JPH01218286A - Color image pickup device - Google Patents

Abstract

PURPOSE:To prevent color shading by eliminating light beams made incident on a photodetection section of each picture element through a color coding filter color element corresponding to an adjacent picture element to each picture element of a solid-state image pickup element. CONSTITUTION:A convex lens 8 of an image forming lens system 3 is arranged near a mosaic filter 2 and the convex lens 8 is bonded to a glass plate 5 of a solid-state image pickup element 1. When lower light beams at the outside of an axis of a maximum image height is made incident on a photodetection section of a picture element, the relation of a reflective index of an adhesive agent layer 6 and an F number of an image forming lens 3 is decided so as to allow the light beams to pass through a point closest to the picture element of the color element of the mosaic filter 2 corresponding to the picture element adjacent to the side close to the optical axis of the image forming lens system 32 with respect to the picture element.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to electronic endoscopes, TV cameras, fiberscopes, and rigid imaging devices using solid-state image sensors having color-encoded filters such as mosaic filters and stripe filters. A TV camera attached to a mirror, etc.

The present invention relates to color imaging devices such as electronic cameras.

[Conventional technology]

As shown in FIG. 23, one of this type of conventional color imaging devices includes a mosaic filter 2 provided on the imaging surface of a solid-state imaging device 1, and an object image formed on the imaging surface by an imaging lens system 3. This is how it was done. As shown in No. 24rXJ, which is an enlarged sectional view of the main part, the solid-state image sensor 1 has a plurality of picture elements 4a arranged two-dimensionally on the imaging surface 4, each having an independent light-receiving section 4b. A glass plate 5 on which a mosaic filter 2 is deposited (in the case of an interference filter) or coated (in the case of an absorption filter) is coated with a transparent adhesive layer such that each color element 2a of the mosaic filter 2 corresponds to each picture element 4a. It was connected to the imaging surface 4 via a cylindrical tube 6.

[Problem to be solved by the invention]

However, in recent years, as the number of picture elements of the solid-state image sensor 1 has increased and the size of the picture elements has progressed, the off-axis principal ray 7 passing through the imaging lens system 3 has become smaller than the solid-state image sensor 1, as shown in FIG. When the incident light is not perpendicular to the imaging surface 4, the imaging lens system 3
Color element 2 corresponding to the picture element 4a adjacent to the side closer to the optical axis of
a and enters the light receiving section 4b of each picture element 4a,
There was a problem that correct colors were not reproduced. This is called color shading, and 7a is the off-axis lower ray.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a color imaging device that reliably prevents color shading.

[Means and effects for solving the problems] A color imaging device according to the present invention includes an imaging lens system, a solid-state imaging device formed by two-dimensionally arranging a plurality of picture elements each having an independent light receiving section, A color encoding filter having a color element corresponding to each picture element and arranged in front of the light receiving section of the solid-state image sensor at a minute interval, the color encoding filter having color elements corresponding to each of the picture elements; disposing a lens close to the color encoding filter in the vicinity of the color encoding filter;
Moreover, it is characterized by satisfying the following conditions.

~ IS- θ, ≦θ+−〇.

However, θ is the incident angle of the light beam that enters the light receiving portion of each picture element of the solid-state image sensor, and θ is the incident angle of the light ray that enters the light receiving part of each picture element of the solid-state image sensor, and θ is the incident angle of the light ray that enters the light receiving part of each picture element of the solid-state image sensor, and θ is the incident angle of the light ray that enters the light receiving part of each picture element of the solid-state image sensor, and θ is the incident angle of the light ray that enters the light receiving part of each picture element of the solid-state image sensor, The incident angle, θ, of a real or virtual light ray that passes through the point closest to each picture element of the corresponding color element and enters the light receiving part of each picture element is n
, is the refractive index of the medium between the color element and the light-receiving surface, and F is the F number of the imaging lens system, then n+ 2F.

Note that the above-mentioned virtual light rays may pass through the color element corresponding to a certain pixel and enter the neighboring pixel, depending on the size of the light-blocking part (protrusion) located between the light-receiving areas and how the incident angle of the light ray is set. Since there are cases where there is no light ray that enters the light receiving section, it is referred to as a hypothetical light ray that is incident on such a case.

By satisfying the above conditions, there will be no light rays that pass through the color elements of the color encoding filter corresponding to the pixels adjacent to each pixel of the solid-state image sensor and enter the light receiving portion of each pixel, resulting in color shading. Specifically, deing is prevented by arranging one lens of the imaging lens system near the solid-state image sensor and selecting the power of the lens so as to satisfy the above conditions.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiment, with the same reference numerals assigned to the same members as in the above-mentioned conventional example.

FIG. 1 shows a first embodiment in which a convex lens 8 of an imaging lens system 3 is disposed near a mosaic filter 2, specifically a glass plate 5 of a solid-state image sensor l.
A convex lens 8 is bonded to the lens.

FIG. 2 shows a second embodiment, which is an optical low-pass filter 9. made of quartz crystal. Infrared light cut filter 10. A block consisting of a convex lens 8 supported by one support frame 11 is fixed to and integrated with the solid-state image sensor 1.

FIG. 3 shows a third embodiment, in which a convex lens 8 is arranged between a solid-state image sensor 1 and a prism 12, and the convex lens 8 is bonded to the solid-state image sensor 1 or the prism 12 with an adhesive. It may be fixed mechanically or it may be fixed mechanically.

FIG. 4 shows a fourth embodiment, in which a positive lens 13 made of a heterogeneous medium lens is used instead of a convex lens 8, an optical low-pass filter 9 and an infrared light cut filter 10.
The solid-state image sensing device 1 is arranged in the vicinity of the solid-state image sensing device 1.

In this embodiment, since the positive lens 1'3 made of a non-uniform medium lens is used, it is mechanically simple and the positive lens 1'3 is made of a non-uniform medium lens.
3 is joined with the optical low-pass filter 9 and the infrared light cut filter 10 to form a sandwich structure, which has the advantage that the positive lens 13, which is sensitive to humidity, can be protected.

FIG. 5 shows a fifth embodiment, in which an infrared cut filter lO and an optical low-pass filter 9 are attached to a convex lens 8 of an imaging lens system 3 consisting of two plano-convex lenses facing each other.
The solid-state image sensing device 1 is made by bonding the two together and fixing it to the solid-state image sensor l.

No. 6 @ shows the sixth embodiment, in which a convex lens 8, which is a cemented lens of a convex lens and a concave lens, is bonded to the front surface of a solid-state image sensor l via an optical low-pass filter 9. By making the number smaller than the Abbe number of the convex lens, there is an advantage that chromatic aberration of magnification can be corrected.

Note that a filter made of an interference film (for example, an infrared cut filter, a YAG Placing a laser cut filter is advantageous because there is little change in the spectral characteristics of the interference filter depending on the location on the screen, and an image with the same color reproduction on the entire screen can be obtained. From the characteristics of the interference filter, it is desirable that the inclination angle of the principal ray be 20 degrees or less, preferably 15 degrees or less.Also, the interference filter may be provided on the air contact surface, or it may be placed on the lens or solid-state image sensor cover glass. Also, since interference filters are thinner than absorption filters, they are particularly advantageous when used in devices that require compactness, such as endoscopes.

Next, conditions to be satisfied by the convex lens 8 or the positive lens 13 disposed near the solid-state image sensor 1 will be explained.

FIG. 7 is a sectional view of a main part of a solid-state image sensor with a mosaic filter.

In order to prevent color shading from occurring, it is necessary that the off-axis lower ray 7a with the maximum image height (the angle of incidence on the glass plate 5 is The side closer to the optical axis of the imaging lens system with respect to the picture element 4a (lower side in Figure 7)
It is sufficient to pass through the point closest to the picture element 4a of the color element 2a of the mosaic filter 2 corresponding to another picture element 4a adjacent to the above, that is, the point A at the upper end or higher. It is sufficient that the inclination angle θ in the adhesive layer 6 is less than or equal to the inclination angle θ in the adhesive layer 6 of the light rays passing through the above point A and entering the element 4a. It shall be within.

Next, the angle θ is expressed as follows.

d, +-d.

t However, n and dl are the refractive index and thickness of the adhesive layer 6, respectively, n and dl are the refractive index and thickness of the mosaic filter=2, P is the pitch of the picture element 4a, and C is the light receiving part 4b. The width is In the drawing, n@+d* is the refractive index and thickness of the glass plate 5, respectively.

Further, as shown in FIG. 8, when a light shielding part 2b of width Δ made of a chromium thin film or the like is formed between each color element 2a of the mosaic filter 2, θ-(n+
>n,) I d, +-d.

n= becomes.

Therefore, the tilt angle θ of the off-axis lower ray 7a in the adhesive layer 6,
is less than or equal to the angle θ given by the above equation, color shading can be prevented. That is, θ, ≦θ
・・・・・・・・・−・ 111 is fine.

Practically speaking, it is possible for some light rays that have passed through adjacent color elements to enter the picture element, so /'%-N t,,,.

θ, ≦ θ + −θ, ・−・・
...-(2) is sufficient, however, θ^ is fl+2F when the F number of the imaging lens system 3 is expressed as F, that is, θ^ is the value that passes through the imaging lens system 3. The opening angle in the adhesive J16 of the light, that is, as long as the amount of legitimate rays incident on the picture element is predominant, the off-axis lower ray 7
This means that the inclination angle θ3 in the adhesive layer 6 of a may be large.

Therefore, if the conditions of the imaging lens system 3, specifically the power of the convex lens 8 or the positive lens 13, are selected so as to satisfy equation (1) or (2), imaging without color shading can be performed.

Next, how to determine the shape of the convex lens 8 will be explained.

In FIG. 9, which is an enlarged view of the main part, the inclination angle θ, L of the off-axis lower ray 7a in the convex lens 8 is θIL−δ−β
−・−・・−・・−・ (4) However, sin (β+θ,) δ−5in −′ () ・・・・− Song (5), where θs and h are respectively off-axis 0 lens 8 of lower ray 7a
The inclination angle and height of the ray just before it enters, nt, and R are the refractive index and radius of curvature of the convex lens 8, respectively.

On the other hand, since the relationship between the tilt angle 0 and θS is nL, it becomes as follows.Therefore, from this equation (8) and the above equation Tl), the value of nL+H is determined so as to satisfy this equation (9). All you have to do is choose.

Note that if the thickness of the convex lens 8 is thin, the height of the light beam is approximately equal to the maximum image height, that is, hbh.

In addition, in Figure 1θ which is an overall view, the position of the exit pupil of the lens group 14 in front of the convex lens 8 measured from the last lens of the lens group 14 is E, and the distance between the last lens of the lens group 14 and the convex lens 8 is E. If d, it can also be expressed as ...−...α・. However, in FIG. 10, the value of E is negative. Therefore, by giving the values of E, d, , h, the values of nL and H can be determined from the above equation +9) and Ql.

Furthermore, in FIG. 11, which is a schematic diagram of the convex lens 8, the angle θ3A of the outgoing ray of the convex lens 8 is approximately as follows, where f is the focal length of the convex lens 8, and θ sa ”nt θ,
-......Li- (turn), so from these two au, as and equation (11), it becomes nt. Therefore, the focal path #11r L that satisfies the second book
The convex lens 8 may be placed in front of the solid-state image sensor 1.

Until now, the solid-state image sensor l has been used in the meridian direction (vertical direction or
The reason why we have been discussing the spacing in the horizontal direction (
If the picture elements are fine even in the horizontal direction, or if the image height in the X direction is extremely high compared to the image height in the X direction, the same conditions as in the vertical direction must be satisfied in the horizontal direction.

That is, the above formula (j
It is necessary to satisfy condition 1 or (2).

However, as shown in Fig. 13, if the color of the mosaic filter does not change in one direction, that is, in the case of a striped filter, it is sufficient that the condition of equation (11 or (2)) is satisfied in the direction perpendicular to the mosaic filter. .

The same applies to the case of a diagonal slide filter.

Next, conditions for preventing dust from being captured on the imaging surface 4 of the solid-state imaging device 1 along with the image will be described.

As shown in FIG. 9, when a convex lens 8 is bonded to the front surface of the solid-state image sensor 1, dust on the front surface (spherical surface) of the convex lens 8 is reflected on the imaging surface 4 of the solid-state image sensor 1, appearing as a black spot image, and is observed. It gets in the way.

Therefore, in order to avoid this, it is necessary that the thickness of the convex lens 8 is thick to some extent, and the thickness of the convex lens 8 and the F number are respectively dL + L + solid bottle image element "From the front of the glass plate 5 of the lens 1 to the imaging surface 4. If the air-equivalent optical path length of is do and the upper limit of the diameter of dust is φ, then dL −+ d c ≧lOφ・F L −−−−−−
- With Q41L, dust is not noticeable.

If it is acceptable for some dust to be seen for practical purposes, the conditions may be relaxed to the following formula 〇Ij.

dL □+d, ≧3φ・F L −・・・−・ α9
t Therefore, if R1''L + 'L is selected so as to satisfy the expression +l+ or (2) and the expression α~ or 09, a color imaging device without color shading and with less noticeable dust can be obtained.

For example, d (-0,4am, F L = 5
, if φ=50/Jm, when nL=t, s, 2〇9
Therefore, d, ≧0°525 III. That is, it is desirable that dL be approximately Q, 5 n or more.

In addition, as shown in FIG. 6, when the convex lens 8 is bonded to the front surface of the solid-state image sensor 1 via the optical low-pass filter 9, the imaging surface of the solid-state image sensor l is connected from the front surface of the convex lens 8. The air conversion length dA up to 4 is dA≧10φFt ・・・・・・−・−α
edA≧3φFL ・・・・・・・−・
- It is sufficient to satisfy either 0η, and it is desirable that d be approximately 0°5° or more.

Furthermore, in order to obtain a color imaging device in which color shading is less likely to occur, it is preferable to provide a horizontally long aperture 15 in the imaging lens system 3, as shown in FIG. 14. However, in this case, As shown in FIG. 12, it is assumed that light entering the mosaic filter obliquely and entering the light receiving portion of an adjacent picture element is likely to occur in the vertical direction.

In this way, the vertical aperture angle of the light flux incident on the imaging surface of the solid-state imaging device becomes smaller than in the case of a circular aperture, so that color shading is less likely to occur. However, in this case, conditional expression (11 or (2)) is applied to the ray passing through the lower end of the rectangular aperture.Here, the sine of the exit angle of the marginal ray in the vertical direction is NA'
Then, F′=□ ・−・・・−・ α
F' determined by 2NA' may be used instead of F in equation (2).

Incidentally, the same applies to the case where mixed incidence of light tends to occur in the horizontal direction.

By the way, in order to not change the brightness of the imaging lens system 3 in FIG. 14, the radius of the circular aperture is set to r.

The lengths of the vertical and horizontal sides of the rectangular aperture 15 are a, respectively.

If a 'ml, tt 1 = a lIa, -
−Ql, while to reduce color shading, a, ≦2r −・・・・・・・・・・−
(2), so by equation Ql and (2), π a .

a, ≧□ ・−・・−・・−(company).

In reality, there are errors in the aperture position, so all ≧a
, However°゛゛゛ (sha) is better.

The shape of the diaphragm 15 is not limited to a rectangle;
The shapes shown in the figures may also be used. Figure 15 shows a horizontally long parallelogram aperture, Figure 16 shows an oval or elliptical aperture which is also horizontally long, and Figure 17 shows a circular aperture with two horizontally extending apertures.
Apertures arranged side by side, Fig. 18 shows a square aperture, Fig. 19,
FIG. 20 shows a diaphragm in which two and three square apertures are arranged in parallel in the horizontal direction. When the diaphragm aperture has a generally long shape in the horizontal direction, such as a rectangle, there are the following advantages. One of these is that many endoscopes have a fixed focus, and when the point image is out of focus, the shape of the point image intensity section becomes similar to the aperture shape, which reduces the horizontal MTF, and as a result, the color difference signal in horizontal scanning. This means that moiré, which tends to be a problem with single-chip color cameras that use color solid-state image sensors, is less likely to occur.

Another problem is that, as shown in Figure 11, when the horizontal pixel pitch of a solid-state image sensor is large, the shape of the circle of confusion that determines the depth of field is not a circle but a horizontally long rectangle. 14 to 17, and 1.
This can almost be achieved with the aperture 15 shown in FIGS. 9 and 20.

The effect of the aperture 15 shown in FIGS. 14 to 20 is as follows.
It goes without saying that the present invention can also be obtained by combining an imaging optical system without a convex lens 8, a telecentering optical system without a convex lens 8, or an imaging optical system that is not a telecentering link.

Although the incident angle of the lower off-axis ray has been described above, it goes without saying that the same condition must be satisfied for the upper off-axis ray.

Furthermore, even without the convex lens 8 or 13, if the objective lens itself satisfies the conditions of formula (1) or (2) above, a color bridge image without color shading can be obtained! It goes without saying that a device can be obtained, and it goes without saying that the present invention is applicable not only to electronic endoscopes but also to ordinary TV cameras, fiberscopes, TV cameras attached to rigid endoscopes, electronic cameras, etc. Not even.

Next, a numerical example is shown below. FIG. 21 shows the structure thereof, and 16 is a YAG laser cut filter.

fl Ken r, wo.

d+ =0.3040 rl+ -1,883M+
-40,78 "8 fables 0.6122 d, -0,3040 rs = 1.5921 ds" 0.3040 nt -1,7291
61'm -54,68r, -0,5933 da"0.4863 ns -1,5927
0Fs -35,29r's =-13,3733 d% -0,0608 r, -■ (Aperture) di -0,1216 r, -3,8365 dy =0.4863 ns -1,8061
ν4 -40.95ra = -1,1410 d, -0,0912 r* =5.2243 d9 -0.6079 ns -1,516
33ν% -64,15r 1゜= -0,7270 d +e"0.3040 n & -1,846
66W h -23,78r + + = -2,9
909 d r+ -0,1520 rth 3″ d+*=0.4255 nt -1,51633
k'q -64,15r,, m 1 d 13-0.3040 ns =1.5407
2 $1= =47.20r+a Field Sod lm-0,1824n *=1.51633
1' * -64,15r Is d+s-0,5635 rrh-2,5312 d+i-0,6079n+e=1.54869
ν+*=45.55rat ψ d+t-0,2432nst-1,51633j'z-
64,15flyzclD f-I F15.0 Object path #-9,1 R-2,531 nL=1.5487 ft=4.613 d, -0,5635 E --1,951 (with respect to the real principal ray )h-0,9
66 θ3=25°P −1lOAIm c =7 μm d1 = 7 μm n+=1.5 F =5 Δ=0 nz=7.5 d t =2 μm θ −9° 46 ′ θ, = 7° 14' FIG. 22 is an aberration curve diagram of the above numerical example.

〔Effect of the invention〕

As mentioned above, the color imaging device according to the present invention has an important practical advantage in that color shading is reliably prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a first embodiment of a color bottle image device according to the present invention, FIGS. 2 to 6 are diagrams showing the configuration of second to sixth embodiments, respectively, and FIGS. 7 to 11 The first figure is an explanatory diagram of the conditions that a convex lens placed near the solid-state image sensor should satisfy in order to prevent color shading.
2 and 13 are diagrams showing examples of arrangement of picture elements and color encoding filters of a solid-state image sensor, respectively, FIGS. 14 to 20 are diagrams showing examples of apertures, and FIGS. 21 and 22. Figures 23 and 24 are diagrams showing the configuration of numerical examples and aberration curve diagrams.
The figures are a diagram showing a configuration example of a conventional example and an enlarged sectional view of a main part, respectively. l... Solid-state image sensor, 2... Mosaic filter, 2a... Color element, 2b... Light shielding part, 3...
...Imaging lens system, 4...Imaging surface, 4a...Picture element, 4b...Light receiving section, 5...Glass plate, 6...
... Adhesive layer, 7 ... Off-axis chief ray, 7a ... Off-axis lower ray, 8 ... Convex lens, 9 ... Optical low-pass filter, 10 ... Red External light cut filter, 11... Support frame, 12... Prism, 13
...Positive lens, 141F3 Fig. 1-4 Off-view Fig. 8 Fig. 11 Fig. 12 Fig. IP 13 Fig. 1-14 Fig. 115 Fig. 116 Fig. 1-17 = -1- Q. Cq Figure 23 Figures 1-24

Claims (1)

[Scope of Claims] An imaging lens system, a solid-state imaging device formed by two-dimensionally arranging a plurality of picture elements each having an independent light-receiving portion, and a solid-state imaging device having a microscopic interval in front of the light-receiving portion of the solid-state imaging device. and a color encoding filter having a color element corresponding to each picture element arranged apart from each other, wherein a lens close to the color encoding filter in the imaging lens system is color encoded. A color imaging device characterized by being arranged near a filter and satisfying the following conditions. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ However, ■ is the incident angle of the light beam that enters the light receiving part of each picture element of the solid-state image sensor, and ■ is the optical axis of the imaging lens system for each picture element. The incident angle of a real or virtual light ray that enters the light-receiving part of each picture element through the point closest to each picture element of the color element corresponding to the picture element adjacent to the side closest to , ■ is n_1
When is the refractive index of the medium between the color element and the light-receiving surface, and F is the F number of the imaging lens system, it is the angle given by ▲There are mathematical formulas, chemical formulas, tables, etc.▼.