Multifocal lens for eyeglass and eyeglass lens

In a multifocal lens for eyeglass provided with visual field areas having different refractive powers, being a distance-vision area and a near-vision area, a multifocal lens for eyeglass (10) is provided, in which the difference of the average surface power D11 of the distance-vision area (11) of the surface (2) on the side of the object and the average surface power D12 of the near-vision area (12) is made mathematically less than the addition power Add. Furthermore, a specific addition power Add is provided by adjusting the average surface power D21 of the distance-vision area of the surface (3) on the side of the eye and the average surface power D22 of the near-vision area. It becomes possible to adjust the average surface powers D11 and D12 of the surface (2) on the side of the object such that the difference of magnification of the distance-vision area and the near-vision area becomes little. Furthermore, it is also possible to make the difference of the average surface powers D11 and D12 of the surface (2) on the side of the object little. Consequently, a multifocal lens can be provided, whereby a comfortable visual field can be obtained, in which there is little jumping and warping of images due to the difference of magnification, and furthermore, the clear-vision area having improved astigmatic aberration is wide, and there is little jumping of images, and the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a multifocal lens for vision-corrective eyeglass 
and an eyeglass lens therewith. 
2. Description of Related Art 
Because a multifocal lens provided with multiple visual field areas having 
different refractive powers, for example, a distance-vision area and a 
near-vision area, can obtain visual fields having different refractive 
powers with a single lens, it can be used as an eyeglass lens for 
correcting vision such as aging vision, and the like. Furthermore, one 
type of multifocal lens is a progressive multifocal lens provided with 
visual field areas in which the refractivity changes progressively. 
Because there are no boundaries in the visual field areas, a progressive 
visual field can be obtained. Furthermore, because it is superior also in 
external view, it is widely used as an eyeglass lens. FIGS. 11A and 11B 
show the general structure of a conventional progressive multifocal lens 
which is widely used as an eyeglass lens. FIG. 11A is an elevational view 
that shows the progressive multifocal lens 1 is provided with a 
distance-vision area 11 for viewing objects at a far distance, and a 
near-vision area 12 for viewing objects at a near distance, the refractive 
power of which is different from that of distance-vision area 11. The near 
vision area 12 is provided below distance-vision area 11. Also, the 
distance-vision area 11 and near-vision area 12 are connected smoothly by 
a progressive area 13, which is a visual field area for viewing objects at 
an intermediate distance. The progressive area 13 is endowed with a 
refractive power that changes continuously. 
FIG. 11B is a sectional view and shows that in a one-piece lens 1 used for 
an eyeglass, there are two surfaces, being a refractive surface 3 on the 
side of the eye and a refractive surface 2 on the side of the viewed 
object. It is necessary to provide these surfaces with all the performance 
required for an eyeglass lens, for example, a vertex power meeting the 
user's prescription, a cylinder power for correcting astigmatism, an 
addition power for correcting aging vision, and furthermore a prism power 
for correcting skew. Therefore, a conventional multifocal lens 1 includes 
a distance-vision area 11 and near-vision area 12, and the surface power 
is adjusted by changing the curvature of refractive surface 2 on the side 
of the object. A progressive multifocal lens further includes a 
progressive area 13. Also, a toric surface is provided on the refractive 
surface 3 on the side of the eye when correction of astigmatism is 
necessary. For simplicity, the explanation is given below, assuming a 
progressive multifocal lens that does not perform correction of 
astigmatism. 
The astigmatic aberration obtained with a conventional progressive 
multifocal lens is shown in FIG. 12. The progressive refractive surface 5 
provided on the surface 2 on the side of the object is a non-spherical 
surface so as to change continuously the surface refractive power. Thus, 
curvature changes according to each area of the surface. For example, a 
schematic configuration of a progressive multifocal lens in which the 
refractive power of distance-vision area 11 is 0.00D and the addition 
power Add is 3.00D. However, when the average surface power D11 of 
distance-vision area 11 is set to 4.00 diopters (D), the average surface 
power of near-vision area 12 becomes 7.00D. Consequently, on surface 2 on 
the side of the object, an astigmatic aberration is caused because a 
difference of curvature is created between the x direction (the direction 
that is horizontal when the eyeglass is worn) and the y direction (the 
direction that is vertical along the lens perpendicular to the x 
direction), crossing from distance-vision area 11 to near-vision area 12. 
Meanwhile, surface 3 on the side of the eye may be a spherical surface 
having a constant curvature. The progressive multifocal lens 1 of the 
present example may include a spherical surface endowed with an average 
surface power D21 which is the same as the average surface power of 
distance-vision area 11, namely, 4.00D. Therefore, the surface on the side 
of the eye has a constant curvature in the x and y directions, and 
fundamentally does not cause an astigmatic aberration. Consequently, in 
lens 1 shown in FIGS. 11A and 11B, the astigmatic aberration of the 
entirety of the lens is the same as the astigmatic aberration of surface 2 
on the side of the object. Astigmatic aberration is represented in diopter 
(D) units, and the drawing of astigmatic aberration shown in FIG. 12 has 
the regions of specific diopters connected by contour lines. In the 
present specification, average surface power indicates the surface 
refractive power in the vicinity of the main line of sight. Average 
surface power D11 of the distance-vision area of the surface on the side 
of the object is the average surface power in the vicinity of main line of 
sight 14 of distance-vision area 11 of the surface on the side of the 
object. Also, average surface power D12 of the near-vision area indicates 
the average surface power in the vicinity of main line of sight 14 of 
near-vision area 12 of the surface on the side of the object. 
A user not having astigmatism can obtain clear vision without perceiving so 
much the fading of an image if the astigmatic aberration appearing in the 
lens is 1.0 diopters or less, preferably 0.5 diopters or less. Therefore, 
in progressive multifocal lens 1, a comparatively wide clear-vision region 
21 having an astigmatic aberration of 1.0 diopters or less, or preferably 
0.5 diopters or less, is placed in distance-vision area 11 in which the 
range of eye movement is great. Furthermore, the required clear-vision 
region following this main line of light 14 is secured by making the 
difference of curvature of the x direction and y direction substantially 
zero in the vicinity of main line of sight 14, which extends from 
distance-vision area 11 toward near-vision area 12, bending somewhat on 
the side of the nose and crowding the vision. Also, an eyeglass lens 9 is 
formed by globe processing lens 1 into a shape matching an eyeglass frame, 
and is provided to the user. 
In a multifocal lens such as a progressive multifocal lens, and the like, 
jumping and warping occurs more easily as the prescription for correcting 
vision is greater. Furthermore, if the addition power Add, which indicates 
the difference of refractive power between the distance-vision area and 
the near-vision area, is great, jumping and warping of images becomes even 
greater because the difference of curvature between the distance-vision 
area and the near-vision area differs greatly. In a progressive multifocal 
lens, the astigmatic aberration appearing in the lens also becomes 
greater, and the clear-vision area becomes narrower because the 
progressive refractive surface is made even more non-spherical. Also, in 
the region where the astigmatic aberration varies greatly, a comfortable 
visual field cannot be obtained because the images warp and jump following 
the movement of the line of sight. Therefore, a progressive refractive 
surface that should provide the user with a comfortable visual field is 
improved by improving the shape of the progressive refractive surface, by 
removing the region in which the astigmatic aberration appears greatly 
from the commonly used regions of the lens, and by preventing sudden 
variation of the astigmatic aberration. 
Furthermore, in a multifocal lens, jumping and warping of images is also 
caused by differences in refractive power (power) between the 
distance-vision area and the near-vision area. That is, distance-vision 
area 11 has a refractive power whereby the focus meets in the distance, 
meanwhile, near-vision area 12 has a refractive power different from that 
of distance-vision area 11 whereby the focus meets nearby. Consequently, 
the magnifications also are not the same, and when a progressive area 13 
is provided, it causes the acquired images to jump and be distorted when 
the eyeglass is worn because the magnification gradually varies in the 
progressive area 13. 
SUMMARY OF THE INVENTION 
Thus, an object of the invention is to provide a multifocal lens and 
eyeglass lens whereby jumping and warping is further controlled and a more 
comfortable visual field can be obtained. It is also an object of the 
invention to provide a progressive multifocal lens or bifocal lens, in 
which the astigmatic aberration is improved substantially to the limit 
through computer-assisted design of the progressive refractive surface. 
That is, the object of the invention is to provide a multifocal lens and 
eyeglass lens whereby the astigmatic aberration can be improved more so 
than the limit that can be obtained with a state-of-the-art progressive 
refractive surface. Also, the object of the invention is to provide a 
multifocal lens and eyeglass lens whereby the difference of magnification 
can be improved while having a refractive power for correction of vision, 
and the jumping and warping of images caused by the difference of 
magnification can be reduced. 
As explained above, in a conventional multifocal lens for eyeglass, two 
visual field areas having different refractive powers are formed. For 
example, a distance-vision area is formed as a first visual field area, 
provided on the surface on the side of the object with an average surface 
power in order to form a visual field area in which it is easy to focus at 
a distance. A near-vision area is formed as a second visual field area, 
provided on the surface on side of the object with an average surface 
power having added an addition power over the average surface power of the 
distance-vision area in order to form a visual field in which it is easy 
to focus nearby. As opposed to this, in the invention, a multifocal lens 
for eyeglass is provided that is manufactured by a design policy entirely 
different from the design policy of the above-mentioned conventional 
multifocal lens for eyeglass, in which the average surface power of the 
near-vision area, being the second visual field area of the surface on the 
side of the object, is less than the value having added the addition power 
to the average surface power of the distance-vision area, being the first 
visual field area. That is, the difference between the average surface 
power of the distance-vision area of the surface on the side of the object 
and the average surface power of the near-vision area is a value 
mathematically smaller than the addition power. Furthermore, in a 
multifocal lens for eyeglass of the invention, a multifocal lens for 
eyeglass is provided, in which the entirety of the lens is endowed with a 
specific addition power by controlling the average surface power of the 
distance-vision area, being the first visual field area of the surface on 
the side of the eye, and the average surface power of the near-vision 
area, being the second visual field area. 
That is, a multifocal lens for eyeglass of the invention that has first and 
second visual field areas having different refractive powers is 
characterized in that, when the value having subtracted the refractive 
power of the first visual field area from the refractive power of the 
second visual field area is taken as the addition power Add, the average 
surface power D11 of the first visual field area of the surface on the 
side of the object and the average surface power D12 of the second visual 
field area, and the average surface power D21 of the first visual field 
area of the surface on the side of the eye and the average surface power 
D22 of the second visual field area, satisfy the following relationships, 
EQU -(L.multidot.n/t)Add&lt;D12-D11&lt;Add (1) 
EQU D21-D22=Add-(D12-D11) (2) 
wherein, L is the distance from the vertex in units of meters (m), t is the 
center thickness of the multifocal lens for eyeglass in units of meters 
(m), and n is the refractivity of the multifocal lens for eyeglass. A 
multifocal lens for eyeglass of the invention includes, of course, a 
multifocal lens such as a bifocal lens, as well as a progressive 
multifocal lens having a progressive area whereby the refractive power 
between the first and second visual field areas changes progressively. 
Consequently, in a progressive multifocal lens of the invention, a 
multifocal lens is also included, which is provided with progressive 
refractive surfaces on both surfaces, being the surface on the side of the 
object and the surface on the side of the eye. 
According to such a multifocal lens for eyeglass of the invention, having a 
design policy different from conventional lenses, because the difference 
of magnification between the distance-vision area and the near-vision area 
can be reduced, and because the properties of aberration can be improved 
over conventional lenses, it becomes possible to provide a multifocal lens 
for eyeglass that minimizes jumping and warping of images and an eyeglass 
lens having globe-processed this lens. 
First, when explaining the difference of magnification of the 
distance-vision area and the near-vision area, the magnification SM of a 
lens is generally represented by the following equation. 
EQU SM=Mp.times.Ms (3) 
Here, Mp is the power factor, and Ms is the shape factor. If distance from 
the vertex L is the distance to the eye from the vertex (inner vertex) of 
the surface of the lens on the side of the eye, Po is the refractive power 
(inner vertex power) of the inner vertex, t is the center thickness of the 
lens, n is the refractivity of the lens, and Pb is the refractive power 
(base curve) of the surface of the lens on the side of the object, these 
values are represented as follows. 
EQU Mp=1/(1-L.times.Po) (4) 
EQU Ms=1/(1-(t.times.Pb)/n) (5) 
In the computation of Equations (4) and (5), diopters (D) are used for the 
inner vertex power Po and the refractive power of the surface on the side 
of the object Pb, and meters (m) are used for distance L and thickness t. 
As is clear from these equations, in a multifocal lens, the magnification 
SM1 of the distance-vision area and the magnification SM2 of the 
near-vision area differ because the refractive power Po differs between 
the distance-vision area and the near-vision area. The size of an image 
visualized by the user also differs according to this difference of 
magnification. Consequently, this difference of magnification also causes 
jumping and warping of images, and the like, in the distance-vision area 
and the near-vision area. 
As opposed to this, a multifocal lens for eyeglass of the invention is a 
multifocal lens in which the average surface powers D12 and D11 are 
controlled such that the difference of magnification between the average 
surface power D11 of the distance-vision area of the surface on the side 
of the object and the average surface power D12 of the near-vision area is 
less than the addition power Add. Therefore, it becomes possible to adjust 
the shape factor Ms represented in Equation (5). Consequently, it is 
possible to reduce the difference of magnification due to the power factor 
Mp represented in Equation (4), and it is possible to reduce the 
difference of magnification between the distance-vision area and the 
near-vision area. Meanwhile, the vertex power Po contributes to correction 
of vision in the distance-vision area and near-vision area, and even if 
the average surface power D12 of the near-vision area of the surface on 
the side of the object is less than the value having added the addition 
power Add to the average surface power D11 of the distance-vision area, in 
a multifocal lens for eyeglass of the invention, it is possible to provide 
a multifocal lens having a specific vision-corrective function by 
controlling the average surface powers D21 and D22 of the surface on the 
side of the eye. Consequently, by using a multifocal lens of the 
invention, it becomes possible to establish the average surface powers D11 
and D12 of the surface on the side of the eye by controlling the 
difference of magnification between the distance-vision area and the 
near-vision area. Also, even in a progressive multifocal lens provided 
with a progressive area, it is possible to control the variation of 
magnification in the progressive area. Therefore, warping and jumping of 
images caused by the difference of magnification can be reduced. 
Thus, the multifocal lens for eyeglass of the invention reduces the 
difference of magnification between the distance-vision area and the 
near-vision area, as opposed to a conventional multifocal lens for 
eyeglass which adjusts the refractive power of the distance-vision area 
and near-vision area only according to the refractive power of the surface 
on the side of the object. The details are explained below. However, to 
reduce the difference of magnification, it is desirable that the average 
surface powers D11 and D12 on the side of the object be set within the 
range indicated by the above Equation (1). Even when the difference 
between the average surface powers D12 and D11 of the surfaces on the side 
of the near-vision area and distance-vision area, that is, the second and 
first visual field areas, are in a range not meeting the above-mentioned 
Equation (1), it is possible to reduce the difference of magnification 
between the first and second visual field areas. However, when it is below 
the range of the above-mentioned Equation (1), because the lens becomes 
thicker, and the astigmatic aberration becomes greater, it becomes less 
useful as a multifocal lens for eyeglass. Therefore, it is desirable that 
the difference between the average surface powers D12 and D11 of the 
surfaces of the second and first visual field areas on the side of the 
object be in the range of the above-mentioned Equation (1). 
Also, for the average surface powers D21 and D22 of the surface on the side 
of the eye, a value can be determined such that a specific prescription 
and addition power are satisfied using average surface powers D11 and D12 
established in the above-mentioned range, and the relationship between the 
average surface powers D21 and D22 of the surface on the side of the eye 
becomes as indicated in the above-mentioned Equation (2). 
Furthermore, for a multifocal lens for eyeglass of the invention, because 
the difference between the average surface power D11 of the 
distance-vision area of the surface on the side of the eye and the average 
surface power D12 of the near-vision area is less than the addition power 
Add, the difference of the average surface powers D12 and D11 between the 
near-vision area and distance-vision area on the side of the object can be 
made to be smaller than that of a conventional multifocal lens for 
eyeglass. That is, in a multifocal lens for eyeglass of the invention, the 
average surface power D11 of the distance-vision area of the surface on 
the side of the object and the average surface power D12 of the 
near-vision area can be made to be within the range of the following 
Equation (6). 
EQU 0&lt;D12-D11&lt;Add (6) 
By establishing the average surface powers D11 and D12 of the 
distance-vision area and near-vision area within such a range, the 
difference of the average surface powers between the distance-vision area 
and near-vision area on the side of the object can be reduced, and the 
variation of the curvature (difference of average surface power) of the 
surface on the side of the object can be reduced. Also, because the 
difference of curvature between the distance-vision area and near-vision 
area for realizing the addition power Add can be distributed also on the 
surface of the lens on the side of the eye, it becomes possible to improve 
the astigmatic aberration more than that of a conventional multifocal 
lens. Consequently, in a multifocal lens for eyeglass of the invention, 
because the astigmatic aberration also can be improved, in addition to the 
effect of being able to reduce the difference of magnification, it becomes 
possible to provide a multifocal lens for eyeglass and eyeglass lens 
endowed with a comfortable visual field in which jumping and warping of 
images is reduced in the distance-vision area and near-vision area, or in 
the progressive area. 
Thus, a conventional multifocal lens for eyeglass is made such that 
vision-corrective functions such as prescriptions other than for the 
purpose of correction of astigmatism, and the addition power Add, and the 
like, are obtained according to the difference of average surface powers 
of only the convex surface on the side of the object. As opposed to this, 
in a multifocal lens of the invention, a specific addition power Add can 
be obtained by variously controlling the average surface powers of the 
first visual field area (e.g., distance-vision area) and second visual 
field area (e.g., near-vision area) on both surfaces, being the surface on 
the side of the object and the surface on the side of the eye. 
Consequently, it is possible to reduce the difference of average surface 
powers between the distance-vision area and near-vision area of the 
surfaces on both sides, and by reducing the difference of curvatures 
between these distance-vision and near-vision areas, the astigmatic 
aberration in the distance-vision area, near-vision area, and even the 
progressive area, caused by the difference of curvatures, can be made 
less. Consequently, a multifocal lens can be provided in a lens having the 
identical conditions such as prescription and addition power, in which the 
clear-vision region is wider, and jumping of images, and the like, when 
the line of sight has moved is reduced. 
In order to reduce astigmatic aberration and secure a large clear-vision 
region, it is desirable that the average surface powers D11, D12, D21, and 
D22 be established so as to make the difference DD1 of the average surface 
powers of the surface on the side of the object, having subtracted the 
average surface power D11 from the average surface power D12, become 
substantially equal to the difference DD2 of the average surface powers of 
the surface on the side of the eye, having subtracted the average surface 
power D22 from the average surface power D21. By setting the differences 
DD1 and DD2 of average surface powers to about the same value, the 
astigmatic aberration caused on the surface on the side of the object and 
the astigmatic aberration caused on the surface on the side of the eye 
together can be reduced. Having conducted various test designs, the 
inventors of the invention were able to confirm that, compared with a 
conventional lens in which the astigmatic aberration is concentrated on 
the surface on one side, the astigmatic aberration can be reduced by 
distributing the astigmatic aberration on the surfaces on both sides, and 
by composing these surfaces to obtain a lens as a whole, as in a lens of 
the invention. 
Also, in a multifocal lens of the invention, the average surface power of 
the distance-vision area D11 of the surface on the side of the object and 
the average surface power D12 of the near-vision area can be made to be 
the same value. That is, when the average surface power D11 of the 
distance-vision area and the average surface power D12 of the near-vision 
area satisfy the following Equation (7), because the surface on the side 
of the object can be formed as a surface which is easy to manufacture, 
such as a spherical surface, it becomes possible to provide in a short 
time and inexpensively a multifocal lens of the invention in which the 
difference of magnification between the distance-vision area and 
near-vision area is minimal. Consequently, a customized eyeglass lens 
matched to the individual conditions of each user can be provided. 
EQU D12-D11=0 (7) 
Furthermore, in a multifocal lens for eyeglass of the invention, because 
the average surface powers D11 and D12 of the first and second visual 
field areas of the surface on the side of the object and the average 
surface powers D21 and D22 of the surface on the side of the eye can be 
controlled, it is possible to reduce the burden on the vision of the user 
who uses the eyeglass by establishing each average surface power such that 
the magnifications of the distance-vision area and near-vision area, that 
is, the first visual field area and second visual field area, become 
substantially equal, or such that the difference of magnification from 
that of the naked eye is reduced. In such a case, the average surface 
powers D11 and D12 may be selected such that the magnifications of the 
first and second visual field areas, the distance-vision area and 
near-vision area, become equal, or such that they approach 1, being the 
magnification of the naked eye. For example, to make the magnifications of 
the near-vision area and distance-vision area equal to the magnification 
of the naked eye, the magnification SM1 of the distance-vision area and 
the magnification SM2 of the near-vision area may be made such that they 
approach the following relationships based on Equation (3). 
EQU SM1=SM2=1 
EQU Mp1.times.Ms1=Mp2.times.Ms2=1 (8) 
Thus, for the multifocal lens of the invention, the astigmatic aberration 
and difference of magnification of the first and second visual field areas 
can be reduced by adjusting the refractive powers of the first and second 
visual fields of both the surface on the side of the object and the 
surface on the side of the eye. Consequently, it is possible to provide a 
progressive multifocal lens and eyeglass lens whereby the jumping and 
warping of images is further reduced, crossing the limit of a conventional 
progressive multifocal lens, in which the astigmatic aberration is 
improved and the optical properties are improved by improving the 
properties of only a single progressive refractive surface. Furthermore, 
it is possible to provide the user with a visual field being one level 
more comfortable. In particular, in a progressive multifocal lens having a 
large addition power, jumping and warping can be reduced to a great extent 
.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
First Embodiment! 
The invention is explained in further detail below while referring to the 
drawings showing the embodiments. FIGS. 1A and 1B show a progressive 
multifocal lens 10 as an example of a multifocal lens of the invention, 
provided with progressive refractive surfaces 5a and 5b on the surface 2 
on the side of the object and the surface 3 on the side of the eye, 
respectively. The progressive multifocal lens 10 of the present example is 
a progressive multifocal lens provided above with a distance-vision area 
11, which is a visual field area for viewing objects at a far distance, 
and provided below with a near-vision area 12, which is a visual field 
area for viewing objects at a near distance, and endowed with a refractive 
power different from that of the distance-vision area 11. The 
distance-vision area 11 and near-vision area 12 are connected by a 
progressive area 13 in which the refractive power changes continuously, in 
the same manner as the conventional progressive multifocal lens shown in 
FIGS. 11A and 11B. As shown in FIG. 1B, the progressive multifocal lens 10 
of the present example is a multifocal lens in which the average surface 
power D11 of the distance-vision area 11 on the side of the object is set 
to 4.00D, the average surface power D12 of the near-vision area 12 is set 
to 5.50D, the average surface power D21 of the distance-vision area 11 on 
the side of the eye is set to 4.00D, the average surface power D22 of the 
near-vision area is set to 2.50D, and the addition power Add of the 
near-vision area 12 in relation to the distance-vision area 11 is 3.00D. 
Consequently, the progressive multifocal lens of the present example is a 
multifocal lens related to the invention, in which the difference of 
average surface power D11 of the distance-vision area 11 on the side of 
the object and the average surface power D12 of the near-vision area is 
less than the addition power Add. Furthermore, because the refractive 
power of the distance-vision area 11 is 0.00D and the addition power Add 
is 3.00D, the progressive multifocal lens 10 of the present example is a 
lens endowed with the identical vision-corrective functions as those of 
the progressive multifocal lens 1 shown in FIGS. 11A and 11B. 
The magnifications of the distance-vision area 11 and near-vision area 12 
of the progressive multifocal lens 10 of the present example become as 
follows when the magnifications SM1 and SM2 of the respective visual field 
areas are sought by applying Equations (3), (4) and (5) described above to 
the distance-vision area 11 and near-vision area 12. First, the 
magnification SM1 of the distance-vision area 11 is expressed as follows. 
EQU SM1=Mp1.times.Ms1 (9) 
Here, Mp1 is the power factor of the distance-vision area, Ms1 is the shape 
factor of the distance-vision area, and these values become as follows 
when considering that the surface power Pb appears as the average surface 
power D11 of the surface 2 on the side of the object. 
EQU Mp1=1/(1-L.times.Po) (10) 
EQU Ms1=1/(1-(t/n).times.D11) (11) 
In the same manner, the magnification SM2 of the near-vision area 12 is 
expressed as follows. 
EQU SM2=Mp2.times.Ms2 (12) 
EQU Mp2=1/(1-L.times.(Po+Add)) (13) 
EQU Ms2=1/(1-(t/n).times.D12) (14) 
Here, Mp2 is the power factor of the near-vision area, Ms2 is the shape 
factor, surface power Pb appears in the average surface power D12 of the 
surface 2 on the side of the object, and the refractive power of the 
near-vision area 12 is the value having added the addition power Add to 
the refractive power of the distance-vision area 11. 
When the distance from the vertex L is set to 15.00 mm (0.0150 m), the 
center thickness t is set to 3.0 mm (0.0030 m), and the refractivity n is 
set to 1.662, in the progressive multifocal lens 10 of the present 
example, because the inner vertex power Po is 0.0D, the additive (join) 
degree Add is 3.00D, the average surface power D11 of the distance-vision 
area is 4.00D, and the average surface power D12 of the near-vision area 
is 5.50D, the respective magnifications SM1 and SM2 and the difference of 
magnification become as follows. 
EQU SM1=1.007, SM2=1.058, 
EQU SM2-SM1=0.051 (15) 
As opposed to this, in the conventional progressive multifocal lens shown 
in FIGS. 11A and 11B, because the average surface power D12 of the 
near-vision area is 7.00D, the respective magnifications SM1 and SM2, and 
the difference of magnification become as follows. 
EQU SM1=1.007, SM2=1.061, 
EQU SM2-SM1=0.054 (16) 
Thus, in the progressive multifocal lens of the present example, it is 
clear that the difference of magnification between the distance-vision 
area 11 and the near-vision area 12 is alleviated by as much as 6% over 
the conventional lens, and that a visual field having less warping and 
jumping of images can be provided to the user. Thus, for the progressive 
multifocal lens 10 as described above, the difference of magnification 
between the distance-vision area 11 and the near-vision area 12 is reduced 
compared with the conventional lens 1, and a comfortable visual field 
having minimal jumping can be provided to the user. 
In a multifocal lens of the invention, when the range in which the 
difference of magnification between the distance-vision area 11 and the 
near-vision area 12 can be reduced is examined, it becomes as follows. For 
example, when eliminating the difference of magnification between the 
distance-vision area 11 and the near-vision area 12, it becomes as follows 
from the above-mentioned Equations (9) and (12). 
EQU Mp1.times.Ms1=Mp2.times.Ms2 (17) 
By assigning and transforming Equations (10), (11), (13), and (14), they 
become as follows. 
EQU (1-L.times.Po).multidot.(1-(t/n)).times.D12)=(1-L.times.(Po+Add)).multidot. 
(1-(t/n).times.D12) (18) 
Furthermore, because the distance from the vertex L and t/n of Equation 
(18) are functions having two or three places following the decimal point, 
if the secondary terms obtained by expansion are ignored (deleted), the 
difference DD1 (D12-D11) of the average surface powers obtained for the 
distance-vision area and near-vision area, in which the difference of 
magnification is substantially equal, becomes approximately as follows. 
EQU D12-D11=-(L.multidot.n/t).times.Add (19) 
Furthermore, in a conventional multifocal lens, the relationship between 
the difference DD1 of the average surface power D11 of the distance-vision 
area 11 and the average surface power D12 of the near-vision area 12, and 
the addition power Add satisfies the following relationship as explained 
above. 
EQU D12-D11=Add (20) 
Consequently, in a multifocal lens of the invention, expressed with the 
following Equation (1), because the difference DD1 of the average surface 
powers is between Equation (19) and Equation (20), it is clear that a 
multifocal lens having a difference of magnification less than that of a 
conventional multifocal lens can be provided. 
EQU -(L.multidot.n/t)Add&lt;D12-D11&lt;Add (21) 
That is, it becomes possible to provide a multifocal lens, in which the 
average surface power D11 of the distance-vision area of the surface on 
the side of the object and the average surface power D12 of the 
near-vision area are within the conditional range of the above-mentioned 
Equation (1), the difference of magnification is less than that of the 
conventional lens, and the jumping and warping of images consequent to 
that is minimal. Even when in a range in which the difference of the 
average surface power D12 of the near-vision area and the average surface 
power D11 of the distance-vision area is less than that of the 
above-mentioned Equation (1), that is, a range not reaching the lower 
limit of the above-mentioned Equation (1), the difference of magnification 
between the distance-vision area and the near-vision area can be reduced 
compared with that of a conventional multifocal eyeglass lens. 
Nevertheless, if the difference between the average surface powers D12 and 
D11 is lower than the range of the above-mentioned Equation (1), because 
the lens becomes thicker and astigmatic aberration becomes greater, it 
becomes less useful as a multifocal lens for eyeglass. 
Also, the average surface power D21 of the distance-vision area 11 of the 
surface on the side of the eye and the average surface power D22 of the 
near-vision area 12 can be determined so as to satisfy a specified 
prescription and addition power by using average surface powers D11 and 
D12 established within the range of Equation (1), and the relationship 
between the average surface powers D21 and D22 of the surface on the side 
of the eye becomes as shown in Equation (2) below. 
EQU D21-D22=Add-(D12-D11) (2) 
However, in the above-mentioned Equations (1) and (2), L is the distance 
from the vertex in units of meters (m), t is the center thickness of the 
multifocal lens for eyeglass in units of meters (m), and n is the 
refractivity of the multifocal lens for eyeglass. 
Furthermore, in a multifocal lens of the invention, by taking the average 
surface powers D11 and D12 of the surface on the side of the object into 
the range of the following Equation (6), the difference DD1 of the average 
surface power D11 of the distance-vision area and the average surface 
power D12 of the near-vision area can be made to be smaller than that of a 
conventional progressive multifocal lens. Therefore, it becomes possible 
to improve the properties of astigmatic aberration of the surface 2 on the 
side of the object. 
EQU 0&lt;D12-D11&lt;Add (6) 
By establishing the average surface powers D11 and D12 in this range, the 
difference DD1 of the average refractive powers of the surface on the side 
of the object can be made to be smaller than the addition power Add. 
Furthermore, as is clear from Equation (2), the difference DD2 of the 
average surface power D22 of the near-vision area 12 of the surface on the 
side of the eye and the average surface power D21 of the distance-vision 
area 11 also can be made to be smaller than the addition power Add. 
Consequently, it is possible to improve the properties of astigmatic 
aberration of the multifocal lens 10 as a whole, both the jumping and 
warping of images due to the difference of magnification and the jumping 
and warping of images due to astigmatic aberration can be reduced, and a 
multifocal lens can be provided, in which the clear-vision region is wide 
and a one-level more comfortable visual field can be obtained. 
The progressive multifocal lens 10 of the present example shown in FIGS. 1A 
and 1B is a progressive multifocal lens included within the range of the 
above-mentioned Equation (6). Furthermore, the example is shown in which 
the difference DD1 of the average surface powers of the surface 2 on the 
side of the object and the difference DD2 of the average surface powers of 
the surface 3 on the side of the eye are equal. FIG. 2 shows the 
astigmatic aberration obtained on surface 2 on the side of the object and 
surface 3 on the side of the eye, of the progressive multifocal lens 10 of 
the present example. For the progressive multifocal lens 10 of the present 
example, the differences DD1 and DD2 of the average surface powers of the 
distance-vision area 11 and near-vision area 12 of the surface 2 on the 
side of the object and the surface 3 on the side of the eye, respectively, 
are both 1.50D, and by establishing the change of curvature in the 
progressive area 13 in roughly the same manner, a substantially same 
drawing of astigmatic aberration can be obtained. Also, the difference DD1 
(D12-D11) of the average surface powers of the surface 2 on the side of 
the object and the difference DD2 (D21-D22) of the average surface powers 
of the surface 3 on the side of the eye both become half of the 3.00D 
difference of average surface powers of the conventional progressive 
multifocal lens 1. Therefore, as shown in FIG. 2, the astigmatic 
aberration caused on the surface 2 on the side of the object and on the 
surface 3 on the side of the eye also become extremely small. 
FIG. 3 shows astigmatic aberration obtained for the progressive multifocal 
lens 10 of the present example. The astigmatic aberration shown in FIG. 3 
is a composite of the astigmatic aberrations caused respectively on the 
surface 2 on the side of the object and the surface 3 on the side of the 
eye. As is clear when comparing the drawing of aberration of the 
progressive multifocal lens of the invention shown in FIG. 3 and the 
drawing of aberration of the conventional progressive multifocal lens 1 
shown in FIG. 12, in the progressive multifocal lens 10 of the present 
example, the line showing the 1.0D astigmatic aberration decreases in the 
direction of the near-vision area 12, and the clear-vision region in the 
distance-vision area 11 is widened. Furthermore, it is clear that the 
position of the line showing the 1.0D astigmatic aberration of the 
near-vision area 12 also is wider on the left and right than the 
conventional progressive multifocal lens 1, and the clear-vision region in 
the near-vision area 12 also is wider. Also, as is clear when comparing 
the positions of the lines showing the astigmatic aberrations of 1.5D, and 
the like, the values of the astigmatic aberrations of the progressive 
multifocal lens 10 of the present example become smaller than the 
astigmatic aberrations in the same locations of the conventional 
progressive multifocal lens 1, and the astigmatic aberrations become 
smaller across the entirety of the lens. Furthermore, it is clear that the 
intervals of the lines connecting the locations of equal astigmatic 
aberration are wider for the progressive multifocal lens 10 of the present 
example, and the variation of the astigmatic aberration also becomes less. 
Thus, the progressive multifocal lens 10 of the present example is 
improved in all aspects over the conventional progressive multifocal lens 
1 when the distribution of astigmatic aberration is compared. 
Consequently, by globe-processing the progressive multifocal lens 10 of 
the invention so as to match the shape of an eyeglass frame, an eyeglass 
lens 9 can be manufactured and supplied, that can provide to the user a 
one-level wider and clearer visual field and images having minimal jumping 
and warping. 
For the progressive multifocal lens 10 of the present example, the 
difference DD1 of the average surface powers of the surface on the side of 
the object and the difference DD2 of the average surface powers of the 
surface on the side of the eye are established identically, and the 
differences of curvature on the surface 2 on the side of the object and 
the surface 3 on the side of the eye become identical. Consequently, 
because the burdens of the differences of curvature appearing as 
properties of aberration are about the same, it is believed that these are 
conditions whereby the properties of aberration can be most improved as a 
progressive multifocal lens 10 including the surface 2 on the side of the 
object and the surface 3 on the side of the eye. 
Not being limited to the progressive multifocal lens of the present 
example, it is obvious that the properties of aberration can be improved 
in a progressive multifocal lens, in which the differences DD1 and DD2 of 
the average surface powers are different, if they are within the range 
shown in the above-mentioned Equation (6). When compared with the 
conventional progressive multifocal lens 1, in which the difference DD1 of 
the average surface powers of the surface on the side of the object is 
equal to the addition power Add, in the progressive multifocal lens 10 
pertaining to the invention, it is possible to reduce the difference DD1 
of the average surface powers on the side of the object more than the 
conventional lens by providing a difference DD2 of the average surface 
powers of the surface on the side of the eye. Thus, astigmatic aberration 
can be controlled. An astigmatic aberration is caused on the surface 2 on 
the side of the eye by providing a difference DD2 of the average surface 
powers on the surface on the side of the eye. Nevertheless, the fact is as 
shown above, that by reducing the share of the surface on the side of the 
object, improving astigmatic aberration on one surface can improve the 
astigmatic aberration of the progressive multifocal lens 10 as a whole. 
Consequently, by providing a difference to the average surface powers D21 
and D22 of the surface on the side of the eye, establishing a difference 
DD2 of the average surface powers of the surface on the side of the eye, 
even if it is little, the average surface powers D11 and D12 of the 
surface on the side can be obtained, having the relationship shown in the 
above-mentioned Equation (6), and the astigmatic aberration of the 
progressive multifocal lens 10 can be improved. Of course, within the 
range of Equation (6), lenses are included in which the difference DD2 of 
the average surface powers of the surface on the side of the eye is 
greater than the difference DD1 of the average surface powers of the 
surface on the side of the object. Even in such multifocal lenses, by 
providing a difference to the average surface powers of the surface on the 
side of the object, even more preferable properties of astigmatic 
aberration can be obtained. Thus, for the progressive multifocal lens of 
the present example, by establishing the differences DD1 and DD2 of the 
average surface powers of both surfaces, two surfaces endowed with 
preferable properties of astigmatic aberration on average can be formed, 
thereby making it possible to improve to a great extent the astigmatic 
aberration of the lens as a whole. 
Thus, for the progressive multifocal lens 10 of the present example, the 
difference of magnification of the distance-vision area 11 and the 
near-vision area 12 can be reduced, and it is possible to improve also the 
properties of astigmatic aberration. Jumping and warping of images can be 
controlled, and a wide clear-vision region can be obtained. Consequently, 
according to the progressive multifocal lens of the present example, a 
more comfortable visual field can be provided. 
Second Embodiment! 
FIGS. 4A and 4B show a different example of a progressive multifocal lens 
of the invention. The progressive multifocal lens 10 of the present 
example also is provided with a distance-vision area 11, which is a visual 
field area for viewing objects at a far distance, and a near-vision area 
12, which is a visual field area for viewing objects at a near distance, 
and endowed with a refractive power different from that of distance-vision 
area 11, and provided below distance-vision area 11. Also, the 
distance-vision area 11 and near-vision area 12 are connected smoothly by 
a progressive area 13, having a refractive power that changes 
continuously. For the progressive multifocal lens 10 of the present 
example, the average surface power D11 of the distance-vision area 11 of 
the surface 2 on the side of the object is set to 4.00D, and the average 
surface power D12 of the near-vision area 12 is set to 4.00D. Also, the 
average surface power D21 of the distance-vision area 11 of the surface 3 
on the side of the eye is set to 6.00D, the average surface power D22 of 
the near-vision area is set to 4.00D, and the addition power Add is set to 
2.00D. Also, the sphere power S of the distance-vision area is -2.00D, the 
center thickness t of the lens is 3.0 mm, and the diameter of the lens d 
is 70.0 mm. Under such conditions, a progressive multifocal lens 10 having 
an astigmatic aberration such as shown in FIG. 5 can be obtained. 
When the difference in magnification between the distance-vision area 11 
and the near-vision area 12 of the progressive multifocal lens 10 of the 
present example is sought using the Equations (3), (4), and (5) explained 
above, it becomes as follows. 
EQU SM1=0.976, SM2=1.007 
EQU SM2-SM1=0.031 (15') 
Also, the progressive multifocal lens 10 of the present example corresponds 
to a lens, in a conventional design wherein 2.00D addition power Add is 
added to the surface 2 on the side of the object, in which the average 
surface power D11 of the distance-vision area on the surface 2 on the side 
of the object is 4.00D, the average surface power D12 of the near-vision 
area is 6.00D, and the average surface powers D21 and D22 of the 
distance-vision area and near-vision area of the surface 3 on the side of 
the eye are both 6.00D. Consequently, when the difference of magnification 
of the distance-vision area and near-vision area of the conventional 
progressive lens corresponding to the lens of the present example is 
sought, it becomes as follows. 
EQU SM1=0.976, SM2=1.011, 
EQU SM2-SM1=0.035 (16') 
Consequently, in a progressive multifocal lens 10 of the present example, 
it is clear that the difference of magnification between far and near can 
be improved as much as 12-13%. In a progressive multifocal lens 10 of the 
invention, by the fact that the difference of magnification is reduced in 
this manner, it becomes possible to improve further over the conventional 
lens the jumping and warping of images arising in a progressive multifocal 
lens caused by the difference of magnification. Therefore, by 
globe-processing the progressive multifocal lens 10 of the present example 
to match an eyeglass frame, a clear eyeglass lens 9 can be provided, in 
which the jumping and warping are improved to a great extent. 
Furthermore, in a progressive multifocal lens of the present example, the 
average surface power D11 of the distance-vision area 11 on the side of 
the object and the average surface power D12 of the near-vision area 12 
are established equally. That is, the average surface power D11 of the 
distance-vision area 11 and the average surface power D12 of the 
near-vision area satisfy the following Equation (7). 
EQU D12-D11=0 (7) 
Therefore, it is possible to configure the surface 2 on the side of the 
object as an extremely simple spherical surface, and by using a 
progressive multifocal lens 10 whereby the manufacturing can be performed 
simply, an eyeglass lens can be provided inexpensively, being an eyeglass 
lens meeting the specifications of each user, in which a comfortable 
visual field having minimal jumping and warping of images can be obtained. 
The invention has been explained above with embodiments of progressive 
multifocal lenses that do not perform correction of astigmatism. However, 
it is of course possible to provide a toric surface for correcting 
astigmatism to the refractive surface 3 on the side of the eye. FIGS. 6A 
and 6B show a progressive multifocal lens 10 in which the properties of a 
toric surface 6 for correcting astigmatism are added to the surface 2 on 
the side of the eye of the progressive multifocal lens 10 described above. 
The progressive multifocal lens 10 of the present example is a progressive 
multifocal lens in which the properties of a toric surface having a 90E 
axis of astigmatism, a -2.00D sphere power, and a -2.00D cylinder power C 
are added. The value Z of the z coordinates of the surface 2 on the side 
of the eye is sought using the following Composite Equation (21) in order 
to compose the toric surface with a progressive refractive surface in 
which the average surface power D21 of the distance-vision area 11 of the 
surface 3 on the side of the eye is 6.00D and the average surface power 
D22 of the near-vision area is 4.00D. 
EQU Z=((Cp+Cx)X.sup.2 +(Cp+Cy)Y.sup.2)/(1+.sqroot.(1-(Cp+Cx).sup.2 X.sup.2 
-(Cp+Cy).sup.2 Y.sup.2)) (21) 
In the above Composite Equation (21), while the eyeglass is being worn, 
when the axis passing through the center of the progressive refractive 
surface from the side of the object to the side of the eye is the z axis, 
the axis orthogonal to the z axis oriented from below to above is the y 
axis, and the axis orthogonal to the z axis oriented from left to right is 
the x axis, X and Y indicate the coordinates of arbitrary points of the x 
and y coordinates, respectively, of the surface on the side of the eye, 
and Z indicates a z coordinate in the direction perpendicular to the 
surface on the side of the eye. Also, curvature Cp is the approximate 
curvature in any point p (X, Y, Z) of the original progressive refractive 
surface not having the properties of the toric surface added, curvature Cx 
is the curvature in the x direction of the toric surface for correction of 
astigmatism, and curvature Cy is the curvature in the y direction. In the 
present example, the average curvature in the radial direction is used as 
the approximate curvature Cp, and the reciprocal of the radius of a circle 
passing through three points, in the xy plane perpendicular to the z axis 
(passing through the center of the lens or the internal vertex (0, 0, 0)) 
including any point p (X, Y, Z) on the original progressive refractive 
surface, being the point p, the point p=(-X, -Y, -Z) rotationally 
symmetric with point p, and the internal vertex (0, 0, 0), is used. 
However, when the point p on the original progressive refractive surface 
is positioned at the internal vertex, the average curvature in the radial 
direction Cp is not defined, and Z=0 in Equation (21). 
An example is described above in which a prescription having established 
the spherical power of the toric surface was added in the vertical 
direction (90E axis) of the lens (that is, when a prescription having 
established the cylinder power of the toric surface was added in the 
left-right direction of the lens), but it is obvious that the invention is 
not limited to this example. That is, the direction of the xy axis is not 
limited to the direction described above, rather it can be established in 
a suitable direction, and the process described above can be performed 
with that coordinate system. For example, even when a prescription having 
established the spherical power of the toric surface is added in the 
left-right direction of the lens, it is possible to provide a method of 
composition using Equation (21) of the present example by only applying an 
operation rotating the directions of the x axis and the y axis, 
respectively, of the xy coordinates 90E to the left in relation to the 
example described above. Furthermore, even when a prescription having 
established the spherical power of the toric surface is added in any 
direction (including diagonal directions) of the lens, it is possible to 
provide a method of composition using Equation (21) of the present example 
by only applying an operation rotating "degrees (" is any angle of 0-360E) 
the x axis and the y axis, respectively, of the xy coordinates. 
By composing the coordinates of the toric surface with the coordinates of 
the original progressive refractive surface not having the 
astigmatism-corrective properties added, using such a Composite Equation 
(21), a progressive multifocal lens of the invention, endowed with 
astigmatism-corrective power, can be obtained. This progressive multifocal 
lens endowed with astigmatism-corrective power is as shown in FIG. 7. In 
regard to the properties of aberration, properties substantially the same 
as those of a conventional lens, having the properties as a progressive 
surface added only to the surface 2 on the side of the object, and having 
the properties of a toric surface added only to the surface 3 on the side 
of the eye, can be obtained. Meanwhile, it is also possible to seek the 
coordinates of the surface 3 on the side of the eye by simply adding the 
coordinates of the toric surface to the coordinates of the original 
progressive refractive surface not having the astigmatism-corrective power 
added. Nevertheless, if simply added coordinates are used, while a 2D 
astigmatic aberration for the purpose of correction of astigmatism 
following the main line of sight may be obtained, as shown with the broken 
line 32 in FIG. 8, it is difficult to secure a stable astigmatic 
aberration when compared to the case shown with the solid line 31 when the 
Composite Equation (21) was used. In particular, variation of the 
astigmatic aberration in the perimeter of the lens is great, and it is 
difficult to secure an astigmatic aberration for correction of 
astigmatism. Also, because variation of the astigmatic aberration is 
comparatively great, it is clear that images tend to jump and warp when 
the eye has moved along the main line of sight compared with the 
progressive multifocal lens 10 manufactured using Composite Equation (21). 
As opposed to this, the absolute values of the astigmatic aberration (solid 
line with black balls 31) following the main line of sight 14, of the 
progressive multifocal lens 10 for correction of astigmatism manufactured 
using Composite Equation (21) of the present example, show that a 2D 
astigmatic aberration that does not hinder the vision-corrective power 
intended for correction of astigmatism can be secured with extreme 
stability substantially across the entire region of the main line of 
sight. Consequently, it is clear that a progressive multifocal lens, 
endowed with an astigmatism-corrective function, in which a comfortable 
visual field having little jumping is secured, can be provided by 
composing the original progressive refractive surface and the toric 
surface using Composite Equation (21). 
Thus, it is possible to add the curvature of a toric surface for correction 
of astigmatism to the surface 3 on the side of the eye, in which the 
average surface power D21 of the distance-vision area 11 and the average 
surface power D22 of the near-vision area 12 differ, and it is possible to 
provide a multifocal lens for eyeglass having astigmatism-corrective power 
by using a multifocal lens of the invention, in which the difference of 
the average surface power D11 of the distance-vision area 11 of the 
surface 2 on the side of the object and the average surface power D12 of 
the near-vision area 12 is less than the addition power Add. Consequently, 
according to the invention, the difference of magnification between the 
distance-vision area 11 and the near-vision area 12 can be reduced, and it 
is possible to provide a multifocal lens endowed with 
astigmatism-corrective power, in which the jumping and warping of images 
is improved. Consequently, it is possible to include an eyeglass lens for 
the purpose of correction of astigmatism as one of a line-up of eyeglass 
lenses based on the invention, and it is possible to provide eyeglass 
lenses for all users, including those having and not having astigmatism, 
in which a one-level more comfortable visual field can be obtained. 
Third Embodiment! 
By using a multifocal lens of the invention, as explained above, it is 
possible to provide the user with an eyeglass lens in which the difference 
of magnification between the distance-vision area 11 and the near-vision 
area 12 is minimal. In the invention, it is further possible to provide a 
multifocal lens in which there is substantially no difference of 
magnification between the distance-vision area 11 and the near-vision area 
12, and the magnifications SM1 and SM2 of the distance-vision area 11 and 
the near-vision area 12 are almost the same. FIGS. 9A and 9B show one 
example of that. The progressive multifocal lens 10 of FIGS. 9A and 9B is 
a progressive multifocal lens in which the main configuration is almost 
the same as those of the progressive multifocal lenses described above. 
The refractive power Po of the distance-vision area is -3.00D, the 
addition power Add is 1.00D, the average surface power D11 of the 
distance-vision area of the surface on the side of the object is 8.00D, 
and the average surface power D21 of the distance-vision area of the 
surface on the side of the eye is 11.00D. The distance from the vertex L 
of the progressive multifocal lens 10 of the present example is 15.0 mm 
(0.0150 m), the center thickness t is 3.0 mm (0.0030 m), and the 
refractivity n is 1.662. Furthermore, the average surface power D12 of the 
near-vision area of the surface on the side of the object is 0.00D, and 
the average surface power D22 of the near-vision area of the surface on 
the side of the eye is 2.00D. Consequently, the progressive multifocal 
lens 10 of the present example is a multifocal lens that satisfies the 
conditions of Equation (1) described above. 
When the difference of magnification between the distance-vision area 11 
and the near-vision area 12 of the progressive multifocal lens 10 of the 
present example is sought, it becomes as follows. 
EQU SM1=0.97, SM2=0.97 
EQU SM2-SM1=0.00 (15") 
Consequently, the multifocal lens 10 of the present example is a 
progressive multifocal lens in which the magnifications of distance-vision 
area 11 and the near-vision area 12 are equal. By using this multifocal 
lens, an eyeglass lens can be provided, in which there is no jumping and 
warping of images due to the difference of magnification. 
Furthermore, in the multifocal lens of the invention, it is possible also 
to make the magnifications of the distance-vision area 11 and the 
near-vision area 12 approach 1, being the magnification of the naked eye. 
It is possible to determine the various average surface powers D11, D12, 
D21, and D22 within the range of the invention, that is, within the range 
of Equation (1) described above, such that the magnification SM1 of the 
distance-vision area and the magnification SM2 of the near-vision area 
satisfy 1 in Equations (9) and (12) described above. For example, in the 
above-mentioned progressive multifocal lens 10, by setting the average 
surface power D11 of the distance-vision area of the surface on the side 
of the object to 24.00D, the average surface power D12 of the near-vision 
area to 15.70D, furthermore the average surface power D21 of the 
distance-vision area of the surface on the side of the eye to 27.00D, and 
the average surface power D22 of the near-vision area to 17.70D, a 
multifocal lens can be provided, in which the magnification SM1 of the 
distance-vision area and the magnification SM2 of the near-vision area are 
1.00, the same magnification as that of the naked eye. 
In a multifocal lens in which the absolute value of the refractive power Po 
of the distance-vision area 11 is small, a multifocal lens can be 
provided, in which the distance-vision area 11 and the near-vision area 12 
become magnification 1 of the naked eye, and have a shape that is 
comparatively easy to realize. The multifocal lens shown in FIGS. 10A and 
10B is a progressive multifocal lens in which the refractive power Po of 
the distance-vision area 11 is -1.50D, the addition power Add is 1.00D, 
the average surface power D11 of the distance-vision area of the surface 
on the side of the object is 11.00D, and the average surface power D21 of 
the distance-vision area of the surface on the side of the eye is 12.50D. 
In this multifocal lens 10, the distance from the vertex L, the center 
thickness t, and the refractivity n are made the same as the conditions 
described above, and by making the average surface power D12 of the 
near-vision area of the surface on the side of the object 3.00D, and the 
average surface power D22 of the near-vision area of the surface on the 
side of the eye 3.50D, a multifocal lens can be realized, in which the 
magnification SM1 of the distance-vision area and the magnification SM2 of 
the near-vision area are 1.00, the same magnification as that of the naked 
eye. In a progressive multifocal lens, by connecting the distance-vision 
area and the near-vision area using a progressive area endowed with a 
progressive refractive surface so as to satisfy the average surface powers 
sought in this manner, a progressive multifocal lens can be provided, in 
which the change of the magnification is extremely small while the 
refractive power changes progressively. 
The invention is explained above based on a progressive multifocal lens, 
but even in a bifocal lens not provided with a progressive area, an 
eyeglass lens can be provided, in which, in the same manner, the 
difference of magnification is minimal and jumping of images is minimal. 
Also, because the difference of the average surface powers on the side of 
the object can be less than that of a conventional lens, a bifocal lens 
can be provided, in which the boundary between far and near can be made 
gentle, and the boundary line does not stand out. Furthermore, eyeglass 
lenses were explained in the above examples, in which visual field areas 
for focusing on two types of distances are provided, being a 
distance-vision area and a near-vision area. However, it is obvious that 
the invention can be applied to a multifocal lens and eyeglass lens 
provided with a third, or more, visual field area having a different 
refractive power. Also, not being limited to the lenses described above, 
it is obvious that the elements of a toric surface for correcting 
astigmatism can be added to the surface on the side of the eye of a 
multifocal lens and eyeglass lens of the invention. 
As explained above, in the invention, in a multifocal lens for eyeglass, 
the difference of the average surface power of the distance-vision area of 
the surface on the side of the object and the average surface power of the 
near-vision area, is made such that it is smaller than the addition power, 
which is different from the design policy of a conventional multifocal 
lens for eyeglass. Also, for the lens as a whole, from the average surface 
power of the distance-vision area of the surface on the side of the eye 
and the average surface power of the near-vision area, a multifocal lens 
for eyeglass can be provided, being endowed with a specific addition 
power. Thus, because optical properties for correction of vision other 
than astigmatism can be added to both surfaces, being the surface on the 
side of the object and the surface on the side of the eye, compared with a 
conventional multifocal lens for eyeglass in which the optical properties 
for correction of vision are added only to the surface on the side of the 
object, it is possible to improve further the astigmatic aberration by 
reducing the difference of the average surface powers on the side of the 
object. Also, it becomes possible to establish freely the average surface 
power of the surface on the side of the object, having a great influence 
on magnification, by combining it with the average surface power of the 
surface on the side of the eye. Also, it becomes possible to reduce the 
difference of magnification of the first and second visual field areas. As 
a result, it becomes possible, for example, to eliminate substantially the 
difference of magnification between the distance-vision area and the 
near-vision area, or to form a distance-vision area and a near-vision area 
having the same magnification as that of the naked eye. Also, even if the 
difference of magnification cannot be eliminated, according to the 
invention, it becomes possible to improve to a great extent the difference 
of magnification between the distance-vision area and the near-vision area 
over a conventional multifocal eyeglass lens. 
Thus, according to the invention, it is possible to provide a multifocal 
lens for eyeglass, in which the difference of magnification can be 
reduced, and in addition, the properties of astigmatic aberration can also 
be improved. Consequently, by using a multifocal lens for eyeglass of the 
invention, an eyeglass lens can be provided, in which the user can obtain 
a comfortable visual field having a wider clear-vision area and having 
little jumping and warping. 
The invention relates to a multifocal lens used as an eyeglass lens. 
According to the invention, it is possible to provide an eyeglass lens, in 
which the difference of magnification between the distance-vision area and 
the near-vision area is minimal, and there is minimal jumping and warping 
of images. Furthermore, an eyeglass lens can be provided, in which the 
properties of astigmatic aberration also can be improved.