CA2452403A1 - Illuminator for optical inspection system - Google Patents

Abstract

An illuminator for use with an optical system for inspecting samples such as experimentally grown proteins includes a light source, a light refracting optical element such as fresnel lens, and an opalescent light diffusing plate disposed between the light source and the fresnel lens. An adjustment device mechanically coupled to the light diffusing plate is operable for varying the optical distance between the light diffusing plate and the light refracting optical element to modulate deflection effect thereof on diffused fight generated by the light diffusing plate so as to control relative levels of resulting diffused light and direct light beamed by the fresnel lens onto the sample.

Description

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 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 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 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 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 .

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 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 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.

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;

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.

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;

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.

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 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 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 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.

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.

Turning now to Fig. 22, the position adjustrr~ent device 120 of illuminator 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 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.

Claims (11)

1. An illuminator for use with an optical system for inspecting a sample received on a sample holder defining an inspection area, comprising:
a light source;
a light refracting optical element disposed between said light source and said inspection area within about a focal length therefrom;
a light diffusing optical element disposed between said fight source and said light refracting optical element;
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 said light diffusing optical element and said fight refracting optical element to modulate deflection effect thereof on diffused light generated by said light diffusing element so as to control relative levels of resulting substantially diffused light and substantially direct light beamed by said light refracting optical element onto said sample.

2. An illuminator according to claim 1, wherein said adjustment device is mechanically coupled to said light diffusing optical element.

3. An illuminator according to claim 1, wherein said illuminator further comprises a support frame to which said light refracting optical element, light diffusing optical element and adjustment device are secured.

4. An illuminator according to claim 1, wherein said adjustment device is further mechanically coupled to said light source to provide simultaneous and equal corresponding variation of the optical distance between said light source and said light refracting optical element when said device is operated.

5. An illuminator according to claim 4, wherein said adjustment device includes a mechanism for varying the distance between said light source and said light diffusing optical element to adjust the density of light directed onto said light diffusing optical element.

6. An illuminator according to claim 1, wherein said light diffusing element is an opalescent plate.

7. An illuminator according to claim 1, wherein said light refracting optical element includes at least one fresnel lens.

8. An illuminator according to claim 1, wherein said light source includes an optical fibres bundle having an illuminating end substantially aligned with said light diffusing element.

9. A method for illuminating a sample to be optically inspected and disposed within an inspection area, comprising the steps of:
i) providing a light source;
ii) disposing a light refracting optical element between said light source and said inspection area within about a focal length therefrom;
iii) disposing a light diffusing optical element between said light source and said light refracting optical element; and iv) varying the optical distance between said light diffusing optical element and said light refracting optical element to modulate deflecting effect thereof on diffused tight generated by said light diffusing element so as to control relative levels of resulting substantially diffused light and substantially direct light beamed by said light refracting optical element onto said sample.

10. A method according to claim 9, wherein said light diffusing element is an opalescent plate.

11. A method according to claim 9, wherein said tight condensing element includes at least one fresnel lens.