JP2003143618A - Color separation optical system and image pickup device employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color separation optical system with an automatic focus detection means suitable for a color video camera and a color television camera or the like and to provide an image pickup device employing the same. SOLUTION: The image pickup device; adopting the color separation optical system having a plurality of prisms, which separate an incident luminous flux into a plurality of color lights in different wavelength bands and emit them; and having an optical split face placed in an optical path of one of a plurality of the prisms and a focus detection means for automatic focusing in an optical path branched by the optical split face, is provided with a means that obtains focus information at a plurality of defocusing positions in the branch optical path without the need for movement in the optical axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color separation optical system and an image pickup apparatus using the same.
The color is separated into three color lights, green light and blue light, and emitted.
It is suitable for a television camera, a video camera or the like provided with a color separation optical system such as a so-called 3P prism and an automatic focus detection means for obtaining a focus signal of a photographing lens by using a light beam passing through the color separation optical system. .

[0002]

2. Description of the Related Art Conventionally, a focus detection method called a hill climbing method has been known as an autofocus method in a photographing device such as a still camera or a video camera. This hill climbing method directly evaluates the sharpness of the image (subject image) and drives the focus lens (focusing lens) to change the focus to find the point where the sharpness of the image is maximum and focus on that point. The in-focus state of the shooting system is obtained as the position.

An in-focus detection apparatus using such an image sharpness evaluation method is disclosed in, for example, Japanese Patent Laid-Open No. 62-103616.
It has been proposed in the publication.

In addition, a so-called wobbling method has conventionally been widely used as one of focus detection methods in video cameras, in which a focus state of an image pickup element is periodically oscillated to monitor a video signal. Japanese Patent Laid-Open No. 61-9
Japanese Patent No. 7616 discloses at least one of imaging lens systems.
The focusing lens is adjusted to the optimum focusing position by vibrating the single lens in the optical axis direction with the vibration coil and comparing the change in the output signal of the image pickup tube with the phase comparator to detect the peak. An automatic focus adjustment device based on the above has been proposed.

Further, in Japanese Patent Laid-Open No. 4-137872,
2. Description of the Related Art A video camera has been proposed which has an automatic focus adjustment device in which an image pickup element is driven by a piezoelectric actuator, and is moved and focused while wobbling.

[0006]

Generally, the method of detecting the focus of the photographing lens by periodically vibrating a part of the image pickup device or the photographing lens, that is, the method of detecting the focus of the photographing lens by performing so-called wobbling is as follows. There was such a problem.

(B) The high-frequency component of the image is smoothed and lost due to the slight vibration of the image to be captured, and the sharpness of the image is reduced. This is because if the recording band of the VTR is narrow to some extent like a home video camera, the deterioration of the high frequency component does not become a problem, but in a color television camera for business use that requires high image quality, the image quality due to wobbling does not increase. The decline becomes a big problem.

(B) Although related to the problem of (a) above, the amplitude of wobbling is limited in order to keep the deterioration of image quality due to wobbling within an allowable value. When the image is greatly blurred, the change in the video signal is small with a small wobbling amplitude, and it is difficult to obtain information about in which direction and how much the focusing lens should be moved. For this reason, if the focus position is largely deviated, it takes time to adjust the focus position, which impairs quick camera work.

On the other hand, in Japanese Unexamined Patent Publication No. 8-502227, a color separation optical system having a plurality of prisms for separating an incident light beam into a plurality of color lights having different wavelength bands and emitting the separated light beams,
A drive is provided in which a light splitting surface is provided in the optical path of one of the plurality of prisms, and a member provided on the exiting surface is moved in an optical axis direction on an exit surface for emitting the light beam split by the light splitting surface. There has been proposed an image pickup apparatus in which a means is provided to effectively prevent a high frequency component of an image from being lowered and to select an optimum wobbling amplitude.

According to the present invention, by appropriately configuring a color separation optical system having a plurality of prisms for separating an incident light beam into a plurality of color lights having different wavelength bands and emitting the separated color lights, highly accurate focusing can be performed without using wobbling. An object of the present invention is to provide a color separation optical system suitable for a video camera, a television camera or the like that can obtain a signal, and an image pickup apparatus using the same.

[0011]

According to a first aspect of the present invention, there is provided a color separation optical system having a plurality of prisms for separating an incident light beam into a plurality of color lights having different wavelength bands and emitting the separated light beams. A light splitting surface is provided in the optical path of one prism of the plurality of prisms, and different light path lengths are provided in the optical axis direction on the exit surface side from which the light beam split by the light splitting surface is emitted. However, an optical means for forming images corresponding to different positions with respect to the optical axis direction on the same surface is provided.

In the color separation optical system of the second aspect of the invention, the light flux from the incident surface is separated into a plurality of color lights having different wavelength bands, the respective color lights are emitted from the emission surface, and are guided to the image pickup element for each color light. A color separation optical system having a plurality of prisms, wherein one prism of the plurality of prisms splits a light beam other than visible light, and a prism is provided between an exit surface of the one prism and an image sensor. Characterized by providing optical means for providing different optical path lengths in the optical axis direction and forming images corresponding to different positions in the optical axis direction on the same plane. .

According to a third aspect of the present invention, in the first or second aspect of the invention, the optical means joins a plurality of prisms, and the incident light incident from one surface of the plurality of prisms has different optical path lengths. It is characterized in that it is configured to be given and emitted from different surfaces.

According to a fourth aspect of the present invention, in the first or second aspect of the invention, the optical means includes a plurality of optical members having different optical path lengths, and one of the plurality of optical members is located in the optical path. It is characterized in that it has a driving unit for driving.

According to a fifth aspect of the present invention, an image pickup device color-separates an incident light beam into a plurality of color lights having different wavelength bands into a part of a camera body in which a lens can be exchanged, and the color beams are emitted from respective emission surfaces to form image pickup elements. In an imaging device provided with the color separation optical system having a plurality of light guiding prisms, the color separation optical system splits and emits a part of a light beam in the optical path of one of the color-separated light beams. Between the exit imaging surface and the focusing imaging element for forming a branching optical path and obtaining a focusing signal of a photographing lens attached to the camera body on the exit surface side of the branching optical path. In addition, the optical means for imparting different optical path lengths with respect to the optical axis direction and forming an image corresponding to different positions with respect to the optical axis direction on the same surface is provided. There is.

According to the sixth aspect of the present invention, an image pickup device color-separates an incident light beam into a plurality of color lights having different wavelength bands into a part of a camera body whose lenses can be exchanged, and emits the light beams from respective emission surfaces to form image pickup devices. In an imaging device provided with the color separation optical system having a plurality of light guiding prisms, the color separation optical system splits and emits a part of a light beam in the optical path of one of the color-separated light beams. A branching optical path is formed, and an imaging element for focusing is provided on the exit surface side of the branching optical path to obtain a focusing signal of a photographing lens attached to the camera body, and the imaging element for focusing is the branching optical path. Are set at different positions in the optical axis direction with respect to the image pickup device provided in the optical path other than, and the signals from the image pickup device provided in the image pickup device and the optical path other than the branching optical path are used. , Is characterized in that a focus signal is obtained.

The invention of claim 7 is characterized in that, in the invention of claim 5 or 6, the luminous flux in the branched optical path is light in the visible wavelength range including green light.

According to an eighth aspect of the present invention, in the fifth, sixth or seventh aspect of the present invention, a focus position control circuit for determining the focus position of the image pickup lens mounted on the camera body from the output signal from the focus image pickup device. And a focusing lens driving means for driving the focusing lens of the imaging lens based on the focusing signal from the focusing position control circuit.

According to the image pickup apparatus of the present invention, a color separation optical system having a plurality of channels for color separation and an image pickup device for each channel are provided in a part of the camera body in which the lens can be exchanged, and thereby an image is obtained. In the image sensor that obtains the signal,
One channel of the color separation optical system uses a light beam other than visible light, gives different optical path lengths in the optical axis direction, and images corresponding to different positions in the optical axis direction. An image is formed on the surface of the image sensor for focusing through an optical means for forming the image on the same surface, and the image is attached to the camera body by using a signal from the image sensor for focusing. The feature is that the focus signal of the lens is obtained.

According to a tenth aspect of the invention, in the invention of the ninth aspect, one channel for obtaining the focusing signal is obtained by branching light that does not include green light, and the focusing signal is
It is characterized in that it is obtained by correcting the difference in image forming position between the focusing channel and the channel of green light or luminance light based on the data on the axial chromatic aberration of the taking lens.

According to an eleventh aspect of the invention, in the tenth aspect of the invention, the light flux incident on the focusing image pickup device is near-infrared light, and is attached to the camera body from an output signal from the focusing image pickup device. A focusing position control circuit for determining the focusing position of the taking lens, and imaging of near-infrared light and visible light based on the focusing signal from the focusing position control circuit based on the data regarding the off-axis chromatic aberration of the taking lens An arithmetic circuit that corrects the position difference,
It is characterized in that it has a focusing lens driving means for driving the focusing lens of the photographing lens based on a signal from the arithmetic circuit.

According to a twelfth aspect of the invention, in the eleventh aspect of the invention, the visible light is green light.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a schematic view of the essential portions of Embodiment 1 of an image pickup apparatus using the color separation optical system of the present invention. In the figure, reference numeral 1 denotes a photographing lens such as a zoom lens, which is detachably attached to the camera body and forms an image of a subject on image pickup devices 3B, 3R, 3G and 4 which will be described later. Reference numeral 2 denotes a color separation optical system, which splits the light from the taking lens 1 into a plurality of color lights having different wavelength bands and into different optical paths to form an image on a plurality of image pickup devices to obtain a color image and at the same time focus. It has a branched optical path for detection.

Reference numeral 201 is a blue separation prism (first prism). Partial surface 212 of the blue separation prism 201
Is provided with a blue reflection dichroic film B, which reflects a light flux of a blue component (blue light), totally reflects it on a surface 211, and emits it from an emission surface (main emission surface) 213. Two
02 is an infrared color separation prism (second prism),
A red reflective dichroic film R is provided on part of the surface 215.

The blue resolving prism 201 and the red resolving prism 202 are arranged with a minute gap therebetween, and the light in the red wavelength band reflected by the red reflection dichroic film R provided on the surface 215 is efficiently totally reflected on the surface 214. The light is emitted from the emission surface (main emission surface) 216.

Reference numeral 203 denotes a prism, which is adhered to the surface 215 of the red separation prism 202, and a part of the green light that has passed through the surface 215 is reflected by the half mirror surface (light splitting surface) 217 so that the exit surface (sub) It is ejected from the emission surface) 218. The optical path reflected by the half mirror surface 217 forms a branched optical path for focus detection.

Reference numeral 204 denotes a green separation prism, which is adhered to the half mirror surface 217 of the prism 203 and emits green light that has passed through the half mirror surface 217 (main emission surface).
Ejected from 219. Ejection surfaces 213, 216, 21
9 are provided with trimming filters (not shown) for blue, red, and green, respectively. Reference numerals 3B, 3R, and 3G denote blue, red, and green image pickup devices (CCD) provided on the main exit surfaces 213, 216, and 219, respectively, and color image signals are obtained from these. Reference numeral 4 is an image sensor for detecting a focus signal.

In this embodiment, the light flux that has passed through the taking lens 1 is incident from the incident surface 211 of the blue separation prism 201. Then, of the incident luminous flux, the luminous flux in the blue wavelength band is reflected by the surface (blue dichroic vapor deposition surface) 212 on which the blue reflection dichroic film B is applied, and then the reflecting surface 211 on the same plane as the incident surface 211 of the blue resolution prism 201.
The light is totally reflected at a, passes through the blue trimming filter, enters the blue image pickup device 3B, and reproduces the color of blue light.

Further, the light flux other than the blue component that has passed through the blue dichroic vapor deposition surface 212 passes through a minute gap between the blue separation prism 201 and the red separation prism 202 to the lens optical axis La.
Incident surface 2 of red separation prism 202 that passes through at a smaller angle and is parallel to the blue dichroic vapor deposition surface 212.
The light is incident on and refracted at 14 and becomes parallel to the lens optical axis La and passes through the red separation prism 202.

Then, of the light fluxes incident on the red separation prism 202, the light flux in the red wavelength band is the surface on which the red reflective dichroic film R is applied (red dichroic vapor deposition surface) 215.
After being totally reflected by the reflecting surface 214a on the same plane as the incident surface 214 of the red separation prism 202, the light passes through the red trimming filter and enters the red image sensor 3R to reproduce the color of the red component. It is carried out.

On the other hand, the light flux of the green component transmitted through the red dichroic vapor deposition surface 215 is incident on the prism 203, and is reflected by the half mirror surface (light splitting surface) 217 to be reflected light and transmitted light.
It is split into two light beams. Of these, half mirror surface 21
The reflected light from 7 is emitted from an emission surface 218 of the prism 203 provided with the focus detection mechanism (driving means) 5, enters a prism X as an optical means to be described later, and is then branched into a plurality of optical paths, respectively, Δd. Light fluxes having different optical path lengths are incident on the image sensor 4 to form green light object images on the surface of the image sensor 4 to obtain a focus signal for the taking lens 1 by a method described later.

The green light transmitted through the half mirror surface 217 of the prism 203 enters the green separation prism 204, exits from the exit surface 219, passes through the trimming filter for green, and is parallel to the lens optical axis La. The light is incident on the image pickup device 3G, and color reproduction of green light is performed.

In this embodiment, three image pickup devices 3B, 3
Color video signals are obtained from R and 3G.

In the present embodiment, the color separation optical system 2 color-separates the light flux from the taking lens 1 into three color lights of blue, red and green lights and guides them to the image pickup devices 3B, 3R and 3G to obtain a color image. It has a three-channel optical path for obtaining a signal and a one-channel optical path for guiding light to the image sensor 4 to obtain a focus detection signal (a branched optical path for focus detection).

FIG. 6 is an explanatory diagram of a so-called hill-climbing focus detection method for obtaining the focus signal of the taking lens 1 in this embodiment.

In the figure, the horizontal axis is the position in the optical axis direction of the image sensor 4, and the vertical axis is the sharpness evaluation value ES of the subject image obtained by the image sensor 4. As shown in the figure, when the position of the image pickup device 4 in the optical axis direction is shifted from the ∞ point to the N point (near point) side as shown by an arrow 4-3, the sharpness evaluation value ES has a peak-like waveform. It becomes A. The peak of this waveform A, that is, the focus position 4-
When the value is 1, the evaluation value ES decreases regardless of which direction the image sensor 4 is displaced. Further, at the position 4-2 of the waveform A, the evaluation value ES increases on the N point side and the evaluation value ES decreases on the ∞ point side, so that the direction of the in-focus position 4-1 can be known. Here, in the present embodiment, evaluation is performed at a plurality of positions (positions in the optical axis direction) of the waveform A by sequentially forming a plurality of images on the image sensor 4 by changing the optical path length by Δd using the prism X. The value ES is obtained, and the in-focus state determination circuit 7 detects the in-focus state. Then, a signal from the focusing position determination circuit 7 is input to the focusing lens drive motor 9 via the connector 8, and the focusing lens drive motor 9 drives the focusing lens.

Thus, in this embodiment, the image pickup device 4
The focus operation is performed by obtaining the direction of the focus position 4-1 in substantially the same manner as when the lens is moved without moving in the optical axis direction.

In this embodiment, part of the green light is reflected by the half mirror surface 217 and emitted from the exit surface 218, and the image is focused on the image sensor 4 via the focus detection mechanism 5 for focus detection. Is forming. At this time, the image formed on the image sensor 4 is a reflected image of an odd number of times, and therefore an inverted image as compared with the images of the image sensors 3B, 3R, and 3G, which are reflected images of an even number (or zero times). Cannot be used at all for focus detection.

The image pickup devices 3B, 3R and 3G are fixed to the exit surface of the color separation optical system by a method described in, for example, Japanese Utility Model Laid-Open No. 63-81481. The position on the optical axis is SMPTE Journal 1989.
September issue, page 647, adjusted based on the criteria described in Mr. Onishi's paper. This color separation optical system
The third prism of the conventional general three-color separation prism is a half mirror surface 217 with a prism 203 and a green prism 2.
It is considered that the prism is divided into two prisms 04. Therefore, the entire prism length can be set to the same optical length as that of the conventional three-color separation prism, the aberration of the photographing lens 1 is not affected, and compatibility is maintained. Also, the color light extracted for focus detection is 60% of the luminance signal.
Since the green light occupies 10%, it is less affected by the axial chromatic aberration of the taking lens 1, and high focusing accuracy can be obtained.

Next, the focus detection mechanism 5 used in this embodiment will be described.

FIG. 2 is a schematic view of the essential portions of Example 1 of the focus detection mechanism in this embodiment. The image emitted from the emission surface 218 of the prism 203 is transmitted through the optical paths x1a,
An optical path difference is given to x1b and x1c to make a plurality of (3 in the figure, but may be 3 or more) branched light, and the optical path length is changed (given) by Δsk and reaches the image sensor 4 on the same plane. ing. The position of the image sensor 4 is substantially in optical alignment with the position on the optical axis of the image sensor 3G with respect to the optical path x1b.
Three image outputs corresponding to the optical paths x1a, x1b, x1c from the image pickup device 4 are input to the focus position determination circuit 7 in FIG. 1 and output as focus position signals at three positions in the optical axis direction. . The focus position signal is transmitted to the taking lens 1 via the connector 8, and the focusing lens drive motor 9 in the taking lens 1 is controlled to adjust the focus position. The first embodiment has features such as a simple and strong structure because it has no driving mechanism for detecting a plurality of focusing signals obtained by the image pickup device 4.

FIG. 3 is a schematic view of the essential portions of Example 2 of the focus detection apparatus according to this embodiment. In the second embodiment, the image sensor 4 is fixed, and the exit surface 218 of the prism 203 is fixed.
A disk Y as an optical member having a transparent rotation axis Ya made of a medium having a refractive index N larger than 1 is inserted between the image pickup device 4 and the image pickup device 4. The disk Y is divided into a plurality of regions Y1, Y2, Y3 ... In the rotation direction, and the thickness in the optical axis direction is changed by Δd in each region. By rotating the disk Y by a drive unit M such as a motor on a plane substantially perpendicular to the optical axis, the optical path length up to the image sensor 4 is changed to form an image on the image sensor 4 at a plurality of different positions in the optical axis direction. The focus detection effect equivalent to wobbling can be obtained. The change amount Δsk of the optical path length when the thickness of the disk Y in the optical axis direction changes by Δd is represented by Δsk = (N-1) Δd. For example, if the disk Y is divided into three regions in the rotation direction, and if it corresponds to 30 frames per second,
The rotation speed RY of the disk Y is RY = 30/3 = 10s- ¹ . In the present embodiment, it is not necessary to keep the angular velocity constant when the disk Y is rotationally driven. For example, in accordance with the amount of blur of the subject, the number of divided regions is increased in order to obtain a defocus width suitable for focus detection. The usage range of the disk Y may be changed depending on whether the amount is large or small.

FIG. 4 is a schematic view of the essential portions of Embodiment 3 of the focus detection mechanism according to this embodiment. In the third embodiment, the image sensor 3
Focusing detection is performed by arranging the image sensor 4 at a position where the optical path length is shifted by Δsk with respect to G in the optical axis direction. In this embodiment, the focus detection output at different positions in the optical axis direction is obtained from the two signals, the signal from the image sensor 3G and the video signal from the image sensor 4.

As described above, in this embodiment, the color separation optical system 2 having a plurality of channels for color separation and the plurality of image pickup devices 3R, 3 are provided in a part of the camera body in which the lens can be exchanged.
G and 3B are provided to obtain color signals.
In addition to the color separation, the color separation optical system has a branch optical path of one channel, and from the output signal from the image pickup device 4 provided in the branch optical path, the focus position of the photographing lens 1 mounted on the camera body is adjusted. Based on a focus signal from the focus position determination circuit and a focus signal from the focus position determination circuit, the focus lens of the photographing lens 1 is driven by the focus lens driving means to perform automatic focus. With such a configuration, focus information is obtained at a plurality of defocus positions without moving in the optical axis direction in the branched optical path.

In the above embodiments, light including green light is branched and used as the focusing channel. But,
This embodiment is applicable not only to a part of green light but also to other colored light or invisible light. Next, an example will be described in which the channel for obtaining the focus signal for achieving the object of the present embodiment does not include green light.

FIG. 5 is a schematic view of the essential portions of Embodiment 2 of an image pickup apparatus having a color separation optical system of the present invention.

In this embodiment, an infrared prism 50 for extracting infrared light is used instead of the prism 203 having a half mirror surface 217 in the color separation optical system 2 as compared with the first embodiment shown in FIG.
1 is used to select near-infrared light from the light flux from the taking lens 1 and guide it to the image pickup device 4, and a focus signal is obtained from this, and other configurations are substantially the same. .

Since this embodiment uses near-infrared light other than visible light, it has the feature that it does not affect the image pickup device when obtaining a color video signal.

In FIG. 5, the light from the taking lens 1 is incident on the incident surface 51 of the first prism (near infrared prism) 501.
1, and reaches the surface 512 which mainly reflects near infrared light. The near-infrared light reflected by the surface 512 is totally reflected by the surface 511, then exits from the exit surface (main exit surface 513), enters the image sensor 4, and forms a near-infrared image on the surface.

On the other hand, the visible light transmitted through the surface 512 is color-separated into three color lights using the three prisms 502, 503 and 504, and an image pickup device 3 for obtaining a color video signal is obtained.
It is incident on B, 3R, and 3G, respectively. That is, of the visible light that has passed through the surface 512 and has entered from the entrance surface 514 of the prism 502, the blue light is the blue light reflection surface 51 of the prism 502.
At 5, the blue light component is reflected. The blue light is totally reflected by the surface 514 and then exits from the exit surface 516 to form a blue light image on the image sensor 3B.

Of the red light and the green light that have passed through the surface 515 and have entered the prism 503 through the surface 517, the red light component is reflected by the red light reflecting surface 518 of the prism 503. The red light is totally reflected by the surface 517 and then emitted from the surface 519 to form a red light image on the image pickup device 3R. Face 51
The green light that has passed through 8 and is incident on the prism 504 passes through the exit surface 520 to form a green image on the image sensor 3G.
Color video signals are obtained by synthesizing the outputs from these three image pickup devices 3B, 3G, and 3R. The holding method of the image sensor 4 and the focus detection method can be the same as those in the above-described embodiments. However, in the present embodiment, the taking lens 1
There is a problem of focusing error due to the axial chromatic aberration of.

As for the taking lens for a commercial color television camera, as described in the article by Mr. Onishi of SMPTE magazine, the axial chromatic aberration changes due to zooming, and the axial chromatic aberration increases toward the telephoto side. . It may also change depending on the focus.

When a human is focusing while looking at the viewfinder, the focus is set to the best focus on the green channel or the luminance channel (combined at a ratio of 60% green, 30% red, and 10% blue). Is normal. Therefore, when the focus signal is obtained from the green channel as in the first embodiment of FIG. 1, there is no problem because it looks as if the human eye is in focus. However, as in the second embodiment of FIG. 5, when the image is not focused, for example, when the image is focused on the near-infrared light, it looks as if human eyes are not in focus. . This focusing error is more remarkable on the telephoto side where the axial aberration is large.

Therefore, in the second embodiment of the image pickup apparatus shown in FIG. 5, a function for correcting this focusing error is added.

In FIG. 5, the output signal from the in-focus position determination circuit 7 is input to the arithmetic circuit 10 in the taking lens 1 via the connector 8. The axial chromatic aberration of the zoom lens is determined as a function of the position of the focusing lens and the focal length (zoom position). In the arithmetic circuit 10, the difference in the axial chromatic aberration between the near infrared light and the light in the visible wavelength region (mainly the green channel or the luminance channel) is stored in advance as data. A signal indicating the state of the zoom lens detected by the focus lens position detector 11 and the zoom position detector 12 is input to the arithmetic circuit 10 to calculate a focus error from the axial chromatic aberration data stored in the arithmetic circuit 10, The focus lens driving motor 9 is controlled after the focus signal input from the controller 8 is corrected.

In the present embodiment, by the above process, a highly accurate automatic focusing operation is performed based on the focusing signal obtained from the near-infrared optical channel (imaging device 4) without any error in axial chromatic aberration. It is possible. Further, since the near-infrared light, which is originally unnecessary for the color television camera, is branched and used for focus detection, the sensitivity of the camera is not lowered, and the near-infrared light to the image pickup devices 3B, 3G, 3R is further reduced. There is also an effect that light can be removed at the same time.

As described above, in this embodiment, the color separation optical system 2
Has an optical path for branching the incident light from the photographing lens 1 into four channels, of which three-channel image pickup devices 3R, 3
A color image is formed from the output signals from G and 3B, and a focus signal is obtained from the remaining 1-channel image sensor 4.

The channel for obtaining the focusing signal at this time is a branch of near-infrared light, and the near-infrared light is calculated by the arithmetic circuit 10 based on the data regarding the axial chromatic aberration of the photographing lens 1 in the focusing signal. Correction of the difference between the image formation positions of light and visible light is added.

Further, in the present embodiment, the channel for obtaining the focusing signal is a branch of light that does not contain green light, and the arithmetic circuit 10 uses the focusing signal to obtain data on the axial chromatic aberration of the taking lens. On the basis of the above, the difference in the image forming position between the focusing channel and the green light or luminance light channel is corrected.

As a result, good automatic focus detection is performed.

[0061]

According to the present invention, by appropriately configuring a color separation optical system having a plurality of prisms for separating an incident light beam into a plurality of color lights having different wavelength bands and emitting the separated color lights, wobbling is not used. It is possible to achieve a color separation optical system suitable for a video camera, a television camera, or the like that can obtain a highly accurate focus signal, and an imaging device using the color separation optical system.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of Embodiment 1 of an image pickup apparatus using a color separation optical system of the present invention.

FIG. 2 is an explanatory diagram of Embodiment 1 of the focus detection mechanism according to the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of a focus detection mechanism according to the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of a focus detection mechanism according to the present invention.

FIG. 5 is a schematic view of a main part of Embodiment 2 of an image pickup apparatus using the color separation optical system of the present invention.

FIG. 6 is an explanatory view of a focus detection method by the hill climbing method used in the present invention.

[Explanation of symbols]

1 Shooting lens Two-color separation optical system 3B Blue color image sensor 3R Red image sensor 3G green image sensor 4 image sensor 5 Mechanism for focus detection 201 Blue prism 202 Red prism 203 prism 204 Green prism 217 Light splitting surface

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03B 13/36 G02B 7/11 D 5C065 17/14 K N F term (reference) 2H011 BA31 BB01 2H042 CA08 CA14 CA17 2H051 AA08 BA45 CB14 EA09 2H083 AA02 AA26 AA28 2H101 EE08 5C065 BB11 CC01 DD01 EE01 EE06 EE13 GG21

Claims (12)

[Claims] 1. A color separation optical system having a plurality of prisms for separating an incident light beam into a plurality of color lights having different wavelength bands and emitting the light, wherein the light is introduced into an optical path of one of the plurality of prisms. A splitting surface is provided, and different light path lengths are provided in the optical axis direction on the exit surface side from which the light beams split by the light splitting surface are emitted, and they correspond to different positions in the optical axis direction. A color separation optical system characterized in that an optical means for forming an image on the same plane is provided. 2. A color separation optical system having a plurality of prisms, each of which splits a light beam from an incident surface into a plurality of color lights having different wavelength bands, emits each color light from an exit surface, and guides the light to an image pickup device for each color light. In the system, one prism of the plurality of prisms splits a light beam other than visible light, and is disposed between the exit surface of the one prism and the image sensor in the optical axis direction. A color separation optical system characterized in that it is provided with optical means for imparting different optical path lengths and forming images corresponding to different positions in the optical axis direction on the same plane. 3. The optical means comprises a structure in which a plurality of prisms are cemented, and incident light beams incident from one surface of the plurality of prisms are provided with different optical path lengths and emitted from different surfaces. The color separation optical system according to claim 1 or 2, wherein 4. The optical unit has a plurality of optical members having optical path lengths different from each other, and has a drive unit for positioning one of the optical members in the optical path. The color separation optical system according to claim 1 or 2. 5. The light beam incident on a part of the camera body with interchangeable lenses is separated into a plurality of color lights having different wavelength bands,
In an image pickup apparatus provided with the color separation optical system having a plurality of prisms which are emitted from respective emission surfaces and guided to an image pickup element, the color separation optical system is provided in the optical path of one of the color separated light beams. A branch optical path for splitting and emitting a part of the light flux, and a focusing image sensor for obtaining a focus signal of a photographing lens attached to the camera body on the exit surface side of the branch optical path; Different optical path lengths are provided in the optical axis direction between the surface and the focusing image pickup device, and images corresponding to different positions in the optical axis direction are formed on the same surface. An image pickup device comprising: 6. The light beam incident on a part of the camera body with interchangeable lenses is separated into a plurality of color lights having different wavelength bands,
In an image pickup apparatus provided with the color separation optical system having a plurality of prisms which are emitted from respective emission surfaces and guided to an image pickup element, the color separation optical system is provided in the optical path of one of the color separated light beams. In, forming a branch optical path for splitting and emitting a part of the light flux, and having a focusing image sensor for obtaining a focus signal of a photographing lens attached to the camera body on the exit surface side of the branch optical path, The focusing image sensor is set at a position different in the optical axis direction with respect to an image sensor provided in an optical path other than the branch optical path, and the focusing image sensor and an optical path other than the branch optical path are set. An image pickup apparatus, wherein a focus signal is obtained by using a signal from an image pickup element provided in. 7. The image pickup device according to claim 5, wherein the light flux in the branched optical path is light in a visible wavelength range including green light. 8. A focusing position control circuit for determining a focusing position of an imaging lens mounted on a camera body from an output signal from the focusing imaging device, and focusing from the focusing position control circuit. 8. The image pickup apparatus according to claim 5, further comprising a focus lens driving unit that drives a focus lens of the image pickup lens based on a signal. 9. A color-separation optical system having a plurality of channels for color separation and an image-capturing device for each channel in a part of a camera body in which a lens is replaceable One channel of the color separation optical system uses a light beam other than visible light, gives different optical path lengths in the optical axis direction, and images corresponding to different positions in the optical axis direction. An image is formed on the surface of the image sensor for focusing through an optical means for forming the image on the same surface, and the image is attached to the camera body by using a signal from the image sensor for focusing. An image pickup apparatus, wherein a focusing signal of a lens is obtained. 10. The one channel for obtaining the focus signal is a branched light not including green light,
The focusing signal is obtained by adding the correction of the difference in image forming position between the focusing channel and the green light or luminance light channel based on the data on the axial chromatic aberration of the taking lens. The image pickup apparatus according to claim 9. 11. A light flux incident on the focusing image sensor is near-infrared light, and a focus position of a photographing lens mounted on a camera body is determined from an output signal from the focusing image sensor. A focus position control circuit, and an arithmetic circuit for adding to the focus signal from the focus position control circuit a correction for the difference between the image formation positions of near infrared light and visible light based on data relating to off-axis chromatic aberration of the taking lens. 11. The image pickup apparatus according to claim 10, further comprising focusing lens driving means for driving a focusing lens of the photographing lens based on a signal from the arithmetic circuit. 12. The image pickup apparatus according to claim 11, wherein the visible light is green light.