JPH0628404B2 - Autofocus mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to improvement of an autofocus mechanism of a video camera.

(B) Conventional technology In an autofocus device for video cameras, the method of using the video signal captured by the video camera itself to evaluate the focus control state is essentially a method in which no parallelism exists and the depth of field is shallow. It has many advantages such as being able to focus accurately on a distant subject. Actual exploitation 57-19
Japanese Patent No. 5278 discloses an example of the autofocus device as described above.

In the prior art, a half mirror is arranged in the optical path between the focus lens and the image pickup element, and the reflected light dispersed by the half mirror is received by a photoelectric conversion element to perform photoelectric conversion. By vibrating in the optical axis direction, the photoelectric conversion output levels on both sides of the vibration are compared to determine the rotation direction of the focus control motor.

(C) Problems to be Solved by the Invention According to the conventional technique, it is necessary to dispose a photoelectric conversion element dedicated to the autofocus separately from the image pickup element, which is inconvenient in terms of space, and the half mirror mounting accuracy is also high. Has a drawback that it greatly affects the autofocus operation.

(D) Means for Solving the ProblemsThe present invention is an interline system in which an image pickup device has photoelectric conversion units and vertical transfer units arranged alternately, and in the vertical direction on the front surface of the image pickup device. One frame or one light-transmitting slit plate in which a plurality of extending through holes are arranged.
By making a reciprocating motion of a predetermined pitch in a field cycle, a first position where the through hole faces the photoelectric conversion unit and a second position where the slit plate itself faces the photoelectric conversion unit are alternately repeated. Arranging an optical path length changing means for changing an optical path length with respect to the photoelectric conversion section, and the focus lens according to a level change of an image pickup video signal obtained from the image pickup device before and after the optical path length changing operation by the optical path length changing means. It is characterized in that a focus lens displacement means for displacing the lens is provided.

(E) Action Since the present invention is configured as described above, the optical path length is changed by the optical path length changing member, and the level of the image pickup video signal changes as if the image pickup element itself changed, and furthermore, it is arranged in front of the image pickup element. It is suitable for miniaturization because it only needs to finely move the thin slit plate.

(F) Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of the apparatus of this embodiment.

(1) is an interline CCD (imaging device) in which photoelectric conversion units (light receiving units) (2) and vertical transfer units (3) are alternately arranged as shown in FIGS. 2 and 3. It is fixed on the optical path from the focus lens (4). (5) has one end fixed to a piezoelectric element (optical path length changing means) (6) arranged in the cabinet of the video camera, and the other end is in contact with a leaf spring (7) also fixed to the cabinet. Good nature,
It is a glass slit plate (optical path length changing member) having a thickness (t), and has a plurality of through holes (8) (8) extending in the vertical direction. The width (pixel width in the horizontal direction) (a1) of the photoelectric conversion part (2) is smaller than the width (b1) of the vertical transfer part (3) and is substantially equal to the width of the through hole (8).

A pulse voltage is supplied to the piezoelectric element (6), and it is always 1 /
With a 60 sec (1 field) cycle (1 frame cycle is also possible), a reciprocating interlocking operation (swing) between the first position shown in FIG. 2 and the second position shown in FIG. 3 in the lateral direction by the slide pitch of (c1). Action). At this first position, the through holes (8), (8) ... Face the photoelectric conversion units (2), (2) ..., and on the photoelectric conversion unit (2) as shown in FIG. The formed light forms an image. Also, in the second position, the through hole
(8) (8) ... Faces the vertical transfer section (3) ..., and the light reaching the photoelectric conversion section (2) passes through the slit plate (5) as shown in FIG. Change.

This change in optical path length will be described in detail with reference to FIG.

According to Snell's law, the following holds: n1sin θ1 = n2 sin θ2. (N1 and n2 are the refractive indices of light in the object I and the object II, respectively, and θ1 and θ2 are the incident angles) Becomes Where n1 is the refractive index in vacuum (even in the atmosphere),
If n2 (= n) is the refractive index in the slit plate,
The relationship between θ1 and θ2 in the figure is as follows.

Next, the variation Δx of the optical path length is calculated with reference to FIG. 7 in which the slit plate (5) of FIG. 6 is enlarged. Let a be the distance between the normal (l1) passing through the incident point and the point exiting the slit plate (5). Than Holds.

Here, if the distance between the focus lens (4) and the CCD (1) is sufficiently large, that is, both θ1 and θ2 are minute angles, Becomes

According to the equation, when a glass-based material is used for the slit plate (5), n = 1.48 to 1.5. Therefore, when it is desired to swing Δx to 100 μm, the slit plate thickness t = 300 μm. That is, it can be seen that the optical path length can be changed by the thin plate. The solid line in FIGS. 6 and 7 shows the optical path when the slit plate (5) is inserted, and the dotted line shows the optical path when it is not inserted.

FIG. 8 shows the relationship between the position of the focus lens (4) and the BPF output for one field in the focus area of the luminance signal in the imaged video signal obtained from the CCD (1), that is, the high frequency component. It is a diagram, and the position where the high-frequency component output (evaluation value) for one field has the maximum value (vertex) is the in-focus position. Explaining the relationship between this characteristic diagram and the swing motion of the slit plate (5), for example, when the focus lens (4) position is A, the slit plate (5) is shown as a vertical sine wave. When the swing action is performed, B
At the PF (10) output, the level fluctuation of the phase amplitude is seen as indicated by NA. Further, when the focus lens (4) is at the B position, that is, at the same BPF output level as when it is at the A position, if the slit plate (5) is caused to perform the swing operation as described above, the BPF (10 ) As indicated by M _A at the output, a level fluctuation occurs in which the amplitude is the same as N _A but the phase is reversed.

The BPF (10) is an output from the sampling circuit (11) that extracts only the portion of the luminance signal in the video signal obtained by the CCD (1) that corresponds to the focus area preset in the center of the screen. Only the high frequency components are separated. The sync signal separated by the sync separation circuit (12) is used for setting the focus area. The output of the BPF (10) is amplitude-detected by the detection circuit (13) and then integrated for each field by the integration circuit (14). This integrated output is delayed by one field in the delay circuit (15). Comparison circuit (16)
Compares the levels of the integrated output and the delayed integrated output, and inputs the comparison output to the focus motor control circuit (17).
Therefore, when the level variation, such as shown in N _A as compared with one field before occurs, Fuo Kas motor (focus lens 5 displacement means) (18), the focus lens 5 (4) CCD
(1) rotates so as to move in a direction away from, when the level variation of the opposite phase as shown in M _A occurs, the focus lens 5 (4) is moved toward the CCD (1) Focus ring (17) to support focus lens (4)
Drive to rotate. As shown by the vertex (P) in FIG. 8, a series of operations is repeated until the amplitude due to the swing operation becomes the minimum, that is, until the output of the integrating circuit (14) reaches the maximum value.

(G) Effect of the Invention As described above, according to the present invention, the position of the image pickup device can be obtained without providing a photoelectric conversion device separately from the image pickup device or actually moving the image pickup device and without increasing the size of the device. It is possible to obtain the same effect as changing the, and it is useful because the direction in which the focus lens should be moved can be easily detected.

[Brief description of drawings]

1 to 8 relate to the first embodiment of the present invention. FIG. 1 is a perspective view of the apparatus, FIGS. 2 and 3 are explanatory views of the swing operation of the slit plate, and FIG. FIG. 5 is an explanatory view of the optical path in the case of FIG. 5, FIG. 5 is an explanatory view of the optical path in the case of FIG. 3, FIGS. 6 and 7 are diagrams illustrating the change of the optical path length by the slit plate, and FIG. 8 is a focus. It is a characteristic view of a lens position and an evaluation value. (1) ... IT-CCD (imaging device), (2) ... photoelectric conversion part (light receiving part), (4) ... focus lens, (5) ... slit plate (optical path length changing member), ( 6) (41) …… Piezoelectric element (optical path length changing means), (18) …… Focus motor (focus lens displacement means).

Claims (1)

[Claims] 1. An autofocus mechanism for changing a distance between the image pickup device and a focus lens so that a high frequency component of a luminance signal in an image pickup video signal obtained from the image pickup device has a maximum value. An interline system in which conversion units and vertical transfer units are alternately arranged, and a light-transmissive slit plate in which a plurality of through holes extending in the vertical direction are arranged on the front surface of the image pickup device. By reciprocating at a predetermined pitch in one frame or one field cycle, the first position where the through hole faces the photoelectric conversion unit, and the second position where the slit plate itself faces the photoelectric conversion unit. By alternately repeating and, the optical path length changing means for changing the optical path length with respect to the photoelectric conversion unit is arranged, and the imaging before and after the optical path length changing operation by the optical path length changing means. Auto-focus mechanism, characterized in that a focusing lens displacement means allowed to displace the focus lens in accordance with the level change of the captured image signal obtained from the child.