JPH06235886A - Image pickup unit - Google Patents

Abstract

PURPOSE:To provide a image pickup unit which is less expensive, and in which an image formation optical system is miniaturized. CONSTITUTION:An image obtained from an objective lens on the top end of the inserting part of an endoscope is transferred on an eyepiece part 9 side by an image guiding fiber bundle 8, a luminous flux from the projecting end face of the image guiding fiber bundle 8 is made to be a nearly parallel luminous flux by a focusing lens 10, passes through a cover glass 11, and is made incident on an optical low-pass filter 12 disposed in the vicinity of the pupil of an adapter 3. The image on the projecting end face of the fiber bundle 8 is formed of many fine luminescent points regularly arrayed and includes a periodical pattern; the luminous flux is separated by the optical low-pass filter 12, passes through a first lens group 13 and a second lens group 14, so that variable power is performed; the luminous flux is made incident on a third lens group 15; and the image is formed on the image pickup surface of a CCD 19 through a cover glass 16, and through a crystal filter group 17 and a color mosaic filter 18 inside a TV camera 4. Thus, a multiple image is formed so as to remove the high-frequency component of the periodical pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for picking up an object including a periodic pattern, for example, an end face image of an image guide of an endoscope by using an image pickup device.

[0002]

2. Description of the Related Art In recent years, an image pickup optical system using a solid-state image pickup device such as CCD has been used in a device for taking an image to be observed on a television monitor. These image pickup devices sample the light intensity distribution on the image pickup surface at a predetermined frequency and convert the light intensity into an electric signal, which is reproduced on a television monitor.

By the way, when the image is reproduced by sampling as described above, only the frequencies up to the Nyquist limit can be reproduced by the sampling theorem, and further, near the Nyquist limit, a false resolution called moire occurs. For this reason, various measures have been taken to give an optical system a low-pass effect so that an image of a frequency near the Nyquist limit is not resolved on the imaging surface.
As disclosed in Japanese Patent Laid-Open No. 5 and Japanese Patent Laid-Open No. 3-114431, a crystal filter is used as the most general optical means.

[0004]

However, when an object including a periodic pattern, for example, an end face image of an image guide of an endoscope is photographed, a pseudo signal is likely to occur, and in order to remove this pseudo signal, It is necessary to use a plurality of crystal filters, that is, about 4 to 7 crystal filters in an endoscope imaging apparatus.

However, since the above-mentioned crystal filter is expensive, when many crystal filters are used, the image pickup apparatus becomes expensive and the image forming optical system of the image pickup apparatus becomes large.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image pickup apparatus which is cheaper and can downsize an imaging optical system.

[0007]

In order to achieve the above object, an image pickup apparatus according to the present invention forms an image of a subject including a periodic pattern on an image pickup means having a discrete image pickup structure by using an image forming optical system. In the imaging device for photographing the subject, an optical low-pass filter having a spatial frequency of the periodic pattern of the subject or a spatial frequency that is an integral multiple thereof as a cutoff frequency is arranged near the pupil of the imaging optical system. It is a thing.

[0008]

[Operation] In the above structure, the subject including the periodic pattern passes through the imaging optical system and is imaged on the imaging means having the discrete imaging structure. Here, by the optical low-pass filter arranged near the pupil of the imaging optical system,
The light flux of the subject is separated to form a multiple image, the spatial frequency of the periodic pattern of the subject or the spatial frequency of an integral multiple thereof is cut off, and the pseudo signal is removed.

Since the optical low-pass filter of the above-mentioned image forming optical system can be realized without using the conventional crystal filter, the image pickup apparatus can be made inexpensive and small.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show an embodiment of the present invention, FIG. 1 is an explanatory diagram of a configuration of an imaging optical system of an image pickup device, FIG. 2 is an explanatory diagram of an endoscope device, and FIG. 3 is an optical low-pass filter. FIG. 4 is an external perspective view, FIG. 4 is an explanatory view of a connecting portion between a camera head and an adapter, FIG. 5 is an explanatory view of a point image on an imaging surface, and FIG. 6 is a frequency characteristic of an optical low-pass filter on a two-dimensional spatial frequency plane. It is the figure shown.

In these drawings, reference numeral 1 denotes an endoscope apparatus as an example of an image pickup apparatus, and the endoscope apparatus 1 is
An endoscope 2, a TV camera 4 connected to the endoscope 2 via an adapter 3, a main body device 5 including a light source device, a signal processing unit and the like (none of which are shown), and the main body device 5 It is mainly composed of a monitor (not shown) connected to.

The endoscope 2 has a flexible insertion portion 6 and a main body portion 7, and an objective lens (not shown) is provided at the tip of the endoscope insertion portion 6. Further, the endoscope 2 has a built-in image guide fiber bundle 8 extending from the exit surface of the objective lens to the eyepiece 9 of the endoscope body 7. A focusing lens 10 is provided behind the image guide fiber bundle 8 of the endoscope main body 7 (on the side of the adapter 3) to convert the light flux from the exit end face of the image guide fiber bundle 8 into a substantially parallel light flux. There is.

The image guide fiber bundle 8 is formed by bundling a plurality of optical fibers in a bale stack.
Since the core of each fiber emits light, the image of the exit end face of the image guide fiber bundle 8 is formed by a large number of minute bright spots which are regularly arranged.

In the drawing, reference numeral 11 is a cover glass provided on the eyepiece 9 of the endoscope 2.

Further, in a state where the eyepiece 9 of the endoscope 2 and the adapter 3 are connected to each other, the optical lowpass filter near the pupil position is sequentially provided in the adapter 3 from the eyepiece 9 side. 12, a first lens group 13, a second lens group 14, a third lens group 15 and a cover glass 16 are arranged.

The first lens group 13 and the second lens group 14 are lens groups which are movable along the optical axis,
Together, they make up the zoom optical system of the zoom lens. Further, the third lens group 15 is the second lens group 1
4 is a lens group for forming an image on the image pickup surface of the CCD 19 through the crystal filter group 17 and the color mosaic filter 18 having an optical low-pass effect arranged in the TV camera 4.

Further, as shown in FIG. 3, the optical low-pass filter 12 disposed near the pupil position is formed with four surfaces perpendicular to the optical axis. An optical low pass filter of such data was used.

As for the shape, in the x-coordinate, y-coordinate, and z-coordinate of FIG. 3, when the angle unit is minute, in the range of x> 0, y ≧ 0, z = y × tan 2 ′ x ≧ 0, y < In the range of 0, z = x × tan 2 ′ x <0, in the range of y ≦ 0, z = −y × tan 2 ′ In the range of x ≦ 0, y> 0, z = −x × tan 2 ′ Further, the refractive index nd of the material is 1.51633, the Abbe number νd
Is 64.1.

Further, as shown in FIG. 2, another optical viewing tube 20 such as a rigid endoscope is formed to be connectable to the adapter 3.

Further, as shown in FIGS. 4 (a) and 4 (b),
A protrusion 21 is formed on the outer surface of the adapter 3 on the TV camera 4 side.
Insert the rotation ring 23 that is inserted into the groove 22 formed in the camera 4 and rotatably hooked to the adapter 3 into
By screwing into the threaded portion 24 screwed on the tip side (adapter 3 side) of the TV camera 4, it becomes possible to position the adapter 3 in the rotational direction when connecting with the TV camera 4. ing.

In the above structure, the image from the objective lens (not shown) provided at the tip of the endoscope insertion portion 6 is
The image guide fiber bundle 8 sends the light beam to the eyepiece 9 side of the endoscope body 7, and in this eyepiece 9, the light flux from the exit end face of the image guide fiber bundle 8 is substantially parallel by the focusing lens 10. The light passes through the cover glass 11 of the eyepiece 9 and enters the optical low-pass filter 12 arranged near the pupil position of the adapter 3.

Here, the image guide fiber bundle 8
The image of the exit end surface of is an image including a periodic pattern formed from a large number of minute bright spots regularly arranged. Then, the light flux forming an image including this periodic pattern is separated by the optical low-pass filter 12, passes through the first lens group 13 and the second lens group 14, and is magnified (zoomed) in a predetermined manner. Then, the light enters the third lens group 15.

Further, the light flux incident on the third lens group 15 passes through the cover glass 16 and is arranged in the TV camera 4 and has a crystal filter group 17 and a color mosaic filter 18 having an optical low pass effect. An image is formed on the image pickup surface of the CCD 19 via.

Here, the point image on the image pickup surface is like a black dot shown in FIG. 5A, and the interval between the point images changes due to zooming. Further, the trap line in the frequency space (the line indicating the position where the spatial frequency response becomes zero (cutoff)) also fluctuates due to zooming, and its frequency is substantially equal to the sampling frequency of the image guide fiber bundle 8. .

The point image on the image pickup surface shown in FIG.
6 shows a point image when the optical low-pass filter 12 is arranged at an angle of 45 degrees.

Next, FIG. 6 shows the frequency characteristics of the optical low-pass filter 12 that produces the separation pattern shown in FIG. 5B above on a two-dimensional spatial frequency plane. Frequency in x direction (horizontal direction), vertical axis is y
Indicates the frequency in the direction (vertical direction). Further, Px and Py represent sampling pitches of the CCD 19 in the x direction and the y direction, respectively, and Px = 9.9 μm and Py = 9.6 μm.

The black dots arranged in a hexagon represent the spatial frequency spectrum of the periodic pattern contained in the image of the end face of the image guide fiber bundle 8 which is the subject. That is, the image guide fiber bundle 8 is formed by bundling a large number of optical fibers in a bale stack, and the core of each fiber emits light. Therefore, the image of the exit end face of the image guide fiber bundle 8 is regularly arranged. It consists of a large number of minute bright spots. The frequency spectrum showing the repeating period of the bright spots is represented by the black dots arranged in the hexagon. On the other hand, the diagonally drawn lines are trap lines of the optical low pass filter 12.

In FIG. 6, two frequency spectra and two trap lines of the image guide fiber bundle 8 are drawn, but this is because this embodiment has a variable power optical system. That is, when the magnification is changed, the size and interval of the bright spots of the image guide fiber bundle 8 on the image plane change. This means that the frequency of the periodic pattern in the image projected on the image pickup surface of the CCD 19 changes. On the wide side (shortest focal length state), the imaging magnification is small and the bright spots are dense, so the frequency of the periodic pattern is high. On the other hand, on the tele side (longest short focal length state), the magnification is large and the bright spots are coarse, so the frequency of the periodic pattern is low. Therefore, the position of the frequency spectrum of the image guide fiber bundle 8 changes on the line connecting the two points according to the magnification change. However, since the optical low-pass filter 12 is provided in front of the variable power optical system, the lap line of the optical low-pass filter 12 also moves between the solid line and the broken line as the magnification changes. As a result, the low-pass effect of removing the pseudo signal does not change even if the scaling is performed. Double circles in the figure are sampling points generated by the regular arrangement of the color mosaic filter 18 provided on the front surface of the CCD 19.

As described above, the optical low-pass filter 12 is provided in the vicinity of the pupil of the imaging optical system for photographing the end face image of the image guide fiber bundle 8 and the light beams are separated to form a multiple image, thereby periodically Remove high frequency components of the pattern,
In other words, it reduces the response. Here, the high frequency component is a frequency corresponding to the sampling pitch of the image guide fiber bundle 8 or an integral multiple thereof.

As described above, by removing the periodic pattern, it is possible to reduce the pseudo signal due to the sampling of the image pickup device, that is, the CCD 19. For example, the relationship between the inclination of the surface of the optical low-pass filter 12 and the amount of deviation of the point image on the imaging surface when the image-forming light flux enters the pupil in parallel is expressed by the following equation.

P = fθ (n−n ′) (1) where P is the amount of deviation of the point image on the imaging surface, f is the focal length of the optical system behind the low-pass filter, and θ is the optical axis. The angles formed by the surface perpendicular to the low-pass filter surface and n and n ′ are the refractive indices of the medium before and after the low-pass filter surface.

If the distance between the two points on the low-pass filter surface is 2P and the sampling pitch of the image guide fiber bundle on the imaging surface (the pitch of the periodic pattern of the object) is S, the following equation (2) is obtained. By substantially satisfying, the pseudo signal can be reduced.

S = 2 × 2P = 4P (2) Incidentally, P, S, f and θ in the present embodiment are set to the following values. P = 6.78 μm (wide side) to 12.82 μm (tele side) S = 27.12 μm (wide side) to 51.27 μm (tele side) f = 22.636 μm (wide side) to 42.793 μm
(Tele side) θ = 2 ′ (0.00058rad) In general, the number of pixels in the image pickup fiber is higher than the number of pixels in the image guide fiber bundle. However, the image quality is deteriorated because the image quality is deteriorated at a frequency lower than the resolution limit, but there is no problem because the image sampled by the image guide fiber bundle has only information up to the sampling frequency of the image guide fiber bundle.

In general, when an image is enlarged or reduced by using a variable power optical system, if an optical low pass filter is arranged behind the variable power optical system, the sampling frequency of the image guide fiber bundle on the image pickup surface is increased. Varies, a deviation occurs between the cutoff frequency of the optical low-pass filter and the sampling frequency of the image guide fiber bundle.

However, in this embodiment, the optical low-pass filter 12 is provided in the vicinity of the pupil, and the variable magnification constituted by the first lens group 13 and the second lens group 14 is provided behind the optical low-pass filter 12. Since the optical system is arranged and the variable power optical system behind this is used to perform variable power,
As can be seen from the proportional relationship between P and f in the equation (1), the multiple image due to the light flux from the optical low-pass filter 12 is changed in accordance with the change in the sampling pitch of the image guide fiber bundle due to the change in magnification. Since the pitch also fluctuates, the response of the sampling pitch of the image guide fiber bundle can always be reduced, which is particularly effective.

Since the optical low-pass filter 12 as described in this embodiment has a directional response, when it is combined with an image pickup device such as the CCD 19, the direction of division of the luminous flux and the direction of the image pickup device. Need to be positioned. For this positioning, when the image sensor and the optical low-pass filter are integrally formed, the positioning may be performed once at the time of manufacturing, but in the case of a separate body, as described in the present embodiment. The relative position in the rotational direction with respect to the optical axis may be fixed to the member on the image sensor side and the member on the optical low-pass filter side.

Further, when a plurality of types of endoscopes can be attached and the sampling frequencies of the image guide fiber bundles of the endoscopes on the imaging surface are different as in this embodiment, the vicinity of the pupil is detected. The optical low-pass filter may be made detachable, and the optimum optical low-pass filter may be selected and attached for each endoscope. With such a configuration, even if dust is attached due to attachment / detachment of the optical low-pass filter, since the optical low-pass filter is far from the image pickup surface, dust is not reflected in the observation image.

Next, another embodiment of the optical low-pass filter is shown in FIGS. 7, 8 and 9. Like the optical low-pass filters 31, 32, 33, even if the ridgeline that divides the pupil does not necessarily intersect with the optical axis, the effect obtained will not change if the cross-sectional areas of the divided light fluxes are substantially equal.

Further, FIG. 10 shows an optical low-pass filter 34 in which the inclination angle of the surface with respect to the optical axis is continuously changed. With such a surface, a spiral intensity distribution is displayed on the image surface, and a low-pass effect can be obtained. In this embodiment, as compared with the optical low-pass filters 31 and 32, there are fewer steps in the effective light flux, and therefore flare due to scattering of light rays is less likely to occur.

Next, FIG. 11 is a diagram showing an optical low-pass filter 35 in which the pupil division surface is formed into a spherical surface to have power. Since the center of curvature of each curved surface of the optical low-pass filter 35 is decentered from the optical axis, the divided light beams form images at positions displaced from the optical axis.

At this time, if the axis of the center of gravity of the light beam divided by each split surface intersects the optical axis, the MTF of the high frequency component increases at the time of defocusing, so the axis of the center of gravity of the light beam should not intersect the optical axis. , Even if each of the divided surfaces is a flat surface (for example, the above-mentioned optical low-pass filters 12, 31,
32, 33, etc.) is the same.

Further, by making these surfaces aspherical, it is possible to enhance the aberration correction capability.

Further, a diffractive lens or an inhomogeneous medium lens, which has been studied recently, may be used.

When a multiple image is formed by each of the optical low pass filters described above, the position of the multiple image changes depending on the angle at which each of the optical low pass filters is arranged.
As shown in FIG. 5A and FIG. 5B described above, it can be arbitrarily selected depending on the direction of the regular pattern of the object to be imaged.

Further, in each of the above-mentioned optical low-pass filters, the heights of the respective divided surfaces are all the same, but even if the heights of the divided surfaces are different, a multiple image is even formed on the image pickup surface. The same effect can be obtained.

Next, FIG. 12 (a) shows an optical low-pass filter 36 whose center of curvature is on the optical axis, but the power of each surface is different, and FIG. 12 (b) is an arrow in the A direction of FIG. 12 (a). It is a perspective view. In this embodiment, instead of forming a multiple image on the image pickup surface, the focal lengths of the optical systems passing through the respective regions are different, so that the minimum circle of confusion is formed between the image forming positions of the light flux passing through the respective optical systems. Since the position comes, the low pass effect can be obtained due to the blurring.

Each of the above-mentioned optical low-pass filters may be formed by joining each of the divided portions individually and joining them. However, if they are formed by molding glass or plastic, the fabrication technique of which has been advanced in recent years, it is cheaper. Can be manufactured.

Further, in each of the optical low-pass filters described above, the ridgeline of division of the light beam is always within the effective light beam. Since the sagging of the ridge line is always generated in manufacturing, the light flux impinging on that portion may become flare. Although the diameter of the light flux varies depending on the optical system, the sag of the ridge line is constant if the manufacturing method is the same, so that the problem of flare is likely to occur in an optical system with a small light flux diameter.

Therefore, when such flare becomes a problem, smearing or Cr is applied on the ridgeline or before the ridgeline.
A light shielding means such as O2-Cr-CrO2 vapor deposition may be provided.

If the response is not sufficiently reduced due to these factors, a crystal filter may be combined. As described above, when the optical low-pass filter is used in combination with the crystal filter, the response of the sampling frequency of the image guide fiber bundle 8 is lowered and changed by the optical low-pass filter 12 as described in the above configuration. Double optical system (first lens group 13,
If the crystal filter group 17 is arranged behind the second lens group 14) and the third lens group 15 and the response of the CCD 19 at the frequency at the Nyquist limit is lowered, the image guide fiber bundle 8 can be changed even if the magnification is changed. It is effective that both the sampling frequency of the signal and the response of the CCD 19 at the Nyquist limit frequency can always be lowered.

As described above, according to the present embodiment, the same effect as that of the plurality of crystal filters can be obtained by increasing the number of division surfaces of the optical low-pass filter arranged in the vicinity of the pupil, and the divided luminous fluxes can be obtained. Since the direction of the can be freely determined by the angle of the surface, the degree of freedom of design is higher than that of the crystal filter in which the polarization direction must be taken into consideration. Further, since it is possible to give power to the pupil division surface and the other surface, it is possible to reduce the number of lenses.

In the present embodiment, the endoscopic device is taken as an example of the image pickup device, but an object including a periodic pattern is imaged on an image pickup means having a discrete image pickup structure by using an image forming optical system. The present invention can also be applied to other image pickup devices.

[0053]

As described above, according to the present invention, an image of a subject including a periodic pattern is formed on the image pickup means having a discrete image pickup structure by using an image forming optical system. In the imaging device, since an optical low-pass filter having a spatial frequency of the periodic pattern of the subject or a spatial frequency that is an integral multiple thereof as a cut-off frequency is arranged in the vicinity of the pupil of the imaging optical system, the optical low-pass filter is This can be realized without using the conventional crystal filter, and the imaging device can be made inexpensive and small.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an image forming optical system of an image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an endoscope apparatus according to an embodiment of the present invention.

FIG. 3 is an external perspective view of an optical low pass filter according to an embodiment of the present invention.

FIG. 4 is an explanatory view of a connecting portion between a camera head and an adapter according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a point image on an image pickup surface according to an embodiment of the present invention.

FIG. 6 is a diagram showing frequency characteristics of an optical low-pass filter according to an embodiment of the present invention on a two-dimensional spatial frequency plane.

FIG. 7 is an external perspective view of an example of another optical low-pass filter according to the present invention.

FIG. 8 is an external perspective view of an example of another optical low-pass filter according to the present invention.

FIG. 9 is an external perspective view of an example of another optical low-pass filter according to the present invention.

FIG. 10 is an external perspective view of an example of another optical low-pass filter according to the present invention.

FIG. 11 is an external perspective view of an example of another optical low-pass filter according to the present invention.

FIG. 12 is an example of another optical low-pass filter according to the present invention, in which (a) is an external perspective view and (b) is an arrow view in the direction A of (a).

[Explanation of symbols]

 1 Endoscope Device 2 Endoscope 3 Adapter 4 TV Camera 8 Image Guide Fiber Bundle 10 Focusing Lens 12 Optical Low Pass Filter 13 First Lens Group 14 Second Lens Group 15 Third Lens Group 17 Crystal Filter Group 18 Color mosaic filter 19 CCD

Front page continuation (72) Inventor Kimihiko Nishioka 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Akira Hasegawa 2-34-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optics Industry Co., Ltd.

Claims (1)

[Claims] 1. An image pickup apparatus for photographing an object including a periodic pattern on an image pickup means having a discrete image pickup structure by using an image forming optical system, the pupil of the image forming optical system. An image pickup apparatus, wherein an optical low-pass filter having a cutoff frequency of a spatial frequency of the periodic pattern of the subject or a spatial frequency of an integral multiple thereof is disposed in the vicinity.