JP4335957B1 - Large optical plate - Google Patents

Abstract

Provided is a large optical plate that is added to an imaging optical system such as various cameras, telescopes, and human eyes to increase the depth of focus and the depth of field when viewing an object.
The large optical plate is a second optical system arranged in front of the first optical system that is an imaging optical system for incident light waves. The size is larger than the incident aperture diameter of the first optical system, and the light beam that has passed through a part of the optical plate is incident on the aperture and then imaged. In this optical plate, the change in thickness or the curvature of the wavefront of transmitted light increases in proportion to the distance from the base point in the optical plate or in proportion to the third power function of the distance. The limit of the thickness is determined by limiting the range in which the depth of focus when the second optical system is provided in front of the first optical system in the above configuration is larger than that of the first optical system alone. To do.
[Selection] Figure 1

Description

  The present invention can be added to imaging optical systems such as various cameras, telescopes, and human eyes to increase the depth of focus of the imaging optical system and extend the depth of field when viewing an object. It relates to an optical plate.

  In general, in an imaging optical system, incident light is collected at each point on the imaging surface, but the imaging position shifts back and forth on the imaging surface depending on the distance to the object. However, since the depth of focus of the lens is limited, in order to obtain a blur-free image, it is necessary to adjust the distance between the lens of the imaging optical system and the imaging surface in accordance with the distance to the object.

  As a method for extending the depth of focus, for example, a method of narrowing the aperture (that is, reducing the aperture diameter) has been known for a long time. However, this method has the disadvantageous effect that the amount of incident light is reduced and the resolution is lowered.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-77914) discloses a technique for imaging an object with a wide range of distance with a single fixed focus by extending the depth of focus. This technique increases the depth of focus by attaching a lens system having negative spherical aberration or an optical plate having an equivalent function in front of the imaging optical system. For example, in the case of an optical plate, the curvature of the wavefront of the light transmitted therethrough increases from the center to the periphery, and as a result, the curvature of the imaging wavefront of the imaging optical system becomes a distorted spherical surface that decreases toward the periphery. By increasing the depth of focus, the depth of focus is extended.

  In general, by increasing the depth of focus of the imaging optical system, it is possible to extend the depth of field when viewing an object. For example, glasses are included in the category of optical plates that are larger than the aperture of the imaging optical system, but in order to extend the depth of field of the eye, which is the imaging optical system, various progressive glasses based on bifocal lenses are proposed. Has been. This technology provides a multifocal lens function at a location corresponding to the perspective inside the optical plate. By viewing the optical plate while changing its position, a wide range of perspective objects can be viewed with little eye strain. It is intended to be. However, in progressive glasses using a bifocal lens, the depth of field cannot be extended with respect to the line-of-sight direction at the same location in the optical plate unless the position in the optical plate is changed.

  On the other hand, in the optical plate of the present invention, the depth of focus can be extended almost uniformly through any aperture in the optical plate through the aperture of the imaging optical system (a general imaging optical system including eyes). The size of the optical plate is not limited to the normal glasses size, and may be a large size that can be attached to a windshield of a car, a train, a train, an airplane, or the like. This is a new type of optical plate not present in the conventional concept.

JP 2004-77914 A T. Aruga, Applied Optics, Vol. 36, 3762-3768 (1997) Ariga Nori, Laser Research, Vol. 32, 352-356 (2004)

  An optical plate that can extend the depth of focus of an imaging optical system in almost the same manner regardless of where the optical plate is viewed is provided.

  By using the large optical plate of the present invention, the depth of focus of the imaging optical system can be increased, and similarly, the depth of field when viewing an object can be increased.

  The large optical plate of the present invention is a second optical system that is arranged in front of the first optical system that is an imaging optical system for incident light waves. The size of the second optical system is larger than the incident aperture diameter of the first optical system. The second optical system and the first optical system are configured such that a part of the transmitted light in the optical plate which is the second optical system is incident on the aperture of the first optical system and forms an image on a predetermined imaging surface. It is. The optical plate as the second optical system has a change in thickness or a wavefront curvature of transmitted light that increases linearly in proportion to the distance from the base point in the optical plate. At that time, the thickness of the optical plate is determined up to a range in which the depth of focus when the second optical system is provided before the first optical system is larger than that when only the first optical system is shown. To do.

  More specifically, the change in the thickness of the optical plate as the second optical system is approximately proportional to the third-order power function of the distance from the base point.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

[Principle of the Invention]
The present invention increases the depth of focus of an imaging optical system by using an optical plate larger than the aperture of the imaging optical system in front of the imaging optical system. For example, as shown in FIG. 1, an optical plate 2 larger than the opening is disposed in front of the imaging optical system 1 so that incident light 3 is imaged after passing through the optical plate 2. The transmitted light 4 that has passed through a part of the optical plate 2 forms an image on the imaging surface 6 by the lens 5 of the imaging optical system. With this optical plate 2, the depth of focus of the imaging optical system 1 can be increased. By increasing the depth of focus in this way, the depth of field when the object is viewed can be extended. In other words, the curvature of the wavefront of the imaging light of the imaging optical system is given by giving the property that the change in the thickness of the optical plate or the curvature of the surface shape increases linearly in proportion to the distance from the base point in the optical plate. Changes, and as a result, the depth of focus increases. Paying attention to the wavefront, due to the characteristics of the optical plate, the curvature of the wavefront after passing through the optical plate increases as it goes in a certain direction from the base point, so the curvature of the wavefront of the imaging light in the next imaging optical system is along that direction. It becomes smaller and becomes a distorted spherical surface compared to the original spherical wavefront of the imaging light without an optical plate.

Next, the principle of the present invention will be physically described using mathematical formulas and the like.
Consider the shape of a general surface. It is assumed that a surface exists so as to be orthogonal to the basic axis (optical axis in the case of an optical system), and the basic axis is z. The shape of the surface is represented by a curve, and a change in the z direction of a curve continuous along a certain direction perpendicular to the z axis, for example, the r direction, is defined as Z (r) as a function of the curve shape. If the distance in the tangential direction of a point on the curve is s and the line element is ds,
ds = {1+ (dZ / dr) ² } ^1/2 dr,
When the change in the z direction of the curve is sufficiently small ((dZ / dr) ² << 1), ds is approximately equal to dr and ds≈dr.

Further, if the inclination angle of the tangent line of the curve with respect to the r direction is θ, the inclination angle θ (r) with r as a variable is expressed as follows as a derivative of Z (r).

  Here, if the curvature of the curve is C, the curvature is defined by C = dθ / ds. Since ds≈dr under the above conditions, the curvature C (r) with r as a variable is approximately expressed by the following equation.

From Equations 1 and 2, the curvature C (r) is as follows using Z (r).

  That is, when the change in the z direction of the curve is sufficiently small, the curvature C (r) is represented by the second derivative of the curve shape Z (r). This is because the tangential inclination angle θ is a derivative of the shape Z, and the curvature C is a derivative of θ, as expressed by the equations 1 and 2.

  The shape of the surface can be treated as the shape of a curve as described above. In the optical plate of the present invention, the change in thickness increases linearly in proportion to the distance from the base point in the optical plate. This is equivalent, but the curvature of the wavefront of the transmitted light also increases linearly in proportion to the distance from the base point in the optical plate. Considering the shape of the wavefront satisfying this condition based on Equation 3, the surface shape Z (r) may be a cubic function, for example. This is because the second-order differentiation of the cubic function becomes a linear function, and the curvature C (r) becomes a linear function of r and changes linearly.

  For easy handling, the optical plate is axisymmetric and its effective radius is a. When ρ = r / a, the surface shape of the cubic function is as follows.

ここで、Ａは３次関数の係数であり、定数である。また、変数ｒを用いると数４は、Ｚ（ｒ）＝Ａ（ｒ／ａ）³、と表される。

Here, A is a coefficient of a cubic function and is a constant. When the variable r is used, Equation 4 is expressed as Z (r) = A (r / a) ³ .

  Considering the curvature based on Equation 4 where the surface shape is a cubic function of the variable r, as described above, the curvature is a second-order derivative of the surface shape. Therefore, the curvature is expressed as a second-order derivative of Z (ρ). It becomes a linear function as shown in the equation.

In the optical plate, the amount of change in radial radius corresponding to the aperture of the imaging optical system
Δρ = ρ ₁ −ρ ₂ ,
And the amount of change in curvature at Δρ,
ΔC (ρ) = C (ρ ₁ ) −C (ρ ₂ ),
And At this time, from Equation 5,
ΔC (ρ) = C (ρ ₁ ) −C (ρ ₂ ) = 6A (ρ ₁ −ρ ₂ ) = 6AΔρ,
Therefore, the amount of change in the partial curvature is as follows.

  Therefore, when the curvature C (ρ) is a linear function of ρ as shown in Equation 5, the curvature changes linearly with respect to the radial direction, so the amount of change in the curvature does not change with ρ and is equal in any part. . Equation 6 means this. This can be understood from the fact that the derivative of the linear function becomes a constant. Further, when the curvature of the wavefront of the light transmitted through the optical plate changes, the curvature of the wavefront of the imaging light of the imaging optical system also changes. This effect is the same everywhere on the optical plate. As a result, it is possible to extend the depth of focus of the imaging optical system in substantially the same manner regardless of where the optical plate is viewed.

  The principle of changing the curvature of the wavefront of the imaging light of the imaging optical system to increase the depth of focus is that ΔC is the amount of change in the curvature of the wavefront of the light incident on the lens of the imaging optical system, f is the focal length of the lens, When Δf is a focal shift amount caused by a change in the curvature of the wavefront of incident light, it is based on the following well-known formula.

An equation similar to Equation 7 is also shown in Equation 21 of Patent Document 1. The focal shift amount due to the partial change in the curvature of the wavefront corresponds to the focal depth extension, and the greater the focal shift amount, the deeper the focal depth. Since ΔC changes in proportion to the coefficient A as shown in Equation 6, the depth of focus can be freely adjusted by changing the value of A.

  In the optical plate of the present invention, the curvature of the wavefront is changed by changing the phase of the transmitted light in accordance with the passing position of the optical plate. Usually, since the distance to the object is sufficiently large with respect to the aperture of the imaging optical system, the wavefront of the incident light is approximately flat. Since the wavefront is an equiphase surface of light, after the incident light is transmitted through the optical plate, in order to increase the curvature of the wavefront as the distance from the base point in the optical plate increases, the optical plate increases as this distance increases. The thickness of the can be increased.

  Next, the fact that the phase of transmitted light is delayed as the thickness of the optical plate of a uniform medium increases will be described using mathematical expressions.

  The thickness (geometric length) of the optical plate that changes according to the value of ρ is expressed as a function w (ρ), and the optical path length (optical length) of transmitted light corresponding to w (ρ) is S ( It is known that the following equation is generally established, where ρ) and n is the refractive index of the optical plate material.

このように、光学板による透過光の位相の遅れは、光路長に比例する。 If the wave number is k (= 2π / λ, where λ is the wavelength) and the phase is ζ, the phase delay is given by the following equation.

Thus, the phase delay of the transmitted light by the optical plate is proportional to the optical path length.

Here, since (n-1) is a constant in Equation 8, the shapes of S (ρ) and w (ρ) are equivalent except for the coefficients. That is, if the function w (ρ) is a cubic function, S (ρ) is also a cubic function. That is, when the surface shape of the optical plate is a cubic function, the curvature of the wavefront of the transmitted light is also a cubic function.

  In order to easily handle the state in which the surface shape of the optical plate is a cubic function, the optical plate is axially symmetric, and the distance from the base point (center in the case of axial symmetry) in the optical plate is changed as in the case of Equation 4. The change in thickness of the optical plate is represented by w (ρ). w (0) is the thickness at the base point (center). When one surface of the optical plate is a flat surface and the thickness is changed by changing the other surface, w (ρ) is a function representing the shape of the surface of the optical plate, and is equivalent to Z (ρ) in Equation 4. Become. Therefore, the shape w (ρ) of the surface of the optical plate can be expressed by the following equation, as in Equation 4.

  In this case, the surface shape is concave, and w (ρ) is a function that gives the height from the bottom of the concave surface at ρ. The coefficient A is equal to w (1) and is the height from the bottom surface at the end ρ = 1 of the optical plate. The greater the value of A, the deeper the depth of focus. Therefore, hereinafter, A will be referred to as the power of the optical plate.

  In the present invention, as shown in FIG. 1, an optical plate 2 larger than the aperture is disposed in front of the imaging optical system 1. For example, when an eye is assumed as the imaging optical system, not only glasses but also a car or a train Since it has a function that can be used even if it is attached to the front glass, the size thereof is much larger than the opening diameter of the eye (the size of the pupil). In actual application of the present invention, the optical plate is designed and manufactured according to Equation 10. At that time, since the shape is determined, the coefficient A defined as the frequency of the optical plate, that is, the height of the end of the concave surface with respect to the center (bottom) of the concave surface may be determined. Since the size of the optical plate of the present invention is sufficiently large compared to the case where an optical plate having the same size as the aperture of the lens of the imaging optical system is used, the setting of the value of the coefficient A is important.

  Here, regarding the setting of the value of the coefficient A, as an empirical rule for obtaining the same depth of focus when the size of the optical plate is changed from the experimental results of various prototype optical plates of the present invention, It is known that if the value is increased from a certain value to m times, the value of A in Formula 10 that is the power of the optical plate may be set to m times. " Further, in the present invention, since the image pickup lens is viewed through the optical plate through one portion of the optical plate, the image pickup lens opening overlaps with the inclined portion where the thickness of the optical plate increases from the base point. In the case of an axially symmetric optical plate that is m times as large as the lens aperture, the value of A should be increased by 2 m compared to the case where the diameter of the optical plate is the same as the aperture diameter of the imaging lens. Laws are also obtained.

  With regard to this rule of thumb, that is, when the diameter of the optical plate is m times the original diameter, and the power A of the optical plate having the diameter m times that of the optical plate is m times (that is, in Equation 4, a and A Can be explained as follows.

  First, it is assumed that imaging cameras having the same aperture diameter are used for two optical plates having different sizes. From the above description, in order to make the depth of focus extension effect equal between two optical plates with different curvatures but with the same aperture, the integral of the curvature within the wavefront aperture, that is, the inclination angle of the tangent of the curve Should be equal between the two optical plates. This is because, in Equation 7, the focal shift amount Δf due to a partial change in the curvature of the wavefront corresponds to the focal depth extension, but the contribution of the shift amount Δf from all points of the aperture increases the entire focal depth extension effect. This is because it is determined.

  Further, as apparent from Equation 2, the integral of the curvature C is the inclination angle θ. When the curvature C is a linear function, the inclination angle θ is a quadratic function. As is clear from Equation 1, when the curvature is small, the inclination angle θ is a derivative of the curve shape Z.

Under the condition of the optical plate of the present invention in which the shape Z of the curve is a cubic function of ρ, when viewed as a function of ρ, a and A are simultaneously multiplied by m, so that the function θ (ρ) is changed to the original function. Can be the same. That is, for two optical plates of different sizes, Z is set to A (r / a) ³ and mA (r / ma) ³ as cubic functions of radius r, and ρ is r / a, r, respectively. / Ma. At this time, the inclination angle θ is the same as θ (r) = θ (ρ) = (3A / a) ρ ² in both cases.

  In addition, the lens of the imaging optical system is axially symmetric. On the other hand, in the region of the optical plate that transmits light that passes through the aperture of the imaging lens during imaging, the shape is not axially symmetric except for the central portion. This is because the shape of the optical plate region acting in the aperture of the imaging lens is not axially symmetric unless the center of the imaging lens coincides with the base point of the optical plate (center in the case of axial symmetry). . In this case, it is difficult to mathematically accurately introduce the setting condition A for a large optical plate. However, setting A as described above is in good agreement with various experimental results in the inventor's experience.

  The example of this invention optical plate and the result of a computer simulation are shown. As an application example to an imaging optical system, first, (1) an example of an optical plate placed in front of a normal imaging camera and the result of a computer simulation thereof are shown, and then (2) glasses when viewed with human eyes An example of a slightly larger optical plate and the result of the computer simulation are shown. In both cases, the results of the computer simulation almost coincide with the experimental results.

  The intensity of the focused beam displayed in the figure of this specification is a numerical value indicating the energy density per unit square meter calculated using meters (m) as a unit of length, and the intensity of incident light is 1 Relative strength. The distance of the object is calculated as infinity (∞). Non-Patent Document 1 (T. Aruga, Applied Optics, Vol. 36, 3762-3768 (1997)) or Non-Patent Document 2 (Nori Ariga, Laser Research, Vol. 32, 352-356 ( 2004))) and the formula improved for non-axisymmetric calculation.

  As an example of placing the optical plate of the present invention in front of an imaging optical system, two application examples of an imaging camera and an eye are shown.

  As an example of the imaging camera, consider a case where the focal length of the lens is 7.5 cm and the effective aperture diameter is 2.5 cm (F3). Here, the effective aperture diameter is defined as a value obtained by dividing the focal length by the F value. Similarly, consider the case where the focal length of the crystalline lens is 24 mm and the effective pupil diameter is 3 mm (F8) as the average pupil diameter.

  As parameters for setting the optical plate, the size of the optical plate, the frequency A, and the refractive index of the material are required. The frequency A is determined according to the above rule of thumb. For simplicity, we will consider an axisymmetric optical plate. Here, the case where an optical plate having a diameter equal to the aperture diameter of the imaging optical system is attached is considered as a reference state. From past theoretical analysis and experiments, it has been found that the optical plate power that can increase the depth of focus without substantially degrading the image quality is about 5 μm for the imaging camera and about 4 μm for the eyes. Therefore, in the case of the imaging camera, the diameter A is 2.5 cm and the frequency A is 5 μm, and in the case of the eye, the diameter 3 mm and the frequency A is 4 μm is treated as the reference state of the optical plate.

  In the case of an imaging camera, for example, when the diameter of the optical plate to be used is 10 cm, which is 4 times the effective aperture diameter of 2.5 cm, and 25 cm, which is 10 times, the frequency A is 40 μm (5 μm × 2 × 10 / 2.5) and 100 μm (5 μm × 2 × 25 / 2.5). Similarly, in the case of the eye, for example, if an optical plate having a diameter of 3 cm, which is 10 times the effective aperture diameter (pupil diameter) of 3 mm (= 0.3 cm), and a diameter of 30 cm, which is 100 times, is attached, 80 μm (4 μm × 2 × 3 / 0.3) and 800 μm (4 μm × 2 × 30 / 0.3). Among these, the value of the second example, that is, the diameter of 10 cm for the imaging camera and the diameter of 3 cm for the eyes is selected as an example, and the result of the computer simulation is as follows compared with the case where no optical plate is attached. Shown in

  First, as an application example of the imaging camera, FIG. 2A shows the distribution of the intensity of the focused beam in the optical axis direction to indicate the depth of focus when no optical plate is attached, and FIG. 2B shows the depth of focus. A focused beam cross-sectional profile in the vicinity of the center of is shown. The wavelength is assumed to be a center wavelength of 0.6 μm, and the refractive index of the optical plate is assumed to be 1.5 as a standard value.

  For comparison, FIG. 3 shows (a) the distribution of the central intensity of the focused beam in the direction of the optical axis when an optical plate having a diameter of 2.5 cm and a frequency of 5 μm, which is equal to the effective aperture diameter of the imaging camera, is attached. A focused beam cross-sectional profile near the center of the focal depth is shown. Comparing FIG. 3 with FIG. 2, it can be seen that the depth of focus is increased by attaching the optical plate. In both FIG. 2A and FIG. 3A, the display area of the intensity distribution in the optical axis direction is 500 μm. When the optical plate is attached, the focal region shifts forward (that is, away from the optical plate) as a side effect.

  FIG. 4 shows a surface shape when the power A is set to 40 μm as an example of an imaging camera optical plate having a diameter of 10 cm, which is four times the effective aperture diameter of 2.5 cm of the imaging camera. An important feature of the present invention is that the surface shape is a cubic function. When one surface of the optical plate is a flat surface, the other surface has such a concave shape.

  In FIG. 5, an optical plate (same as in FIG. 4) having a diameter of 10 cm and a frequency of 40 μm is installed in front of an imaging camera having an effective aperture diameter of 2.5 cm, and the central intensity of the focused beam when viewed through the optical plate The optical axis direction distribution was shown. The center of the imaging camera was placed at a distance of about 1/3 and 2/3 of the radius from the center of the axisymmetric optical plate, at a position of 1.6 cm in FIG. 5 (a) and 3.2 cm in FIG. 5 (b). Show the case and compare. The display area of the intensity distribution is 500 μm, as in FIGS.

Comparing FIG. 5 with FIG. 2, it can be seen that the depth of focus is increased by the optical plate. Further, when comparing (a) and (b) in FIG. 5, the peak value in (b) is smaller in the intensity distribution, and it seems that the width is broadened, but the same intensity level, For example, the width is almost equal at a level of about 1.75 × 10 ¹⁰ (the vibration-like portion is considered as a smoothed curve). From this, it can be seen that although not shown here, as demonstrated by experiments, substantially the same depth of focus extension effect can be obtained even when the position of the camera lens is changed in the optical plate. In addition, it can be seen that the depth of focus is extended to substantially the same level as compared with the case of FIG. 3A at this intensity level. Further, comparing FIG. 5 with FIG. 3 (when an optical plate having the same diameter as the aperture of the camera is attached), it can be seen that the amount of shift of the focal region to the front is small and the side effects of the optical plate are small.

  FIG. 6 shows an example of a focused beam cross-sectional profile in the direction perpendicular to the surface of the optical plate when the optical plate is attached. This example is a cross-sectional profile near the center of the focal depth in the case of FIG. The display width is 50 μm as in the case of FIGS. 2B and 3B. Since the surface shape of the portion of the optical plate that enters the aperture of the imaging camera is non-axisymmetric, the focused beam cross-sectional profile is also asymmetric. In the case of axial symmetry, a cross-sectional profile is generated in which side lobes are generated around the main lobe by the Bessel function as shown in FIGS. 2 and 3, whereas in the case of non-axisymmetric, only the main lobe is obtained as shown in FIG. The characteristic is that the cross-sectional profile is monotonically decreasing. In addition, it can be understood that high resolution is maintained because the width of the main lobe is similar to that when the optical plate is not attached as shown in FIG. Furthermore, it can also be seen from FIG. 6 that a tilt effect occurs and the center of the focused beam shifts laterally as a side effect of the optical plate because it is viewed through the inclined portion of the surface shape change of the optical plate.

  Next, a usage example of the optical plate for glasses will be described. For comparison, FIG. 7 shows a case in which an optical plate is not attached to the eye. (A) Concentrated beam center intensity distribution in the optical axis direction to indicate the depth of focus; A cross-sectional profile is shown. The wavelength is assumed to be the center wavelength of the eye sensitivity of 0.55 μm, and the refractive index of the optical plate is assumed to be 1.5 as a standard value.

  FIG. 8 shows (a) the distribution of the central intensity of the focused beam in the direction of the optical axis and (b) the depth of focus when an optical plate having a diameter of 3 mm and a frequency of 4 μm is attached in front of the eye. A focused beam cross-sectional profile near the center is shown. Comparing FIG. 8 with FIG. 7, it can be seen that the depth of focus is increased by attaching the optical plate. The display area of the intensity distribution in the optical axis direction shown in FIGS. 7A and 8A is 200 μm. When an optical plate is attached, the focal area shifts forward as a side effect.

  FIG. 9 shows a surface shape when the power A is 80 μm as an example of an optical plate for eyeglasses having a diameter of 30 mm, which is 10 times the effective aperture diameter of 3 mm. An important feature of the present invention is that the surface shape is a cubic function. When one surface of the optical plate is a flat surface, the other surface has such a concave shape.

  FIG. 10 shows an optical axis direction distribution of the focused beam center intensity when an optical plate (same as in FIG. 9) having a diameter of 30 mm and a frequency of 80 μm is attached in front of the eye and viewed through the optical plate. The case where the center of the eye is placed at the position of (a) 5 mm and (b) 10 mm at a distance of about 1/3 and 2/3 of the radius from the center of the axisymmetric optical plate is compared. The display area of the intensity distribution in the optical axis direction is 200 μm as in FIGS. 7 (a) and 8 (a).

Comparing FIG. 10 with FIG. 7, it can be seen that the depth of focus is increased by the optical plate. Further, comparing (a) and (b) in FIG. 10, the peak value is smaller in (b) in the intensity distribution, and at first glance, it seems that the width is wider, but the same intensity level. For example, at a level of about 0.75 × 10 ¹⁰ , the widths are almost equal. From this, it can be seen that although not shown here, as demonstrated by experiments, substantially the same depth of focus extension effect can be obtained even when the position of the camera lens is changed in the optical plate. In addition, it can be seen that the depth of focus is extended to substantially the same level as compared with the case of FIG. 8A at this intensity level. Further, comparing FIG. 10 with FIG. 8 (when an optical plate having the same diameter as the opening diameter of the eye is attached), as in the case of the above-described imaging camera, the amount of shift to the front of the focal region is small, and the optical plate It can be seen that the side effects are small.

  FIG. 11 shows an example of a focused beam cross-sectional profile in a direction perpendicular to the surface of the optical plate when the optical plate is attached. This example is a cross-sectional profile near the center of the focal depth in the case shown in FIG. The display width is 100 μm as in the case of FIGS. 7B and 8B. Since the surface shape of the portion of the optical plate that enters the eye opening is non-axisymmetric, the focused beam cross-sectional profile is also asymmetric. (1) In the case of axial symmetry, a cross-sectional profile in which side lobes are generated around the main lobe by the Bessel function as shown in FIGS. 7 and 8, whereas (2) in the case of non-axial symmetry, As shown in FIG. 11, the profile is a monotonically decreasing cross-sectional profile of only the main lobe. In addition, it can be understood that high resolution is maintained because the width of the main lobe is similar to that when no optical plate is attached as shown in FIG. Further, as in the case of the above-described imaging camera, since the image is viewed through the inclined portion of the surface shape change of the optical plate, a tilt effect occurs, and the center of the focused beam is slightly shifted to the side as a side effect of the optical plate. This can also be seen from FIG.

  When manufacturing the optical plate of the present invention, it is necessary to set the power A of the optical plate to an appropriate value. When the frequency A is increased, the depth of focus is increased, but the contrast of the image is deteriorated, and the image quality is deteriorated. That is, the depth of focus and the image quality are in a trade-off relationship. Therefore, in order to obtain an optimum state that suits the user's purpose, it is desirable to set the power A of the optical plate to an appropriate value.

  In the above formulas and examples in the explanation of the principle, an axially symmetric optical plate is used for easy handling. However, the shape of the cubic function, which is a feature of the optical plate of the present invention, does not need to be axially symmetric, and even if it is a cubic function with respect to one axial direction orthogonal to the optical axis, instead of the radial direction, The principle of the invention is similarly established. In this case, the base point in the optical plate used in the above definition may be set at the end instead of the center.

  The optical plate of the present invention can be used even if it is sufficiently larger than the aperture of the imaging optical system. However, the larger the size of the optical plate, the more the change in thickness or shape in the region near the base point (or center) in the optical plate. Since it becomes small, processing of such a surface shape becomes difficult with accuracy, and the effect deteriorates. As a countermeasure in this case, instead of setting the radial variable ρ to 0 at the base point, the value is set to a moderately large value. For example, the value of ρ at the base point is 0.1, and ρ = 0.1 to 1.0. The method of determining is good.

  The above-described optical plate of the present invention is large and has the function of increasing the depth of focus almost similarly regardless of where it is seen. This feature can be used in other ways as well.

  For example, in the case of a wide-field imaging camera, the aperture diameter of the lens is much larger than the effective aperture diameter (F value / focal length). When an axisymmetric optical plate is used with a wide-field camera, the power of the optical plate is equivalently increased with respect to a light beam with a large incident angle corresponding to a wide field of view. That happens.

  However, this problem can be solved by using the optical plate of the present invention. In order to solve this problem, for example, an axially symmetric optical plate having a reasonably large diameter may be manufactured, and only a necessary aperture diameter may be cut and used in a region between the center and the end. In this case, the depth of focus becomes substantially the same regardless of the position within the aperture diameter deviated from the cut optical axis (that is, off-axis).

  When the optical plate of the present invention is used as an optical plate placed in front of the eyes, in addition to the function of extending the depth of focus, it is possible to obtain convenience that cannot be obtained by other techniques. Whether it is glasses or when attached to the windshield of a car or train, the eyes are corrected not only for people with good eyes but also for glasses with hyperopia, myopia, astigmatism, and bifocals. This also means that an effect can be obtained by using the optical plate of the present invention. When used for the above glasses, it may be used in connection with the already used correction glasses, or may be a surface shape in which the surface shape of the optical plate of the present invention is superimposed on the surface shape of the eyeglass lens.

  The optical plate of the present invention does not need to be orthogonal to the optical axis of the imaging optical system, and may be placed in an inclined state. When attached to the windshield of a car or train, the optical plate is often installed at an angle when viewed from the observer. This is because the optical plate is installed obliquely with respect to the optical axis, but based on Equation 8, the optical plate with respect to the optical axis is equal to the optical path length when the optical plate is perpendicular to the optical axis. It is desirable to set the frequency A according to the angle.

  In addition, since it is necessary to increase the frequency when the size of the optical plate is increased, the deterioration of the focal depth extension effect in the region close to the center of the optical plate and the deterioration of the image quality in the region close to the edge can be applied. Since there is a limit to the size of the optical plate, it must be devised. As described above, when used for a windshield or for a window glass of a building or the like, a plurality of optical plate regions can be provided for one glass. For example, the configuration of the optical plate according to the present invention can be easily increased by adopting the arrangement in a matrix.

  Although the stereoscopic image display technology has recently advanced, the technology of the optical plate of the present invention can be expected to be effective in reducing eye muscle fatigue when viewing a stereoscopic image. Since the depth of field is almost the same regardless of where the optical plate is viewed, not only the glasses-type optical plate for 3D movies but also the display surface of PCs and DVD devices for 3D images An optical plate can also be expected as a new application.

It is a utilization conceptual diagram of this invention large sized optical board. An example of a focused beam by an imaging camera (without an optical plate), assuming an effective aperture diameter of 2.5 cm and a focal length of 7.5 cm, (a) optical axis direction distribution of focused beam center intensity, (b) It is a figure which shows a condensing beam cross-sectional profile. Examples of a focused beam obtained using an optical plate having the same diameter as the effective aperture diameter of the imaging camera, showing (a) the distribution of the focused beam center intensity in the optical axis direction and (b) the focused beam cross-sectional profile. It is. It is a figure which shows the example of the surface shape of this invention optical plate put in front of an imaging camera. An example of the distribution of the central intensity of the focused beam in the optical axis direction when the optical plate of the present invention is placed in front of the imaging camera and viewed through the optical plate, assuming an optical plate with a diameter of 10 cm, and (a) the center position of the camera is When the distance is 1.6 cm from the center of the optical plate, (b) shows the case where the center position of the camera is a distance of 3.2 cm from the center of the optical plate. It is a figure which shows the example of a condensing beam cross-sectional profile at the time of seeing through an optical plate by placing the optical plate of this invention in front of an imaging camera, and assumes an optical plate with a diameter of 10 cm. An example of a focused beam by eyes (without an optical plate), assuming an effective aperture diameter (pupil diameter) of 3 mm and a focal length of 24 mm, (a) optical axis direction distribution of focused beam center intensity, (b) It is a figure which shows a light beam cross-sectional profile. It is an example of a focused beam obtained by using an optical plate having the same diameter as the effective aperture diameter of the eye, and shows (a) the distribution of the focused beam center intensity in the optical axis direction and (b) the focused beam cross-sectional profile. is there. It is a figure which shows the example of the surface shape of this invention optical plate for glasses put in front of eyes. An example of the distribution of the central intensity of the focused beam in the optical axis direction when the optical plate of the present invention is placed in front of the eye and viewed through the optical plate, assuming an optical plate with a diameter of 30 mm, and (a) the center position of the eye is optical When the distance is 5 mm from the center of the plate, (b) is a diagram showing the case where the center position of the eye is a distance of 10 mm from the center of the optical plate. It is a figure which shows the example of a condensing beam cross-sectional profile at the time of putting the optical board of this invention in front of eyes and seeing through an optical board, and assumes an optical board with a diameter of 30 mm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging optical system 2 Large optical plate 3 Incident light 4 Transmitted light 5 Imaging lens 6 Imaging surface

Claims (1)

A second optical system arranged in front of the first optical system which is an imaging optical system for incident light waves,
The second optical system is an optical plate, the size of which is larger than the incident aperture diameter of the first optical system,
In the second optical system and the first optical system, a part of the transmitted light in the optical plate which is the second optical system is incident on the opening of the first optical system and forms an image on a predetermined imaging surface. Configuration,
It said second optical system is an optical plate, Chi lifting the characteristic change in the thickness is schematically proportional to the thickness of the axial symmetry to the third-order power function of the distance from the base point in the optical plate is increased ,
The base point in the optical plate is shifted from the optical axis of the first optical system , and the change in the thickness of the optical plate is caused by the depth of focus when the second optical system is provided in front of the first optical system. However, the large optical plate which is the second optical system is limited to a range showing a characteristic that is larger than that of the first optical system alone.

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