JP2990722B2 - Video camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera that performs high-resolution shooting by moving an image formed on a solid-state image sensor.

2. Description of the Related Art In general, the resolution of a video camera is determined by the number of pixels of an image sensor used. Therefore, in order to obtain a high-resolution image, the number of pixels must be increased. However, an imaging device having a large number of pixels is expensive because it is difficult to manufacture.

For this reason, conventionally, various measures for increasing the resolution without increasing the number of pixels of the image sensor have been considered, for example, JP-A-54-129821, JP-A-63-42614, and JP-A-
8-195369, 59-15378, 59-194577, 60-27279
No., 60-54576, 63-284979, 63-284980, JP-A-1-137781, etc., the image sensor and the image formed by various methods are shifted by a relatively small distance, A method of increasing the apparent number of pixels in the shift direction by synthesizing images captured by the imaging element at a position (so-called “pixel shifting” method) is disclosed.

On the other hand, a solid-state imaging device using a CCD or the like generally has a certain degree of sensitivity to light in the infrared region, and thus has different sensitivity characteristics from human vision. Therefore, when capturing a color image, a luminosity correction filter (infrared cut filter) is provided in the optical system in order to match human vision.

Problems to be Solved by the Invention With the miniaturization of video cameras, it is desired to reduce the size of the optical system. However, various essential components such as a pixel shift mechanism, a lens, and a visibility correction filter for achieving the above-described high resolution are required. Therefore, there is a limit to miniaturization.

An object of the present invention is to solve such a problem and to provide a video camera mechanism that can be downsized while having high resolution.

Means for Solving the Problems In order to achieve the above object, in a video camera according to the present invention, an image pickup device, an optical system for forming an image on the image pickup device, and a moving image to be formed are moved on the image pickup device. A video camera provided with an imaging movement optical element to be operated, wherein the imaging movement optical element is provided with a function of a visibility correction filter.

By moving the image formed on the image sensor by the imaging moving optical element and synthesizing the image captured by the image sensor at each position, it is apparent that the number of image sensors has increased. High-resolution shooting can be performed. At this time, by providing the function of a visibility correction filter to the imaging movement optical element, it is not necessary to separately provide a visibility correction filter in the optical system, and the size of the optical system of the video camera can be reduced.

Embodiment FIG. 1 is a schematic diagram of an imaging optical system of a three-plate still video camera according to an embodiment of the present invention. The light passing through the lens 10 passes through the half mirror 40 and the mechanical shutter 42, and is guided to the low-pass filter 14. The half mirror 40 is used to guide a part of the incident light to the finder system 41, but the thickness thereof is so small that the influence of the aberration on the image pickup device 12 can be ignored. Instead of a half mirror that spatially divides incident light, a quick return mirror that temporally divides the incident light may be used.

The mechanical shutter 42 is usually arranged near the color separation prism 48 or is built in the imaging lens 10. In the case where the color separation prism is disposed in front of the color separation prism 48 as shown in FIG.

The low-pass filter 14 has a configuration in which a plurality of quartz low-pass filters 46 are supported on a rotating support 45 that rotates around a central axis 44. Filter 46
Can be replaced. Multiple crystal low pass filters
Reference numerals 46 each have a different cutoff frequency, and one having a suitable cutoff frequency is selected according to a shooting mode described later. FIG. 1 shows a mechanism in which a plurality of low-pass filters are replaced by rotation.
In addition, replacement may be performed by moving in parallel in a vertical direction or a direction perpendicular to the paper surface. In the present embodiment, the thickness of each of the plurality of crystal low-pass filters 46 is approximately 3 mm, but each thickness must be optically identical to the image sensor. In this embodiment, since the position of the image sensor 12 is fixed, assuming that the thickness of the crystal low-pass filter 46 is d and the refractive index is N, d (1-1 /
N) (ie, the amount of decrease in the optical path length by the low-pass filter, and when the low-pass filter is composed of a plurality of elements, Must be the same. As described below, the equivalent number of pixels of the image sensor 12 changes depending on the shooting mode. However, when the number of pixels increases, generally, the total thickness d of the crystal low-pass filter must be reduced. At that time, in order to eliminate a change in aberration with respect to the imaging lens 10, it is necessary to further use a correction glass for the low-pass filter so that the amount of decrease in the optical path length is the same as the amount of decrease in the optical path length by the other low-pass filters. is there.

The light that has passed through the low-pass filter 14
Led to. The imaging movement optical element 11 is composed of a flat plate that stands upright with respect to the optical axis 18 and a support that holds it and rotates around a rotation axis. This plane plate is a plane plate which is transparent to visible light and has a thickness of about 1 to 1.5 mm. As will be described in detail later, the angle between this plane plate and the optical axis 18 (90 ° in a normal state). ) Is changed to change the image formation position on the image sensor 12. In the present embodiment, infrared absorbing glass (for example, C-500S, CM-500S (trademark) manufactured by HOYA) is used as a material of the flat plate.
Etc.), and also serves as a correction filter for compensating the sensitivity of the CCD image sensor 12 in the infrared region to match the visibility. In addition, it is possible to use a flat plate made of various infrared shielding materials according to the photosensitive characteristics of the image sensor.

A color separation prism 48 is arranged at the rear of the imaging movement optical element 11. The dichroic film of the color separation prism 48 separates the incident light into three primary colors of R, G, and B, and guides them to the corresponding imaging devices 12a, 12b, and 12c. Each image sensor 1
Since 2a, 12b and 12c may be used for a single color, inexpensive ones can be used.

The operation of the imaging movement optical element 11 in the above structure
This will be described in detail with reference to the drawings. Flat plate 30 of the imaging moving optical element 11
Is tilted from the position perpendicular to the optical axis 18 of the imaging lens 10 by a small angle Δθ, and the position indicated by the solid line in FIG.
When at 30a, the optical axis 18 passing through the imaging lens 10 etc.
The upper incident light is refracted as shown by the solid line, and is displaced downward parallel to the optical axis 18 by Δ. A shooting mode in which the downwardly displaced image is shot by the image sensor 12 and used as an image signal as it is is referred to as mode I (natural image mode I).

On the other hand, when the flat plate 30 is
Symmetrically to 30a, it is inclined by Δθ on the opposite side, and when it is at the position 30b shown by the dotted line, the incident light on the optical axis is displaced upward by Δ in parallel. A shooting mode in which an image displaced upward in this way and an image displaced downward as described above are successively photographed, and a photographing mode in which they are combined into one image signal is referred to as a mode II (natural image mode II). I do. FIG. 3A shows the arrangement of pixels (unit photosensitive units) on one image sensor 12, and the total displacement 2 · Δ by the imaging moving optical element 11 is shown.
Is a half of the array pitch of the pixels of the image sensor 12 (for example,
If the image is shifted in the vertical direction in FIG. 3, then 2.Δ = dy /
2) is equivalent to doubling the number of pixels of the image sensor 12 (FIG. 3 (b)). In this way,
The resolution in the direction to shift the image is improved.

FIG. 2B shows the displacement of light when the rotation axis of the plane plate 30 is brought on the optical axis 18 (and perpendicular to the optical axis 18). FIG. 2 (c) shows the two positions 30a,
A case where an image is captured by the image sensor 12 when the plane plate 30 is at a position 30c perpendicular to the optical axis 18 in addition to 30b is shown.
In this case, by setting 2.Δ = dy / 3, a high resolution equivalent to triple the number of pixels in the vertical direction of the image sensor 12 can be obtained.

In the present embodiment, three image sensors 12a, 12b, 12c
Is 1/3 pitch in the horizontal direction (dx / 3) as shown in FIG.
They are staggered one by one. Therefore 3 shifted by dx / 3
Signals obtained by the two image sensors 12a, 12b, and 12c were treated as luminance signals representing only contrast, and by superimposing them, the number of photosensitive portions of the image sensor was substantially tripled in the horizontal direction. The same high resolution effect as described above can be obtained (this is called a character mode). Thus, in the present embodiment, the natural image mode I, the natural image mode II, the character mode,
Photographing with three different resolutions can be performed.

FIG. 5 shows the electrical configuration of the still video camera of this embodiment. The control device 26 controls the three image sensors 12a, 12b, 12c, issues a switching command for the crystal low-pass filter 46 to the low-pass filter switching device 24 in accordance with the state of the mode selection switch 28, and performs signal processing. The sampling of the image data in the circuit 22 is controlled. In the natural image mode I, data sampled from the signals of the three image sensors 12a, 12b, and 12c is used as it is as one complete image data. When the natural image mode II and the character mode are selected, the plane moving plate 25 of the imaging moving optical element 11 is moved (temporally shifted by pixels) by the imaging moving device 25 and photographed twice (or three times). The image data is temporarily stored in the storage device 23 and then combined to form one completed image data.

FIGS. 6, 7, and 8 show changes in the MTF curve when temporal pixel shift is performed. These figures show the optical axis 18 behind the lens 10.
A flat plate 30 having a thickness of 1 mm is inserted vertically into the
9 shows the result of computer simulation when the angle of 0 is changed. FIG. 6 shows a case where the plane plate 30 of the imaging moving optical element 11 is tilted clockwise by 0.5 ° from a direction perpendicular to the optical axis 18, and FIG. 7 shows a case where the plane plate 30 is perpendicular to the optical axis 18. FIG. 8 shows that the plane plate 30 is positioned at 0.
The figure shows a case where it is tilted counterclockwise by 5 °. Flat plate 3
It can be seen that although the aberration slightly varies with the inclination of 0, the MTF hardly changes as shown in the figure. MTF
Is not shown, but hardly changes off-axis.

Assuming that the thickness of the flat plate 30 is t, the refractive index is N, the inclination with respect to the optical axis 18 is θ, and the amount of displacement of the optical axis due to the inclination θ is Δ, when θ is small, between t and θ, There is a relationship. Since the optical axis displacement amount Δ is determined with respect to the pixel pitch of the image sensor (dy in FIG. 3), (2 · Δ = dy
/ 2), assuming that Δ = 0.005 mm (5 μm) and N = 1.538, θ = 50 ′ ({1}) when t = 1.0 mm. Therefore, by distributing the inclination angle θ of the plane plate 30 symmetrically with respect to a plane perpendicular to the optical axis 18 (a plane parallel to the imaging plane) by Δθ (= θ / 2), the plane plate 30 is moved in one direction. Compared to tilting by θ = 1 °, the aberration due to the tilt of the plane plate 30 can be halved, and the effect on the image quality can be minimized.

Note that the deflection angle 0.5 ° of the plane plate 30 in the above simulation is about 5 μm as the deflection Δ of the optical axis on the image plane.
In the case of a mechanism as shown in FIG.
The amount of movement of the tip in the optical axis direction is about 0.4 mm.

As a method of driving the imaging movement optical element 11, a method of continuously rotating a flat plate around an axis perpendicular to the optical axis has been conventionally proposed. However, in this embodiment, high-resolution imaging (natural image mode II) is performed. In character mode), two or more shots (frame shots) must be performed to form one screen. Therefore, it is necessary to drive the flat plate 30 at a high speed to suppress exposure unevenness during that time. In such a case, it is desirable to use a piezoelectric element or the like to swing around an axis perpendicular to the optical axis. For example, in the rotation around the optical axis, even if the flat plate is directly driven by a DC motor and rotated at 3600 rpm, it takes 8 msec for the flat plate to rotate 180 °. Further, taking into account the stabilization time of start / stop, the shortest frame shooting interval is more than ten msec. On the other hand,
When the flat plate is swung around an axis perpendicular to the optical axis by using a piezoelectric element, the displacement amount may be about 0.5 mm as described above, so that a frame shooting interval of about 2 to 3 msec is sufficient. It is. This is 1/500 when converted to shutter speed
In seconds, exposure unevenness between frames can be almost ignored in normal shooting.

As described above, in the present embodiment, the imaging movement optical element 11
By using a luminosity correction filter for the flat plate 30 constituting the above, the distance between the imaging lens 10 and the color separation prism 48 can be reduced as compared with the case where they are separately provided. This not only contributes to downsizing of the still video camera, but also to cost reduction by sharing parts. Further, as shown in FIGS. 2 (a), (b), and (c), by oscillating the flat plate 30 symmetrically with respect to a plane perpendicular to the optical axis 18, the one-side deflection angle is reduced. That is, aberration fluctuation can be minimized. This facilitates the design and evaluation of the imaging lens 10.

In the above embodiment, three image sensors 12 are provided in the horizontal direction.
According to the spatial pixel shift arrangement of a, 12b, 12c (FIG. 4),
Although high resolution is obtained in the vertical direction by temporal pixel shift (by the imaging moving optical element 11; FIG. 2), the vertical / horizontal direction may be reversed. If the number of imaging elements is two or more, such spatial pixel shift can be used. However, the configuration according to the present invention in which both the imaging movement optical element for temporal pixel shift and the visibility correction filter are used does not perform spatial pixel shift (that is, only one image sensor). But
Applicable.

Effects of the Invention As described above, according to the present invention, since the imaging movement optical element and the visibility correction filter in the optical system of the high-resolution video camera are integrated, the size of the optical system can be reduced. And at the same time lower costs.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an optical system of a still video camera according to an embodiment of the present invention, and FIGS.
FIG. 3C is a cross-sectional view showing three modes of the swing of the imaging movement optical element of the embodiment. FIG. 3A is a diagram of an actual pixel array of the image sensor of the embodiment, and FIG. FIG. 4 is a diagram showing an equivalent pixel array when temporal pixel shifting is performed by an imaging moving optical element. FIG. 4 is a diagram showing a state of spatial pixel shifting arrangement of three imaging elements of the embodiment. FIG. 6 is a block diagram showing an electrical configuration of the embodiment, FIGS. 6 to 8 are graphs showing changes in MTF when temporal pixel shift is performed, and FIG. 6 shows a plane plate perpendicular to the optical axis. FIG. 7 shows the case where the plane plate is perpendicular to the optical axis, and FIG. 8 shows that the plane plate is tilted counterclockwise by 0.5 ° from the direction perpendicular to the optical axis. This is shown. 10 imaging lens 11 imaging moving optical element 12a, 12b, 12c imaging element 18, optical axis 40 half mirror 41 finder 42 shutter 14 interchangeable low-pass filter 44 ... Low-pass filter rotating shaft, 45 ... Rotating support 46 ... Low-pass filter, 47 ... Motor 48 ... Color separation prism

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-73133 (JP, A) JP-A-61-142885 (JP, A) JP-A-62-90087 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04N 5/225-5/238 G03B 11/00-11/06

Claims (3)

(57) [Claims] 1. A video camera comprising an image sensor, an optical system for imaging an image on the image sensor, and an optical image moving optical element for moving the image to be imaged on the image sensor. A video camera characterized in that a moving optical element has a function of a visibility correction filter. 2. The video camera according to claim 1, wherein the imaging movement optical element is a parallel plate made of a material having an infrared shielding property and arranged perpendicular to the optical axis of the optical system. 3. The video camera according to claim 2, wherein the parallel plate is swung substantially symmetrically about an axis perpendicular to the optical axis.