive index layer is a material of which refractive
15 index is equal to or more than 2.0 (for example, 2.0 to
2.5). The low refractive index material constituting the
low refractive index layer is a material of which
refractive index is less than 1.6.
A metal oxide can be used as the high refractive
20 index layer. For example, the high refractive index
material is preferably one of In203, Sn02, ZnO, ITO, or an
alloy thereof, or a transparent conductive material
having ZnO doped with A1 or Ga. Alternatively, it is
preferably made of any one of Ti02, Nb205, Zr02, Ta205.
25 For example, the low refractive index material is
preferably MgF2, A1F3, Si02.
Fig. 2A is a schematic cross sectional view
illustrating an example of a configuration of the semitransparent
layer. In the example of the configuration
30 illustrated in Fig. 2A, a high refractive index layer sH
and a low refractive index layer 5L are stacked on a
principal plane of the base material layer 3.
Hereinafter, an example of a layer configuration of the
semi-transparent layer 5 and the base material layer 3
will be shown.
5 Layer configuration: (low refractive index
layer/high refractive index layer) base material layer
Low refractive index layer: Si02 (THL: about 20 nm)
High refractive index layer: TiOz or Nb2O5 (THH:
about 60 nm)
10 Base material layer: polyimide, COP or PC (THs: 10
pm to 90 pm)
Fig. 2B is a figure illustrating a simulation
result of optical characteristics expected from the layer
configuration as illustrated in Fig. 2A. Fig. 2B
15 illustrates reflectance R [%I and transmittance T [%I
with respect to wavelength h [nml of the incident light.
As illustrated in Fig. 2B, according to the above
configuration, the reflection characteristics of which
reflectance is 30+10% in the visible light region are
20 obtained. Hereinafter, the simulation condition of the
reflectance and transmittance will be shown.
Simulation condition: an angle formed by a line
normal to the sample and the optical axis of the incident
light is considered as 37 degrees, and each of the
25 reflectance and transmittance at each wavelength was
calculated. The reflectance is obtained by the ratio of
the reflection light that is output in the specular
direction of the sample.
SWPF (Short Wave Pass Filter) design method can be
30 used, so that the semi-transparent layer 5 has the
predetermined reflectance and transmittance. The SWPF is
a filter that transmits light at a short wavelength side
and blocks (reflects) light at a long wavelength side.
The basic design of the SWPF can be expressed by the
following expression using a layer thickness H satisfying
5 the relationship of: (refractive index of high refractive
index material) x H = h/4 (A: design central wavelength)
and a layer thickness L satisfying the relationship of:
(refractive index of low refractive index material) x L =
h/4.
10 L/~@H@L.. .@ L@H@L/~=L/(~H L) "HL/~( a portion of
I ! . . . represents a repetition, and n is an integer
representing the number of repetitions.))
For example, a film of PC (refractive index 1.59)
is used as the base material layer 3, the first layer
15 (L/2) of the above expression may be deemed as a PC film.
Therefore, the above expression is simplified as shown in
the expression (1) below.
(HL) "HL/~ (n is an integer representing the number
of repetitions) expression (1)
20 The design central wavelength is set, and the layer
thickness H and the layer thickness L are designed
fundamentally. Further, through optimization, target
reflection characteristics (light transmission
characteristics) are obtained. The layer configuration
25 of the semi-transparent layer 5 is not limited to what is
illustrated in Fig. 2. The layers may be configured to
be stacked in order on the base material layer, with the
low refractive index layer stacked first, and as
necessary, multiple high refractive index layers and low
30 refractive index layers may be further be stacked.
Dry process such as evaporation method, sputtering
method, Chemical Vapor Deposition (CVD) can be applied as
the method for forming the semi-transparent layer 5 on a
principal plane of the base material layer 3.
(Reflection prevention layer)
5 The reflection prevention layer 7 is formed on a
principal plane opposite to the surface formed with the
semi-transparent layer 5 with respect to the base
material layer 3. The reflection prevention layer 7 is
provided to prevent the light that enters into the
10 optical function device 1 from the surface formed with
the semi-transparent layer 5 and advances through the
inside of the optical function device 1 from being
reflected at the output surface side of the optical
function device 1 and returning back to the inside of the
15 optical function device 1.
When the reflection prevention layer 7 is formed on
the base material layer 3, the effective reflectance at
the interface between the base material layer 3 and the
reflection prevention layer 7 for the light incident from
20 the side of the base material layer 3 is preferably set
as low as possible. In particular, the effective
reflectance close to a wavelength 555 nm where a relative
luminosity is high is preferably set at a low value.
More specifically, in the wavelength band of 400 nm to
25 650 nm, the average effective reflectance is preferably
equal to or less than 1.2%, and more preferably, equal to
or less than 0.5%. This is because, when the optical
function device is incorporated into the image-capturing
device, and the average effective reflectance in the
30 wavelength band of 400 nm to 650 nm is equal to or less
than 1.2%, the occurrence of the ghost is suppressed.
Also, when the average effective reflectance in the
wavelength band of 400 nm to 650 nm is equal to or less
than 0.5%, the ghost is suppressed to a level that is
almost unnoticeable even when the recorded image is
5 enlarged.
In this case, the effective reflectance is what can
be obtained from the following relationship where the
reflectance obtained only by measuring the base material
layer that is not formed with the optical function layer
10 such as the semi-transparent layer and the reflection
prevention layer is denoted as Ro.
(effective reflectance) = (measurement value of
reflectance of sample) - Ro/2
The reason why Ro is divided by 2 is to obtain the
15 amount of contribution of one of the surfaces, among the
contribution of the interface made between the incident
side and the output side of the light.
For example, the reflection prevention layer 7 is a
stacked body including materials of which refractive
20 indexes are different, and may be a layer obtained by
stacking inorganic material by evaporation method or
sputtering method, or a layer obtained by applying
organic material by wet coating. Alternatively, a layer
called moth-eye having fine and dense pits and
25 projections formed on the surface may be used as the
reflection prevention layer 7.
Fig. 3A is a schematic cross sectional view
illustrating an example of configuration of a reflection
prevention layer formed by stacking an inorganic material.
30 In the example of configuration as illustrated in Fig. 3A,
the semi-transparent layer 5 is formed on one principal
plane of the base material layer 3. Further, the
reflection prevention layer 7 is formed on a principal
plane opposite to the surface formed with the semitransparent
layer 5. The reflection prevention layer 7
5 is configured to include a high refractive index layer
7Hl, a low refractive index layer 7Ll, a high refractive
index layer 7H2r and a low refractive index layer 7~2,
which are stacked in order. Alternatively, the layers
may be stacked in order with the low refractive index
10 layer stacked first, but 7,, and 7H2r 7~1a nd 7~2n eed not
be made of the same type of material. A material
constituting the high refractive index layer and a
material constituting the low refractive index layer may
be selected from the same ones that are applied to the
15 semi-transparent layer 5.
The reflection prevention layer constituted by
stacking layers of which refractive indexes are different
is configured such that the reflection light from each
interface interfere with each other, and the reflection
20 light is reduced by the effect of interference of the
light. Therefore, the design of the reflection
prevention layer 7 is basically the same as the design of
the semi-transparent layer 3, and the design method of
the above SWPF can be applied.
25 Hereinafter, an example of layer configuration of
the base material layer 3 and the reflection prevention
layer 7 will be shown. The layer configuration explained
below is obtained from the method of SWPF explained above.
Layer configuration: base material layer/(high
30 refractive index layer l/low refractive index layer
l/high refractive index layer 2/low refractive index
layer 2 )
Base material layer: polyimide, COP or PC (THs: 10
pm to 90 pm)
High refractive index layer 1 : Ti02 or Nb2O5 (THH1:
5 about 15nm)
Low refractive index layer 1: Si02 (THL1: about 30
nm
High refractive index layer 2 : Ti02 or Nb2O5 (THH2:
about 120 nm)
10 Low refractive index layer 2: Si02 (THL2: about
95nm)
Fig. 3B is a figure illustrating a simulation
result of optical characteristics expected from the layer
configuration as illustrated in Fig. 3A. Fig. 3B
15 illustrates, with a solid line AR, a calculation result
of the effective reflectance Re of the optical device
having the reflection prevention layer 7. Among the
contribution to the effective reflectance of the optical
device without the reflection prevention layer 7, i.e.,
20 to the reflectance of the interface between the incident
side and the output side of the light, a broken line CL
illustrates a calculation result of the contribution of
only one surface. Hereinafter, the simulation condition
of the effective reflectance will be shown.
25 Simulation condition: an angle formed by a line
normal to the sample and the optical axis of the incident
light is considered as 37 degrees, and each of the
reflectance at each wavelength was calculated. The
effective reflectance is obtained from the ratio of the
30 reflection light that is output in the specular direction
of the sample. In addition, the layer configuration of
the base material layer 3 and the semi-transparent layer
5 is the same as what is illustrated in Fig. 2A.
By taking an average in a wavelength band of 400 nm
to 650 nm with the layer configuration as described above,
5 an effective reflectance of almost 0.4% is obtained. As
necessary, multiple high refractive index layers and low
refractive index layers may be further be stacked.
As the reflection prevention layer 7, a layer
applied with organic material may be used. For example,
10 silicone resin including alkoxysilane silane and silane
coupling material (SiOz fluorine polymers, refractive
index: 1.3 to 1.4) and fluorine-based resin such as
polytetrafluoroethylene (PTFE)) (refractive index: 1.3 to
1.4) can be used as the organic material.
15 Similar to forming the semi-transparent layer 5,
methods for forming the reflection prevention layer 7 on
a principal plane of the base material layer 3 can be
selected, as necessary, from dry process such as
evaporation method, sputtering method, and CVD or wet
20 process such as spin coating, dip coating, roll coating,
gravure coating, and die coating.
As described above, the effect of the reflection
prevention by stacking layers of which refractive indexes
are different is due to the effect of interference of the
25 reflection light. More specifically, the effect of
reflection prevention by forming a stacked body includes
wavelength dependency and layer thickness dependency.
The moth-eye is formed with many dense pits and
projections with a pitch less than the wavelength of the
30 light to be transmitted, and the effect of the reflection
prevention by the moth-eye is not greatly dependent on
the wavelength. This is because the moth-eye acts like a
layer of which effective refractive index continuously
changes along the depth direction of the moth-eye
structure with respect to the incident light. This is
5 also because the effect of the reflection prevention by
the moth-eye does not depend on the effect of
interference. Therefore, by using the moth-eye,
reflection characteristics where the average reflectance
is 0.3% or less in the wavelength band of the visible
10 light can be obtained.
Fig. 4 is a figure illustrating an effective
reflectance Re [%I with respect to a wavelength h [nm] of
incident light when moth-eye is formed on the base
material layer 3 as the reflection prevention layer 7 .
15 In the example illustrated in Fig. 4, reflection
characteristics where the average reflectance is about
0.7% can be obtained in the wavelength band of 400 nm to
650 nm. Hereinafter, a measurement device and a
measuring method of the reflectance for calculating the
20 effective reflectance will be shown. Fig. 5 illustrates
an overview of spectroscopy of reflection light.
Measurement device: ultraviolet-visible
spectrophotometer (UBest V560 made by JASCO Corporation)
Measuring method: an angle formed by a line normal
25 to the sample and the optical axis of the incident light
was set as 37 degrees, and the reflection light is
detected with a detector, so that each of the reflectance
at each wavelength was measured. As illustrated in Fig.
5, the reflection light from a sample 41 is detected such
30 that a detector D detects the light reflected by a mirror
M.
To manufacture the moth-eye, for example, a method
for transferring the irregular shapes of the master
(original) and a method for replicating the irregular
shapes of the master (original) using nanoimprint are
5 known. When making the master, etching and electron beam
exposure and the like can be used. Examples of transfer
methods applicable to replication of the irregular shapes
of the master include a method for pouring energy raycurable
resin into a cast and emitting the energy ray to
10 cure the resin, a method for transferring the shape by
applying heat and pressure to the resin, or a method for
providing a resin film from a roll and transferring the
shape of the cast by applying heat (laminate transfer
method) .
15 (Reduction of warping)
In this case, in a preferred embodiment, first, one
of the semi-transparent layer 5 and the reflection
prevention layer 7 is formed on the base material layer 3,
and thereafter, the other of the semi-transparent layer 5
20 and the reflection prevention layer 7 is formed on the
base material layer 3. In other words, the semitransparent
layer 5 and the reflection prevention layer 7
are not formed in an overlapping manner on the principal
plane of the same side of the base material layer 3. If,
25 for example, the reflection prevention layer is formed on
the semi-transparent layer in an overlapping manner,
substantially all the incident light enters into the
optical function device, and on the surface that is not
formed with the reflection prevention layer and the semi-
30 transparent layer, reflection to the inside of the
optical function device occurs. More specifically,
neither the reflection prevention layer nor the semitransparent
layer achieves the intended function.
The semi-transparent layer 5 and the reflection
prevention layer 7 are formed on the principal planes
5 opposite to each other, and there is a secondary
advantage in that this reduces the warping of the optical
function device 1. It should be noted that the "warpingu
in this case includes not only one-dimensional bending
but also two-dimensional distortion.
10 When the semi-transparent layer and the reflection
prevention layer are formed on the surfaces opposite to
each other with respect to the base material layer, the
effect of improving the warping of the optical function
device is found in the following procedure.
15 A sample SS-1 and a sample SS-2 were prepared, in
which only semi-transparent layer was formed on one
surface of the base material layer. A sample BS-1 and a
sample BS-2 were prepared, in which the semi-transparent
layer was formed on one surface of the base material
20 layer, and the reflection prevention layer was formed on
the opposite surface. The semi-transparent layer and the
reflection prevention layer of each sample were formed by
stacking inorganic materials of which refractive indexes
are different. The base material layer uses a PC of
25 which thickness is about 90 pm.
When the size of warping of each sample was
measured using a compact laser interferometer made by
FUJIFILM Corporation (F601 (flat surface measurement)),
the following result was obtained.
3 0 Sample SS-1: 0.708 pm, sample SS-2: 0.691 pm
Sample BS-1: 0.606 pm, sample BS-2: 0.669 pm
In this case, the size of warping of each sample is
a difference between the highest point and the lowest
point in the measurement region (36 mmU).
As compared with a case where only the semi-
5 transparent layer is formed on one surface of the base
material layer, the size of warping can be reduced when
the semi-transparent layer and the reflection prevention
layer are formed on the surfaces opposite to each other
with respect to the base material layer. This is
10 considered to be because a film stress by a semitransparent
layer and a film stress by a reflection
prevention layer are cancelled, and the size of the
warping is reduced.
When the optical function device is incorporated
15 into an image-capturing device and the like, the warping
of the optical function device is preferably suppressed.
In particular, when the optical function device is used
as a semi-transparent mirror of a semi-transparent
mirror-fixed-type image-capturing device, warping is
20 preferably suppressed. When the semi-transparent mirror
is greatly warped, the reflection light which is meant to
come into the AF module propagates in a direction
different from the design, and there is adverse effect
on the AF.
25 Figs. 6A and 6B are schematic line diagrams
illustrated to explain how the AF is affected by warping
of the semi-transparent mirror in a semi-transparent
mirror-fixed-type image-capturing device. Figs. 6A and
6B schematically illustrates a cross sectional surface
30 including the image-capturing-based optical axis in a
semi-transparent mirror-fixed-type image-capturing device.
When the semi-transparent mirror 1 0 1 is in a flat
plate shape as illustrated in Fig. 6A, a subject light B
is assumed to enter at an angle of a with respect to the
normal line NA on the semi-transparent mirror 101. At
5 this occasion, the direction in which the reflection
light ROA propagates forms an angle of -a with respect to
the normal line NA.
When the semi-transparent mirror 1 0 1 is greatly
warped and the cross section is an arc shape as
10 illustrated in Fig. 6B, the normal line NB to the tangent
plane upon which the subject light B enters is assumed to
form an angle of P with respect to the normal line NA.
At this occasion, the reflection light ROB propagates in
a direction displaced by an angle of 2P with respect to
15 ROA. Fig. 6B illustrates a case where the semitransparent
mirror 1 0 1 protrudes with respect to the
light incident side, but the case where it protrudes with
respect to the light output side is the same.
As described above, in the configuration in which
20 the reflection light Ro is used for the AF, the
performance of the AF is greatly affected by the warping
of the semi-transparent mirror. Therefore, the reduction
of warping of the optical function device contributes to
the improvement of the AF performance of the semi-
25 transparent mirror-fixed-type image-capturing device.
c2. Second embodiment>
Subsequently, the second embodiment will be
explained. The second embodiment relates to a semitransparent
mirror-fixed-type image-capturing device in
30 which an optical function device of which internal
multiple reflection is suppressed is provided as a semitransparent
mirror.
[Image-capturing device]
The image-capturing device includes an optical
function device, a first light receiving device for
5 receiving transmission light from the optical function
device, and a second light receiving device for receiving
reflection light from the optical function device,
wherein the optical function device fixes the light
incident side with respect to the first light receiving
10 device.
The optical function device includes a base
material layer, a semi-transparent layer formed on a
principal plane of the base material layer, and a
reflection prevention layer formed on a principal plane
15 opposite to the surface formed with the semi-transparent
layer. The semi-transparent layer reflects incident
light with a ratio defined in advance, and transmits the
remaining light. The reflection prevention layer
prevents the light advancing in the base material layer
20 from being reflected by an interface between the base
material layer and the reflection prevention layer and
from being returned back to the inside of the base
material layer. In the optical function device, internal
multiple reflection is suppressed.
25 Therefore, this suppresses emission of high-order
unwanted light from the optical function device, and this
suppresses the appearance of a ghost. This also
suppresses mixing of the noise light in the reflection
light from the optical function device, and the AF can be
30 performed reliably.
(Configuration of image-capturing device)
Fig. 7A is a schematic cross sectional view
illustrating overview of an image-capturing device
according to the second embodiment. Fig. 7B is a
schematic line diagram enlarging and illustrating a
5 portion close to the optical function device. The
schematic configuration of the image-capturing device as
illustrated in Fig. 7A is like what is illustrated in Fig.
10A, but an image-capturing device 11 according to the
second embodiment has a first light receiving device 31
10 instead of the film. For example, the first light
receiving device 31 is an image-capturing device such as
a CCD and a CMOS, and functions as an image sensor.
As illustrated in Fig. 7A, a replaceable imagecapturing
optical system 23 is attached to a housing 21
15 constituting a main body of the image-capturing device 11.
An image-capturing lens 25, a diaphragm, and the like are
arranged in a lens barrel 27, which constitute the imagecapturing
optical system 23. The image-capturing lens 25
of the image-capturing optical system 23 is driven by a
20 focus driving system (not shown), which enables AF
operation. It should be noted that the image-capturing
optical system may be integrally formed with a housing.
Inside of the housing 21, an optical function
device 1 is fixed as a semi-transparent mirror. Above
25 the optical function device 1, a second light receiving
device 33 is provided. The second light receiving device
is, for example, an image-capturing device. The imagecapturing
device has, for example, the function of the AF
sensor. When the AF sensor is arranged as the second
30 light receiving device, it is preferably an AF sensor of
phase difference detection method, but may have a
function of an AF sensor of contrast AF method. The
phase difference detection method and the contrast AF
method may be combined as the AF method. In order to
perform high performance AF even in a dark place or for a
5 subject of a low contrast, AF assist light may be
generated, and the AF evaluation value may be formed from
the returned light.
At the side opposite to the image-capturing lens 25
with respect to the optical function device 1, the first
10 light receiving device 31 is provided. In Fig. 7A, a
shutter mechanism is not shown, but either of a
mechanical shutter or an electronic shutter can be
applied.
The image-capturing device 11 is provided with a
15 display 37 having a function of electronic view finder.
The display 37 is a flat display such as a liquid crystal
display (LCD) and an organic EL (Electroluminescence:
Electroluminescence effect). The display 37 receives a
video signal obtained by causing a signal processing unit
20 (not shown) to process an image-capturing signal
retrieved from the second light receiving device 33
serving as the image-capturing device or the first light
receiving device 31, and displays a current subject image
(motion picture). In the example as illustrated in Fig.
25 7A, the display 37 is provided at the back side of the
housing 21, but this is not limited thereto.
Alternatively, it may be provided on the upper surface of
the housing, and may be a movable-type or a detachabletype.
30 (Arrangement of optical function device)
In this case, the angle at which the optical
function device 1 is fixed will be explained with
reference to Fig. 7B. In a preferable embodiment, the
optical function device 1 is fixed such that an angle 6
formed by the normal line N to the principal plane of the
5 optical function device 1 and the optical axis of the
subject light B is as follows: 5~45d egrees. This is
because, by doing so, the distance for which the subject
light passes the optical function device l(which may be
referred to as an optical distance) can be reduced, and
10 the degradation of the image quality can be reduced. In
addition, this is because it is possible to reduce a
shift d of the light bundle, which is caused when the
subject light is refracted at the interface of the
optical function device 1. Further, this is because, the
15 smaller the angle 5 is, the smaller the reflectance of
the reflection prevention layer is, and the effect of the
reflection prevention by the reflection prevention layer
is increased (low reflection) .
In Fig. 7B, the optical function device 1 is fixed
20 such that the reflection prevention layer 7 is at a side
closer to the first light receiving device 31. On the
contrary, the reflection prevention layer 7 may be at a
side closer to the image-capturing lens 25, but the
optical function device 1 is preferably fixed such that
25 the reflection prevention layer 7 is at a side closer to
the first light receiving device 31. This is because
when the AF module having the AF sensor as the second
light receiving device is arranged above the optical
function device 1, the light that does not pass through
30 the inside of the optical function device 1 can be used
for the AF.
According to the second embodiment, the optical
function device 1 is provided as the semi-transparent
mirror, and therefore, the emission of high-order
unwanted light to the image-capturing device 31 is
5 suppressed. Therefore, the digital image obtained by the
image-capturing device 11 is made with the appearance of
ghost suppressed. When the AF module having the AF
sensor as the second light receiving device is arranged,
mixing of the noise light into the AF module is reduced,
10 and therefore, the AF can be performed reliably. Further,
as compared with the semi-transparent mirror made by
depositing the optical thin film on one surface, warping
of the optical function device 1 is reduced. Therefore,
the reflection light from the optical function device 1
15 can be reliably guided to the second light receiving
device 33.
[Example]
Five types of sample S1 to sample S5 were prepared
as optical function devices, and for each sample,
20 reflectance with respect to wavelength h [nml of
incident light was measured, and each effective
reflectance Re [%I was obtained from the measurement
result. Subsequently, the sample S1 to the sample S5
were respectively incorporated into the image-capturing
25 devices, and images were taken in a dark room using a
light source device as a subject.
(Sample S1 to sample S3)
A PC of which thickness is about 90 pm was used as
a base material layer, and four layers which were
30 arranged Nb20,/Si02/Nb205/Si02f rom the side close to the
base layer material were stacked as the reflection
prevention layer by a sputtering method. The thickness
of each layer in each sample was different from each
other. On a surface opposite to the surface formed with
the reflection prevention layer, a semi-transparent layer
5 was formed, which was constituted by Nb205/Si02 arranged
from the side closer to the base material layer.
(Sample S4)
The sample S4 was prepared in the same manner as
the sample S1 except that two layers including Nb205/Si02
10 arranged from the side closer to the base material layer,
were stacked as the reflection prevention layer.
(Sample S5)
A sample having only a base material layer having
neither the reflection prevention layer nor the semi-
15 transparent layer formed thereon was prepared as the
sample S5.
Fig. 8 is a figure illustrating an effective
reflectance Re [%I with respect to a wavelength h [nm] of
incident light, concerning sample S1 to sample S5.
20 Hereinafter, a measurement device and a measuring method
of the reflectance for calculating the effective
reflectance will be shown.
Measurement device: ultraviolet-visible
spectrophotometer (UBest V560 made by JASCO Corporation)
25 Measuring method: an angle formed by a line normal
to the sample and the optical axis of the incident light
was set as 37 degrees, and the reflection light was
detected with a detector, and each of the reflectance at
each wavelength was measured. As illustrated in Fig. 5,
30 the reflection light from a sample 41 is detected such
that a detector D detects the light reflected by a mirror
M.
Figs. 9A to 9E are figures for explaining images
captured by a light source device, concerning sample S1
to sample S5. Figs. 9A, 9B, 9C, 9D and 9E are figures
5 respectively corresponding to the samples S1, S2, S3, S4
and S5. In Fig. 9, a shaded portion is a region
corresponding to ghost. In the sample S1, no ghost was
confirmed even when the captured image is enlarged. In
the sample S2, ghost was hardly confirmed. In the sample
10 S3, the ghost is clearly confirmed, and the ghost seemed
to be reddish. In the sample S4 and the sample S5, the
ghost is clearly confirmed. For each sample, an average
effective reflectance in a wavelength band of 400 nm to
650 nm is shown as follows.
sample S1. . -0.49 [%I
sample S2. . -1.13 [%I
sample S3. . -1.24 [%]
sample S4. . -3.08 [%I
sample S5. . .4.39 [%I
Hereinafter, the details of the subject and the
image-capturing conditions are shown.
Subject: evaluation/adjustment light source device
(DNP Standard Color Viewer Lamps HDF-51F made by Dai
Nippon Printing Co., Ltd.)
25 Image-capturing condition: IS0 200, F 5.6, exposure
time 1/60 seconds, DRO auto setting, focal length of
image-capturing lens is 18 mm, distance from subject is
about 1 m
From Fig. 8 and Fig. 9, it is understood that
30 appearance of ghost is suppressed by reducing the
reflectance caused by the reflection at the interface at
the light output side of the optical function device.
The color of the appearing ghost is the same as the
result expected from the measurement result of the
reflectance, and this fact also indicates that occurrence
5 of ghost is suppressed by suppressing occurrence of
multiple reflections within the optical function device.
As described above, according to the preferred
embodiment, multiple reflections within the optical
function device can be suppressed, and therefore, the
10 image-capturing device can be configured such that
appearance of ghost is suppressed.
c 3 . Modification
Heretofore, a preferred embodiment has been
explained, but a preferred example is not limited to the
15 above explanation, and various kinds of modifications can
be made.
For example, the optical function device 1 can also
be applied not only to the image-capturing device but
also to reflection mirrors and the like of an exposure
20 device and a microscope. As necessary, a hard coating,
an antifouling coating, a self-cleaning layer, an IR cut
filter, a W cut filter, and the like may be further
stacked in the configuration.
In the above explanation, for example, a digital
25 camera is used as an example of the image-capturing
device 11, but the above configuration may be applied to
a digital camera capable of capturing motion picture.
For example, the disclosure of the present
application may be configured as follows.
30 (1)
An optical function device including:
a base material layer;
a semi-transparent layer formed on a principal
plane of the base material layer, the semi-transparent
layer reflecting light of incident light at a ratio
5 determined in advance and passing remaining light; and
a reflection prevention layer formed on a principal
plane opposite to the principal plane of the base
material layer with respect to the base material layer,
the reflection prevention layer preventing reflection of
10 the light passing through the base material layer.
(2)
The optical function device according to (I),
wherein the base material layer is made of an optically
isotropic material.
15 (3)
The optical function device according to (1) or (2),
wherein a thickness of the base material layer is equal
to or less than 100 pm.
( 4 )
20 The optical function device according to any one of
(1) to (3), wherein an average of an effective
reflectance of the reflection prevention layer in a
wavelength band of 400 nm to 650 nm is equal to or less
than 1.2%.
25 ( 5 )
The optical function device according to any one of
(1) to ( 4 ) , wherein the semi-transparent layer and the
reflection prevention layer are made of a same material.
(6)
3 0 The optical function device according to any one of
(1) to (5), wherein the semi-transparent layer and the
reflection prevention layer are formed by sputtering
method.
( 7 )
The optical function device according to any one of
5 (1) to (5), wherein the semi-transparent layer and the
reflection prevention layer are formed by evaporation
method.
(8
The optical function device according to any one of
10 (1) to ( 4 ) , wherein the reflection prevention layer is a
moth-eye layer.
(9
An image-capturing device includes an optical
function device including:
a base material layer;
a semi-transparent layer formed on a principal
plane of the base material layer, the semi-transparent
layer reflecting light of incident light at a ratio
determined in advance and passing remaining light; and
20 a reflection prevention layer formed on a principal
plane opposite to the principal plane of the base
material layer with respect to the base material layer,
the reflection prevention layer preventing reflection of
the light passing through the base material layer, the
25 image-capturing device further includes a first light
receiving device for receiving transmission light from
the optical function device and a second light receiving
device for receiving reflection light from the optical
function device.
30 (10)
The image-capturing device according to (9),
wherein the first light receiving device is a first
image-capturing device, and the second light receiving
device is a second image-capturing device.
(11)
5 The image-capturing device according to (lo),
wherein the second light receiving device is an autofocus
sensor.
(12)
The image-capturing device according to (ll),
10 wherein the autofocus sensor is an autofocus sensor of
phase difference detection method.
(13)
The image-capturing device according to any one of
(9) to (12), wherein an angle formed by a normal line to
15 a principal plane of the optical function device and an
optical axis of subject light is less than 45 degrees.
(14
The image-capturing device according to any one of
(9) to (13), wherein the principal plane on which the
20 reflection prevention layer is formed is a principal
plane at a side close to the first light receiving device.
REFERENCE SIGNS LIST
1 Optical function device
25 3 Base material layer
5 Semi-transparent layer
5~ High refractive index layer
5 L Low refractive index layer
7 Reflection prevention layer
30 7~1, 7~2 High refractive index layer
7~1 7~2 Low refractive index layer
11 Image-capturing device
21 Housing
23 Image-capturing optical system
25 Image-capturing lens
5 27 Lens barrel
31 First light receiving device
33 Second light receiving device
37 Display

CLAIMS
1. An optical function device comprising:
a base material layer;
5 a semi-transparent layer formed on a principal
plane of the base material layer, the semi-transparent
layer reflecting light of incident light at a ratio
determined in advance and passing remaining light; and
a reflection prevention layer formed on a principal
10 plane opposite to the principal plane of the base
material layer with respect to the base material layer,
the reflection prevention layer preventing reflection of
the light passing through the base material layer.
15 2. The optical function device according to claim 1,
wherein the base material layer is made of an optically
isotropic material.
3. The optical function device according to claim 1,
20 wherein a thickness of the base material layer is equal
to or less than 100 pm.
4. The optical function device according to claim 1,
wherein an average of an effective reflectance of the
25 reflection prevention layer in a wavelength band of 400
nm to 650 nm is equal to or less than 1.2%.
5. The optical function device according to claim 1,
wherein the semi-transparent layer and the reflection
30 prevention layer are made of a same material.
6. The optical function device according to claim 1,
wherein the semi-transparent layer and the reflection
prevention layer are formed by sputtering method.
5 7. The optical function device according to claim 1,
wherein the semi-transparent layer and the reflection
prevention layer are formed by evaporation method.
8. The optical function device according to claim 1,
10 wherein the reflection prevention layer is a moth-eye
layer.
9. An image-capturing device comprising:
an optical function device including a base
15 material layer, a semi-transparent layer formed on a
principal plane of the base material layer, the semitransparent
layer reflecting light of incident light at a
ratio determined in advance and passing remaining light,
and a reflection prevention layer formed on a principal
20 plane opposite to the principal plane of the base
material layer with respect to the base material layer,
the reflection prevention layer preventing reflection of
the light passing through the base material layer;
a first light receiving device for receiving
25 transmission light from the optical function device; and
a second light receiving device for receiving
reflection light from the optical function device.
10. The image-capturing device according to claim 9,
30 wherein the first light receiving device is a first
image-capturing device, and the second light receiving
device is a second image-capturing device.
11. The image-capturing device according to claim 9,
wherein the second light receiving device is an autofocus
5 sensor. Z
. ,
12. The image-capturing device according to claim 11,
wherein the autofocus sensor1is an autofocus sensor of
phase difference detection method.
10
13. The image-capturing device according to claim 9,
wherein an angle formed by a normal line to a principal
plane of the optical function device\and an optical axis
of subject light is less than 45 degrees.
14. The image-capturing device according to claim 9,
wherein the principal plane on which the reflection
prevention layer is formed is a principal plane at a side
close to the first light receiving .device.