Note: Descriptions are shown in the official language in which they were submitted.
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ILLUMINATOR FOR OPTICAL INSPECTION SYSTEM
Field of iinvention
The present invention relates to the field of illumination devices, and more
particularly to illuminators for use with optical systems such as microscopes
or
microscopic imaging systems for inspecting samples, in the form of droplets
containing biological structures such as protein crystal or cellular
materials.
Background of invention
In the past decades, optical inspection technologies have been widely used in
many industrial and scientific applications, by which visual characteristics
of samples
may be studied while being revealed through proper illumination. In the
pharmaceutical and medical fields, such optical inspection systems are used to
monitor the evolution of crystal growth experiments over time to select only
the
samples presenting successful crystallization results, which samples are
subsequently characterized using x-ray diffraction analysis. Such a crystal
monitoring system is disclosed in U.S. Patent No. 6,529,612 B1 issued on March
4,
2003 to Gester et al, and in IJ.S. Published Patent application no.
2003!0099382 A1
dated May 29, 2003 to Ganz et al., and in Published International PCT
Application
no. W001109595 A1 to Stewart et al.
Referring to Fig. 1, the technique generally used to grow protein crystals is
called vapour diffusion, according to which a small volume of protein sample
is added
to a corresponding volume of a crystallization solution to form a drop of
liquid 30 that
is deposited onto a receiving surface 32 of a well cover 34. The well 36 is
conveniently supported on a tray knot shown) designed to support a plurality
of
identical wells, each being used as a holder for a specific sample such as
drop 30.
Each well 36 also includes a reservoir 38 for receiving a predetermined volume
of
crystallization solution as indicated at 40, to provide chemical exchange with
sample
drop 30 through vapour diffusion phenomena as indicated by arrows 42. In
practice,
the drop 30 is deposited onto the bottom side of the welt cover 34 when the
latter is
disposed upside down, the latter being then put in the position shown in Fig.
1 so
that drop 30 adheres to receiving surface 32 through capillarity forces. A
further drop
31 containing a smaller volume of liquid is represented in dotted line, which
smaller
drop 31 exhibits different optical characteristics upon illumination as will
be explained
later in detail. It can be seen that respective shapes of drops 30, 31 are
different due
to the distinct volume of liquid forming each of drops 30,31, which takes
different
shapes under opposing gravity and capillarity forces. Different optical
characteristics
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may also be found between drops of similar volumes, but exhibiting different
convexity profiles due to various levels of spreading onto the receiving
surface 32.
The well cover 34 and reservoir 38 are both made of an appropriate transparent
material such as glass or plastic allowing light rays generated by illuminator
44 to
pass there through and be received by a camera objective 46 characterized by
field
of view 48 which is part of an optical inspection system. The camera objective
46
may be selected according to its magnification power and resolution, depending
upon
the dimensions of samples as well as of structures contained therein and to be
analyzed. For example, macroscopic or microscopic images may be selectively
obtained using two cameras provided with respective objectives having the
required
optical features, which cameras may be conveniently mounted on a same
inspection
station provided with two illuminators based on the concept of invention. For
the
purpose of illustration, the ,scale used to represent the well 36 is voluntary
enlarged
with respect to the scale used to present illuminator 44 and objective 46, and
is
therefore not representative of the actual size of a typical sample with
respect to the
elements of the optical inspection system. According to a first known
illumination
technique as shown in Fig. 1, the illuminator 44 includes a linear
illumination source
powered by an electrical supply 51, such as neon tube 50, onto which a
diffusion
plate 52 is disposed to generate fight rays represented at 54 which are
transmitted
through the well reservoir 38, drop 30 and well cover 34 to reach camera
objective
46, whereby an image of drop 30 is captured by the camera. It can be seen that
the
directions of light rays 54 are distributed over a wide angular range from 8 _
-90° to
B = +90° as indicated by curved arrows 56. As a result of such uniform,
diffused
illumination, a given point of drop 30 within the inspecting area defined by
the
receiving surfiace 32 and positioned at an inspection plan represented by axis
35,
receives transmitted light rays according to a similar light direction
distribution as
shown in the graph of Fig. 2 representing light intensity as a function of
light direction
angle within the -90° - +90° range. It is to be understood that
even if a single plane of
illumination is represented in Fig. 1, a symmetrical distribution of
illumination planes
defined through revolution about optical axis 41 is actually involved, and a
distribution
of light intensity profile curves similar to curve 58 may be associated with
such
distribution of illumination planes. It can be seen from the intensity curve
58 of Fig.
2, that light intensity raises from a null value at ~ --. -90° to a
maximum intensity at
about 8 = -62° ; which maximum intensity is substantially maintained at
that
maximum level at tight direction between ~ _ -62° to By = +62° ,
for then dropping to
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null value from B = +62° to B = +90°. Such diffused illumination
characterized by
substantially uniform intensity profile with respect to light direction of
incidence may
prove to be appropriate for certain types of samples, while being
inappropriate for
others as will now be explained with respect to Figs. 3a and 3b. In Fig. 3a,
larger
drop 30 as referred to above, is represented in the form of an image delimited
within
the field of view 48 or camera objective 46 shown in Fig. 1. It can be seen
that the
border area 33 of large drop 30 is distinctively visible using the illuminator
44 of Fig.
1, as well as protein crystals 60, 62. However, the contrast obtained through
such
substantially diffused illumination is not sufficient to reveal the presence
of a further
protein crystal 64 characterized by different light transmitting properties.
Furthermore,
turning now to Fig. 3b presenting an image obtained using the same illuminator
44
as referred to above, the latter has been used to direct light rays toward a
smaller
drop 31 as described above with respect to Fig. 1, it can be seen that while
protein
crystals 67, 68 may be rendered visible, neither border area 39 of smaller
drop 31
nor a further protein crystal 69 shows a sufficient contrast to be
distinctively located
in the image as represented by dotted lines.
Turning now to Fiig. 4, another prior art illuminating device uses a bundle of
optical fibers 70 having an illuminating output end 72 being disposed behind
the focal
plane 74 of a light refracting element such as Fresnel lens 76, so that light
rays 78
coming from illumination output 72 are redirected as refracted rays 78' at the
other
side of lens 76 toward an image converging point 80 located beyond the object
inspecting plane represented by axis, 35 so as to illuminate either large drop
30 or
small drop 31 according to typical illumination profile as represented by the
graph of
Fig. 5. It can be seen that the shown intensity curve 82 is characterized by a
peak
maximum intensity centered at 8 = 0°, at both sides of which the light
intensity
decreases from ~ = 0° toward B = -90° passing at a null value at
about 8 = -53° ,
and from B = 0° toward ~ _ +90° passing through null intensity
at about 8 = +53° .
Turning now to Figs. 6a and 6b representing images obtained using such
convergent
illumination technique for the inspection of larger drop 30 and smaller drop
31,
respectively, while crystal 67 contained in drop 31 is clearly distinct as
well as
crystals 68, 69 as opposed to the image of Fig. 3b where same crystal 69 is
not
visible, the image of large drop 30 as shown in hiig. 6a is characterized by
an
excessive level of contrast whereby crystal 60 is masked by the dark shadow
near
drop border area 33, even if crystals 62, 64 are rendered clearly distinct in
the center
area of drop 30 .
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Turning now to Fig. 7, there is illustrated a variant of the illumination
arrangement of Fig. 4, wherein a diffusing plate 84 of a same type as plate 52
used
in the illumination arrangement of Fig. 1, is disposed between Fresnei lens 76
and
well 36 in order to obtain a flattened intensity profile curve 86 as shown in
the graph
of Fig. 8 when compared with narrow intensity amplitude curve 82 shown in the
graph of Fig. 5 as obtained with the illumination arrangement of Fig. 4. An
illuminator
based on a similar approach is disclosed in U.S. F~atent no. 5,051,872 issued
on
September 24, 1991 to Anderson. Referring to Fig. 9b, it can be seen that a
sufficiently contrasted image of small drop 31 is obtained using such more
diffused
illumination, whereby all crystals 67, 68 are well defined. While crystal 69
is made
visible, the contrast exhibited by the image of Fig. 3b might not be
sufficient to
provide accurate localization and characterization of crystal 69. However,
turning to
the image of larger drop 30 as shown in Fig. 9a, it can be seen that crystal
60 is still
masked in a shadow area near border 33, which may affect image analysis even
if
crystals 62, 64 are clearly distinct. Therefore, while presenting an
improvement over
the basic, convergent illumination arrangement of Fig. 4, illumination
efficiency of the
arrangement depicted in Fig. 7 which combines FrE~snel lens 76 and diffusing
plate
84 mainly depends upon an appropriate selection of diffusion capacity value
characterizing the diffusing element used, which might not be appropriate to
provide
an optimal contrast for most samples inspected.
Turning now to Fig. 10, an alternate known location for the light diffusing
element 88 consists of placing it near or in contact with the light
illumination output
end 72 of optical fiber bundle 70 so as to obtain an illumination profile
curve 90 as
presented in the graph of Fig. 11 characterized by a significant light
intensity
distribution from 8 = ~70° to 8 = +70°, which exhibits a higher
peak intensity level
near B = 0° as compared with curve 86 shown in Fig. 8 obtained with the
illumination
arrangement of Fig. 7, the former peak being nevertheless lower as compared to
curve 82 shown in Fig. 5 obtained with the illuminating arrangement of Fig. 4.
Turning
now to Fig. 12b, it can be seen that crystal 69 contained in small drop 31 is
clearly
distinct as opposed to the image of the same crystal shown in Fig. 9b due to
the
enhanced contrast provided by the illumination arrangement of Fig. 10. While
crystals 67, 68 are still distinct in the image of smaller drop 31 shown in
Fig. 12b, it
can be seen from Fig.12a that even if the contrast level is reduced as
compared with
the image of the same larger drop 30 shown in Fig. 6a as obtained with the
basic
conversion illumination arrangement of Fig. 4, the contrast level
characterizing
border area 33 of drop 30 still further masks crystal 60, which is also the
case with
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the image of the same crystal shown in Fig. 9a as obtained with the
illumination
arrangement using diffusing plate as shown in Fig. 7.
Referring now to Fig. 13, ahother prior art illumination approach consists of
affixing upon the illuminated side of Fresnel lens 7fi a diffusing layer 92 to
provide a
5 flattened intensify profile curve 94 as shown in Fig. 14, which exhibits a
certain level
of contrast as compared with the profile obtained using the basin illuminator
44
described before with respect to Fig. 1, which profile is represented at 96 in
dotted
line on the graph of Fig. 14. Referring to Fig. 15a, it can be seen that the
image of
large drop 30 is not too contrasted, therefore allowing proper localization
and
analysis of crystal 60 while being sufficient to distinctly view crystals 62,
64 .
However, turning to Fig. 15b, the image of the small drop 31 does not exhibit
sufficient contrast to provide proper localization of crystal 69 even if
crystals 67, 68
as well as border of drop 31 are clearly distinct.
From the foregoing examples of prior art illumination arrangements, it can be
concluded that there is still a need for an improved illuminator that present
the
required flexibility to adjust illumination characteristics and therefore
controlling
contrast of the image of samples subjected to such illumination.
Summary of invention
It is a main object of the present invention 'to provide an illuminator for
use
with an optical system for inspecting a sample, which provides improved
control over
the illumination characteristics depending upon the optical behavior of the
samples
subjected to illumination.
According to the above main object, from a broad aspect of the present
invention there is provided an illuminator for use with an optical system for
inspecting
a sample received on a sample holder defining an inspection area. The
illuminator
comprises a light source, a light refracting optical element disposed between
the fight
source and the inspection area within about a focal length therefrom, and a
light
diffusing optical element disposed between the light source and the light
refracting
optical element. The illuminator further comprises an adjustment device
mechanically
coupled to one of said light diffusing optical element and said light
refracting optical
element and operable for varying the optical distance between the light
diffusing
optical element and the light refracting optical element to modulate
deflection effect
thereof on diffused light generated by the light diffusing element so as to
control
relative levels of resulting substantially diffused light and substantially
direct light
beamed by the light retracting optical element onto the sample.
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According to the above main object of the present invention, from a further
broad aspect, there is provided a method for illuminating a sample to be
optically
inspected and disposed within an inspection area. "fhe method comprises the
steps
of: i) providing a fight source; ii) disposing a light refracting optical
element between
the light source and the inspection area within about a focal length
therefrom;
disposing a light diffusing optical element between the light source and the
light
refracting optical element; and varying the optical distance between the light
diffusing
optical element and the light refracting optical element to modulate
deflecting effect
thereof on diffused light generated by the light diffusing element so as to
control
relative levels of resulting substantially diffused fight and substantially
direct light
beamed by the light refracting optical element onto the sample.
Brief description of the drawings
Fig. 1 is a schematic view of a basic illuminator using a diffusion plate with
a
conventional light source;
Fig. 2 is a graph showing a typical intensity profile curve as a function of
light
direction angle, as obtained using the basic illuminator of Fig. 1;
Figs. 3a and 3b show image representations of samples illuminated with the
basic arrangement of Fig. 1, respectively involving a large drop of liquid
sample and
a smaller drop of liquid sample, both containing protein crystals to be
inspected;
Fig. 4 is a schematic view of another prior art illumination arrangement
involving the use of a refracting element for converging light rays toward the
inspected sample, with an optical fiber bundle illumination source;
Fig. 5 is a graph showing a typical intensity profile curve obtained with the
prior art illumination arrangement of Fig. 4;
Figs. 6a and 6b show image representations of samples illuminated with the
basic arrangement of Fig. 4, respectively involving the large and small drops
of liquid
referred to above;
Fig. 7 is a schematic view of a further prior art illumination arrangement
using
a diffusion plate disposed between the refracting element and the sample;
Fig. 8 is a graph showing a typical intensity profile curve as obtained using
the illumination arrangement of Fig. 7;
Figs. 9a and 9b show image representations of samples illuminated with the
basic
arrangement of Fig. 7, respectively involving the large and small drops of
liquid
referred to above;
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Fig. 10 is a schematic view of a still further prior art illumination
arrangement
using a refracting element and a diffusing element juxtaposed to the optical
fiber
bundle illumination source;
Fig. 11 is a graph showing a typical intensity profile curve as obtained with
the illumination arrangement of Fig. 10;
Figs. 12a and 12b show image representations of samples illuminated with
the basic arrangement of Fig. 10, respectively involving the large and small
drops of
liquid referred to above;
Fig. 13 is a schematic view of a still further prior art illumination
arrangement
wherein the refracting element is provided with a diffusion layer opposed to
its
illuminated side;
Fig. 14 is a graph showing a typical flattened intensity profile curve as
obtained with the illumination arrangement of Fig. 13;
Figs. 15a and 15b show image representation of samples illuminated with the
basic arrangement of Fiig. 13, respectively involving the large and small
drops of
liquid referred to above;
Fig. 16 is a detailed elevation view of a sample inspection system integrating
an illuminator according to the invention, showing the diffusion plate and
optical fiber
source assembly in a first position when used in a light divergent mode;
Fig. 17 is a three dimensional further detailed view of the illuminator shown
in
Fig. 16;
Fig. 18 is an elevation view of the sample inspection system of Fig. 16,
wherein the diffusion plate and optical fiber source assembly have been
displaced to
a position distal from the refracting element, when the illuminator is used in
a light
convergent mode; and
Fig. 19 is a schematic view of the illuminator as set in the position of Fig.
18
when used in the light convergent mode;
Fig. 20 is a graph showing a typical intensity profile curve as obtained with
the illuminator as set in the position of Fig. 18 when used in the lighfi
convergent
mode, as compared with the substantially uniform profile curve obtained with
the
prior art illumination arrangement of Fiig. 1;
Figs. 21a and 22h show image representations of samples illuminated with
the illuminator as set in the position of Fig. 20, respectively involving the
large and
small drops of liquid referred to above;
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Fig. 22 is an elevation view of the sample inspection system of Fig. 16,
wherein the diffusion plate and optical fiber source assembly of the
illuminator are
further displaced to a second, intermediary position in the light divergent
mode;
Fig. 23 is a schematic view of the illuminator as set in the position of Fig.
22
when used in the light divergent mode; Fig. 24 is a graph showing a typical
intensity
profile curve as obtained with the illuminator as set in the position of Fig.
23 when
used in the light divergent mode, as compared with the substantially uniform
profile
curve obtained with the prior art illumination arrangement of Fig. 1;and
Figs. 25a and 25b show image representations of samples illuminated with
the basic arrangement of Fig. 23, respectively involving with the illuminator
as set in
the position of Fig. 20, respectively involving the large and small drops of
liquid
referred to above.
Detailed description of the preferred ernbodimenit
Referring now to Fig. 16, a sample optic>al inspecting system generally
designated at 100 is shown, which integrates an illuminator according to a
preferred
embodiment of the invention as generally designated at 102, which system 100
is
adapted to the monitoring of protein crystallization experiments carried out
employing
a plurality of samples supported on a tray 104 that is positioned within the
field of
view 106 of an optical objective 108 that is provided on a digital CCD camera
110.
The tray 104 is handled by a gripping tool 112 provided at the working end 114
of a
robot arm 113 as part as a robotic tray handling system (not shown). There is
provided a frame plate 116 for supporting camera 110 through holder 118, and
under
which is attached a holding block 119 for supporting the illuminator 102 that
will now
be described in detail with reference to . Fig. 17. The illuminator 102
includes a
position adjustment device generally designated at 120 formed by a main
flanged
mounting block 122 to which is secured through bolts 124 a L-shaped holder 126
defining a grooved U-shaped opening 128 adapted to receive a diffusing optical
element in the form of a diffusing plate 130 whose transverse position may be
adjusted by sliding along the groove 132. The diffusing plate 130 is
preferably of an
opalescent type to provide substantially uniform light diffusion without
preferential
direction, such as 50mm x 62.5mm opal diffusing glass model H43-043 supplied
by
Edmund Industrial Optics (Barringtion,NJ). Traversing the main mounting block
122
is a vertically extending bore adapted to receive the upper end portion of a
first
vertically extending shaft 132 allowing vertical position adjustment of
mounting block
122. The lowermost end of shaft 132 engages a corresponding bore provided on a
fixed mounting member 134 firmly secured through bolts 136 to a vertical
supporting
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plate 138. Vertically extending through fixed mounting block 134 is a thin
opening
140 communicating with the cavity defined by bore 142. The block 134 is also
provided with a. transverse threaded bore adapted to receive a set screw 143
allowing insertion of the lower end of shaft 132 within fixed mounting block
134 and
firm securing thereto. In a same way, the uppermost end of shaft 132 is
secured to
the uppermost portion of supporting plate 138 using a similar fixed mounting
block
134' as better shown in Fig. 16. Also secured to main mounting block 122 is a
second vertically extending shaft 144 for supporting a vertically adjustable
mounting
member 146 having a bore vertically extending there through adapted to engage
with
shaft 144 and be selectively raised or lowered at a desired position using set
screw
148. Bearing on a shouldered front portion 150 of mounting member 146 is a
further
mounting member 152 provided with a vertically extending bore adapted to
receive
an optical fiber bundle 154 used as a light source when connected to a proper
illumination device such ~s a high intensity incandescent or halogen light
source. For
example, a 150 W light source such as model DCR III using EKE lamp no. A20800
and optical fibers bundle no. A8031.40R from Schott-Fostec (Auburn, NY) can be
used. The position of illuminating end 156 of optical fibres bundle 154 with
respect to
the diffusing plate 130 is rendered adjustable by operation of set screw 158
allowing
to selectively tighten or loosen the front portion of mounting member 152
against
fibre bundle 154. In a similar manner, the main mounting block 122 is made
displaceable with respect to shaft 132 using set screws 160 shown in Fig. 16
which
can be selectively tighten or loosen on the main mounting block 122, to allow
the
position adjustment device 120 to be vertically displaced with respect to
shaft 132 to
a desired illumination position. Also secured to mounting plate 138 is a
refracting
optical element holding assembly formed by pairs of walls 162, 162' secured to
the
edge of plate 138 through bolts 163, and by front transverse wall 164 secured
to
walls 162, 162' by bolts 166. Walls 162, 162' are each provided with an inner
groove
168 for receiving the lateral edged of fresnel lens 110 used as refracting
optical
element. It is to be understood that one or more fresnel lenses can be used to
form
light refracting element 170, as well as any other appropriate standard
condensing
lens. A 6 inch, fresnel lens assembly such as model H32-594 supplied by Edmund
Industrial Optics (Barringtion,NJ) may be used. It can be seen that walls 162,
162'
and 164 as shown in Fig. 17 are not illustrated in the elevation view of Fig.
16 to
better show relative position of the diffusing plate holder 126 and fresnel
lens 170
which are separated by an optical distance d=df in Fig. 16 and as will be
later
explained in more detail. The illuminator 102 itself is made vertically
adjustable with
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respect to the frame plate 116 using a pair of further mounting blocks 172,
172'
secured to mounting plate 138 and receiving respective shafts 174, 174'
against
which blocks 172, 172' can be selectively tightened or loosened using set
screws
175. Secured at the lower most end of shaft 174, 174' is a stopping block 176
5 defining the lower most position of blocks 172, 172'. It can be appreciated
from Fig.
16 in view of the prior art illumination arrangement of Fig. 13 that the
relative position
between diffusing plate holder 126 supporting the diffusing element 130, and
fresnel
lens 170 is somewhat similar to the relative position of corresponding
elements
shown in Fig. 13, so that similar images of large and small drops of liquid,
as
10 represented in Figs. 15a and 15b respectively, or any other samples for
which
variations of three-dimensional shapes affect their optical behaviour when
subjected
to illumination, may be obtained using the illuminator setting shown in Fig.
16
according to a divergent mode of illumination. However, the setting of an
illuminator
according to the invention may be adjusted so as to control relative levels of
diffused
light and direct light beamed by the refracting optical element 170 for
obtaining the
desired image contrast adapted to the sample under inspection.
Referring now to Fig. 18, it can be seen that the position adjustment device
120 is set at a lower position as compared to the illumination setting of Fig.
16 in
such a manner that the distance between the holder 126 supporting the light
diffusing
optical element 130, and the light refraction optical element 170 is set at a
larger
value d=d2 as compared to set distance d, shown in Fig. 16.
Turning now to Fig. 19, the schematic optical representation of the
illuminator
setting of Fig. 18 is shown. Since the light diffusing optical element 130 is
disposed
in front of focal plan axis 178, the illuminator works according to a
convergent
illumination mode as opposed to the divergent illumination mode obtained with
the
setting shown in Fig. 16.
Turning now to Fig. 20, it can be seen that the intensity profile curve 180
obtained using the optical configuration shown in Fig. 19 exhibits more
contrast as
compared with the basic flattened intensity profile characterizing prior art
illuminator
described above with reference to Fig. 1 and as indicated by curve 96 in
dotted line.
Turning now to Fig. 21b representing an image of small drop of liquid 31
inspected using the illumination setting of Figs. 18 and 19, all protein
crystals 67, 68
and 69 are made clearly distinct. However, turning to Fig. 21a representing an
image
of large drop of liquid 30, it can be seen that the resulting contrast is to
high so that
the dark shaded border area 33 of drop 30 adversely masks protein crystal 60
even if
crystals 62, 64 are still distinct.
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Turning now to Fig. 22, the position adjustrr~ent device 120 of illuminator
102
is shown in an intermediate position as compared to the settings of Figs. 16
and 18
so that holder 126 supporting the light diffusing element 130, and light
refracting
element 170 are now separated by a distance d=d3 , wherein d, < d3 < d2 .
Turning now to Fig. 23 showing a schematic optical diagram of such
illuminator setting, it can be seen that the light diffusing element 130 is
positioned
behind focal plane axis 178 of light refracting element 170, implying that the
illuminator is used according to a divergent illumination mode to produce an
intensity
profile such as shown by curve 182 of Fig. 24, which is characterized by a
reduced
level of contrast as compared with the contrast level obtained with the
setting of Figs.
18 and 19 as shown by curve 180 of Fig. 20, but still presenting an enhanced
contrast when compared with the flattened profile 96 as obtained with the
basic prior
art illumination device of Fig. 1:
Turning now to Fig. 25a showing an image of a large drop of liquid 30 that
can be obtained using the illuminator setting of Figs. 22 and 23, it can be
appreciated that an optimal contrast level is achieved permitting accurate
localization
of all crystals 62, 64 and 60 as well as of crystals 87, 68 and 69 contained
in small
drop of liquid 31 in the image shown in Fig. 21b obtained with the same
illumination
setting. Therefore, the illuminator setting of Figs. 22 and 23 provides
optimal relative
levels of resulting substantially diffused light rays such as 184 from
incident rays 184'
in Fig. 23 and substantially direct light rays such as 186 from incident rays
186', as
beamed by the refracting optical element 170 onto sample 30 or 31.
In operation, for a given tray of sample wells representative of various
optical
characteristics that may be observed in the context of the specific
experiments that
have to be carried out, the user proceeds with an initial calibration of the
illuminator
by displacing the position adjustment device 120 as shown in Fig. 16 until the
position providing optimal contrast for most of representative samples is
reached.
Such procedure may be repeated for any new series of experiments involving
samples presenting a different optical behaviour under illumination. A further
setting
that can be made during the calibration phase consists of adjusting the
distance
between the illumination end 156 of optical fibre light source 154 and the
diffusing
element 130 disposed on holder 126, as designated as I=I, in Fig. 16 to adjust
the
density of light directed onto the light diffusing element 130 while varying
the
illuminated area thereof. For example, when the illumination end 156 is
brought in a
proximal position as shown in dotted lines in Fig. 22 where I=12, a same
luminous
energy is distributed over a reduced area designated at 188 as compared with
the
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larger area 190 of the bottom surface of diffusing element 130. It can be also
appreciated that the position adjustment device 120 is mechanically coupled to
fibre
bundle light source 154 through mounting members 146, 152 to provide
simultaneous and equal corresponding variation of the distance s between
illumination end 156 and light refracting optical element 170 when the device
120 is
operated to vary the distance d between the diffusing plate 130 and the
fresnel lens
170, so that s=s3 =h+d3 in the position shown in Fig. 22, s=s~ =h,+d, in the
position
shown in Fig. 16 and s=s2 =I,+d2 in the position shown in Fig. 18. It should
be noted
that either in a convergent or divergent illumination mode, the contrast is
enhanced
when the diffusing element and optical fibre source assembly are displaced
away
from the focal plane axis of the refracting element, whereas the contrast is
reduced
when the illumination end of optical fibre source is moved away from the
diffusing
element.
It is to be understood that the illuminator and illumination method according
to
the present invention may be employed either in combination with a light
transmission-based inspection system such as described above in the context of
the
preferred embodiment, or with a reflection-based inspection system, provided
the
relative positions of the sample, illuminator and inspection camera are set
accordingly. Furthermore, the inspection system may be a standard microscope,
and
therefore need not be necessarily provided with a camera.
