JP3283051B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device used in an endoscope or the like.

[0002]

2. Description of the Related Art A fiberscope using an image guide fiber is often used as an endoscope.
Recently, however, videoscopes using various solid-state imaging devices instead of image guides have also been widely used.

[0003] The imaging method of the video scope mainly includes a frame sequential method and a dot sequential method. Here, the dot-sequential method means that a color coding filter (usually called a color mosaic filter or the like) in which minute color filters are integrated in a mosaic shape corresponding to each picture element of the solid-state imaging device is used. Are provided on the incident side of the camera to obtain a color signal.

When a mosaic type image sensor is used, each color filter is arranged on each picture element of the solid-state image sensor. However, if the distance between the filter and the light-receiving surface of the light-receiving element of the solid-state image sensor is large, light rays that make a large angle of incidence on the solid-state image sensor will pass through the color filter before being incident on picture elements that should be incident. And the image obtained by incident on a picture element adjacent to it is uneven in color (called color shading).
May occur. This is because color shading cannot be prevented by a lens system of a type that is obliquely incident on the image sensor, such as the one described in Japanese Patent Application Laid-Open No. 62-173415 shown in FIG.

As a means for solving the above-mentioned disadvantage, there is an optical system described in Japanese Patent Application Laid-Open No. 2-74912.

This optical system is as shown in FIG. 23. In order from the object side, a concave lens and a convex lens of strong negative power, a brightness stop, an infrared cut filter, a cemented lens, a field lens, and an optical system closest to the image side. A low-pass filter is arranged.

In this optical system, a convex lens is arranged before the aperture stop in order to correct coma and astigmatism generated by a concave lens having a strong negative power. The convex lens also corrects the chromatic aberration of magnification generated by the concave lens.

However, this optical objective lens has a large number of constituent lenses.

If the number of lenses is reduced to achieve a relatively simple configuration, the power of each lens increases as a whole, and various aberrations increase accordingly. In order to correct this aberration, the overall length of the lens system becomes longer, and the compactness required by the endoscope cannot be maintained. In addition, if the rear group cemented lens is a single lens, chromatic aberration of magnification cannot be sufficiently corrected.

An optical low-pass filter using a quartz filter or the like disposed immediately before a solid-state image sensor becomes difficult to process as the size of the solid-state image sensor becomes smaller as the endoscope becomes thinner, and becomes very expensive.

[0011]

When observing the inside of a human body using an endoscope, a phenomenon called moiré, which is caused by interference between a subject and a solid-state image pickup device such as a CCD, hardly occurs. However, if the observed subject has a small white brightness even in the human body, when this is imaged by a CCD, a color moiré called false white occurs around the white brightness. In addition, the endoscope may be used not only for medical purposes but also for industrial purposes, for observing and inspecting inside a water pipe or an engine. In this case, there are many objects having a high spatial frequency as subjects, and moiré easily occurs, which hinders actual use. An object of the present invention is to provide an imaging apparatus used in an endoscope or the like that can perform good imaging by removing the occurrence of moire as described above.

[0012]

According to the present invention, there is provided an imaging apparatus comprising:
It has a sporadic sampling structure and
Including an image sensor with an extreme limit and an aperture stop
An imaging optical system for forming an object image on the image sensor;
Optical low-pass effect located near the aperture stop
And the following condition (A) is satisfied.
It is characterized by. (A) S / 2 ≦ f _R sin ｛| θ _m || n ₁ −n ₀ | / n ₀ } ≦ 3S | θ _m | <90 °, where S is a minimum sample for obtaining a luminance signal of the image sensor.
Ring spacing, θ _m is the normal to the surface with optical low-pass effect
Sampling direction of the angle difference between the plane and the normal to the reference plane of that plane
Are the maximum values of the absolute values of the components, and n ₀ and n ₁ are light
Refractive index of each medium sandwiching a surface with a biological low-pass effect, f _R
Is the focal length of the optical system on the image side of the aperture stop.

Here, an aspect of providing an optical low-pass effect in the imaging apparatus having the above-described configuration will be described.

As a method for giving an optical low-pass effect to a refracting surface, for example, there is a method of giving uniform directional high-order aberration to an image forming surface. FIG. 13 shows the configuration of an optical system that employs the above-described method. In the horizontal scanning direction H of the CCD, blurring due to higher-order aberrations is given. The filter 1 having a substantially wavy surface having one or more periods is arranged in the direction in which the filter 1 is moved. This filter 1 is C
It has a cylindrical shape in a plane shape substantially perpendicular to the horizontal scanning direction of the CD3.

Next, the principle of the moiré removing means will be described.

FIG. 14 shows a rear group behind the aperture stop in the optical system having the above configuration. The focal length of the lens unit 2 of the rear group in the optical system of FIG as f _R, is a normal angle with respect to the optical axis is arranged a filter 1 with a surface R ₁ is theta.

Here, if the rear lens unit 2 has a well-corrected spherical aberration, the axial rays converge on the image plane as shown by the broken line in FIG. However, this axial ray by placing the filter 1 will have an angle of delta _i with respect to the optical axis is refracted by the surface R ₁ of the filter.

At this time, the deviation B of the on-axis ray from the optical axis on the image plane 4 is as shown by the following equation (1). B = f _R sinΔ _i (1) or Δ _i ≒ θ (n ₁ −n ₀ ) / n 0 (2) where n ₀ and n ₁ are the refraction of the medium on the object side and the image side of the surface R ₁ , respectively. Rate. Therefore, B is represented as follows. _{B ≒ f R sin {θ (} n 1 -n 0 / n 0)} (3) Figure 15 is a plane having other optical low pass effect, a shape obtained by further providing the undulations with complex shapes.

In FIG. 15, the optical axis is the z-axis, the CCD is
When the scanning direction is taken on the x-axis and the vertical direction is taken on the y-axis, a surface having undulations only in the x-direction as shown in FIG. 15 can be expressed by the following equation (4). z = f (x) (4) In this case, the above value is referred to as a shift amount from the reference plane.

[0020] At this time, the change delta _i of the ray angle due to inclination of the surface is expressed by the following equation (5). Δ _i = df (x) / dx (5) The following equation is obtained from equation (1). B = f _R sin {df (x) / dx (n ₁ −n ₀ ) / n ₀ } (6) Also, what kind of higher-order aberrations are generated by the surfaces shown in FIGS. 14 and 15 is shown. FIG. 16 and FIG. 17 are respectively shown.

As already described by the equation, the relationship between the surface shape and B is as shown by the equations (3) and (6).

FIG. 16A shows the deviation of the surface shape from the reference surface. Here, the reference surface can be considered as a surface in a state where the spherical aberration of the optical system is sufficiently corrected, and is not necessarily a plane.

FIG. 16B is a graph showing B obtained from the equation (3).
Are shown.

When a surface having this shape is used, the spot is separated into two points as shown in FIG. Where ΔB is
This is the absolute value of the maximum location of B. Therefore, the response (MT
F) is close to a cosine curve as shown in FIG.

FIG. 17A shows a surface in which the reference surface has a swell of one cycle or more in the range of the aperture of the aperture stop. 6)
The shape is as shown in FIG. When a surface having such a shape is used, the spot becomes almost rectangular as shown in FIG. 19A, so that the MTF is as shown in FIG. 19B, and the MTF is lower than that of FIG. Then, the MTF is low, but at high frequencies, the MTF is well-pressed.

Next, a combination shown in FIG. 20 combining the above-mentioned surface shapes having the optical low-pass effect is also conceivable.

According to this surface shape, an MTF as shown in FIG. 21 can be obtained.

The above description has described one direction on one surface. However, it is also possible to produce such an optical low-pass effect in other directions, for example other planes in the vertical direction. In this case, a low-pass effect may be simultaneously generated in two or more directions on the same surface, and the surface may be rotationally symmetric with respect to the optical axis.

When an effect is simultaneously generated in one direction on two surfaces, the surface is expressed by the following equation (7). z = f (x) × g (y) (7) The rotationally symmetric surface is represented by the following equation (8). Here, how to take the reference plane will be described.

According to the present invention, the effect of an optical low-pass filter is provided by deforming one surface of an objective lens whose aberration has been well corrected. Therefore, the reference surface is a surface on which various aberrations are satisfactorily corrected when the deformation is removed. More specifically, the surface having the effect of the optical low-pass filter of the present invention,
Since it is often provided near the pupil of the objective lens,
The plane that minimizes spherical aberration is the reference plane.

In the present invention, the shape of the reference surface is a flat surface, a spherical surface,
If the reference surface is a spherical surface, for example, any one of a spheroid and a hyperboloid of revolution, a surface having a radius of curvature that minimizes spherical aberration is considered as the reference surface. When the reference surface is a spherical surface, the amount of deviation from the reference surface is the so-called aspherical amount itself.

Here, as can be seen from FIGS. 18, 19 and 21, the value of ΔB determines the spot diameter. The value of this ΔB the formula (3), Equation (6) together, the difference in angle between the normal of the normal to the reference plane of the surface having an optical low-pass effect and theta to when the maximum value and theta _m following Can be expressed by the following equation. _{ΔB = f R sin {| θ} m | (n 1 -n 0) / n 0} (9) provided that | θ _m | <90 ° mainstream thing is as a simultaneous equation of the solid-state imaging device, Vol. 37 Journal of the Institute of Television Engineers 10 (1983) pp. 89-96
This is based on the imaging method described in “Field accumulation mode CCD single-plate colorization method”.

According to the imaging system described in the above-mentioned document, a color filter array having a color arrangement as shown in FIG. 24 is arranged in front of a solid-state imaging device, and an image signal is read out in a vertical direction (vertical direction in the drawing). That is, the signals of the two pixels are mixed. That is, the first field (A field)
Then, horizontal scanning is performed by mixing two vertical pixels as shown on the right side of the figure. In the second field (B field), horizontal scanning is performed one pixel at a time in the vertical direction as shown on the left side of the figure. Do. At this time, the luminance signals of the n-th line and the (n + 1) -th line in the A field are represented by Y _{An ′} Y _{An + 1} ,
N lines in the B field, the n + 1 line luminance signal and _{Y Bn 'Y Bn + 1,} charge respectively Mg of each pixel by light after each filter transmittance (magenta), Ye (yellow), G (green), Cy (cyan )
The luminance signal is obtained as follows.

[0034] _{Y An = (Ye + Mg)} + (Cy + G) = Y An + 1 = (Ye + G) + (Cy + Mg) = 2R + 3G + 2B Y Bn = (Mg + Ye) + (G + Cy) = Y Bn + 1 = (G + Ye) + (Mg + Cy) = 2R + 3G + 2B this When such a solid-state imaging device is used, the cutoff frequency v _c of the horizontal low-pass filter generally satisfies the following relationship. ν _n ≦ ν _c ≦ ν _s (10) where ν _s is the sampling frequency of the luminance signal of the solid-state imaging device, and ν _n is the Nyquist limit frequency.

Further, from FIGS. 18, 19 and 21, the cutoff frequency due to the spot shape is shown in FIG.
(B) can be moved within the following range. ４ΔB ≦ ν _c ≦ 3 / 4ΔB (11) Assuming that the minimum sampling interval for obtaining the luminance signal of the solid-state imaging device is S, the following relationship is established. _{ν s = 1 / s = 2ν} n (12) first when the ν _s = ν _n, the relationship between [nu _n and .DELTA.B, equation (10) becomes as it follows from (11). １ ／ ΔB ≦ ν _n ≦ 3 / 4ΔB (13) Next, when ν _c = ν _s , the relationship between ν _s and ΔB is as follows. ４ΔB ≦ ν _s ≦ 3 / 4ΔB (14) Equations (13) and (12) and Equations (14) and (12)
And the following relations (15) and (16) are obtained respectively. 1/2 S ≦ ΔB ≦ 3 / 2S (15) S ≦ ΔB ≦ 3S (16) Also, the following equation (17) is obtained from the equations (15) and (16). S / 2 ≦ ΔB ≦ 3S (17) The following relationship is obtained from Expression (17) and Expression (19) relating to ΔB. _{S / 2 ≦ f R sin {} | θ m | (n 1 -n 0) / n 0} ≦ 3S However | a <90 ° | θ _m.

In FIG . 14, the refractive index of the medium sandwiched between the refraction surfaces is
It satisfies the relationship of “incident side ≦ exit side”.
It is clear that exactly the same argument holds even if the relationship is reversed.
It is easy. However, in this case , instead of n ₁ −n ₀ , n
₀ it is necessary to make the -n _1. Therefore, two cases
In summary, it can be expressed as follows.

[0037] _{(A) S / 2 ≦ f} R sin a <90 ° which is the aforementioned conditions _{(A) | {| θ m} || n 1 -n 0 | / n 0} ≦ 3S | θ m. That is, by satisfying this condition, moiré caused by the image pickup device and the subject can be effectively removed.

If the upper limit of this condition is exceeded, the optical low-pass effect is too strong, resulting in a blurred image. If the lower limit is exceeded, moire cannot be removed.

[0039]

Next, an embodiment of the image pickup apparatus according to the present invention will be described.

[0040] Figure 1 is a diagram showing an arrangement of the present invention, the objective lens includes a first lens L ₁ having a negative refractive power, a second lens L ₂ having a positive refractive power, an aperture stop S When, a third lens L ₃ of the positive lens is more configuration as the fourth lens L ₄ of the negative lens. Further a stop S between the third lens L ₃ are arranged a filter group F, on the image side of the fourth lens L ₄ is is disposed a CCD cover glass C. The r ₄ is a surface having an optical low-pass effect.

As described above, in the conventional example shown in FIG. 23, the cemented lens on the image side of the stop is integrated with the field lens function without deteriorating the aberration correction capability, and the birefringent plate disposed immediately before the image pickup device is provided. It has been lost.

[0042] Further is corrected by causing astigmatism positive in the second lens L ₂ generate astigmatism negative produced by the first concave lens L _1.

Thus, coma and astigmatism generated in the front unit on the object side of the stop are removed in the front unit.

The rear group on the image side of the aperture stop has a function as a field lens so that a principal ray is incident on the image pickup device almost perpendicularly. The distance between the S and the third lens L ₃ this time aperture opened to some extent, the third lens L
₃ of power can be suppressed small astigmatism occurring at the surface on the object side of the third lens L ₃ so as not too strong. Further, the astigmatism generated in the front group is made negative and balanced with the astigmatism generated on this surface.

In this way, the distance between the aperture stop S and the third lens is widened to be advantageous for aberration correction, and the filter group F can be disposed here.

As described above, various aberrations other than chromatic aberration can be satisfactorily corrected. Chromatic aberration can also be corrected independently for the front group and the rear group. By having the second lens L ₂ is arranged before the words stop S,
Chromatic aberration of the first lens L ₁ and can cancel by the second lens L _2. The rear group also third lens L ₃ negative chromatic aberration generated in the third lens L ₃ and can be sufficiently corrected at the junction surface of the fourth lens L _4.

Further, the size of the front unit can be reduced by increasing the power of both the first lens and the second lens.

As described above, the configuration of the imaging apparatus can be simplified by the low-pass filter used in the present invention.

The focal length f _R of the rear lens group of the first embodiment is f _R =
2.531. The sampling interval is 5.42.
μ.

The solid-state image pickup device used is of the type described in the above-mentioned document described with reference to FIG.

The surface having a low-pass effect according to the present invention has an optical axis
z, the horizontal scanning direction of the CCD is x, the direction perpendicular to the above scanning direction
The direction is y, and z = f (x) × g as a function form of this surface
Assuming (y), it is represented by the following equation. f (x) = Ex⁴+ Fx⁶+ Gx⁸+ Hx¹⁰+ Ix¹²+ Jx¹⁴+ Kx¹⁶  (I8) g (y) = C (C is a constant) (19) This shape becomes a shape as shown in FIG.
The shape has undulations only in the horizontal scanning direction of the CCD.
You.

In this embodiment, the diameter of the aperture stop is set to 0.1.
4 mm.

FIG. 4 shows the inclination of the surface shape.
_m is | θ _m | = 0.377 °. FIG. 5 shows f _R sin {θ (n ₁ −n ₀ ) / n ₀ } according to this surface shape, and f _R sin {| θm | (n ₁ −n ₀ ) / n ₀ } = 0.0087.

Further, when this optical system is actually traced by a computer using a ray, the amount of lateral aberration in the CCD horizontal scanning direction (x direction) on the axis is evaluated on a Gaussian image plane as shown in FIG.
Very consistent with FIG. That is, it is understood that the condition (A) is effective.

FIG. 7 shows the MTF of the first embodiment. The sampling frequency is 184 lines / mm.

The data of this embodiment is as follows. Example 1 f = 1.000, F / 5.535, IH = 0.8134, object distance = -9.8592 r ₁ = ∞ d ₁ = 0.2254 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 0.5365 d ₂ = 0.3521 r ₃ = 1.5395 d ₃ = 0.9225 n ₂ = 1.64769 ν ₂ = 33.80 r ₄ = -0.9365 d ₄ = 0.1056 r ₅ = ∞ (aperture) d ₅ = 0.0211 r ₆ = ∞ (aspheric) d ₆ = 0.2817 n ₃ = 1.52287 ν ₃ = 59.89 r ₇ = ∞ d ₇ = 0.0211 r ₈ = ∞ d ₈ = 1.0563 n ₄ = 1.52000 ν ₄ = 74.00 r ₉ = ∞ d ₉ = 0.8190 r ₁₀ = 1.6405 d ₁₀ = 1.2622 n ₅ = 1.72916 ν ₅ = 54.68 r ₁₁ = -1.6059 d ₁₁ = 0.6232 n ₆ = 1.84666 ν ₆ = 23.78 r ₁₂ = ∞ d ₁₂ = 0.2817 n ₇ = 1.52287 ν ₇ = 59.89 r ₁₃ = ∞ Aspheric coefficient E = -0.13388 × 10 ² , F = 0.19179 × 10 ⁴ , G = -0.10971 × 10 ⁶ , H = 0.32108 × 10 ⁷ , I = -0.50865 × 10 ⁸ , J = 0.41464 × 10 ⁹ , K =-0.13616 × 10 ¹⁰ f _R = 2.531 With the configuration shown in FIG. 2, the conventional crystal shown in FIG. 23 can be eliminated.

Also in the second embodiment, a surface having an optical low-pass effect is arranged on the surface immediately after the aperture stop. This surface is z =
This is a two-dimensional orthogonal function represented by f (x) × g (y). At this time, the functions f (x) and g (y) have the same shape as the expression (18), and the coefficients thereof are the same, as described in the data shown later.

In the second embodiment, for example, x is a CCD
Assuming that the horizontal direction and y are vertical directions, the sampling frequency in each direction and the direction of the angle in that direction may satisfy the condition (A).

In the above-mentioned planes, the function components f (x) and g (y) of the planes that can be expressed by orthogonal functions may be the same plane or different planes. In any case, if the surface is arranged near the stop, almost the same effect can be obtained.

[0060] In the lens group rear group in the second embodiment from the tenth surface to fourteenth surface, the focal length _{f R} of the synthesis of this lens group is 2.415. The sampling interval is 5.9 μm in both the horizontal and vertical directions.

The solid line shown in FIG. 8 represents the surface shape in the x direction. The y-direction has the same shape. The dotted line indicates f _R
sin {θ ((n ₁ −n ₀ ) / n ₀ )}, and f
_{The value of R} sin {θ _m ((n ₁ −n ₀ ) / n ₀ )} is
0.0081.

FIG. 9 shows the amount of lateral aberration in each of the horizontal and vertical directions of the CCD of this embodiment. FIG. 10 shows the MTF in each of the horizontal and vertical directions of the CCD. The sampling frequency is 169.5 lines / mm in both the horizontal and vertical directions of the CCD. If the MTF is about 30% or less, there is no practical problem,
In this embodiment, an image from which moiré has been removed can be obtained.

The data of Example 2 are as follows. Example 2 f = 1.000, F / 5.088, IH = 0.8575, object distance = -10.3935 r ₁ = ∞ d ₁ = 0.2376 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 0.5877 d ₂ = 0.6713 r ₃ = 2.1437 d ₃ = 0.4852 n ₂ = 1.64769 ν ₂ = 33.80 r ₄ = -1.1471 d ₄ = 0.1114 r ₅ = ∞ (aperture) d ₅ = 0.0223 r ₆ = ∞ (aspheric) d ₆ = 0.2970 n ₃ = 1.52287 ν ₃ = 59.89 r ₇ = ∞ d ₇ = 0.0223 r ₈ = ∞ d ₈ = 1.1136 n ₄ = 1.52000 ν ₄ = 74.00 r ₉ = ∞ d ₉ = 0.0742 r ₁₀ = 2.7122 d ₁₀ = 0.8166 n ₅ = 1.51633 ν ₅ = 64.15 r ₁₁ = -0.8444 d ₁₁ = 0.2240 n ₆ = 1.84666 ν ₆ = 23.78 r ₁₂ = -2.1696 d ₁₂ = 0.5197 r ₁₃ = 2.8953 d ₁₃ = 0.5197 n ₇ = 1.77250 ν ₇ = 49.66 r ₁₄ = ∞ d ₁₄ = 1.2177 n ₈ = 1.52287 ν ₈ = 59.89 r ₁₅ = ∞ Aspheric coefficient E = -0.11428 × 10 ² , F = 0.14731 × 10 ⁴ , G = -0.75823 × 10 ⁵ , H = 0.19968 × 10 ⁷ , I = -0.28464 × 10 ^{8 , J = 0.20879 × 10 9,} K = - 0.61693 × 10 9 f _R = 2.413

In the third embodiment, both the optical system and the CCD are the same as those in the first embodiment, and only the surface having an optical low-pass effect has a different shape.

The shape of a surface having an optical low-pass effect can be expressed by a piecewise polynomial, and is expressed by the following expression (20) when expressed in polar coordinates for easy understanding.

In each of the coefficient values of the above equation in the third embodiment,
a₀, A₁Is as follows. a₀= 3.44633 × 10^-4  a₁= −4.9483 × 10^-3  And C_nAre as follows. C₄= −0.33398 × 10 C₆= 0.23727 × 10³  C₈= −0.67312 × 10⁴  C₁₀= 0.97698 × 10⁵  C₁₂= −0.77675 × 10⁶  C₁₄= 0.31031 × 10⁷  C₁₆= −0.50536 × 10⁷  The solid line shown in FIG. 11 indicates the optical roper used in the third embodiment.
This is the shape of the surface that has the effect. R = 0 and r =
There is a non-differentiable discontinuity in the portion of 0.14.

The dotted line in FIG. 11 indicates f _R si of this embodiment.
n {θ ((n ₁ −n ₀ ) / n ₀ )}.

Also, f _R sin θ _m ((n ₁ −n ₀ ) / n
₀ ) The value of｝ is 0.0086.

FIG. 12 shows an MTF according to the third embodiment. When this MTF is compared with that of the first embodiment, in the third embodiment, M
It can be seen that TF is strongly suppressed. This is because it includes a linear portion having a planar shape.

In each of the above embodiments, the reference surface for providing the effect as an optical low-pass filter is a flat surface. That is, other lens data (r, d, n,
When the shape of only this surface is changed without changing (v), the spherical aberration of the entire system is minimized when the surface is flat.

[0071]

According to the present invention, moiré and the like can be reduced in an image pickup apparatus having an image pickup device having a discrete sampling structure and an image pickup optical system for forming an image on an object surface having a Nyquist limit by sampling of the image pickup device. It can be removed completely.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of embodiments 1 and 3 of the present invention.

FIG. 2 is a diagram showing a configuration of a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a shape of a surface having an optical low-pass effect according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the inclination of the surface.

[5] by the face _{f R sin {θ ((n} 1 -n 0)
/ N ₀ )｝

FIG. 6 is a diagram illustrating lateral aberration of the optical system according to the first embodiment.

FIG. 7 is a diagram showing an MTF of the optical system.

FIG. 8 is a diagram illustrating a shape of a surface having an optical low-pass effect according to the second embodiment.

FIG. 9 is a diagram illustrating a lateral aberration of the optical system according to the second embodiment.

FIG. 10 is a diagram illustrating an MTF of the optical system according to the second embodiment.

FIG. 11 is a diagram illustrating a shape of a surface having an optical low-pass effect according to the third embodiment.

FIG. 12 is a diagram illustrating an MTF of an optical system according to a third embodiment.

FIG. 13 is a diagram showing a basic configuration of the device of the present invention.

FIG. 14 is a view for explaining a surface having an optical low-pass effect used in the present invention and an effect of the surface.

FIG. 15 is a diagram showing a surface having another optical low-pass effect.

FIG. 16 is a diagram showing a shift amount of the plane shown in FIG. 14 from a reference plane and a distance from an optical axis on an imaging plane.

17 is a diagram showing the amount of deviation of the plane shown in FIG. 15 from the reference plane and the distance from the optical axis on the image plane

FIG. 18 is a diagram showing the MTF and the intensity of the spot in the x direction on the surface shown in FIG. 14;

19 is a graph showing the relationship between the spot intensity in the x direction of the surface shown in FIG.
Diagram showing TF

FIG. 20 is a diagram showing a surface shape having an optical low-pass effect of a combination of FIGS. 14 and 15;

FIG. 21 shows spot intensity distribution and MTF of the surface shown in FIG.
Figure showing

FIG. 22 is a sectional view of a conventional example.

FIG. 23 is a sectional view of another conventional example.

FIG. 24 illustrates an example of an imaging method.

Claims (1)

(57) [Claims] An imaging device having a discrete sampling structure and having a Nyquist limit due to sampling; an imaging optical system including a brightness stop for forming an object image on the imaging device; and the brightness stop and a refracting surface having an optical low-pass effect which is arranged in the vicinity of, the optical Russia
The refracting surface having a multipath effect is at least
The spot of the imaging optical system is divided into two points in the scanning direction.
Surface shape with separating action and spot strength of the imaging optical system
Combined with a surface shape that has the effect of making the degree closer to a rectangular shape
An imaging device having a shape and satisfying the following condition (A). (A) S / 2 ≦ f _R sin ｛| θ _m || n ₁ −n ₀ | / n ₀ } ≦ 3S | θ _m | <90 ° where S is the minimum sampling for obtaining a luminance signal of the image sensor. The interval, θ _m is the maximum value of the absolute value of the component in the sampling direction of the angular difference between the normal to the surface having the optical low-pass effect and the normal to the reference surface of the surface, and n ₀ and n ₁ are the optical low-pass, respectively. The refractive index f _R of each medium sandwiching the surface having the effect is the focal length of the optical system on the image side of the aperture stop.