JPH0548951A - Image pickup device - Google Patents

Abstract

PURPOSE:To cope with the change of the focal distance of an image pickup lens with a phase type optical low-pass filter when the phase type optical low- pass filter is arranged in front of the image pickup lens and to collect a large amount of information for detecting focusing at the time of AF. CONSTITUTION:The device consists of an image pickup lens 20 with variable focal distance, a solid-state image pickup element 30 forming the optical image of an object via the lens 20, a phase type optical low-pass filter 10 provided freely rotatably in front of the lens 20, and a means rotating the filter 10 corresponding to the focal distance of the lens 20 for the purpose of eliminating a prescribed space frequency component equivalent to the picture element pitch of the element 30. A means which rotates the optical low-pass filter 10 by 90 deg. from the state where the space frequency component in the horizontal direction can be eliminated or retracted from the image pickup system when the focusing is detected by an AF detection circuit 36, and which restores the original state of the filter 10 when the image is picked up is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device, and more particularly to an image pickup device using a phase type optical low pass filter.

[0002]

2. Description of the Related Art Generally, in a solid-state image sensor (CCD) used in a video camera or an electronic still camera,
Since the incident light image is sampled by the sensors arranged at regular intervals in the vertical direction and the horizontal direction, the highest spatial frequency that can be resolved is ½ of the sampling spatial frequency determined by the array of sensors, that is, the Nyquist frequency. Frequency. If the incident light image includes a spatial frequency higher than the Nyquist frequency, the image is folded back within the normal band to generate a false signal or a moire effect.

Therefore, in this type of image pickup apparatus, this high frequency is removed by an optical low-pass filter (hereinafter referred to as OLPF) before sampling.
This OLPF is a crystal OLP that utilizes the birefringence of a crystal.
F or a phase type OLP whose surface is periodically changed into an uneven shape
F, and the phase type OLPF has an advantage of low cost because it can be mass-produced by molding. Incidentally, the OLPF is generally arranged closer to the CCD than the variable power system of the taking lens.

Further, an autofocus device (AF device)
One of them is to perform focus detection based on an output signal from a CCD that photoelectrically converts subject light incident through the OLPF to adjust the focus of the photographing lens. That is,
The high-frequency component of the output signal obtained from the CCD is extracted and integrated, and the integrated value is used as the AF evaluation value for focus determination.
The focus of the taking lens is adjusted so that the evaluation value becomes maximum.

[0005]

By the way, the phase type OL
If the PF is arranged in front of the taking lens whose focal length (shooting magnification) is variable, the phase-type OLPF cannot cope with the change in the focal length of the taking lens, and it becomes impossible to remove a desired spatial frequency component. .. If the phase type OLPF is arranged in front of the taking lens, the back length of the taking lens can be shortened, which is advantageous in terms of space.
Also, ghosts are less likely to appear. Further, there is an advantage that the unevenness of the phase type OLPF can be increased, the optical specifications can be loosened, and the OLPF can be easily removed from the optical system when adjusting the back focus of the taking lens, which facilitates the adjustment.

On the other hand, the AF device of the above conventional image pickup device is
As shown by the solid line in FIG. 6, the MTF (modulation transfer functi) of a predetermined spatial frequency (f _c ) component is calculated by the OLPF.
Video signal with reduced on) (information in range A shown by diagonal lines)
Since the focus detection is performed based on the
There is a problem that it is difficult to focus on the subject having the predetermined spatial frequency component.

An object of the present invention is to deal with a change in the focal length of a photographing lens with one phase type OLPF when the phase type OLPF is arranged in front of the photographing lens.
An object of the present invention is to provide an imaging device that is advantageous in terms of space and cost. Another object of the present invention is to provide an image pickup apparatus capable of removing a false signal by the OLPF and capable of obtaining a large amount of information for focus detection during AF.

[0008]

In order to achieve the above-mentioned object, the present invention comprises a taking lens having a variable focal length, a solid-state image pickup device on which a subject light image is formed through the taking lens,
The phase-type optical low-pass filter rotatably arranged in front of the photographing lens, and the phase-type optical low-pass filter for removing a predetermined spatial frequency component corresponding to the pixel pitch of the solid-state image sensor are focused on the photographing lens. And a means for rotating according to the distance.

In order to achieve the above-mentioned other object, the present invention is arranged rotatably around an optical axis of a solid-state image pickup device on which a subject light image is formed through a photographing lens and an optical axis of a photographing optical system. An optical low-pass filter for removing spatial frequency components in the horizontal direction corresponding to the pixel pitch of the solid-state image sensor, and focus detection based on an output signal obtained from the solid-state image sensor, and focus adjustment of the taking lens. And the optical low-pass filter is rotated by 90 ° from the state in which the spatial frequency component in the horizontal direction can be removed when the focus is detected by the auto-focus device, and the optical low-pass filter is returned to the original state at the time of photographing. And a means for returning to.

Further, a solid-state image pickup device on which a subject light image is formed through a taking lens, and a horizontal space corresponding to the pixel pitch of the solid-state image pickup device are arranged so as to be movable back and forth with respect to the taking optical system. An optical low-pass filter that removes frequency components, an in-focus detection is performed based on an output signal obtained from the solid-state image sensor, and an auto-focus device that adjusts the focus of the photographing lens, and an in-focus detection by the auto-focus device is performed. Means for retracting the optical low-pass filter from the photographing optical system, and causing the optical low-pass filter to enter the photographing optical system during photographing.

[0011]

According to the present invention, since the phase-type OLPF is arranged in front of the taking lens, it is advantageous in terms of space, and the optical specifications of the phase-type OLPF are loosened so that the phase-type OLPF can be easily manufactured. Further, this phase type OLPF rotates corresponding to the focal length of the photographing lens, and the pitch of the unevenness in the horizontal direction of the phase type OLPF is substantially changed. As a result, a predetermined spatial frequency component corresponding to the pixel pitch of the solid-state image sensor is removed regardless of the change in the focal length of the taking lens.

According to another aspect of the present invention, when the focus is detected, the OLPF is rotated by 90 ° or retracted from the photographing optical system, and a predetermined spatial frequency component in the horizontal direction corresponding to the pixel pitch of the solid-state image sensor. Is not removed, the amount of information for focus detection is increased, and the OLPF is used during shooting.
Is returned to the original state to remove the predetermined spatial frequency component so that no spurious signal is generated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an image pickup apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention. In the figure, the subject light is the phase type OLPF 10 and the photographing lens 20.
An image is formed on the light receiving surface of the CCD 30 via the, and converted into signal charges of an amount corresponding to the intensity of light by each sensor of the CCD. This CCD 30 is driven by a CCD driver 31,
The signal charges converted by the CCD 30 are sequentially read out, processed by the process circuit 32, and then applied to the encoder circuit 34 and the AF detection circuit 36.

The AF detection circuit 36 is composed of a high-frequency BPF, an integration circuit, etc., extracts only the high-frequency component in the luminance signal input from the process circuit 32, integrates it, and outputs it to the microcomputer 38 as an evaluation value for focusing determination. Output. The microcomputer 38 outputs a control signal to the focus drive mechanism 40 so that the evaluation value input from the AF detection circuit 36 becomes maximum, and thereby the focus lens in the taking lens 20 is driven to perform focusing.

When a zoom button (not shown) is operated on the operation unit 42, the microcomputer 38 outputs a control signal to the zoom drive mechanism 44, which causes the taking lens 2 to operate.
The variable power lens system in 0 is driven to perform zooming, and the phase type OLPF 10 is rotated via the rotating mechanism 46 as described later. Next, the phase type OLPF 10
The reason why is rotated according to the zooming of the taking lens 20 will be described.

In the photographing optical system shown in FIG. 1, P is the pitch of the phase type OLPF 10 (lenticular killer lens) f _{T is} the focal length of the photographing lens 20 at tele time f _{L is} the focus of the phase type OLPF 10 (lenticular killer lens). Distance Δ; If the beam separation width of the phase-type OLPF 10 is used, the following relational expression holds.

[0017] Now, as shown in FIG. 2, a phase type OLPF having a pitch P.
When 10 is rotated by an angle θ, the apparent pitch P ′ in the horizontal direction is Can be represented by

Therefore, assuming that the wide-angle focal length of the taking lens 20 is f _w , the following equation is obtained from the equations (1) and (2). The relationship is established. Further, when deforming the second (3), and _{^{θ = cos -1 (f w /}} f T) ... (3) '.

That is, by rotating the phase type OLPF by the angle θ shown in the equation (3) ′, the phase type OLPF corresponding to the focal length f _w is obtained. FIG. 3 is a plan view of the phase type OLPF 10, the photographing lens 20 and the like shown in FIG.
FIG. 4 is a sectional view taken along line 4-4 of FIG. As shown in these drawings, the phase type OLPF 10 is rotatably arranged on the front surface of the taking lens 20, and is connected by a connecting member 21 so as to be integrally rotatable with a zoom cam barrel 22 of the taking lens 20. There is.

Therefore, the zoom motor 23 causes the gear 2
When the zoom cam barrel 22 is rotated via the ring gear 4 and the ring gear 25, the zoom lens groups 20A and 20B are moved by the cam grooves 22A and 22B of the zoom cam barrel 22 to perform zooming, and the phase is changed via the connecting member 21. Type OL
The PF 10 is rotated. Note that the relationship between the rotation angle of the zoom cam barrel 22 and the focal length due to the rotation angle is such that the cam grooves 22A, 2A of the zoom cam barrel 22 satisfy the formula (3) ′.
2B is formed.

Although the phase type OLPF is rotated in conjunction with the zoom cam barrel in the above embodiment, the present invention is not limited to this, and an independent driving means for rotating the phase type OLPF is provided as shown in FIG. The phase type OLPF may be rotated according to the focal length of the photographing lens. That is,
FIG. 5 is a cross-sectional view of essential parts showing another embodiment of the image pickup apparatus according to the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 4, in this embodiment, the phase type OLPF 10 can be rotated at an appropriate angle from the motor 26 via the gear 26A and the ring gear 10A. In the image pickup apparatus having the above configuration, the microcomputer 38 shown in FIG.
Focusing at 0 is executed. In this case, first, the phase type OLPF 10 is rotated by 90 ° via the rotary mechanism 46 (the motor 26 in FIG. 5 to the gear 26A and the ring gear 10A), and then the evaluation value input from the AF detection circuit 36 is maximized. A control signal is output to the focus drive mechanism 40 to drive the focus lens in the taking lens 20 to focus. Then, when the shutter release button is fully pressed in the operation unit 42, the phase type OLPF 10 is rotated to a predetermined rotation position according to the focal length of the taking lens 20, and then the shutter is released.

That is, at the time of AF, the phase type OLPF1
0 is rotated by the motor 26 so that the angle θ shown in FIG. 2 becomes 90 °. As a result, the phase type OL
The PF 10 cannot remove a specific spatial frequency component in the horizontal direction, and the subject light having the characteristic that the MTF with respect to the spatial frequency is shown by the alternate long and short dash line in FIG. 6 enters the CCD 30. Therefore, the AF detection circuit 36 shown in FIG.
Can output an evaluation value for more reliable focusing determination based on a video signal (information in areas A and B shown by hatching in FIG. 6) in which the MTF does not significantly decrease.

When performing photography after AF is performed in this way, first, the phase type OLPF 10 is set to an angle θ that satisfies the expression (3) ′ based on the current focal length of the taking lens 20. Rotate and then release the shutter for recording. In the embodiment shown in FIG. 5, the phase type OLP is used.
Although the F10 is arranged rotatably in front of the taking lens 20, the present invention is not limited to this, and it may be arranged rotatably on the CCD side of the zooming system of the taking lens 20.
In this case, the phase type OLPF 10 does not have to be rotated in accordance with the change in the focal length of the taking lens 20, and may be rotated by 90 ° only during AF. A crystal OLPF may be used instead of the phase type OLPF. Further, although the OLPF is rotated by 90 ° during AF, the present invention is not limited to this, and the OLPF may be retracted from the photographing optical system during AF. However, when the optical path length of the taking lens changes due to the retracting of the OLPF, it is necessary to insert a dummy glass or the like having a predetermined thickness in place of the OLPF so that the optical path length does not change.

[0025]

As described above, according to the present invention, since the phase type OLPF is arranged in front of the photographing lens, it is advantageous in terms of space, and the optical specifications of the phase type OLPF are loosened. Has various advantages such as easy manufacturing. Further, since the phase type OLPF is rotated according to the focal length of the photographing lens,
It is possible to remove a predetermined spatial frequency component corresponding to the pixel pitch of the solid-state image sensor regardless of the change in the focal length of the taking lens.

Further, since the OLPF is rotated by 90 ° or retracted from the photographing optical system when the focus is detected, the MTF of the subject light incident on the solid-state image pickup device (particularly the OLPF).
Does not reduce the horizontal cutoff spatial frequency component), which increases the amount of information for focus detection, and makes it easy to detect focus even for a subject including the cutoff spatial frequency component of OLPF, which has been difficult in the past. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention.

FIG. 2 is a diagram used for explaining the principle of the present invention.

FIG. 3 is a plan view of the phase-type OLPF, the taking lens, and the like of FIG.

4 is a cross-sectional view taken along line 4-4 of FIG.

FIG. 5 is a cross-sectional view of essential parts showing another embodiment of the image pickup apparatus according to the present invention.

FIG. 6 is a graph showing MTF with respect to spatial frequency.

[Explanation of symbols]

 10 ... Phase type OLPF 20 ... Photographing lens 21 ... Connection member 22 ... Zoom cam cylinder 23 ... Zoom motor 26 ... Motor 30 ... Solid-state image sensor (CCD) 36 ... AF detection circuit 38 ... Microcomputer 44 ... Zoom drive mechanism 46 ... Rotation mechanism

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number for FI Technical indication H04N 5/335 V 8838-5C (72) Inventor Katsuo Asami 2-26-30 Nishiazabu, Minato-ku, Tokyo Issue Fuji Shashin Film Co., Ltd. (72) Inventor Naoki Takatori 2-26-30 Nishiazabu, Minato-ku, Tokyo Fuji Shashin Film Co., Ltd. (72) Masaaki Orimoto 2-26-30 Nishiazabu, Minato-ku, Tokyo Fuji Fujishin Film Co., Ltd.

Claims (4)

[Claims] 1. A photographic lens with a variable focal length, a solid-state image sensor on which a subject light image is formed via the photographic lens, and a phase-type optical low-pass filter rotatably arranged in front of the photographic lens. And means for rotating the phase-type optical low-pass filter corresponding to the focal length of the photographing lens to remove a predetermined spatial frequency component corresponding to the pixel pitch of the solid-state image sensor. Imaging device. 2. A solid-state image sensor on which a subject light image is formed through a photographing lens, and a horizontal arrangement corresponding to a pixel pitch of the solid-state image sensor, which is rotatably arranged around an optical axis of a photographing optical system. A phase-type optical low-pass filter that removes spatial frequency components in the direction, an autofocus device that performs focus detection based on an output signal obtained from the solid-state image sensor, and performs focus adjustment of the taking lens, and the autofocus device. Means for rotating the phase-type optical low-pass filter by 90 ° from the state in which the spatial frequency component in the horizontal direction can be removed at the time of focusing detection by, and returning the phase-type optical low-pass filter to the original state at the time of photographing. An imaging device characterized by the above. 3. A photographing lens having a variable focal length, a solid-state image pickup device on which a subject light image is formed via the photographing lens, and a phase-type optical low-pass filter rotatably arranged in front of the photographing lens. And an autofocus device that performs focus detection based on an output signal obtained from the solid-state image sensor, and performs focus adjustment of the photographing lens, and the phase-type optical low-pass filter when focus detection by the autofocus device is performed. The phase-type optical low-pass filter is rotated by 90 ° from a state in which the horizontal spatial frequency component can be removed, and the phase-type optical low-pass filter is removed in order to remove the horizontal spatial frequency component corresponding to the pixel pitch of the solid-state image pickup device during photographing. An image pickup apparatus comprising: a unit that rotates according to the focal length of the image pickup unit. 4. A solid-state image pickup device on which a subject light image is formed through a taking lens, and a horizontal space which is arranged so as to be movable back and forth with respect to the taking optical system and corresponds to a pixel pitch of the solid-state image pickup device. An optical low-pass filter that removes frequency components, an autofocus device that performs focus detection based on an output signal obtained from the solid-state image sensor, and performs focus adjustment of the photographing lens, and a focus detection by the autofocus device. An image pickup apparatus comprising: a unit that retracts the optical low-pass filter from the photographing optical system and causes the optical low-pass filter to enter the photographing optical system during photographing.