Lens meter utilizing three different wavelengths

A lens meter is provided which includes a light source portion (1) which emits measuring light (P) having at least three different wavelengths; a light receiving portion (3) which receives the measuring light (P) which has passed through a to-be-inspected lens immersed in a liquid (12) as a medium; an in-medium optical characteristic measuring device for measuring an optical characteristic of the lens (13) in the medium about each wavelength, based on a deviated quantity of the measuring light detected by the light receiving portion (3); a refractive index calculating device for calculating a refractive index of material of the lens (13), based on a difference of the optical characteristic of the lens in the medium among the wavelengths; and a converting device for converting the optical characteristic of the lens (13) in the medium into an optical characteristic of the lens (13) in the air, based on the refractive index calculated by the refractive index calculating device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a lens meter capable of measuring the 
characteristics of a lens to be inspected while immersing the lens in a 
liquid, and relates to a measuring vessel for use in the lens meter. 
2. Description of Related Art 
A lens meter is known in which a lens to be inspected is laid on a lens 
receiving plate, a beam of measuring light emitted by a light source is 
then projected onto the lens, and the measuring light which has passed 
through the lens is received by a photoelectric sensor. The lens meter 
calculates a difference between a light receiving position on the 
photoelectric sensor where the measuring light is received when the lens 
is laid on the lens receiving plate and a light receiving position on the 
photoelectric sensor where the measuring light is received when the lens 
is not laid thereon. According to the difference, the optical 
characteristic of the lens, namely, the power distribution of the lens is 
measured in the air. This type of lens meter is used to measure the 
optical characteristic of a lens, such as a spectacle lens or a hard 
contact lens (HCL), which is rigid in material. 
Some lenses to be inspected are made of soft material. If a soft contact 
lens (SCL), for example, is laid on the lens receiving plate to measure 
the optical characteristic thereof in the air, the shape of the soft 
contact lens is deformed during measurement because of gravity. 
Additionally, the soft contact lens has another feature in that its 
material itself holds plenty of water. For this reason, if much time is 
consumed for measurement, the soft contact lens is dried up with the lapse 
of time and thereby undergoes a change in refractive index of its material 
itself. This makes it difficult to accurately measure the optical 
characteristic of the soft contact lens by the use of the conventional 
lens meter in which the optical characteristic of a lens to be inspected 
is measured in the air. In addition, the adhesion of water droplets to the 
surface of the lens causes the scattering of measuring light and makes it 
difficult to accurately measure the optical characteristic thereof. 
In order to solve these problems, there has been attempted the experiment 
of immersing a lens to be inspected in a liquid and measuring the optical 
characteristic of the lens. Referring especially to a soft contact lens, a 
lens mater has been developed in which the soft contact lens is immersed 
in a liquid (e.g., physiological salt solution) contained in a transparent 
vessel (e.g., transparent cell) so as to prevent the soft contact lens 
from being naturally dried up and being deformed by its own weight and 
thereafter the optical characteristic of the soft contact lens is 
measured. This type of lens meter is capable of measuring the optical 
characteristic of the soft contact lens with accuracy because the soft 
contact lens is prevented from being naturally dried up and being deformed 
by its own weight. 
However, since the refractive index of a liquid is larger than that of air, 
the optical characteristic of the soft contact lens which has been 
measured in the liquid apparently becomes smaller than that measured in 
the air. Generally, measurement values obtained by measurement in the air 
are used for the optical characteristic of a lens, such as a spectacle 
lens or a contact lens, to be inspected. For this reason, when a contact 
lens is measured, a difference occurs between a measurement value obtained 
in the liquid and a measurement value obtained in the air. Conventionally, 
this difference has been corrected in such a way that the refractive index 
of the material of a soft contact lens and the refractive index of a 
liquid in which the soft contact lens is immersed are input to an 
arithmetic means of a lens meter, so that a measurement value obtained by 
measurement of the soft contact lens in the liquid is converted into a 
measurement value obtained by measurement thereof in the air. 
In detail, on the supposition that the thickness of the contact lens is 
very thin, the refractive index S.sub.0 of the contact lens in the air is 
obtained by the following equation: 
EQU S.sub.0 =1/f.sub.0 =(n-1)(1/r.sub.1 -1/r.sub.2) (1) 
wherein f.sub.0 is a focal length of the contact lens in the air, n is a 
refractive index of material of the contact lens, and r.sub.1 and r.sub.2 
are radii of curvature of the respective surfaces of the contact lens. 
On the other hand, the refractive index S.sub.w of the contact lens 
immersed in a liquid is obtained by the following equation: 
EQU S.sub.w =1/f.sub.w ={(n-n.sub.w)/n.sub.w }(1/r.sub.1 -1/r.sub.2)(2) 
wherein f.sub.w is a focal length of the contact lens in the liquid, and 
n.sub.w is a refractive index of the liquid. 
In this example, let it be supposed that a beam of measuring light passes 
through a transparent cell and reaches a light receiving portion of the 
lens meter through the air. Additionally, let it be supposed that both a 
liquid layer existing on the side of the rear surface of the transparent 
cell and a cell wall of the transparent cell are thin enough to be 
negligible. 
If so, Eq. (2) can be approximated to the following equation: 
EQU S.sub.v =1/f.sub.v =1/(n.sub.w .multidot.f.sub.w) (3) 
wherein S.sub.v is an apparent refractive index, and f.sub.v is an apparent 
focal length. 
That is, the apparent refractive index S.sub.v differs from the refractive 
index S.sub.0 in the air. 
The refractive index S.sub.0 in the air is obtained from the apparent 
refractive index S.sub.v in the liquid on the basis of the following 
equation: 
EQU S.sub.0 =(n-1){S.sub.v .multidot.n.sub.w /(n-n.sub.w)} (4) 
This means that the apparent refractive index S.sub.v in the liquid is 
convertible to the refractive index S.sub.0 in the air if both the 
refractive index n.sub.w of the liquid and the refractive index n of the 
material of the contact lens are known. 
In some cases, there is a need to measure optical characteristics of soft 
contact lenses fitted over the eyes of a subject in an ophthalmic hospital 
or a contact lens clinic. In these cases, it is often impossible to trace 
a manufacturer (maker) of the soft contact lenses fitted over the 
subject's eyes or ascertain a trade mark including, for example, an 
article number thereof. Therefore, the refractive index of material of the 
soft contact lens is often unknown. Even if data concerning the 
manufacturer has been obtained, the refractive index of the material of 
the soft contact lens varies because of adhesion of protein to the soft 
contact lens which is caused by wearing the soft contact lens 
continuously. This variation is unpredictable. Therefore, it is impossible 
to convert a measurement value of the soft contact lens measured in a 
state of being immersed in a liquid into a measurement value of the 
identical soft contact lens measured in the air with accuracy. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a lens meter 
which is capable of accurately converting a measurement value of the 
optical characteristic of a lens to be inspected which has been measured 
in a liquid into a measurement value of the optical characteristic of the 
identical lens measured in the air even if the refractive index of 
material of the lens is unknown and to provide a measuring vessel for use 
in the lens meter. 
In order to achieve the object, a lens meter according to an aspect of the 
present invention comprises a light source portion for emitting measuring 
light having at least three different wavelengths; a light receiving 
portion for receiving the measuring light which has passed through a lens 
to be inspected, the lens being immersed in a liquid as a medium; an 
in-medium optical characteristic measuring means for measuring an optical 
characteristic of the lens in the medium about each wavelength, based on a 
deviated quantity of the measuring light detected by the light receiving 
portion; a refractive index calculating means for calculating a refractive 
index of material of the lens, based on a difference of the optical 
characteristic of the lens in the medium among the wavelengths; and a 
converting means for converting the optical characteristic of the lens in 
the medium into an optical characteristic of the lens in the air, based on 
the refractive index calculated by the refractive index calculating means. 
Preferably, the light source portion comprises monochromatic light emitting 
sources different in emission wavelength from each other, or the light 
source portion comprises a light emitting source which emits measuring 
light having a wavelength distribution and a plurality of filters each of 
which allows the measuring light of the three different wavelengths to 
pass through. Preferably, if the light source portion comprises the 
monochromatic light emitting sources, the light receiving portion 
comprises a filter capable of resolving measuring light into measuring 
light of at least three different wavelengths and a light receiving sensor 
for receiving the resolved measuring light, and the monochromatic light 
emitting sources are simultaneously turned on to emit light. In this 
situation, it is desirable that the wavelength of the measuring light 
comprises a red wavelength, a green wavelength, and a blue wavelength. 
However, if the material of the contact lens or the liquid does not 
possess extraordinary absorbing properties and if the wavelengths are 
apart from each other at a distance more than a fixed distance, only 
infrared rays of light may be used as the measuring light. 
The lens meter further comprises a splitting optical member, situated 
between the light source portion and the lens or situated between the lens 
and the light receiving portion, for splitting the measuring light into 
numbers of measuring light. A distribution of the optical characteristic 
of the lens is measured according to the numbers of measuring light. 
In order to achieve the object, a lens meter according to another aspect of 
the present invention comprises a light source portion for emitting 
measuring light having at least two different wavelengths, a light 
receiving portion for receiving the measuring light which has passed 
through a lens to be inspected, the lens being immersed in a liquid as a 
medium; an in-medium optical characteristic measuring means for measuring 
an optical characteristic of the lens in the medium about each wavelength, 
based on a deviated quantity of the measuring light detected by the light 
receiving portion; a material presuming means for presuming a material of 
the lens, based on a difference of the optical characteristic of the lens 
in the medium between the wavelengths; a refractive index storing means 
for storing a refractive index of the material of the lens; and a 
converting means for converting the optical characteristic of the lens in 
the medium into an optical characteristic of the lens in the air, based on 
the refractive index of the material presumed by the material presuming 
means. 
This invention has the advantage that a measurement value of the optical 
characteristic of the lens to be inspected which has been measured in a 
state of being immersed in a liquid is convertible into a measurement 
value of the optical characteristic of the lens which has been measured in 
the air with accuracy even if the refractive index of the material of the 
lens is unknown. 
A measuring vessel used to measure an optical characteristic of a contact 
lens while immersing the contact lens in a liquid according to an aspect 
of the present invention has projections for positioning the contact lens. 
A measuring vessel used to measure an optical characteristic of a contact 
lens while immersing the contact lens in a liquid according to another 
aspect of the present invention has a lens setting surface having a shape 
to fit a curved surface of the contact lens. 
A measuring vessel used to measure an optical characteristic of a contact 
lens while immersing the contact lens in a liquid according to still 
another aspect of the present invention comprises a vessel body and a lid 
member. The vessel body has projections for positioning the contact lens, 
and the lid member has air holes through which bubbles in the vessel body 
are discharged.

DETAILED DESCRIPTION OF THE EMBODIMENT 
In FIG. 1, reference numeral 1 designates a light source portion, reference 
numeral 2 designates a lens receiving plate, and reference numeral 3 
designates a light receiving portion. The light source portion 1 includes 
three LEDs 4, 5, 6, two dichroic prisms 7, 8, and a collimation lens 9. 
The LEDs 4, 5, 6 serve as monochromatic light sources which emit beams of 
measuring light P having at least three different wavelengths. The LED 4 
emits red measuring light, the LED 5 emits green measuring light, and the 
LED 6 emits blue measuring light. The dichroic prism 7 is a long-pass 
filter and has a mirror surface 7a which reflects the green and blue 
measuring light while allowing the red measuring light to pass through. 
The dichroic prism 8 is a short-pass filter and has a mirror surface 8a 
which reflects green measuring light while allowing blue measuring light 
to pass through. Instead of the LEDs 4, 5, 6, semiconductor lasers (LD) 
may be used as monochromatic light sources. If so, polarization beam 
splitters may be used in place of the dichroic prisms 7, 8 because 
polarized light of the semiconductor laser (LD) can be used. The 
collimation lens 9 converts the beams of the measuring light emitted by 
the LEDs 4, 5, 6 into parallel rays. For example, a microlens array 10 is 
disposed in a measuring optical path between the lens receiving plate 2 
and the collimation lens 9. The microlens array 10 has microlenses 10a as 
shown in, for example, FIG. 2. The number of the microlenses 10a is, for 
example, 1,000. Each of the microlenses 10a has substantially the 
identical focal length. According to the parallel light rays, the 
microlenses 10a generate condensed light rays the number of which 
corresponds to the number of the microlenses 10a. 
A measuring vessel 11 is set on the lens receiving plate 2. The measuring 
vessel 11 is filled with a preserving liquid 12, such as physiological 
salt solution. A soft contact lens as a lens 13 to be inspected is 
immersed in the liquid 12. The measuring vessel 11 has lens positioning 
projections 11a, a top cover glass 11b, and a reverse cover glass 11c. By 
the lens positioning projections 11a, the lens 13 to be inspected is 
situated in the vicinity of a back focal point of the microlens array 10 
in the measuring vessel 11. Images of point sources corresponding to the 
microlenses 10a are formed on the lens 13. The condensed light rays Pi 
which have passed through the lens 13 are each guided to the light 
receiving portion 3 through a relay lens 14. The light receiving portion 3 
comprises a COD camera. The COD camera is made up of a TV lens 3a and a 
light receiving COD sensor 3b. 
A principal light ray Ps of the condensed light ray Pi which strikes the 
lens 13 is parallel to an optical axis 01 of the measuring optical path. 
After passing through the lens 13, the principal light ray Ps is 
deflected. The degree of deflection of the principal light ray Ps depends 
on both the height h of incidence from the optical axis 01 and the power 
of the lens 13 at the position of incidence. The height h of incidence of 
the principal light ray Ps is known according to the respective 
microlenses 10a. The power S of the surface 13a of the lens 13 at each 
position is obtained from the following equations: 
EQU S=tan (.theta.(10.multidot.h)) (5) 
EQU .theta.=tan.sup.-1 {(h-.beta..multidot.hi)/Z} (6) 
wherein .theta. is a deflected angle of the principal light ray Ps which 
has passed through the lens 13, hi is a height at the light receiving CCD 
sensor 3b, .beta. is a relay magnification, and Z is a distance from the 
reverse 13b of the lens 13 to the relay lens 14. Accordingly, if the 
unknown height hi at the light receiving CCD sensor 3b is obtained, the 
deflected angle .theta. is obtained from Eq. (6). Accordingly, the power S 
thereof is obtained from Eq, (5). In other words, based on the quantity of 
deviation from a reference position on the light receiving CCD sensor 3b 
where the principal light ray Ps is received when the lens 13 is not set 
in the measuring optical path, the refractive index of the lens 13 in the 
medium can be measured when the lens 13 is set in the measuring optical 
path. Since this measuring principle is not directly pertinent to the 
present invention, see Japanese Patent Application Laid-Open Publication 
No. Hei 7-189289 if necessary. Referring to the position of the microlens 
array 10, the microlens array 10 may be situated between the lens 13 and 
the light receiving portion 3, not between the light source portion 1 and 
the lens 13. 
The LEDs 4, 5, 6 are turned on and driven one after the other. The beams of 
measuring light P from the LEDs 4, 5, 6 are individually deflected by the 
lens 13 and are successively received by the light receiving CCD sensor 
3b. Received-light outputs of the light receiving CCD sensor 3b are input 
to a processing circuit 15 one after the other. The degree of deflection 
of the measuring light P caused by the lens 13 depends on its wavelength. 
Therefore, as a result of measuring the power distribution of the lens 13 
by the use of the three measuring light P with wavelengths differing from 
each other, a different optical characteristic value can be obtained as to 
each wavelength. This optical characteristic value is a value obtained in 
a state in which the lens 13 to be inspected is immersed in the liquid as 
a medium. Therefore, it is required to convert it into an optical 
characteristic value obtained in the air. 
A description will now be given of the principle of converting the three 
different optical characteristic values as to the respective wavelengths 
into the optical characteristic values of the lens 13 in the air. 
Generally, it is known to use Herzberger's dispersion formula as a means 
for obtaining a refractive index of an optical glass with respect to a 
wavelength. This dispersion formula is 
EQU n.lambda.=1+(n.sub.d -1){1+B(.lambda.)+A(.lambda.)/V.sub.d }(7) 
wherein n.lambda. is a refractive index of an optical glass with respect to 
a wavelength of .lambda., n.sub.d is a refractive index of the optical 
glass in the air with respect to D-lines, V.sub.d is Abbe number, and 
B(.lambda.) and A(.lambda.) are variables according to the wavelength of 
.lambda. but are constants directly obtained by fixing the wavelength of 
.lambda.. 
If the term (1/r.sub.1 -1/r.sub.2) in Eq. (2) is replaced with R, Eq. (2) 
is transformed as follows: 
EQU n=(n.sub.w /R).multidot.(Sw+R) (2)' 
If the refractive index obtained when measurement is carried out in a 
wavelength of .lambda..sub.1 is n.sub.1, and the refractive power in the 
wavelength of .lambda., is S.sub.w 1, Eq. (2)' is expressed as follows: 
EQU n.sub.1 =(n.sub.w /R).multidot.(S.sub.w 1 +R) (8) 
On the other hand, Eq. (7) can be transformed into the following dispersion 
formula including the wavelength of .lambda.. 
EQU n.sub.1 =1+(n.sub.d -1){1+B(.lambda..sub.1)+A(.lambda..sub.1)/V.sub.d}(7)' 
If the refractive index n.sub.1 is deleted from Eqs. (8) and (7)', the 
following equation (9) is obtained. 
EQU (n.sub.w /R).multidot.(S.sub.w1 +R)=1+(n.sub.d -1) {1+B (.lambda..sub.1)+A 
(.lambda..sub.1)/V.sub.c} (9) 
In Eq. (9), the refractive index n.sub.w of the medium is known, and the 
constants A(.lambda..sub.1) and B(.lambda..sub.1) can be fixed because the 
measuring wavelength is known. The refractive power S.sub.w1 is an optical 
characteristic value in the wavelength of .lambda..sub.1 obtained by the 
measurement. Still unknown values are n.sub.d, V.sub.d, and R. If the 
refractive powers S.sub.w2 and S.sub.w3 in the measuring wavelengths 
.lambda..sub.2 and .lambda..sub.s are respectively obtained as above, the 
following equations are obtained. 
EQU (n.sub.w /R).multidot.(S.sub.w2 +R)=1+(n.sub.d 
-1){1+B(.lambda..sub.2)+A(.lambda..sub.2)/V.sub.d} (10) 
EQU (n.sub.w /R).multidot.(S.sub.w3 +R)=1+(n.sub.d 
-1){1+B(.lambda..sub.3)+A(.lambda..sub.3)/V.sub.d} (11) 
There are three kinds of unknown values as mentioned above, and there are 
three equations. Accordingly, the refractive index n.sub.d of material in 
D-lines in the air is obtained by solving the simultaneous equations 
according to Eqs. (9), (10), and (11). Accordingly, if a calculation value 
of this refractive index n.sub.d is used as the refractive index n of the 
material in Eq. (4), it is possible to, according to Eq. (4), obtain the 
refractive power S.sub.o of the lens 13 in the air, in other words, obtain 
a power distribution which is an optical characteristic value at each 
position on the surface of the lens 13. 
The processing circuit 15 includes a means for obtaining an optical 
characteristic of the lens 13 in the medium as to each wavelength from a 
quantity of deviation of measuring light P detected by the light receiving 
portion 3, a refractive index calculating means for calculating a 
refractive index of material of the lens 13 as to each wavelength, and a 
means for, according to a refractive index obtained by the refractive 
index calculating means, converting the optical characteristic in the 
medium into an optical characteristic of the lens 13 in the air. 
According to Herzberger's dispersion formula, in the case of general 
optical glass, the constants A(.lambda.) and B(.lambda.) which are each a 
function of a wavelength are obtained from the following equations. 
EQU A(.lambda.)=-1.294878+0.088927.lambda..sup.2 +0.37349/(.lambda..sup.2 
-0.035)+0.005799/(.lambda..sup.2 -0.035).sup.2 
EQU B(.lambda.)=0.001255-0.007058.lambda..sup.2 +0.00107/(.lambda..sup.2 
-0.035)+0.0002180/(.lambda..sup.2 -0.035).sup.2 
If the lens 13 to be inspected is a soft contact lens, resin is used as 
material. Additionally, if these values are impossible to apply, 
experimental data about each material of the lens 13 is obtained, values 
in the equations of A(.lambda.) and B(.lambda.) are then recalculated, and 
the results are beforehand stored in a storing means, because the soft 
contact lens is limited in material. 
Modification 1 
FIG. 3 shows a modification of the light source portion 1. In this 
modification, the light source portion 1 is made up of a light emitter 16, 
a collimation lens 9, and three filters 17, 18, and 19. As shown in FIG. 
4, the filters 17, 18, and 19 are attached to a rotary plate 20. The 
filters 17, 18, and 19 are inserted into the measuring optical path or are 
removed therefrom by turning the rotary plate 20 on an axis 0.sub.2. The 
filter 17 allows red measuring light P to pass through, the filter 18 
allows green measuring light P to pass through, and the filter 19 allows 
blue measuring light P to pass through. The rotation of the rotary plate 
20 makes it possible to successively obtain optical characteristic values 
in a medium in each wavelength. 
Modification 2 
FIG. 5(a) shows a modification of the light receiving portion 3. If the 
monochromatic light sources 4, 5, and 6 are used as the light source 
portion 1, dichroic prisms 21, 22 may be situated between the TV lens 3a 
and the three light receiving CCD sensors 3b. The dichroic prism 22 has a 
reflection surface 22a which reflects green and blue measuring light while 
allowing red measuring light to pass through. The dichroic prism 21 has a 
reflection surface 21a which reflects the blue measuring light while 
allowing the green measuring light to pass through. If the light receiving 
portion 3 comprises the so-called three-plate type light receiving CCD 
sensor 3b, the monochromatic light sources 4, 5, 6 are simultaneously 
turned on to emit light, and thereby measurement values about the lens 13 
to be inspected in the air are obtained. 
FIG. 5(b) shows another modification of the light receiving portion 3. If 
the monochromatic light sources 4, 5, and 6 are used as the light source 
portion 1 and if the light receiving portion 3 comprises the so-called 
monoplate type light receiving CCD sensor provided with a filter 3' that 
consists of R, G, and B in front of each pixel of the light receiving CCD 
sensor 3b, the resolving power in measurement is lowered to one third. 
However, measurement values about the lens 13 to be inspected in the air 
can be obtained by turning on the monochromatic light sources 4, 5, and 6 
simultaneously to emit light, as in the modification of FIG. 5(a). 
Additionally, the size of the lens meter can be diminished. Of course, the 
arrangement of R, G, and B of the filter 3' is not limited to this 
modification. 
Modification 3 
FIG. 6 shows a modification in which a net pattern plate 23 serving as a 
splitting optical member is disposed in place of the microlens array 10 so 
that a net pattern is projected onto the lens 13 to be inspected. As shown 
in FIG. 7, the net pattern plate 23 has plenty of slits 23a arranged 
vertically and horizontally. Areas excluding the slits 23a of the net 
pattern plate 23 intercept light. A beam of measuring light P passes 
through the slits 23a and is split into many rays. These rays are guided 
to the lens 13. The measuring light P' of the net pattern is projected 
onto the lens 13. When passing through the lens 13, the net-patterned 
measuring light P' is deflected because of the optical characteristic of 
the lens 13. When the lens 13 is out of the measuring optical path, the 
same pattern as the pattern of the net pattern plate 23 is formed on the 
light receiving CCD sensor 3b. When the lens 13 with a convex spherical 
power is in the measuring optical path, a net pattern 24 similar to but 
smaller in size than the pattern of the net pattern plate 23 is formed 
thereon, as shown in FIG. 8(a). When the lens 13 with a concave spherical 
power is in the measuring optical path, a net pattern 24 similar to but 
larger in size than the pattern of the net pattern plate 23 is formed 
thereon, as shown in FIG. 8(b). According to a variation in pattern size 
of the net pattern 24, the power distribution of the lens 13 is obtained. 
The net pattern plate 23 may be situated between the lens 13 and the light 
receiving portion 3. 
Modification 4 
FIG. 9 shows a modification of the measuring vessel 11. In this 
modification, a lens setting surface 11d is formed corresponding to the 
shape of the lens 13. For measurement, the lens 13 is set upside down. 
Modification 5 
FIG. 10 shows a modification in which the measuring vessel 11 is usable 
both as a measuring vessel and as a preserving vessel. The measuring 
vessel 11 is made up of a vessel body 11A and a lid member 11B. A screw 
portion 11e is formed on the outer circumference of the upper part of the 
vessel body 11A. A screw portion 11f for engagement with the screw portion 
11e is formed on the inner circumference of the lid member 11B. The lid 
member 11B is made from transparent material. The lid member 11B has air 
holes 11g through which bubbles of a preserving liquid 12 are discharged. 
According to this modification, the measuring vessel 11 also serves as a 
preserving vessel. 
Modification 6 
In the aforementioned embodiment, the optical characteristic of the lens 13 
in a medium is measured by the use of measuring light P with three 
different wavelengths. However, for the measurement, use may be made of 
measuring light P with two different wavelengths, instead of the measuring 
light P with three different wavelengths. In this modification, it is 
impossible to directly obtain the refractive index, Abbe number, and the 
like of the material of the lens 13, but it is possible to obtain the 
difference between the refractive Powers of the two different wavelengths 
in a medium. Referring to the type of a contact lens, a quick judgment can 
be formed as to whether the lens 13 is a soft contact lens or a hard 
contact lens. Additionally, since the soft contact lens is limited in 
material, the material of the lens 13 is presumable from the difference 
between the refractive powers of the two different wavelengths in the 
medium. Therefore, by storing the refractive index of the material of the 
lens 13 beforehand, the refractive power of the lens 13 in the medium is 
convertible to that in the air regardless of the fact that the refractive 
index of the material of the lens 13 cannot be found directly. Therefore, 
the processing circuit 15 is required to include a material presuming 
means for presuming the material of the lens 13 from a difference in 
optical characteristic of the lens in a medium about each wavelength, a 
refractive index storing means for storing the refractive index of the 
lens material, a converting means for converting an optical characteristic 
of the lens 13 in the medium into that in the air on the basis of the 
refractive index of the material presumed by the material presuming means.