JP2716041B2 - Imaging optical system for solid-state imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a camera, and more particularly to an imaging optical system for a solid-state imaging device using a color separation filter.

2. Description of the Related Art As is well known, some color solid-state imaging devices have a color separation filter disposed on the surface of an imaging cell array in order to output color-separated video signals. Optical low-pass to eliminate such high-frequency image incident light in order to prevent false colors from being generated in the reproduced image due to incident light representing a picture having a frequency higher than the spatial frequency of the segment arrangement of the color separation filter. A filter is provided in front of the image sensor.

For example, in a conventional imaging optical system such as a video camera,
This low-pass filter is arranged immediately before the image sensor.
For this reason, the optical system lens has been designed so that its flange back is long and a low-pass filter is provided there. Therefore, a lens system having a large aperture and a long lens length, such as a retro type lens, must be used, and the lens system has been increased in size.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact imaging optical system for a solid-state imaging device that solves the drawbacks of the related art.

DISCLOSURE OF THE INVENTION According to the present invention, an optical low-pass filter is disposed in front of or near a lens system, so that a lens having a short back focus can be used in an imaging optical system. Therefore, a lens with a small lens diameter can be used in order to obtain the same brightness as the conventional one.

According to the present invention, an imaging optical system for a solid-state imaging device that forms an image of an object field on an imaging cell array of a color solid-state imaging device in which a color separation filter is disposed on the imaging cell array is provided. A lens that is arranged on the axis and forms an image on the imaging cell array, and is arranged on the optical axis opposite to the color solid-state imaging device with respect to the lens, and includes a color separation filter of light incident from the object scene An optical filter for removing a component of an image having a spatial frequency higher than the spatial frequency of the color filter segment array.

DESCRIPTION OF THE EMBODIMENTS Next, with reference to the accompanying drawings, embodiments of the imaging optical system for a solid-state imaging device according to the present invention will be described in detail.

Referring to FIG. 1, there is shown an embodiment in which the present invention is applied to an imaging optical system of a camera having a color solid-state imaging device 10. The color solid-state imaging device 10 is, for example, a charge transfer device such as a CCD, and a color separation filter 14 is provided on a surface of the imaging cell array 12. The color separation filter 14 has a number of color filter segments arranged so as to separate light directed to each imaging cell of the imaging cell array 12 into three separated colors. This figure shows these configurations conceptually in a somewhat exaggerated manner for convenience of display.

In front of the imaging cell array 12, a zoom lens 18 having a magnification of about 1.5 in this embodiment on a main optical axis 16 of the array 12 is provided.
Are arranged. In the present embodiment, the lens 18 is a concave-convex zoom lens composed of two groups of a front lens group 20 and a rear lens group 22. 3, the front lens group 20 is movable back and forth in the optical axis 16 direction A, as shown in FIG.
The rear lens group 22 moves back and forth in the direction B of the optical axis 16 to realize a zoom function. The lens position shown in FIG. 1 is in the wide-angle end state, and the lens position shown in FIG. 2 is in the telephoto end state. In the following figures, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

A stop 24 is provided on the optical axis 16 in front of the front lens group 20, and an optical low-pass filter 26 is further provided in front of the stop 24. As the low-pass filter 26, for example, a filter in which fine particles of a transparent material having a different refractive index are dispersed in a flat plate of a transparent resin material is used. The low-pass filter 26 removes a picture component having a spatial frequency substantially higher than the spatial frequency of the segment arrangement of the color separation filter 12 from the incident light incident on the optical axis 16 from the object field. In the present embodiment, the filter 26 is disposed in front of the zoom lens, and the component of the frequency to be removed changes on the image forming side as the focal length changes. However, in this embodiment, the magnification is low, and there is no practical problem. This prevents a false color from being generated in a reproduced image from the solid-state imaging device 10 due to such incident light representing a spatially high-frequency pattern.

In this embodiment, the low-pass filter 26 is disposed in front of the lens 18 by focusing on the fact that the incident light from the object field is substantially parallel light in the front part of the lens 18. This eliminates the need for the lens 18 to form a space for disposing the low-pass filter 26 as in the related art.
Can use a lens having a short back focus and a short flange back. Therefore, a lens with a small lens diameter can be used in order to obtain the same brightness as the conventional one.

Originally, the low-pass filter 26 needs to precisely align the optical axis 16 in the rotational direction with respect to the arrangement of the imaging cells of the imaging device 10. However, in this embodiment, the low-pass filter 26
Since the lens is disposed in front of the lens 18, the adjustment operation can be easily performed, and a high-precision mounting device is not required. For example, this operation can be performed while reproducing a video signal output from the image sensor 10 on a video monitor and viewing the reproduced image.

FIG. 6 shows an example of a conventional imaging optical system for comparison.
In this conventional example, a low-pass filter 26 and a diaphragm 2 are arranged on the optical axis 16 of the image sensor 10 from the imaging cell array 12 toward the field.
4. The zoom lenses 50 are arranged in this order. Lens 5
0 has a zoom function of about 1.5 times, and thereafter, the lens group 52 is movable back and forth in the optical axis 16 direction A, thereby realizing the zoom function. In this conventional example, since the low-pass filter 26 is disposed immediately before the image sensor 10, the lens 50 is
It is a reverse telephoto type (retro focus type) designed to have a long flange back and a long back focus. Therefore, it is necessary to use a lens having a large diameter and a long focal length as the lens 50, and the entire optical system is thereby enlarged.

Table 1 shows an example of design values when the same brightness and zoom magnification specifications are realized in the embodiment of the present invention shown in FIG. In this example, brightness F is 3.5, focal length at wide-angle end
This is a zoom lens with fW of 19.695 mm and telephoto end focal length fT of 26.68 mm. The angles of view are 31.2 ° and 23.3 °, respectively. As shown in FIG. 1, ten surfaces of five lenses 18 and a low-pass filter
It consists of 26 surfaces. The stop 24 is disposed between the second and third surfaces or between the eighth and ninth surfaces. 4 and 5 show aberration diagrams at the finite distance. FIG. 4 shows the case where the lens position is in the wide-angle end state, and FIG. 5 shows the case where the lens position is in the telephoto end state.

As can be seen from the above, in this embodiment, the optical low-pass filter 26 is disposed at the afocal portion of the lens system 20, for example, in front, so that the imaging optical system has a short back focus or a short flange back, for example, Telephoto (telephoto) lenses can be used. Therefore, a lens having a considerably small aperture can be used at the same brightness as the conventional one. As a result, the optical low-pass filter may have a small aperture size.

As described above, according to the present invention, since the optical low-pass filter is disposed in the afocal portion on the object field side in the lens system, for example, a lens such as a telephoto type having a short back focus or a short flange back is used. It can be used in an imaging optical system, and an optical low-pass filter having a small shape can be used. Further, the exit pupil becomes longer, and the influence of color shading is small. Therefore, the entire imaging optical system can be made smaller and lighter than before.

[Brief description of the drawings]

1 and 2 are explanatory views showing an embodiment in which the present invention is applied to an imaging optical system of a camera having a color solid-state imaging device. FIG. 1 shows a case where a lens position is in a wide-angle end state. 2 shows the case where the lens position is in the telephoto end state, FIG. 3 is an explanatory view showing the principle configuration of the embodiment shown in FIGS. 1 and 2, and FIGS. 4 and 5 are FIGS. FIG. 4 shows aberration diagrams at a finite distance in a design example when the same specifications of brightness and zoom magnification as those of the conventional example shown in FIG. FIG. 6 shows a case where the lens position is in the telephoto end state. FIG. 6 is a view similar to FIG. 1 showing an example of an image forming optical system of a conventional solid-state imaging device camera. Explanation of reference numerals of main parts 10: color solid-state imaging device 12: imaging cell array 18: lens 26: optical low-pass filter

Continued on the front page (72) Inventor Masafumi Inaya 2-26-30 Nishiazabu, Minato-ku, Tokyo Fuji Photo Film Co., Ltd. (72) Inventor Kazunori Ohno 1-324 Uetakecho, Omiya City, Saitama Prefecture Co., Ltd. (56) References JP-A-62-278519 (JP, A)

Claims (2)

(57) [Claims] 1. An imaging optical system for a solid-state imaging device, wherein a color separation filter forms an image of an object field on the imaging cell array of a color solid-state imaging device disposed on the imaging cell array.
The imaging optical system is disposed on an optical axis of the imaging cell array, a telephoto lens that forms the image of the object field on the imaging cell array, and the color solid-state imaging device with respect to the lens. Is a component of the image which is disposed on the optical axis on the opposite side of the object field and has a higher spatial frequency than the spatial frequency of the color filter segment array of the color separation filter among light incident from the object field. And an aperture provided between the optical filter and the lens, the aperture being provided to the lens by adjusting an amount of light emitted from the optical filter. An imaging optical system for a solid-state imaging device. 2. An imaging optical system for a solid-state imaging device according to claim 1, wherein said lens is a zoom lens.