JP2012194388A - Bifocal lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bifocal lens capable of preventing spoiling of an appearance of a wearer by eliminating a clear border line between a close range section and a distant range section as well as preventing jumping of images.SOLUTION: A bifocal lens 10 has a distant range refractive power surface 1 in a top section and a close range refractive power surface 2 in a bottom section, either on a front surface or a back surface. The distant range refractive power surface 1 and the close range refractive power surface 2 come into contact only at one punctuate connecting section 3. In addition, the inclinations of the distant range refractive power surface 1 and the close range refractive power surface 2 in a vertical direction at the connecting section 3 are made identical. A curved surface interpolation surface 6 smoothly connecting the distant range refractive power surface 1 and the close range refractive power surface 2 exists in between the distant range refractive power surface 1 and the close range refractive power surface 2.

Description

  The present invention relates to a bifocal lens, and more particularly, to a bifocal lens excellent in appearance.

  As the multifocal power lens, a progressive multifocal power lens and a bifocal lens are two mainstreams. As shown in FIG. 15, the progressive multifocal power lens is formed by a distance refracting power surface 300, a near refracting power surface 301, and an intermediate progressive zone 302.

  In addition, as shown in FIG. 16A, the bifocal lens has a type in which a near-distance lens 101 having a small diameter called a small ball is incorporated in the distance lens 100, and an upper portion as shown in FIG. In addition, there is an EX type in which a distance lens 200 is arranged at a lower portion and a near lens 201 is attached to the lower lens 200 and bonded together. The bifocal lens described in Patent Document 1 below is the former type, but the rotational symmetry axis of the near portion is more than the normal of the object side surface of the distance portion with respect to the horizontal plane in the wearing state. The outer appearance is improved by setting it to be greatly inclined and forming the boundary line between the lower portion of the near portion and the far portion in a substantially arc shape (see paragraph 0017 of the same document).

Japanese Patent Laid-Open No. 10-186290

  In the progressive multifocal refractive power lens, the distance power surface 300 and the near power surface 301 are formed of a continuous toric surface. Therefore, the distance power surface 300 and the near power surface 301 There is no step between them, and the appearance of the wearer is not impaired. However, this continuous change in the frequency of the surface induces image shaking, and may be uncomfortable for some wearers.

  On the other hand, the bifocal lens does not cause image shake unlike the progressive multifocal power lens. However, the conventional bifocal lens has a refracting power surface on the upper surface of the outer surface or inner surface opposite to the refracting power surface (spherical surface or aspheric surface) on the outer surface (front surface) or inner surface (rear surface), and close to the lower surface. A spherical surface or a toric surface, which is calculated so that a specified power can be obtained, is synthesized with a single curvature, and each surface has a physically different single curvature. Therefore, instead of providing a clear image to the wearer, as shown by reference numeral 102 in FIG. 16A and reference numeral 202 in FIG. As a result, there is a problem that a clear boundary appears, impairing the appearance of the wearer, and causing a rapid difference in imaging magnification called image jump.

  Even in the bifocal lens described in Patent Document 1, a clear boundary line appears between the near portion and the far portion (see FIG. 15 of the same document). It was.

  The present invention solves the above-mentioned problems, and it is possible to eliminate a clear boundary line between the near portion and the far portion and prevent the wearer from damaging the appearance, and to perform an image jump. An object is to provide a bifocal lens that can be prevented.

  The bifocal lens of the present invention is a bifocal lens in which a distance refracting power surface is formed at an upper portion and a near refracting power surface is formed at a lower portion, and the distance refracting power surface and the near refracting power are formed. The surface is in contact with only one spot-like coupling portion, and the vertical refractive power surface and the near-side refractive power surface in the coupling portion have the same vertical inclination, Between the near refractive power surfaces, a curved interpolation surface that smoothly connects the far refractive power surface and the near refractive power surface is used.

  According to this, the distance refracting power surface and the near refracting power surface are in contact with only one point-like coupling portion, and the distance refracting power surface and the near refracting power surface are between the distance refracting power surfaces. Therefore, a clear boundary line does not appear between the distance refracting power surface and the near refracting power surface. Therefore, the appearance of the wearer is prevented from being impaired and image jump is prevented.

  Here, in the front view, when defining an orthogonal coordinate system in which the left-right direction in the bifocal lens is the X-axis, the up-down direction is the Y-axis, and the front-rear direction is the Z-axis, the interpolation surface is the distance refractive power surface And the first point on the boundary line (hereinafter referred to as “distance boundary line”) between the interpolation surface and the first point, the X coordinate value is the same as the first point, and the Y coordinate value from the first point. The second point on the distance-use power surface having a large X, and the boundary line between the near-surface power surface and the interpolation surface having the same X coordinate value as the first point (hereinafter referred to as “near-use boundary line”) The third point above and the fourth point on the near refractive power surface whose X coordinate value is the same as that of the first point and whose Y coordinate value is smaller than that of the third point. , A curve obtained by a predetermined interpolation method is formed from a plane connecting a plurality of portions between the second point and the third point in the X-axis direction. It is possible to be.

  Moreover, if the distance boundary line and the distance boundary line are both composed of one or a plurality of straight lines when viewed from the front, the calculation for interpolation is simple and the design is easy. is there.

  Further, the interpolation method may be an N-spline interpolation method, for example.

  According to the present invention, the distance power surface and the near power surface are in contact with only one point-like coupling portion, and the distance power surface is between the distance power surface and the near power surface. Since the interpolation surface is a curved surface that smoothly connects the surface and the near power surface, no clear boundary line appears between the far power surface and the near power surface. Therefore, the appearance of the wearer is prevented from being impaired and image jump is prevented.

It is a front view of the bifocal lens concerning one embodiment of the present invention. It is a perspective view which shows the orthogonal coordinate system and interpolation line in the embodiment. It is a figure for demonstrating the interpolation method. It is the schematic for demonstrating the state before couple | bonding with a coupling | bond part. It is the schematic for demonstrating the state which couple | bonded with the coupling | bond part and is not adjusting the inclination. It is the schematic for demonstrating the state which couple | bonded with the coupling | bond part and matched the inclination and defined the interpolation line. It is a figure for demonstrating the coupling | bond part of an Example. It is a front view for demonstrating the distance boundary line and near boundary line of an Example. It is a front view for demonstrating the interpolation surface of an Example. It is a figure which shows the line which forms the surface of the lens of an Example. It is S frequency distribution map of the lens of an Example. It is C frequency distribution map of the lens of an Example. It is an example which used the far boundary line and the near boundary line as a curve. This is an example in which the coupling portion is provided at the edge of the lens. It is a front view of the conventional progressive multifocal refractive power lens. It is a front view of the conventional bifocal lens.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the left and right, up and down towards the wearer when wearing spectacles using a bifocal lens, respectively, left and right and up and down in the bifocal lens, the front for the wearer, The front side of the bifocal lens is the rear side.

  In the bifocal lens 10 of the embodiment shown in FIG. 1, a distance refracting power surface 1 is formed above the lens rear surface (inner surface), and a near refracting power surface 2 is formed below the lens rear surface. The distance-use refracting power surface 1 and the near-use refracting power surface 2 are in contact with each other only at one point-like coupling portion 3. In other words, the connecting portion 3 that is a connecting portion between the distance-use refracting power surface 1 and the near-use refracting power surface 2 is dot-like and has only one place. In the coupling portion 3, there is no step in the front-rear direction (lens depth direction) between the distance-use refractive surface 1 and the near-side refractive surface 2, and the distance from the distance-use refractive surface 1 in the coupling portion 3 The inclination of the refractive power surface 2 in the vertical direction is the same. Between the distance power surface 1 and the near power surface 2 (a portion having a gap other than the coupling portion 3), the distance power surface 1 and the near power surface 2 are smoothly connected and forward. The curved interpolation surface 6 is convex. The interpolation surface 6 is a surface that generates astigmatism. Hereinafter, in the lens 10, a portion where the rear surface is the interpolation surface 6 is an astigmatism portion 16, and a portion where the rear surface is the distance refractive power surface 1 is a distance portion. 11. A portion whose rear surface is the near refractive power surface 2 is referred to as a near portion 12.

  The distance boundary line 4 that is a boundary line between the distance power surface 1 and the interpolation surface 6 and the near boundary line 5 that is a boundary line between the near power surface 2 and the interpolation surface 6 are both front surfaces. It consists of two straight lines when viewed. Specifically, the distance boundary line 4 includes a linear left distance boundary line 4L extending obliquely leftward and upward from the coupling portion 3 toward the edge of the left side portion 10L of the lens 10 in front view, and the coupling portion 3 to the lens. 10 is formed of a straight right-side distance boundary line 4R extending obliquely upward to the right toward the edge of the right side portion 10R. The near boundary line 5 includes a straight left side boundary line 5L that extends obliquely downward to the left from the coupling portion 3 toward the edge of the left side portion 10L of the lens 10 and the right side of the lens 10 from the coupling portion 3 when viewed from the front. It is composed of a straight right-side near boundary line 5R extending obliquely downward to the right toward the edge of the portion 10R. The distance boundary line 4 and the near boundary line 5 overlap only at the coupling portion 3 in a front view. In the embodiment, the left far boundary line 4L and the right far boundary line 4R, and the left near boundary line 5L and the right near boundary line 5R are respectively axes extending in the vertical direction through the coupling portion 3 (described later). Is equivalent to the Y axis), but is not necessarily symmetrical.

  In addition, the interpolation plane 6 includes a left interpolation plane 6L between the left far boundary line 4L and the left near boundary line 5L (that is, the left side from the coupling unit 3), the right far boundary line 4R, and the right near line. It consists of a right interpolation surface 6R between the boundary line 5R (that is, on the right side of the coupling part 3).

  Here, as shown in FIG. 2, in the front view, the left and right direction of the lens 10 is the X axis (where the right direction is the positive direction), the up and down direction is the Y axis (where the upward direction is the positive direction), and the front and rear direction is the Z axis. Define a Cartesian coordinate system with axes (however, the forward direction is the positive direction). In FIG. 2, only the rear surface of the lens 10 is shown. The interpolation surface 6 is on the distance-use refractive power surface 1 having the same X coordinate value as that of the first point P1 and the first point P1 on the distance boundary line 4 and having a larger Y coordinate value than the first point P1. The second point P 0, the third point P 2 on the near boundary line 5 having the same X coordinate value as the first point P 1, and the first point P 1 have the same X coordinate value as the first point P 1. 3 of the curve obtained by the following interpolation method passing through the fourth point P3 on the near refractive power surface 2 whose Y coordinate value is smaller than the point P2 of 3 (hereinafter referred to as “ This is referred to as an “interpolation line.”) A plurality of CLs are connected in the X-axis direction. The difference in the Y coordinate value between the point P0 and the point P1 and the difference in the Y coordinate value between the point P2 and the point P3 are calculated from the inclination in the Y-axis direction at the lower end portion of the distance refractive power surface 1, The inclination in the Y-axis direction at the upper end of the refractive power surface 2 is calculated and determined in consideration of the interpolation between the points P1 and P2 using these inclinations. Good. Here, in each case, the interval in the X-axis direction of the interpolation line CL described later is set to 1 mm. In FIG. 2, for the sake of emphasis, the distance between the points P0 and P1 and the distance between the points P2 and P3 are shown longer than actual.

  As an interpolation method, an N-spline interpolation method that interpolates with an N-spline function (natural spline function) using the following equation was used. In the embodiment, N = 3, and the interpolation line CL is determined every 1 mm in the X-axis direction.

This interpolation method will be described with reference to FIG. In FIG. 3, an alternate long and short dash line labeled x = 0 is the Z axis, X ₀ , X ₁ , X ₂ , and X ₃ are Y coordinate values, and z ₀ , z ₁ , z ₂ , and z ₃ are Z coordinate values. It is. In the embodiment, as shown in FIG. 3, four interpolation points (X ₀ , z ₀ ), (X ₁ , z ₁ ), (X ₂ , z ₂ ) corresponding to the above points P0, P1, P2, and P3. , (X ₃ , z ₃ ), i = 1, i = 2, i = 3, that is, between points P0 and P1, between points P1 and P2, and at point P2, The interval between P3 is approximated by an Nth order expression (third order expression in the embodiment) shown in [Equation 1], and a coefficient C of each Nth order expression is obtained by an N-spline interpolation method. Since this method of obtaining is well known, the description thereof is omitted here. Then, the section of i = 2 corresponding to the interpolation plane 6 is interpolated by an Nth order equation with the coefficient C substituted. In other words, an expression obtained by substituting the coefficient C in z ₂ (X) in [Equation 1] is an expression of the interpolation line CL.

  Next, a method for designing the lens 10 will be described. In this design method, the following calculation is performed based on the prescription frequency of the wearer.

  First, the curvature of the outer refractive power surface is calculated to determine the outer refractive power surface. Further, the distance refracting power surface 1 is determined by obtaining the distance portion curvature radius and the distance portion astigmatism curvature radius of the inner refracting power surface from the distance power. Furthermore, the near-use refractive power surface 2 is determined by obtaining the near-use part radius of curvature and the near-part astigmatism curvature radius of the internal refractive power surface from the near-use power. Since the determination method of these surfaces is well known, the description thereof is omitted here.

And one coupling | bond part 3 of the refracting power surface 1 and the near refracting power surface 2 is defined. Specifically, as shown in FIG. 4, first, a certain point P _L on the distance power surface 1 is defined as a coupling portion 3, and the near power surface having the same X coordinate value and Y coordinate value as the point P _L. 2 is such that the point P _S above the point P _L overlaps the point P _L , that is, the Z coordinate value difference (step difference at the coupling portion 3) d between the point P _L and the point P _S is eliminated. and height z _L in the Z-axis direction of the first point P _L, and calculates the height z _S in the Z-axis direction at the point P _S of the near optical power surface 2, such that z _L = z _S, The near power surface 2 (or the far power surface 1) is moved in the Z-axis direction. Thereby, as shown in FIG. 5, the point P _L and the point P _S are coupled, and the coupled portion becomes the coupled portion 3. Although the setting location of the coupling part 3 is arbitrary, it is assumed here that the location is a predetermined distance from the geometric center of the lens 10 along the Y-axis direction. The geometric center of the lens 10 is set on the distance-use refractive power surface 1.

Next, an inclination S _{L in} the vertical direction (Y-axis direction) of the distance refractive power surface 1 in the coupling portion 3 and an inclination S _{S in} the Y-axis direction of the near refractive power surface 2 in the coupling portion 3 are calculated, In order to prevent the surface shape from being bent or warped at the boundary of the coupling portion 3, the near refractive power surface 2 is coupled at the coupling portion 3 so that S _L = S _S. Tilt to one.

  Further, the area of the interpolation plane 6 is set. That is, when viewed from the front, the linear left boundary line 4L extending obliquely leftward from the coupling part 3 toward the edge of the left side part 10L of the lens 10 and the edge of the right side part 10R of the lens 10 from the coupling part 3 The distance boundary line 4 is set by arbitrarily defining a linear right distance boundary line 4R extending obliquely upward to the right. Further, in a front view, a straight left side boundary line 5L that extends obliquely downward to the left from the coupling part 3 toward the edge of the left side part 10L of the lens 10, and from the coupling part 3 to the edge of the right side part 10R of the lens 10. The near-use boundary line 5 is set by arbitrarily defining a straight right-hand side near-use boundary line 5R extending obliquely downward to the right. Note that the near boundary line 5 overlaps with the far boundary line 4 only at the coupling portion 3, and the other part is below the far boundary line 4 (the far refractive power surface 1 across the far boundary line 4. On the opposite side).

  Then, the points P1 on the distance boundary line 4 are set at predetermined intervals (here, the interval along the X-axis direction is set to 1 mm), and the interpolation line CL is determined for each point P1 as follows.

The point P1 (x _L , y _L ) and the point P2 (x _S , y _S ) on the near boundary line 5 that is vertically opposite (that is, has the same X coordinate value) are The respective Z coordinate values z (x _L , y _L ) and z (x _S , y _S ) are calculated from the formula and the formula for the near refractive power surface 2. Note that x _L and x _S are X coordinate values, and x _L = x _S. Y _L and y _S are Y coordinate values. Furthermore, the point P1 (x _L, y _L) and Y axis along with + 1 mm point of the distance power plane _{1 P0 (x L, y L} +1) and point P2 (x _S, y _S) of Y For the point P3 (x _S , y _S −1) on the near-side refractive power surface 2 that is −1 mm along the axis, the respective Z The coordinate values z (x _L , y _L +1) and z (x _S , y _S −1) are calculated. The coordinate value “1” corresponds to a length of 1 mm. And these four points _{P0 (X 0, z 0)} , P1 (X 1, z 1), P2 (X 2, z 2), P3 (X 3, z 3) ( where, X ₀ = y _L +1, _{z 0 = z (x L,} y L +1), X 1 = y L, z 1 = z (x L, y L), X 2 = y S, z 2 = z (x S, y S), X ₃ = y _S −1, z ₃ = z (x _S , y _S −1)), the coefficient C of the Nth order equation shown in [Equation 1] is obtained by using the N-spline interpolation method. By substituting the obtained coefficient C into [Equation 1], the expression z ₂ (X) is determined. This expression z ₂ (X) defines an interpolation line CL for interpolating between the points P1 and P2.

  As described above, the interpolation line CL is defined for each point P1 on the far boundary line 4 set at a predetermined interval, and the interpolation plane 6 is constructed by connecting these interpolation lines CL (see FIG. 6). .

  As described above, in the lens 10, the distance refractive power surface 1 and the near refractive power surface 2 are not a linear coupling portion having a step in the lens depth direction as in a conventional bifocal lens. In addition, the connection is made only by one point-like coupling part 3, and the distance between the distance refractive power surface 1 and the near refractive power surface 2 on both sides of the coupling part 3 is from the distance refractive power surface 1 to the near refractive power surface. Interpolated with a smooth curved surface over surface 2. Therefore, according to the lens 10, the original effect of the double focus lens that it is difficult to feel a shake because there is no progressive zone is not impaired, and a clear boundary line appears between the distance portion 11 and the near portion 12. Therefore, the appearance of the wearer can be prevented from being impaired and image jump can be prevented.

Next, examples will be described. Table 1 shows the prescription power, lens data, and front surface data of the examples. The lens 10 according to the embodiment has a single-centered circular shape when viewed from the front, has a front surface that is a spherical surface, and generates a distance refracting power surface 1, a near refracting power surface 2, and an interpolation surface 6. First, based on the data in Table 1, the data for the far-power surface 1 shown in Table 2 is calculated, and the far-power surface 1 (= D _L ) is determined by the following equation [Equation 2]. The data of the near power surface 2 shown in Table 3 was calculated, and the near power surface 2 (= D _S ) was determined by the following equation [Equation 3].

In the above [Expression 2] and [Expression 3], x is a distance from the optical center, θ is an angle with respect to the optical center, K is an aspherical coefficient, A1, A2, A3, and A4 are constants, and R _LS and R _SS are rear surfaces. the radius of curvature, R _LC, R _SC is a cylindrical surface radius of curvature, in the case of the astigmatic power is + is the SIN and COS. In addition, those with LS as subscripts are related to the rear surface of the distance portion, those with LC are related to the astigmatic surface of the distance portion, and those with SS are the rear surface of the near portion. And those with SC are related to the astigmatic surface of the near portion. Thus, R _LS, the R _LC of Table 2 R _S, corresponds to R _C, R _SS, R _SC is equivalent to R _S, R _C of Table 3. Further, since the distance-use refracting power surface 1 and the near-use refracting power surface 2 are both designed as spherical surfaces, K = 1 and A1, A2, A3, and A4 are all 0. In addition, since the front surface is also a spherical surface, the optical center coincides with the geometric center.

  Next, as shown in FIG. 7, the coupling portion 3 is set at a position 7 mm lower than the geometric center O in the Y-axis direction, and the Z of the far-side refractive power surface 1 and the near-side refractive power surface 2 in the coupling portion 3 is determined. The coordinate value and the inclination in the Y-axis direction were calculated, and the respective differences were obtained. In the present embodiment, the Z-coordinate difference between the distance refracting power surface 1 and the near refracting power surface 2 in the coupling portion 3 is 0.08, and the difference in the vertical inclination is 1.23 °. The near refracting power surface 2 was moved in the Z-axis direction and tilted with respect to the far refracting power surface 1 so as to eliminate the difference therebetween.

  Then, as shown in FIG. 8, the left far boundary line 4L and the right far boundary line 4R are set at an angle of 40 ° from the coupling portion 3 to the axis X1 parallel to the X axis through the coupling portion 3. It is assumed that the straight line extends obliquely upward to the left and obliquely upward to the right, and the left-side near boundary line 5L and the right-side near boundary line 5R are inclined at an angle of 50 ° with respect to the axis X1 from the coupling portion. A straight line extending downward and obliquely downward to the right is used.

Next, as shown in FIG. 9, a point P1 (x _L , y _L ) on the far-boundary boundary line 4 and a point P2 (x _S , y _S ) on the near-boundary boundary line 5 (where x _L = For x _S ), the respective Z coordinate values z (x _L , y _L ) and z (x _S , y _S ) are calculated, and the point P1 (x _L , y _L ) is +1 mm along the Y axis For the point P0 (x _L , y _L +1) and the point P3 (x _S , y _S −1) obtained by −1 mm along the Y axis of the point P2 (x _S , y _S ), the respective Z coordinate values z ( x _L , y _L +1) and z (x _S , y _S −1) were calculated. Then, a curve passing through these four points P0, P1, P2, and P3 was obtained by the N-spline interpolation method, and a portion between the obtained points P1 and P2 was defined as an interpolation line CL (see FIG. 3).

  Interpolation lines CL are generated as described above for all points P1 with the distance in the X-axis direction set to 1 mm from one end to the other end of the distance boundary line 4, and the plane connecting these interpolation lines CL is interpolated. Surface 6 was designated. The hatched portion in FIG. 9 indicates the area of the interpolation plane 6.

  FIG. 10 is a perspective view of a line forming the rear surface of the lens 10 of the embodiment as viewed from a position slightly behind the lens 10, and the near power from the distance power surface 1 through the interpolation surface 6. It can be seen that the line continues smoothly to the surface 2.

  11 and 12, the lens 10 designed as described above is actually created by measuring the power by molding the front surface according to the data in Table 1 and cutting the rear surface according to the above design. 11 is an S frequency distribution diagram, and FIG. 12 is a C frequency distribution diagram. The broken lines in the figure indicate the far boundary line 4 and the near boundary line 5 in design. In the lens 10, as can be seen from FIG. 11, the S frequency is distributed so that the distance portion 11 and the near portion 12 are clearly separated, and there is no progressive zone, so it is difficult to feel the image shake. Then, in the vicinity of the point-like coupling portion 3, the distance portion 11 is switched to the near portion 12, and the distance between the distance portion 11 and the near portion 12 on both sides of the coupling portion 3 is the distance between the front surface and the rear surface. The astigmatism portion 16 is a curved surface that smoothly connects the use portion 11 and the near portion 12. Therefore, since a clear boundary line does not appear between the distance portion 11 and the near portion 12, it is possible to prevent the appearance of the wearer from being impaired and to prevent image jump.

  <Modification> A modification will be described below.

  The left far boundary line 4L may extend from the coupling part 3 to the left in the front view, or the right far boundary line 4R extends from the coupling part 3 to the right in the front view. May be. The same applies to the left-side near boundary line 5L and the right-side near boundary line 5R. However, the distance boundary line 4 and the near boundary line 5 are configured to overlap only at the coupling portion 3 in a front view. That is, the left far boundary line 4L extends from the coupling part 3 to the left in the front view, and the right far boundary line 4R extends from the coupling part 3 to the right in the front view. When 4 is a straight line extending right side, the left-side near boundary line 5R is obliquely lower left from the coupling part 3 in the front view, and the right-side near boundary line 5R is right from the coupling part 3 in the front view. It extends obliquely downward.

  Further, the far boundary line 4 and the near boundary line 5 may be curved in front view. For example, as shown in FIG. 13, the distance boundary line 4 may be U-shaped, and the near boundary line 5 may be inverted U-shaped. In FIG. 13 and FIG. 14 described later, the same reference numerals are given to the same elements as those in the above embodiment. In addition, one of the far boundary line 4 and the near boundary line 5 may be a line composed of one or a plurality of straight lines, and the other may be a curve.

  Further, the coupling portion 3 may be provided on the edge of the lens 10. For example, as shown in FIG. 14, the coupling portion 3 is provided on one edge of either the left side portion 10L or the right side portion 10R of the lens 10, and the distance boundary line 4 and the near boundary line 5 are respectively connected to the coupling portion 3. To the left edge 10L or the right edge 10R of the lens 10 to the other edge, and the near boundary line 5 is arranged below the distance boundary line 4 so that the distance boundary line 4 An interpolation plane 6 may be formed between the boundary line 5 and the boundary line 5. In the example of FIG. 14, both the far boundary line 4 and the near boundary line 5 are configured by a single straight line when viewed from the front. If each of the distance boundary line 4 and the near boundary line 5 is a line composed of one or a plurality of straight lines, the calculation is simple and the design is easy.

  Further, as an interpolation method, other interpolation methods such as a Lagrange interpolation method may be used.

DESCRIPTION OF SYMBOLS 1 ... Distance refracting power surface 2 ... Near refracting power surface 3 ... Coupling part 4 ... Distant boundary line 5 ... Near boundary line 6 ... Interpolation surface 10 ... Double focus lens

Claims (4)

In the bifocal lens in which the distance refracting power surface is formed at the top and the near refracting power surface is formed at the bottom, the front surface or the rear surface is formed.
The distance refracting power surface and the near refracting power surface are in contact with only one point-like coupling portion,
The inclination in the vertical direction of the distance power surface and the near power surface in the coupling portion is the same,
A distance between the distance refracting power surface and the near refracting power surface is a curved interpolation surface that smoothly connects the distance refracting power surface and the near refracting power surface. Double focus lens.   When an orthogonal coordinate system is defined in which the left-right direction in the bifocal lens is X-axis, the vertical direction is the Y-axis, and the front-rear direction is the Z-axis in front view, the interpolation plane is the distance refractive power surface and the interpolation The first point on the boundary line with the surface (hereinafter referred to as “distance boundary line”), the X coordinate value is the same as the first point, and the Y coordinate value is larger than the first point. The second point on the distance power surface, the boundary line between the near power surface and the interpolation surface, which has the same X coordinate value as the first point (hereinafter referred to as “near boundary line”). ) And the fourth point on the near refractive power surface whose X coordinate value is the same as that of the first point and whose Y coordinate value is smaller than that of the third point. A curve obtained by a predetermined interpolation method is composed of a plane formed by connecting a plurality of portions between the second point and the third point in the X-axis direction. Bifocal lens of claim 1 wherein symptoms.   The bifocal lens according to claim 2, wherein each of the far boundary line and the near boundary line is composed of one or a plurality of straight lines in a front view.   4. The bifocal lens according to claim 2, wherein the interpolation method is an N-spline interpolation method.

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