JPH10186290A - Double focus lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a thin and light-weighted double focus lens of an excellent appearance to which aberration is excellently corrected. SOLUTION: A far distance part 1 has a diopter degree of -15 to +8, and a surface on an object side of the far distance part 1 is formed aspheric. And, assuming that a height along a direction perpendicular to an optical axis of the far distance part 1 be y, and a distance at the height y along the optical axis between a virtual sphere based on a top radius of curvature of the sapheric surface on the object side of the far distance part and the aspheric surface on the object side of the far distance part be dx, this lens is designed to meet a requirement of 1×10<-6> <|dx/y|<5×10<-1> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bifocal lens, and more particularly to a bifocal lens used as an aid in accommodation of the eye.

[0002]

2. Description of the Related Art In a conventional bifocal lens which is usually used for assisting the accommodation power of an eye, a distance portion for viewing a long-distance object and a near portion for viewing a short-distance object are both spherical lenses. It is formed with. In addition, 63-478
No. 49 discloses a bifocal lens having an intensity for correcting aphakic eyes (distance power of +8 to +20 diopters) and having aspherical surfaces in both the distance portion and the near portion. Have been.

[0003]

In a conventional bifocal lens in which both a base lens forming a distance portion and a small ball forming a near portion are formed of spherical lenses, the distance portion has a positive power (vertex). In the case of a plus lens having refractive power, the lens center thickness in the distance portion becomes large, and in the case of a minus lens having a negative power, the lens edge thickness in the distance portion becomes large. As a result, both the plus lens and the minus lens increase the weight of the entire lens. In addition, since the distance portion and the near portion are both spherical lenses, aberrations cannot be satisfactorily corrected.

On the other hand, the application of the conventional bifocal lens disclosed in Japanese Utility Model Publication No. 63-47849 is limited to a plus lens for correcting aphakic eyes. In addition, the introduction of the aspherical surface causes the boundary between the base ball and the small ball to be greatly distorted from the arc shape, which is not preferable in appearance. The present invention has been made in view of the above-described problems, and has as its object to provide a bifocal lens that is thin, lightweight, has good appearance, and has aberrations well corrected.

[0005]

In order to solve the above-mentioned problems, in the present invention, there is provided a distance portion having a refracting surface on the object side and a refracting surface on the eye side for viewing a long-distance object; A bifocal lens having a near portion formed on a part of the far portion for viewing a near object;
It has a power greater than diopter and less than +8 diopter, the object-side surface of the distance portion is formed in an aspherical shape, and has a height along a direction perpendicular to the optical axis of the distance portion. y, along the optical axis of the distance portion between the virtual sphere based on the vertex radius of curvature of the object-side aspheric surface of the distance portion at the height y and the object-side aspheric surface of the distance portion. Provided is a bifocal lens characterized by satisfying a condition of 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ when a distance is dx.

According to a preferred aspect of the present invention, the height of the distance portion along a direction perpendicular to the optical axis is defined as y, and a point on the object-side aspherical surface of the distance portion at the height y. Let x be the distance along the optical axis of the distance portion between the vertex of the object-side aspheric surface of the distance portion and R be the radius of curvature of the vertex of the object-side aspheric surface of the distance portion. When the coefficient is κ and the n-th order aspheric coefficient is Cn, the object-side aspheric surface of the distance portion is

X = (y ² / R) / ｛1+ (1-κ · y ² / R
_{^{2) 1/2} + C 4 ·}} y 4 + C 6 · y 6 + C 8 · y 8 + C
Represented by formula ₁₀ · y ^10, the fourth-order aspherical coefficients C ₄ is, | satisfies <1 × 10 ^-3 conditions | C _4.

According to another aspect of the present invention, a distance portion for viewing a distant object having a refractive surface on the object side and a refractive surface on the eye side, and a part of the distance portion Wherein the distance portion has a power greater than -15 diopters and less than +8 diopters, wherein the near vision portion has a near vision portion for viewing near objects. The object-side surface of the portion is formed in a rotationally symmetric aspherical shape, and the height along a direction perpendicular to the rotational symmetry axis of the near portion is y, and the object-side surface of the near portion at height y is y. The distance along the rotational symmetry axis of the near portion between the virtual sphere based on the apex radius of curvature of the aspheric surface and the aspheric surface on the object side of the near portion is dx.
And a bifocal lens characterized by satisfying the following condition: 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹

[0008] According to still another aspect of the present invention,
Having a refracting surface on the object side and a refracting surface on the eye side, a distance portion for viewing a long-distance object, and a near portion for viewing a short-distance object formed in a part of the distance portion. Wherein the distance portion has a power greater than −15 diopters and smaller than +8 diopters, and includes an object-side surface of the distance portion and an object-side surface of the near portion. The surface is
Both are aspherical, the height along the direction perpendicular to the optical axis of the distance portion is y, and a virtual spherical surface based on the vertex radius of curvature of the object-side aspheric surface of the distance portion at height y. When the distance along the optical axis of the distance portion between the distance portion and the aspherical surface on the object side of the distance portion is dx, 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ Provided is a bifocal lens that satisfies conditions.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The bifocal lens according to the present invention has a distance power of -15 diopters to +8 diopters, and at least one of an object-side surface of a distance portion and an object-side surface of a near portion. One is formed in an aspherical shape, and the refractive surface on the eye side is used for correcting astigmatism and the like. First, in the present invention, when the object-side surface of the distance portion is formed in an aspherical shape, the aspherical surface satisfies the following conditional expression (1). 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ (1) where, y: height along the direction perpendicular to the optical axis of the distance portion dx: distance of the distance portion at height y Distance along the optical axis of the distance portion between the virtual sphere and the aspheric surface of the distance portion based on the apex radius of curvature of the aspheric surface

By forming the object-side surface of the distance portion to be aspherical, the thickness and weight of the lens can be reduced, and the astigmatism of the sagittal image surface and the astigmatism of the meridional image surface in the distance portion can be reduced. Both aberrations can be kept small. However, when the value goes below the lower limit of conditional expression (1), the shape of the aspheric surface becomes too close to the spherical surface, so that the thickness and weight of the lens cannot be sufficiently reduced, and the correction of astigmatism is also insufficient. . On the other hand, when the value exceeds the upper limit of conditional expression (1), the thickness and weight of the lens can be sufficiently reduced, but correction of astigmatism becomes excessive.

In the present invention, when the object-side surface of the near portion is formed in a rotationally symmetric aspherical shape, the aspherical surface satisfies the following conditional expression (2). 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ (2) where, y: height along the direction perpendicular to the rotational symmetry axis of the near portion dx: near portion at height y Distance along the rotational symmetry axis of the near portion between the virtual sphere and the near aspheric surface based on the apex radius of curvature of the aspheric surface of the lens

By forming the object-side surface of the near portion to be aspherical, both the astigmatism of the sagittal image surface and the astigmatism of the meridional image surface in the near portion can be reduced. However, when the value goes below the lower limit of conditional expression (2), the shape of the aspheric surface becomes too close to the spherical surface, and the correction of astigmatism becomes insufficient. On the other hand, when the value exceeds the upper limit of conditional expression (2), the correction of astigmatism becomes excessive.

In the present invention, the aspheric surface on the object side of the distance portion can be represented by the following equation (a).

Equation 4] ^{x = (y 2 / R)} / {1+ (1-κ · y 2 / R 2) 1/2} + C 4 · y 4 + C 6 · y 6 + C 8 · y 8 + C 10 · y 10 (A) where: y: height along the direction perpendicular to the optical axis x: distance along the optical axis between a point on the aspheric surface at the height y and the vertex of the aspheric surface R: the aspherical surface Apex radius of curvature κ: cone coefficient Cn: nth order aspheric coefficient

In this case, it is preferable that the fourth-order aspherical surface coefficient C ₄ satisfies the following conditional expression (3) on the object-side aspherical surface of the distance portion. | C ₄ | <1 × 10 ⁻³ (3) When the value exceeds the upper limit of conditional expression (3), the lens edge thickness in the distance portion becomes large in the minus lens, and the lens center thickness in the distance portion becomes large in the plus lens. It gets bigger.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the first embodiment and the second embodiment,
The height along the direction perpendicular to the optical axis is y, the distance along the optical axis between the point on the aspheric surface at the height y and the vertex of the aspheric surface is x, and the vertex radius of curvature of the aspheric surface is Assuming that R is R, the conic coefficient is κ, and the nth order aspherical surface coefficient is Cn, each aspherical surface is represented by the following equation (a).

Equation 5] ^{x = (y 2 / R)} / {1+ (1-κ · y 2 / R 2) 1/2} + C 4 · y 4 + C 6 · y 6 + C 8 · y 8 + C 10 · y 10 (A)

[First Embodiment and First Comparative Example] FIG.
FIG. 2A is a diagram illustrating a configuration of a bifocal lens according to a first example of the present invention, and FIG. 2A is a front view of the bifocal lens in a wearing state as viewed from an object side along an optical axis of a distance portion. (B) is a side view of the bifocal lens in the wearing state. The first embodiment is an example in which the present invention is applied to a minus lens having a distance power of -5 diopters, and the object side surface of the distance portion is formed in an aspherical shape. On the other hand, in the first comparative example, the object-side surface of the distance portion is formed in a spherical shape. Referring to FIG. 1, the bifocal lens according to the first embodiment includes a distance portion 1 and a near portion 2 formed at a part thereof. Optical axis AX1 passing through center O1 of distance section 1
The thickness at the center of the distance portion along the distance is the lens center thickness T1 of the distance portion 1, and the thickness at the periphery of the distance portion along the optical axis AX1 is the lens edge thickness T2 of the distance portion 1. .

By the way, according to the prior art, the near portion 2
When the normal line N1 of the object-side surface of the distance portion 1 passing through the optical center O2 of the lens is made to coincide with the rotational symmetry axis AX2, the boundary line 3 ′ between the near portion and the distance portion becomes circular. It will be greatly distorted outward and the appearance will be impaired. In the first embodiment, the lower portion of the near portion 2 and the far portion 1 are set by setting the rotational symmetric axis AX2 of the near portion 2 to be larger than the normal line N1 with respect to the horizontal plane in the wearing state. Is formed in a substantially arc shape. As described above, by inclining the rotational symmetric axis AX2 of the near portion 2 with respect to the normal line N1, the near portion region (regardless of the aspherical shape of the far portion 1 and the addition of the near portion 2). (A region defined by the boundary with the distance portion) can be made constant.

The following Table (1) shows values of data of the first embodiment of the present invention and values of data of the first comparative example according to the prior art. In Table (1), R1 is the vertex radius of curvature (mm) of the object-side surface of the distance portion, R2 is the vertex radius of curvature (mm) of the eye-side surface of the distance portion, and T1 is the distance radius of the distance portion. The lens center thickness (mm), T2 is the lens edge thickness (mm) of the distance portion,
D1 represents the outer diameter (diameter: mm) of the lens of the distance portion.

[0019]

[First Comparative Example] R1 = 400 R2 = 80 T1 = 1.5 D1 = 60 T2 = 6.2 [First Example] R1 = 400 R2 = 80 T1 = 1.5 D1 = 60 T2 = 6.0 κ = −20 C ₄ = 0.5 × 10 ⁻⁶ C ₆ = −0.3 × 10 ⁻⁹ C ₈ = 0.1 × 10 ⁻¹² C ₁₀ = −0.2 × 10 ⁻¹⁶ [Condition-corresponding values of the first embodiment] (1) When y = 10 | dx / y | = 0.43 × 10 ^{−3 When} y = 20 | dx / y | = 0.28 × 10 ⁻² y | Dx / y | = 0.70 × 10 ⁻² (3) | C ₄ | = 0.5 × 10 ⁻⁶

FIG. 2 is a diagram showing astigmatism in the distance portion of the first embodiment, and FIG. 3 is a diagram showing astigmatism in the distance portion of the first comparative example. 2 and 3, the vertical axis indicates diopter, and the horizontal axis indicates the angle of incidence (degree) on the pupil of the wearer's eye. 2 and 3, M indicates astigmatism on the meridional image plane, and S indicates astigmatism on the sagittal image plane. Referring to FIG. 2 and FIG. 3, the astigmatism of the meridional image plane is -1.0 diopter at the maximum in the first comparative example, whereas the astigmatism and the sagittal of the meridional image plane are in the first embodiment. Both astigmatism on the image plane are suppressed to 0.5 diopter or less. Also, referring to Table (1),
In the first embodiment according to the present invention, the lens edge thickness T2 of the distance portion is 0.2 mm smaller than that of the first comparative example.

[Second Embodiment and Second Comparative Example] FIG.
FIG. 7A is a diagram illustrating a configuration of a bifocal lens according to a second embodiment of the present invention, and FIG. 7A is a front view of the bifocal lens in a wearing state as viewed from an object side along an optical axis of a distance portion. (B) is a side view of the bifocal lens in the wearing state. The second embodiment is an example in which the present invention is applied to a plus lens having a distance power of +5 diopter, and the object-side surface of the distance portion is formed in an aspherical shape. On the other hand, in the second comparative example, the object-side surface of the distance portion is formed in a spherical shape. Referring to FIG. 4, the bifocal lens according to the second embodiment includes a distance portion 1 and a near portion 2 formed in a part thereof. Optical axis AX1 passing through center O1 of distance section 1
The thickness at the center of the distance portion along the distance is the lens center thickness T1 of the distance portion 1, and the thickness at the periphery of the distance portion along the optical axis AX1 is the lens edge thickness T2 of the distance portion 1. .

By the way, according to the prior art, the near portion 2
When the normal line N1 of the object-side surface of the distance portion 1 passing through the optical center O2 of the lens is made to coincide with the rotational symmetry axis AX2, the boundary line 3 ′ between the near portion and the distance portion becomes circular. It is greatly distorted inward, and the appearance is impaired. In the second embodiment, the lower portion of the near portion 2 and the far portion 1 are set by setting the rotational symmetric axis AX2 of the near portion 2 smaller than the normal N1 with respect to the horizontal plane in the wearing state. Is formed in a substantially arc shape. As described above, by inclining the rotational symmetric axis AX2 of the near portion 2 with respect to the normal line N1, the near portion region (regardless of the aspherical shape of the far portion 1 and the addition of the near portion 2). (A region defined by the boundary with the distance portion) can be made constant.

The following Table 2 shows the values of the specifications of the second embodiment of the present invention and the values of the specifications of the second comparative example according to the prior art. In Table (2), R1 is the vertex radius of curvature (mm) of the object-side surface of the distance portion, R2 is the vertex radius of curvature (mm) of the eye-side surface of the distance portion, and T1 is the distance radius of the distance portion. The lens center thickness (mm), T2 is the lens edge thickness (mm) of the distance portion,
D1 represents the outer diameter (diameter: mm) of the lens of the distance portion.

[0024]

[Second Comparative Example] R1 = 80 R2 = 357.5 T2 = 1.0 D1 = 60 T1 = 5.6 [Second Example] R1 = 80 R2 = 360.5 T2 = 1.0 D1 = 60 T1 = 5.2 κ = −1.8 C ₄ = 0 C ₆ = 0.5 × 10 ⁻¹⁰ C ₈ = 0 C ₁₀ = 0.1 × 10 ⁻¹⁵ [ ^{Conforming to} the condition of the second embodiment] Value] (1) When y = 10 | dx / y | = 0.70 × 10 ^{−3 When} y = 20 | dx / y | = 0.52 × 10 ^{−2 When} y = 30 | dx / y | = 0.14 × 10 ⁻¹ (3) | C ₄ | = 0

FIG. 5 is a diagram showing astigmatism in the distance portion of the second embodiment, and FIG. 6 is a diagram showing astigmatism in the distance portion of the second comparative example. 5 and 6, the vertical axis represents diopter, and the horizontal axis represents the angle of incidence (degree) on the pupil of the wearer's eye. 5 and 6, M indicates the curvature of the meridional image plane, and S indicates the curvature of the sagittal image plane. Referring to FIG. 5 and FIG. 6, the curvature aberration of the meridional image plane is +1.6 diopter at the maximum in the second comparative example, whereas the curvature aberration of the meridional image plane and the sagittal image plane in the second embodiment are maximum. Both the curvature aberrations are suppressed to 0.5 diopter or less. Also, referring to Table (2),
In the second embodiment according to the present invention, the lens center thickness T1 of the distance portion is 0.4 mm smaller than that of the second comparative example.

[Third Embodiment and Third Comparative Example] In the third embodiment, the object side surface of the near portion having an addition power of +2 diopter in the bifocal lens of the first embodiment having a distance power of +5 diopter is used. Is formed in an aspherical shape. Meanwhile, the third
In the comparative example, the object-side surface of the near portion is formed in a spherical shape. Table 3 below summarizes data values of the third example of the present invention and data values of the third comparative example according to the related art. In Table (3), R3 is the vertex radius of curvature (mm) of the object-side surface of the near portion, R4 is the vertex radius of curvature (mm) of the near-side eye-side surface, and T3 is the near radius of the near portion. Lens center thickness (m
m), and D2 represents the lens outer diameter (diameter: mm) of the near portion.

[0027]

[Third Comparative Example] R3 = 155 R4 = 80 T3 = 1.95 D2 = 30 [Third Example] R3 = 155 R4 = 80 T3 = 1.95 D2 = 30 κ = −1.7 C ₄ = 0.42 × 10 ⁻⁶ C ₆ = −0.15 × 10 ⁻⁸ C ₈ = 0.36 × 10 ⁻¹¹ C ₁₀ = 0.19 × 10 ⁻¹³ [Conditional value of the third embodiment] (2) When y = 5 | dx / y | = 0.40 × 10 ^{−4 When} y = 10 | dx / y | = 0.20 × 10 ^{−3 When} y = 15 | dx / y | = 0.13 × 10 ^-2

FIG. 7 is a diagram showing astigmatism in the near portion of the third embodiment, and FIG. 8 is a diagram showing astigmatism in the near portion of the third comparative example. 7 and 8, the vertical axis represents diopter, and the horizontal axis represents the angle of incidence (degree) on the pupil of the wearer's eye. 7 and 8, M indicates the curvature aberration of the meridional image plane, and S indicates the curvature aberration of the sagittal image plane. Referring to FIGS. 7 and 8, in the third comparative example, the curvature aberration of the meridional image surface is -0.15 diopter at the maximum, whereas in the third embodiment, the curvature aberration of the meridional image surface and the sagittal image surface are different. Are suppressed to 0.05 diopter or less.

[0029]

As described above, according to the present invention, -15
A bifocal lens having a dioptric power larger than diopter and smaller than +8 diopter, thin, lightweight, good in appearance, and well corrected in aberration can be realized.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of a bifocal lens according to a first embodiment of the present invention, wherein (a) shows a bifocal lens in a wearing state from an object side along an optical axis of a distance portion; It is the front view which looked at, and (b) is a side view of the bifocal lens in a wearing state.

FIG. 2 is a diagram illustrating astigmatism in a distance portion according to the first embodiment.

FIG. 3 is a diagram illustrating astigmatism in a distance portion of a first comparative example.

FIG. 4 is a view showing a configuration of a bifocal lens according to a second embodiment of the present invention, wherein (a) shows a bifocal lens in a wearing state from an object side along an optical axis of a distance portion; It is the front view which looked at, and (b) is a side view of the bifocal lens in a wearing state.

FIG. 5 is a diagram illustrating astigmatism in a distance portion according to a second embodiment.

FIG. 6 is a diagram illustrating astigmatism in a distance portion of a second comparative example.

FIG. 7 is a diagram showing astigmatism in a near portion of the third embodiment.

FIG. 8 is a diagram illustrating astigmatism in a near portion of a third comparative example.

[Explanation of symbols]

 Reference Signs List 1 distance portion 2 near portion AX1 optical axis of distance portion AX2 rotational symmetry axis of near portion O1 center of distance portion O2 center of near portion N1 normal line

Claims (7)

[Claims] An object-side refracting surface, an eye-side refracting surface, and a distance portion for viewing a long-distance object, and a part of the distance portion for viewing a short-distance object. Wherein the distance portion is larger than -15 diopters and +
The diopter has a power less than 8 diopters, the object-side surface of the distance portion is formed in an aspherical shape, and a height along a direction perpendicular to an optical axis of the distance portion is y,
The distance along the optical axis of the distance portion between the virtual spherical surface based on the apex radius of curvature of the aspheric surface on the object side of the distance portion at the height y and the object-side aspheric surface of the distance portion is dx. Where: 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ . 2. A height of the distance portion along a direction perpendicular to the optical axis is defined as y, and a point on the object-side aspherical surface of the distance portion at a height y and the object side of the distance portion. Let x be the distance along the optical axis of the distance portion between the vertex of the aspheric surface of R, the radius of curvature of the vertex of the aspheric surface on the object side of the distance portion be R, the conic coefficient be κ, and the nth order non when the spherical coefficient was Cn, the aspherical surface on the object side of the distance portion is ## EQU1 ## ^{x = (y 2 / R)} / {1+ (1-κ · y 2 / R of
_{^{2) 1/2} + C 4 ·}} y 4 + C 6 · y 6 + C 8 · y 8 + C
Represented by formula ₁₀ · y ^10, the fourth-order aspherical coefficients C ₄ is, | C ₄ | <bifocal according to claim 1, characterized by satisfying the 1 × 10 ^-3 conditions lens. 3. A distance portion for viewing a distant object having a refracting surface on the object side and a refracting surface on the eye side, and formed on a part of the distance portion to view a short distance object. Wherein the distance portion is larger than -15 diopters and +
The object-side surface of the near portion is formed in a rotationally symmetric aspherical shape, and the height along a direction perpendicular to the rotational symmetry axis of the near portion is y.
Along a rotationally symmetric axis of the near portion between a virtual sphere based on the vertex radius of curvature of the aspheric surface on the object side of the near portion at height y and the aspheric surface on the object side of the near portion. Distance d
A bifocal lens characterized by satisfying the following condition: 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ 4. A far vision part having a refracting surface on the object side and a refracting face on the eye side for viewing a long-distance object, and viewing a short-distance object formed in a part of the far vision part. Wherein the distance portion is larger than -15 diopters and +
The object-side surface of the distance portion and the object-side surface of the near portion both have an aspheric shape, and have a power smaller than 8 diopters, and are in a direction perpendicular to the optical axis of the distance portion. Let y be the height along
The distance along the optical axis of the distance portion between the virtual spherical surface based on the apex radius of curvature of the aspheric surface on the object side of the distance portion at the height y and the object-side aspheric surface of the distance portion is dx. Where: 1 × 10 ⁻⁶ <| dx / y | <5 × 10 ⁻¹ . 5. A height of the distance portion along a direction perpendicular to the optical axis is defined as y, and a point on the object-side aspherical surface of the distance portion at the height y and the object side of the distance portion. Let x be the distance along the optical axis of the distance portion between the vertex of the aspheric surface of R, the radius of curvature of the vertex of the aspheric surface on the object side of the distance portion be R, the conic coefficient be κ, and the nth order non when the spherical coefficient was Cn, the aspherical surface on the object side of the distance portion is Equation 2] ^{x = (y 2 / R)} / {1+ (1-κ · y 2 / R of
_{^{2) 1/2} + C 4 ·}} y 4 + C 6 · y 6 + C 8 · y 8 + C
Represented by formula ₁₀ · y ^10, the fourth-order aspherical coefficients C ₄ is, | C ₄ | <bifocal according to claim 4, characterized by satisfying the 1 × 10 ^-3 conditions lens. 6. A distance portion for viewing a long-distance object having a refractive surface on the object side and a refractive surface on the eye side, and a short-distance object formed on a part of the distance portion. In the bifocal lens including the near portion, the object-side surface of the far portion is formed in an aspherical shape, and depends on the aspheric shape of the far portion and the addition of the near portion. A bifocal lens in which the shape of the near portion region is made substantially the same without performing the above. 7. The bifocal lens according to claim 6, wherein an object-side surface of the near portion is formed in an aspherical shape.