Lens meter

A lens meter has a single point-like light source, a collimator lens for collimating the light from the point-like light source and causes it to enter a lens to be examined, a plural-aperature stop disposed immediately reawardly of the lens to be examined and having three or more apertures, a light-receiving optical system including a prism assembly for separating the light beams from the plural-aperture stop on the light-receiving surface thereof, and an array light-receiving element disposed at the focus position of the light-receiving optical system for measuring the refractive value of the lens to be examined by the mutual positional relation between the received light beams.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a lens meter used in ophthalmic hospitals, by 
opticians, etc., to measure the refractive value, i.e., the degree of 
spherical refraction, the degree of astigmatic refraction, the astigmatic 
angle and the degree of prism, of lenses for spectacles. 
2. Related Background Art 
The conventional lens meters are generally designated such that the image 
of a chart illuminated by a light source is formed by an auxiliary lens. 
The image of the chart is observed by means of a telescope adjusted to 
infinity through a lens to be examined. The chart is moved in the 
direction of the optic axis so as to enable the image of the chart to be 
clearly seen, and at that point of time, the position of the chart 
graduated in diopter is read to thereby obtain the measured value of the 
refractive power. 
Recently, use has been made of automatic measuring lens meters of the type 
in which the measured value is obtained by depressing a button after 
manual adjustment of the lens meters. However, like popular lens meters, 
such lens meters are complex because of the presence of mechanically 
movable portions. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a lens meter which has 
no movable parts and is simple in construction. 
It is also an object of the present invention to provide an inexpensive 
lens meter which adopts a single point-like source as a measuring light 
source.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 which shows an optical arrangement of a first 
embodiment of the present invention, there are disposed on an optic axis 
of a point-like light source 1 comprising a light-emitting diode, in 
succession from the light source 1 side, a convex lens 2 as a collimator 
lens, a lens 3 to be examined, a 6-aperture stop 4, a prism 5, a convex 
lens 6, a cylindrical concave lens 7 and a linear photosensor array 8 such 
as a CCD. The light source 1 is provided at the focus position of the 
convex lens 2, and the 6-aperture stop 4 is disposed in proximity to the 
rear surface of the lens 3 to be examined. The sensor array 8 is provided 
at the focus position of the convex lens 6. The cylindrical concave lens 7 
whose generator is in the direction of array arrangement of the sensor 
array 8 expands light in a direction perpendicular to the direction of 
arrangement of the sensor array 8 and ensures that the light beam impinges 
on the sensor array even if the light beam moves in the direction 
perpendicular to the direction of arrangement of the sensor array 8. 
Accordingly, the light beam emitted from the light source 1 is collimated 
by the convex lens 2 and enters the lens 3 to be examined, and the light 
beam refracted in conformity with the refractive powers of various 
portions of the lens 3 to be examined enters the 6-aperture stop 4. 
Referring to FIG. 2 which is a plan view of the 6-aperture stop 4, this 
6-aperture stop 4 has six openings 4a, 4b, 4c, 4d, 4e and 4f each provided 
at an angle of 60.degree.. The light beam having emerged from the lens 3 
to be examined is made into six light beams by the 6-aperture stop 4, and 
these light beams enter the prism 5 which deflects the light beams so as 
to be separated on the light-receiving surface. At this time, the light 
beams enter the prism 5 with an iclination corresponding to the refractive 
power of the lens 3 to be examined. 
Now, when the lens 3 to be examined is removed and a parallel light beam 
enters the 6-aperture stop 4, the light beams having emerged from the 
6-aperture stop 4 will be imaged on concentric circles corresponding to 
the openings in the 6-aperture stop 4 if received by a two-dimensional 
surface. The following is done to cause these light beams to move on a 
one-dimensional light-receiving line parallel to a segment 4a-4b passing 
through the openings 4a and 4b in the 6-aperture stop 4. The light beams 
passing through the openings 4c and 4d disposed with an inclination of 
60.degree. with respect to the openings 4a and 4b are rotated 
counter-clockwise by 60.degree. and displaced downwardly by 1/3 of the 
distance between images 8a and 8b, and the light beams passed through the 
openings 4e and 4f are rotated clockwise by 60.degree. and displaced 
downwardly by 2/3 of the distance between images 8a and 8b, whereby on the 
linear photo-sensor array 8 which is the light-receiving surface, there 
are obtained, in succession from above, images 8a, 8c, 8e, 8b, 8d and 8f 
corresponding to the equidistantly disposed openings 4a, 4c, 4e, 4b, 4d 
and 4f, as shown in FIG. 3. 
Thus, when the same operation as the operation effected when the lens 3 to 
be examined was absent is applied to the light beams refracted by the lens 
3 to be examined and passed through the 6-aperture stop 4, there are 
obtained on the linear photosensor array 8 images corresponding to the 
openings 4a, 4c, 4e, 4b, 4d and 4f at intervals corresponding to the 
refractive power of the lens 3 to be examined. The refractive power in 
each meridian direction can be found from these image intervals by the use 
of operation means M. 
In the description of the case where the lens 3 to be examined is absent, 
the image intervals on the sensor array 8 have been described as being 
equal, whereas the image intervals need not always be equal, but by making 
the amount of deflection of the light beam small, for example, within a 
range in which no hindrance occurs to the measurement of the distance 
between images, the length of the sensor array 8 can be shortened to a 
certain degree. 
The prism 5 is used to rotate and deflect the light beams thus passed 
through the 6-aperture stop 4. FIG. 4 illustrates the meridian rotating 
function of this prism 5, and it is a view in which a trapezoidal prism 5A 
is disposed so that the trapezoidal portion thereof is seen in the plane 
of the drawing sheet. Seeing the incident light ray onto and the emergent 
light ray from the trapezoidal prism 5A from this direction, the image on 
the bottom surface is inverted in the plane of the drawing sheet, while 
inversion of the image does not occur in a plane perpendicular to the 
plane of the drawing sheet. If the prism 5A is rotated, e.g., by 
90.degree. about the optic axis of FIG. 5 and disposed so that the 
rectangular portion of the bottom surface thereof is seen in the plane of 
the drawing sheet, the direction of the image does not change in the plane 
of the drawing sheet but is inverted in the plane perpendicular to the 
plane of the drawing sheet and thus, the image is rotated by 180.degree.. 
When the trapezoidal prism 5A is thus rotated about the optic axis, the 
image is rotated about the same axis twice the angle of rotation of the 
prism. 
In the present embodiment, the sensor array 8 is disposed in the direction 
of the openings 4a-4b and the meridian direction 4c-4d has an angle of 
60.degree. with respect thereto and therefore, if the prism 5A is disposed 
in the light beam from the opening 4c and is rotated by 30.degree. about 
the center line of the light beam, the inclination in the direction of the 
openings 4c-4d, can be changed into the direction of the openings 4a-4b, 
i.e., the direction of the sensor array 8. Accordingly, by endowing the 
prism 5 with the structure of the prism 5A and rotating it by 30.degree. 
about the optic axis, the prism 5 can be made to perform the meridian 
rotating function. 
For the light beams passed through the other openings 4d, 4e and 4f, the 
meridian can likewise be rotated by the prism 5 having the structure of 
the prism 5A and these light beams can be imaged on the sensor array 8. 
FIG. 5 illustrates the deflecting function of the prism 5, and shows that 
by a wedge prism 5B being disposed in the light beam, the light beam is 
refracted and deflected. Accordingly, by endowing the prism 5 with a 
structure equal to the structure in which the wedge prism 5B is disposed 
in the light beams passed through each of the openings 4a-4f and suitably 
selecting the inclination of exit surface of each prism 5B, the light 
beams can be deflected so as to be imaged at a certain interval on the 
sensor array 8. 
FIG. 6 is a cross-sectional view of a prism 5 comprising six small prisms 
having the structure of the trapezoidal prism 5A shown in FIG. 4 as well 
as the structure of the wedge prism 5B shown in FIG. 5. The light beams 
from openings 4a, 4b, 4c, 4d, 4e and 4f may pass through the respective 
small prisms 5a, 5b, 5c, 5d, 5e and 5f, and the light beams in the small 
prisms 5c, 5d, 5e and 5f may be totally reflected by respective surfaces 
5c', 5d', 5e' and 5f' and meridian rotation thereof may be accomplished 
thereby. The entrance and exit surfaces of the small prisms 5a-5f are 
formed into suitably inclined surface so that light beams may be imaged at 
reference intervals on the sensor array 8 when the lens 3 to be examined 
is removed so that a parallel light beam may enter the 6-aperture stop 4. 
The prism 5 can be integrally made in a mold. 
In this manner, the light beams passing through the openings 4a-4f in the 
6-aperture stop 4 can be imaged on the sensor array 8 through the prism 5, 
the convex lens 6 and the cylindrical concave lens 7. Since the sensor 
array 8 is provided at the focus position of the convex lens 6, the 
positions of the light beams on the sensor array 8 are displaced in 
proportion to the inclination of the light beam in a plane containing the 
center of each opening 4a-4f and the optic axis O with respect to the 
optic axis O. Accordingly, by measuring the position of each imaging point 
on the sensor array 8, the inclination of the light beam in each meridian 
direction, i.e., the refractive power in each meridian direction, can be 
known. 
Now, the variation in the refractive power of a lens having astigmatism in 
the meridian direction is sine-wave-like and therefore, if the refractive 
powers in three meridian directions are known, the refractive power in the 
other directions can all be found by calculation. Accordingly, if the 
refractive powers in three meridian directions are found from the 
intervals between the images 8a-8b, 8c-8d and 8e-8f on the sensor array 8, 
the refractive power of the lens 3 to be examined in each meridian 
direction can be found. 
Also, considering, for example, the direction of the openings 4a-4b, the 
two light beams passed through the openings 4a and 4b are dispersed by an 
equal amount and therefore, the degree of prism can be found as the 
average value of the deviations of the images 8a and 8b from a 
predetermined position. The other directions can also be found from the 
corresponding image positions in a similar manner. As regards the degree 
of prism, if two directions are known, the other directions can be found 
by calculation. Also, in a case where the lens 3 to be examined is 
eccentrically placed, an influence similar to that in the case where there 
is the degree of prism is imparted to the light beam. 
FIG. 7 shows a state in which the light beams on three linear photosensor 
array 8A, 8B and 8C are imaged according to a second embodiment of the 
present invention. Images 8Aa and 8Ab are formed by light beams passed 
through openings 4a and 4b, respectively, and likewise, images 8Bc, 8Bd, 
8Ce, and 8Cf are formed by light beams passed through openings 4c, 4d, 4e 
and 4f, respectively. 
The second embodiment is the same as the first embodiment except the prism 
5, the cylindrical concave lens 7 and the sensor arrays 8. Three sensor 
array 8A, 8B and 8C are disposed instead of the sensor array 8, and 
corresponding to the sensor arrays 8A, 8B and 8C, cylindrical concave 
lenses 7a, 7b and 7c, not shown, are provided instead of the cylindrical 
concave lens 7. A prism 5', not shown, in which the angles of inclination 
of the entrance and exit surfaces of the prism 5 are adjusted is disposed 
so that light beams passed through openings 4a-4b, 4c-4d and 4e-4f may be 
imaged on the three sensor arrays 8A, 8B and 8C, respectively. 
As in the first embodiment, if the refractive power and the degree of prism 
of the lens 3 to be examined change, the images 8Aa, 8Ab, 8Bc, 8Bd, 8Ce 
and 8Cf on the respective sensor arrays 8A, 8B and 8C move in the 
directions of array arrangements in response thereto and therefore, by 
measuring the amounts of movement thereof, the refractive power and the 
degree of prism of the lens 3 to be examined can be known. In this case, 
there is a disadvantage that the number of the sensor arrays 8 and the 
number of the cylindrical concave lenses 7 must be increased as compared 
with the first embodiment, but there is an advantage that the amounts of 
movement of the images on the sensor arrays 8A-8C are easy to see and easy 
to measure. 
Still another embodiment of the present invention will now be described 
with reference to FIG. 8. In FIG. 8, there are disposed, along a light 
beam emitted from a point-like light source 1, a collimator lens 2, a 
plural-aperture stop 14, a prism assembly 15 comprising a plurality of 
wedge prisms for deflecting light beams separated by the plural-aperture 
stop 14, a light-receiving optical system 16 for receiving the light beams 
deflected by the prism assembly 15, and a two-dimensional array sensor 
light-receiving element 18 such as a CCD (charge coupled device) dispersed 
at the focus position of the light-receiving optical system 16. A lens 3 
to be examined is inserted between the collimator lens 2 and the 
plural-aperture stop 14. The number of the apertures of the 
plural-aperture stop 14 may be three or more, and in the present 
embodiment, the plural-aperture stop 14 has four apertures 14a-14d as 
shown in FIG. 9, and the prism assembly 15 is comprised of four wedge 
prisms 15a-15d as shown in FIG. 10. 
In FIG. 8, the light beam from the point-like light source 1 is collimated 
by the collimator lens 2 and then enters the lens 3 to be examined, and 
the light beam passed through the lens 3 to be examined is separated into 
four light beams through the four apertures 14a-14d of the plural-aperture 
stop 14, and those light beams are deflected by the prisms 15a-15d, 
respectively, of the prism assembly 15, pass through the light-receiving 
optical system 16 and are received by the array sensor light-receiving 
element 18 such as a CCD disposed on the focal plane of the 
light-receiving optical system 16. 
FIG. 11 shows the positions of four light beams A-D received on the array 
sensor light-receiving element 18, and arrows indicate the directions in 
which the light beams A-D move by the focal length of the lens 3 to be 
examined. Where there is a degree of astigmatism in the lens 3 to be 
examined, the positions of the light beams on the array sensor 
light-receiving element 18 become deviated from the directions of arrows 
in FIG. 11. Also, if the lens 3 to be examined becomes eccentric relative 
to the optic axis of the apparatus, the positions of the light beams will 
generally move. 
To measure the refractive value, i. e., the degree of spherical refraction, 
the number of astigmatic refraction and the astigmatic angle, of the lens 
3 to be examined from the position of the light beams on the array sensor 
light-receiving element 18, five unknown quantities in addition to two 
unknown quantities of eccentricity can be found by calculation if the 
two-dimensional positions of a minimum of three light beams are known. 
To find the position of the light beams on the array sensor light-receiving 
element 18, for example, the level may be determined and binarized and the 
central position of the light beams may be calculated from that position. 
For example, FIG. 12 is an enlarged view of the light beam A, and signals 
may be read out along the arrangement of elements concerned therewith and 
the level may be determined and the signals may be made into such a binary 
signals as shown in FIG. 13, and the positions thereof may once be stored 
in a memory, whereby the center of the light beam may be calculated. 
In FIG. 8, the prism assembly 15 functions to separate the light beams on 
the array sensor light-receiving element 18 and, if this prism assembly 15 
is absent, when the lens 3 to be examined is not inserted, the light beams 
passing through the apertures 14a-14d of the plural-aperture stop 14 will 
converge at a point on the array sensor light-receiving element 18. If the 
light beams are only separated from one another, it will be possible to 
find the individual coordinates of the light beams, and as long as the 
light beams are separated from one another, the directions of the wedges 
of the prism assembly 15 can be freely selected.