JP2008058412A - Imaging optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system including a prism in which the deterioration of definition of a picked-up image is suppressed without impairing characteristics of a thin film formed on the reflection surface, and to provide an imaging apparatus. <P>SOLUTION: In the imaging optical system at least including the prism 150 and a lens system which are arranged in this order from the object side toward the image surface side, the prism 150 is provided with a reflection surface which reflects light made incident, a thin film which is formed on the reflection surface and is composed of one layer and a metal film 155 formed on the thin film, wherein a film thickness of the thin film satisfies a conditional expression: p/10≤(np(λ)/nA(λ))×d(λ)×β≤p. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging optical system and an imaging apparatus, and more particularly to an imaging optical system and an imaging apparatus including a prism having a thin film formed on a reflecting surface.

  In recent years, digital still cameras (hereinafter simply referred to as digital cameras) capable of converting an optical image of a subject into an electrical image signal and outputting it have rapidly spread. In recent years, in particular, a digital camera with a high-magnification zoom is demanded, and a compact camera that is further reduced in size and thickness is demanded.

  In order to achieve compactness, for example, a camera using a retractable structure in an imaging optical system has been proposed. However, when the retractable structure is used, there is a problem that an actuator and a mechanism part for expanding and contracting the lens system are required, and the configuration of the lens barrel is complicated.

On the other hand, as another means for realizing downsizing, a technique has been proposed in which a reflecting member is provided in the imaging optical system and the optical axis of the imaging optical system is bent (for example, Patent Documents 1 and 2). Patent Document 1 and Patent Document 2 disclose a configuration in which a prism having an internal reflection surface that bends a light beam by 90 ° is disposed in a lens group disposed closest to the object side in an imaging apparatus including a zoom lens system. . In the imaging devices described in Patent Literature 1 and Patent Literature 2, subject light incident on the prism is reflected by the internal reflection surface and converged on the imaging device. That is, in the imaging devices described in Patent Literature 1 and Patent Literature 2, the thickness of the imaging device is set to be larger than that of the prism and the prism by bending in a plane perpendicular to the optical axis of the lens group on which the object light is incident. It can be determined by the lens element arranged on the side. Thus, Patent Documents 1 and 2 are able to provide an imaging device with a reduced thickness.
JP 2004-004533 A JP 2003-202500 A

  In order to bend the incident light beam inside the prism, a metal film is provided on the reflection surface inside the prism made of glass, for example. The metal film can be formed on the glass surface by a method such as vapor deposition or sputtering, but a protective film may be provided between the glass surface and the metal film in order to improve the adhesion between the glass and the metal film. .

  Moreover, since the reflectance of a metal film becomes low compared with the case where light is reflected by total reflection, it is also generally performed to provide an increased reflection film between the glass and the metal film. However, when a thick film, such as a protective film or a reflection-enhancing film, is provided between the reflecting surface of the prism and the metal surface, there is a problem in that the resolution of an image to be captured is deteriorated.

  Accordingly, an object of the present invention is to provide an imaging optical system and an imaging apparatus including a prism in which degradation of resolution of an image to be captured is suppressed without impairing characteristics of a thin film formed on a reflecting surface.

The object of the present invention is achieved by an imaging optical system having the following configuration.
An imaging optical system that forms an optical image of a subject on an imaging device,
Including at least a prism and a lens system arranged in order from the object side to the image plane side,
The prism is
A reflective surface that reflects incident light;
A thin film formed on the reflecting surface and composed of one layer;
A metal film formed on the thin film,
An imaging optical system, wherein the thin film satisfies the following conditional expression (1).
p / 10 ≦ (np (λ) / nA (λ)) × d (λ) × β ≦ p
However,
λ: Median value of the wavelength band to be used among the wavelength bands of incident light β: Image magnification of the lens system arranged on the image plane side from the prism p: Size of one pixel of the image sensor d (λ): At wavelength λ Thin film thickness np (λ): Refractive index of prism at wavelength λ nA (λ): Refractive index of thin film at wavelength λ.

  According to the present invention, it is possible to provide an imaging optical system and an imaging apparatus including a prism in which degradation of resolution of an image to be captured is suppressed without impairing characteristics of a thin film formed on a reflective surface.

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating a configuration of a lens barrel in the first embodiment. FIGS. 1A to 1D are a top view, a front view, a bottom view, and a cross-sectional side view of a lens barrel 100, respectively. Represents. The lens barrel 100 includes a first holding unit 101 that holds the most object side lens unit L1, a second holding unit 102 that holds the reflective optical unit L2 including the prism 150, and a third holding unit that holds the image side lens unit L3. And a holding unit 103.

  As shown in FIG. 1D, the zoom optical system L and the image sensor 110 are held inside the lens barrel 100. The image sensor 110 is, for example, a CCD (Charge Coupled Device) that converts an optical image formed by the zoom optical system L into an electrical image signal. Note that the imaging element may be a CMOS (Complementary Metal-Oxide Semiconductor) or a MOS sensor.

  The zoom optical system L includes, in order from the subject side, a most object side lens unit L1, a reflection optical unit L2, and an image side lens unit L3. The zoom optical system L performs zooming and focusing by moving each lens group in the optical axis direction, and forms an optical image of the subject on the image sensor 110.

  The most object side lens unit L1 includes a plurality of lens elements, and guides incident subject light to the reflection optical unit L2. Each lens element constituting the most object side lens unit L1 is arranged along the Z-axis direction. The reflective optical unit L2 includes a prism 150 and a plurality of lens elements. Here, the prism 150 is a reflecting member that reflects light from the subject on the inner surface of the reflecting surface and bends its optical axis to approximately 90 degrees. The reflective surface of the prism 150 is provided with a protective film or a reflective film, which will be described later, and a metal film, and the optical axis of light incident from the Z-axis direction is bent in the −Y-axis direction.

  The image side lens unit L3 includes a plurality of lens elements, and condenses the subject light reflected by the reflection optical unit L2 on the image sensor 110. The lens elements constituting the image side lens unit L3 are arranged along the Y-axis direction, and the optical axis forms an angle of about 45 degrees with respect to the reflecting surface of the prism 150. As described above, since the zoom optical system L includes the reflection optical unit L2, a part of the zoom optical system can be arranged in the Y-axis direction, so that the camera body can be reduced in thickness and size. The arrangement of the zoom optical system described above is merely an example. For example, the prism 150 may be arranged so as to reflect the optical axis of light incident from the Z-axis direction in the X-axis direction. In such a case, the image side lens unit L3 and the image sensor 110 are arranged along the X-axis direction.

  Next, a detailed configuration of the reflective optical unit L2 will be described. FIG. 2 is a schematic enlarged view of the second holding unit 102 that holds the reflective optical unit L2. In FIG. 2, components other than the prism 150 and a part of the lens barrel are omitted for easy understanding of the position of the prism 150. A reflection optical unit L2 including a prism 150 is held inside the second holding unit 102, an entrance port 201 is provided on the object side, and an exit port 202 is provided on the image side.

  In the second holding unit 102 configured as described above, light incident from the incident port 201 is incident on the reflecting surface of the prism 150 at an incident angle of approximately 45 degrees and is reflected in the direction of the exit port 202. The light that has passed through the exit port 202 is guided to the image side lens unit L3, and an optical image of the subject is formed on the image sensor 110.

FIG. 3A is a schematic cross-sectional view of the second holding portion 102, and FIG. 3B is an enlarged view of the A portion. FIG. 4 shows a case where light is incident in the enlarged view of FIG. As shown in the upper diagram, in the present embodiment, a protective film 152 is provided between the reflecting surface of the prism 150 and the metal film 155 in order to improve adhesion. Incident light 604 is transmitted through the prism 150, part of which is reflected at the interface between the prism 150 and the protective film 152 and propagates as reflected light 605. Part of the incident light beam 604 is transmitted through the prism 150 and the protective film 152, reflected at the interface between the protective film 152 and the metal film 155, and propagates as reflected light 606. For this reason, the separation distance d ′ between the light beam 605 and the light beam 606 changes according to the film thickness of the protective film 152. The relationship between the thickness d of the protective film and the separation distance d ′ is expressed by the following equation.
d ′ (λ) = (np (λ) / nA (λ)) × d (λ) (1)
Where d ′ (λ): separation distance of the light beam 605 and the light beam 606 at the wavelength λ
d (λ): film thickness of the protective film 152 at the wavelength λ
np (λ): Refractive index of prism at wavelength λ
nA (λ): the refractive index of the protective film at the wavelength λ.

Further, when the image magnification of the lens system (that is, the image side lens unit L3) disposed on the image plane side from the prism 150 is β, the separation distance d ′ satisfies the following expression.
p / 4 <d ′ × β <p (2)
Substituting equation (1) into equation (2),
p / 4 ≦ (np (λ) / nA (λ)) × d (λ) × β (λ) ≦ p (3)
Where p is the size of one pixel of the image sensor. The film thickness d of the protective film 152 is set so as to satisfy Expression (3).

  When the values of d ′ × β and (np (λ) / nA (λ)) × d (λ) × β (λ) exceed the upper limits of the expressions (2) and (3), the separation distance d ′ Therefore, a large low-pass effect is generated and the resolution performance is deteriorated. On the other hand, the lower limit is set so that the film can be formed relatively easily. However, p / 4 or less may be used if the film thickness can be reduced by technical advancement. Further, even if it is a case of p / 10 or less, the resolution performance is not affected.

More preferably, the film thickness d of the protective film 152 is set so as to satisfy the following expression.
p / 4 ≦ (np (λ) / nA (λ)) × d (λ) × β (λ) ≦ p / 2 (4)
By setting the film thickness d (λ) so as to satisfy Expression (4), it is possible to further suppress the deterioration of resolution.

Here, the size of one pixel of the image sensor 110 is p = 2.5 μm, the refractive index of the prism is np (λ) = 1.88, the refractive index of the protective film is nA (λ) = 1.45, and the image side lens unit L3. The condition of the film thickness d (λ) of the protective film when the image magnification β = 1.5 is preferably in the following range from the equation (3).
0.32 μm ≦ d ≦ 1.29 μm
Further considering the wavelength, the film thickness d is
0.4λ ≦ d ≦ 0.82λ
It is desirable that

Further, from the equation (4), the condition of the film thickness d (λ) of the protective film is
0.32 μm ≦ d ≦ 0.65 μm
It is desirable that

  In this way, by forming the protective film according to the film thickness conditions shown in this embodiment, an imaging optical system including a prism with little deterioration in resolution can be obtained without impairing the adhesion between the reflecting surface of the prism and the metal film. Can be provided.

  Note that since the refractive indexes of the prism 150 and the protective film 152 change depending on the wavelength, each formula shown in this embodiment is appropriately changed in accordance with the refractive index and wavelength of the wavelength band actually used. Also good.

(Embodiment 2)
Next, an imaging optical system according to Embodiment 2 will be described. FIG. 5 is an enlarged view of a part of the prism included in the second embodiment. The prism according to the present embodiment has substantially the same configuration as the prism according to the first embodiment. However, the reflection surface of the prism is provided with an increased reflection film 160 for improving the reflectance instead of the protective film 152. Is different. In the present embodiment, a two-layer thin film (increased reflection film) is formed on the reflection surface. For convenience of explanation, the same parts as those in the first embodiment will be described with the same reference numerals.

  In FIG. 5, incident light 704 is transmitted through the prism 150, and part of the transmitted light is reflected at the interface between the prism 150 and the first thin film and propagates as reflected light 705. Further, a part of the light transmitted through the prism further passes through the first and second thin films, and then is reflected at the interface with the metal film 155 and propagates as reflected light 606. For this reason, as in the first embodiment, the separation distance d ′ between the light beam 705 and the light beam 706 changes according to the film thicknesses d1 and d2 of the increased reflection film 160.

  In the present embodiment, a simulation was performed on the reflectance at each interface of the prism, the enhanced reflection film, and the metal film. In order to calculate simply, the simulation was performed on the assumption that the material of the prism was a glass material having no wavelength dependency, and the thin film material was also small in wavelength dependency.

図６（ｂ）は、プリズム１５０の一部の拡大図と反射特性を示す図である。図６（ａ）と異なりプリズム１５０の反射面には増反射膜１６０ｂと金属膜１５５が設けられる。表２は増反射膜１６０ｂ及び金属膜１５５の膜構成を示す。図６（ｂ）及び表２から、増反射膜１６０ｂは４層の薄膜と１層の金属膜が積層され、ｐ偏光およびｓ偏光ともに約８０％程度以上の反射率であることが分かる。図６（ａ）、（ｂ）の結果から、プリズムと増反射膜との界面におけるｐ偏光の反射率は小さく、金属膜との界面における反射率は大きい。これに対して、プリズムと増反射膜との界面におけるｓ偏光の反射率は大きく、金属膜の界面に到達する光線強度は低い。このようにｐ偏光とｓ偏光の反射面は異なっており、反射面による光線分離が発生していることがわかる。

FIG. 6A is an enlarged view of a part of the prism 150 and a reflection characteristic. The reflection surface of the prism 150 is provided with an increased reflection film 160a. Table 1 shows the film configuration of the enhanced reflection film 160a. As shown in FIG. 6A and Table 1, the reflective film 160a is formed by laminating four thin films, and the reflectance of p-polarized light is low while the reflectance of s-polarized light is high. From this, it can be seen that most of the s-polarized light is reflected in the vicinity of the interface between the prism 150 and the increased reflection film 160a, and the p-polarized light is transmitted through the increased reflection film 160a.

FIG. 6B is an enlarged view of a part of the prism 150 and a diagram showing reflection characteristics. Unlike FIG. 6A, the reflective surface of the prism 150 is provided with an increased reflection film 160 b and a metal film 155. Table 2 shows the film configuration of the reflective reflection film 160b and the metal film 155. From FIG. 6B and Table 2, it can be seen that the reflective reflection film 160b is formed by laminating four layers of thin films and one layer of metal film, and has a reflectance of about 80% or more for both p-polarized light and s-polarized light. From the results of FIGS. 6A and 6B, the reflectance of p-polarized light at the interface between the prism and the increased reflection film is small, and the reflectance at the interface with the metal film is large. On the other hand, the reflectance of s-polarized light at the interface between the prism and the increased reflection film is large, and the light intensity reaching the interface between the metal films is low. Thus, it can be seen that the reflection surfaces of the p-polarized light and the s-polarized light are different, and the light beam is separated by the reflective surface.

For example, when the design center wavelength λ = 550 nm, the refractive index nd = 2.3 of TiO ₂ , and the refractive index nd = 1.45 of SiO ₂ , the total thickness of the increased reflection film is
1.0 × 0.55 × 2.3 + 0.5 × 0.55 × 1.45 = 1.66 μm.
The separation distance d ′ of light rays in the film configuration of Table 2 is as follows: d ′ = 1.5λ × 2 × sin 45 ° = 1.16 μm under the condition where the incident angle is 45 degrees.
It becomes.

For this reason, when the magnification of the optical system located on the image plane side from the prism 150 is enlarged to about 1.5 to 2 times, the resolution performance is affected, and the image quality deteriorates. Therefore, it is preferable to make the thickness of the increased reflection film thinner. For example, the increased reflection film may be formed by laminating two thin films as shown in Table 3. FIG. 7A is a diagram showing the reflection characteristics in the film configuration of Table 3. From FIG. 7A and Table 3, the reflectance of s-polarized light and p-polarized light at the interface between the prism and the increased reflection film is 40% or less. Therefore, most of the incident light is transmitted through the enhanced reflection film formed by laminating two thin films.

Table 4 shows a film configuration when a metal film 155 is further provided in addition to the film configuration of Table 3. FIG. 7B is a diagram showing the reflection characteristics in the film configuration of Table 4. From FIG. 7B and Table 4, it can be seen that the reflectance of s-polarized light and p-polarized light is about 80% or more.

  7A and 7B, most of the light incident on the prism in which the two-layer thin reflection film 160 and the metal film 155 are laminated is transmitted through the reflection film 160, and the metal film. Reflected at 155. That is, since both s-polarized light and p-polarized light are reflected by the metal film, it is possible to suppress image quality deterioration due to light beam separation.

In order to suppress the deterioration of the image quality, not only the film thickness of the reflective reflection film is reduced, but the prism material may be changed to a material having a higher refractive index. Table 5 shows the film configuration when a prism having a high refractive index is used, and FIG. 8A shows the reflection characteristics. From FIG. 8A and Table 5, the reflectance is 10% or less for both s-polarized light and p-polarized light, and most of the incident light is transmitted through the increased reflection film 160.

Table 6 shows a film configuration when a metal film is further provided in addition to the film configuration of Table 5. FIG. 8B is a diagram showing the reflection characteristics in the film configuration of Table 6. The reflectance of both s-polarized light and p-polarized light is 70% or more, and most of the incident light is reflected.

As shown in FIGS. 8A and 8B, by changing the material of the prism to a material having a high refractive index, most of the light incident on the prism is transmitted through the increased reflection film and reflected by the metal film. Therefore, it is possible to suppress image quality deterioration due to light beam separation. At this time, it is desirable to set the film thickness of the reflective reflection film so as to satisfy the following conditions.
0.1λ ≦ d ≦ 1.0λ (5)
Here, d is the total thickness of the thin film (film thickness of the enhanced reflection film).
When the film thickness d is less than or equal to the lower limit of the formula (5), it becomes difficult to control the film thickness and the adhesion is deteriorated, which adversely affects the environmental resistance performance of the thin film. On the other hand, when the film thickness d exceeds the upper limit, the image quality deteriorates due to light beam separation.

The film thickness d preferably further satisfies the following formula.
0.5λ ≦ d ≦ 1.0λ

  It should be noted that the reflectance of s-polarized light in the prism provided with only the increased reflection film is higher than the reflectance of s-polarized light in the prism provided with the increased reflection film and the metal film at the median of the wavelength bands to be used among the wavelength bands of the incident light. Needs to be sufficiently small, for example, 50% or less is desirable.

In addition, as in the first embodiment, resolution degradation can be suppressed by setting the film thickness d so as to satisfy the following expression.
p / 10 ≦ (np (λ) / nA (λ)) × d (λ) × β (λ) ≦ p (6)
Where d ′ (λ): separation distance of light rays at wavelength λ
d (λ): film thickness of the enhanced reflection film at wavelength λ
np (λ): Refractive index of prism at wavelength λ
nA (λ): When the upper limit of the average value expression (6) of the refractive index of the light-reflecting film at the wavelength λ is exceeded, the separation distance of the light beam exceeds the spatial resolution of the image pickup device, and a large low-pass effect is generated and resolution. Performance deteriorates.

On the other hand, the lower limit is set to a condition that makes it relatively easy to form a film, but is not limited to this as long as the film thickness can be reduced by technical progress. For example, even if it is p / 10 or less, the resolution performance is not affected.

Further, the film thickness d is preferably set so as to satisfy the following formula.
p / 4 ≦ (np (λ) / nA (λ)) × d (λ) × β (λ) ≦ p / 2

  As described above, by configuring the increased reflection film according to the film thickness condition described in this embodiment, it is possible to provide an imaging optical system including a prism with little deterioration in resolution without impairing the increased reflection characteristic.

(Embodiment 3)
Next, a digital still camera (hereinafter simply referred to as a digital camera) of Embodiment 3 will be described. The digital camera according to the present embodiment includes the imaging optical system according to the first and second embodiments. For convenience of explanation, the same parts as those in the first and second embodiments will be described with the same reference numerals.

  FIG. 9 is a schematic configuration diagram of the digital camera 1000, where (a) is a front view and (b) is a rear view. In FIG. 9, a digital camera 1000 includes a housing 2, an optical viewfinder 1103, a strobe 1104, a shutter button 1105, a battery unit 1106, an image storage unit 1107, an image display unit 1108, a zoom position switching unit 1109, and an embodiment. The zoom lens unit 1101 and the lens barrel 1110 have the same configuration as that of 1 or 2.

  The lens barrel 1110 has substantially the same configuration as in the first and second embodiments. That is, the lens barrel 1110 includes a first holding unit that holds the most object side lens unit L1, a second holding unit that holds the reflective optical unit L2 including the prism 150, and a third holding unit that holds the image side lens unit L3. The zoom optical system L and the image sensor 110 are held inside, but unlike the above embodiment, the prism 150 reflects the optical axis of light incident from the Z-axis direction in the X-axis direction. Placed in

  The battery unit 1106 is a secondary battery such as a dry battery or a lithium ion battery, for example, and supplies power to the digital camera 1000. The image storage unit 1107 is, for example, a semiconductor memory that stores the image signal converted into an electrical signal by the image sensor 110. Note that the image storage unit 1107 may be configured to be removable from the housing 2. The image display unit 1108 is, for example, a liquid crystal monitor or an organic EL monitor that displays the image signal output from the image sensor 110 or the image signal stored in the image storage unit 1107 as a visible image. The zoom position switching unit 1109 is operated by the user and switches the zoom optical system L to the telephoto side or the wide angle side.

  With this configuration, the thickness of the digital camera of this embodiment can be reduced, and a compact digital camera can be provided. In addition, by providing a protective film or an increased reflection film on the prism reflection surface in the lens barrel 1110 under the conditions described in the first and second embodiments, the resolution of the image to be captured can be reduced without deteriorating the characteristics of the thin film. A digital camera in which deterioration is suppressed can be provided.

  Although the digital camera of this embodiment includes an optical viewfinder, an electronic viewfinder using liquid crystal may be used. Alternatively, such a function may be realized by the image display unit 1108 without providing a finder.

  In the first to third embodiments, the case where a zoom lens is used has been described as an example. However, the same effect can be obtained even with a fixed focus.

  The optical system of the present invention and the prism included in the optical system are suitable for a digital camera, a digital video camera, a mobile phone terminal with a camera function, a PDA, an in-vehicle camera, and the like that require a high-quality captured image.

Schematic showing the configuration of the lens barrel in the first embodiment Schematic enlarged view of a second holding unit that holds the reflective optical unit in the first embodiment. 3A is a schematic sectional view of the second holding portion, and FIG. 3B is an enlarged view of the A portion. The enlarged view of the A section in which light entered in Embodiment 1. Partial enlarged view of the prism in the second embodiment 6A is an enlarged view of a part of the prism and a diagram showing the reflection characteristics, and FIG. 6B is an enlarged view of a part of the prism and a diagram showing the reflection characteristics. FIG. 7A is a diagram showing the reflection characteristics in the film configuration of Table 3, and FIG. 7B is a diagram showing the reflection characteristics in the film configuration of Table 4. FIG. 8A shows the reflection characteristics, and FIG. 8B shows the reflection characteristics in the film configuration of Table 6. Schematic configuration diagram of a digital camera according to Embodiment 3

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Lens barrel 101 1st holding | maintenance part 102 2nd holding | maintenance part 103 3rd holding | maintenance part 110 Image pick-up element 150 Prism 152 Protective film 155 Metal film 604 Incident light 605,606 Reflected light

Claims (4)

An imaging optical system that forms an optical image of a subject on an imaging device,
Including at least a prism and a lens system arranged in order from the object side to the image plane side,
The prism is
A reflecting surface that reflects incident light;
A thin film formed on the reflecting surface and composed of one layer;
A metal film formed on the thin film,
An imaging optical system, wherein the thickness of the thin film satisfies the following conditional expression:
p / 10 ≦ (np (λ) / nA (λ)) × d (λ) × β ≦ p
However,
λ: Median value of the wavelength band to be used among the wavelength bands of incident light β: Image magnification of the lens system arranged on the image plane side from the prism p: Size of one pixel of the image sensor d (λ): At wavelength λ Thin film thickness np (λ): Refractive index of prism at wavelength λ nA (λ): Refractive index of thin film at wavelength λ. The thin film further comprises a plurality of layers,
The imaging optical system according to claim 1, wherein the thickness of the thin film satisfies the following conditional expressions.
0.1λ ≦ d (λ) ≦ 1.0λ
p / 10 ≦ (np (λ) / nA (λ)) × d (λ) × β ≦ p
However,
λ: Median value of the wavelength band to be used among the wavelength bands of incident light β: Image magnification of the lens system arranged on the image plane side from the prism p: Size of one pixel of the image sensor d (λ): At wavelength λ Thin film thickness np (λ): Refractive index of prism at wavelength λ nA (λ): Average value of refractive index of thin film at wavelength λ.   The imaging optical system according to claim 1, wherein the reflecting surface of the prism reflects incident light so as to bend the optical axis of the imaging optical system by approximately 90 degrees. The imaging optical system according to claim 1 or 2,
An imaging apparatus comprising: an imaging sensor that receives an optical image of a subject formed by the imaging optical system, converts the optical image into an electrical image signal, and outputs the electrical image signal.

Images