TRINOCULAR ZOOM STEREO MICROSCOPE. Mod. FORINST XTS O1 1

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1 TRINOCULAR ZOOM STEREO MICROSCOPE Mod. FORINST XTS O1 1 Stereo microscope model XTS O1 is especially recommended for the analysis of graphisms on paper texture. Introduction: Microscopes are instruments that allow the viewing of objects with medium/high magnification. Every microscope is made up essentially of two basic optic units: a lens and an eyepiece. The distance between the eyepiece and the object being observed is invariable in any type of microscope and the object is focused by means of the mechanical adjustment of the optic system being used. The document being examined must be suitably illuminated: from below (transmission illumination) by means of the special illumination systems supplied with the instruments described below; they can also be illuminated laterally or in alignment with the lens (reflection illumination). To increase the magnification, additional lenses can be used or the eyepieces can be substituted with other models that allow greater magnification. 1 REV1.0 [FORINST reserves the right to make changes, technical or other, without notice] 1

2 There are essentially two types of (optic) microscopes: BIOLOGICAL MICROSCOPES and STEREO MICROSCOPES. Biological microscopes have optical systems that achieve extreme magnifications, 20X 1000X and greater. This is why biological microscopes or better for observing microorganisms (cells, fibers, bacteria, which are typically placed on the slides). These microscopes are not suitable for observing opaque or thick bodies. There are monocular biological microscopes (for viewing with one eye only), binoculars (for observing with both eyes) and trinoculars 2. However, the image will not be seen three-dimensionally because there is only one viewing lens. On the contrary stereo microscopes are characterized by a 3D view of what is being observed because they have pairs of lenses and eyepieces that work simultaneously to give a realistic vision of the object being examined. Normally these instruments have magnifications that vary from 10X to 90X but they can reach as much as 180X in the more sophisticated versions (extremely expensive, but necessary in cases where tremendous performances are required). Stereo microscopes are the best for viewing graphisms and paper texture. Why a stereo microscope is the best choice for analyzing graphisms: First and foremost, as mentioned earlier, the stereo microscope is an instrument that allows you to see graphisms in 3D because when observing an exhibit from two slightly different angles, unlike a biological microscope, you obtain the two images needed for stereoscopic vision. Basic notions about stereoscopy Anyone who looks at a computer screen realizes they are looking at images in an unreal scene. This difference occurs because in the three-dimensional world our eyes give us two images that are different from each other. This is possible because our eyes are in two different positions in space, separated from each other by approximately 65 mm, so the brain receives two graphic representations. These are subsequently processed to create one image containing a precise depth perception. When observing physical objects, our vision is stereoscopic because each eye has its own vision of the object. However, when looking at a photograph of the same object, we see an image without any information regarding depth: the image is flat because both eyes are looking at the same information. The principle of three dimensionality Why can humans see objects with three-dimensional vision? Basically, as explained earlier, our eyes are located a short distance from each other and consequently each eye sends the brain a two-dimensional image taken from a point of view that is slightly different from that of the other eye. A simple test is to look at an object very close to you, first with one eye and then with the other: you will macroscopically notice the difference between the images provided by each eye. Though it is the same object, it will be observed from two different vantage points (slightly different perspective angles) and this is the basis of so-called stereoscopic vision. 2 Trinocular microscopes have an additional optical pathwayway to allow image acquisition by means of the camera or digital photo camera) 2

3 How to reproduce reality? To obtain stereo vision, we need to have two images of the same object observed from two different points of view and make sure each eye can see only the image pertaining to it. Subsequently, by analyzing the differences between the two images (by means of the parallax), our brain allows us to perceive the depth of what we are observing. This is why stereo microscopes have two different optical pathwayways. The stereo microscope shows the objects mainly by reflected light and its magnifying power, typically 8X - 50X, is less than that of biological microscopes. In fact with stereo microscopes you cannot see micrometric dimensions 3. Apparently the magnifying factor of the stereo microscope (not very high) may seem like a limitation. On the contrary, the stereo microscope has many advantages (most of which make it unique; at least when used by an expert specialized in the analysis of documents). The main advantages are: a) The stereo microscope operates at a distance from the document to be examined. This is a significant advantage because it allows the operator to easily position the various illuminating systems without touching the exhibits and without needing to fasten the sheets of paper with rigid metal supports that would have disastrous effects on the document itself, i.e. tears or cuts caused by the mechanical parts. b) The stereo microscope is suitable for observing a target that is already visible with the naked eye: a handwritten or typewritten text, an alphanumeric character, initials, a signature, etc. As a result it is extremely user-friendly, even for nonexperts. Quite the opposite, when using a biological microscope you can only see tiny samples that are invisible to the naked eye. Moreover, the small portion of the document to be examined (in order to be focused), must be positioned a few millimeters away from the lens. This requires placing the document on an X-Y table which moves by micrometric increments. Otherwise, the least distraction while sliding the document can cause you to move it a few tenths of a millimeter too far and lose the graphism point being analyzed. c) A strong magnifying power (for analyzing graphisms) is superfluous because an expert graphologist never has to view a single fiber of cellulose in the paper texture. A graphism subjected to such a high magnifying factor entirely loses its meaning. A graphologist specialized in analyzing documents must be able to easily discern: - The level of indentation of the grooves on a manuscript; - The presence of toner microgranules on the sheet to verify whether the document was printed by a laser printer or photocopied and therefore is not a genuine document; - Whether a color printer was used to generate an (apparently) monochromatic document; - Whether the characters have been generated by an inkjet printer or a laser printer (if a laser printer was used, the stereoscopic vision will show the characters in relief ); - Traces of abrasions (suspected forgery of graphisms to alter a date, etc.); - Variations in the hue of the ink pigments, as in the case of a corrections/additions to texts using a different writing instrument on a will, etc. to alter the true content of the pre-existing text) etc. For the sake of completeness, we have provided a concise list of the other types of microscopes on the market. Monocular microscope A microscope having a single optical pathway: the observer looks at the specimen with only one eye. 3 A micrometer corresponds to one thousandth of a millimeter. 3

4 Binocular microscope A microscope having two different optical pathwayways: this allows the observer to use both eyes. Some types of binocular microscopes allow a three-dimensional view of the objects. Ours is this type and it is called a stereoscopic microscope). Trinocular microscope Similar to the binocular microscope, but with the addition of a third optical pathway to allow image acquisition with photo cameras/ cameras, etc. by means of the third mechanical/optical union mentioned above. Inverted microscope A special type of compound microscope, presented around the year 1850, which illuminates the specimen from above and allows you to observe it from below (ergo the name inverted or reversed). Under the specimen is a prism reflecting the beams of the optic tube. Thanks to this device it is possible to observe chemical reactions without allowing the gases or effervescence generated from them to disturb the vision. This is why this type of microscope is also called chemical microscope. It is also suitable for viewing specimens in Petri dishes or flasks for tissue cultures. Light-field microscope In light-field microscopy (by reflected light) the light hits the flat details in the specimen (perpendicular to the optical axis) and is reflected in the lens where it appears light in the image. The contrast is obtained by means of significant variations in terms of absorption and reflection on the planar surface. In other words, the light that hits the nonplanar areas of the surface is deviated and appears dark in the image. This makes it possible to indirectly reconstruct the microstructures of the texture being examined. Specific surface treatments (chemical and mechanical) make it possible to highlight what you want to observe in the analysis (grains, inclusions, etc.). Polarizing microscope This is a compound microscope which casts a beam of polarized light generated by a special prism (see Nicol prism) through the specimen. A second prism, inserted in the eyepiece, serves as an analyzer. These instruments are used for analyzing minerals (crystallography, etc.) to study the crystalline structures. They produce particular images and colorings when polarized light passes through them. Phase contrast microscope The phase contrast microscope exploits the interference between the direct light from the source and the deviated light (diffracted) by the specimen to better highlight the details of the specimen. The ring-shaped device reduces the intensity of the diffused light and at the same time introduces a phase shift of one-fourth of a wavelength between the two parallel incident rays on the specimen. This type of microscope is used (in biology and medicine, etc.) for studying biological tissues. Its main advantage is that it does not require the use of artificial dyes to observe the specimens in vita. Dark-field microscope The dark-field microscope works on the principle of dark-field illumination. This produces the inverse of the image contrast obtained by analysis in a light field. The deviated light is gathered and appears light in the image, while the directly reflected light contributes nothing in forming the image. Even in the case of surfaces having local inclinations, you can obtain a reflection that contributes to the image and produces 4

5 bright spots. As a result, this technique is insensitive in the case of irregular surfaces. However, this kind of microscope makes it possible to observe the color variations of a microstructure which are extremely difficult to discern in the case of light-field analyses. The illumination by reflection on a dark field is obtained by using a ring-shaped mirror that wraps around the path of the light beam in substitution of the semireflecting mirror. Metallographic microscope The metallographic microscope is typically used in the high-precision mechanics industry. This instrument has ultra-high magnifying factors and in the case of opaque objects it cannot view in transparency. On the contrary, metal specimens are observed by reflection. As a result, the optic unit of the microscope does not catch the light traversing the specimen but the light reflected by the specimen. The metallographic microscope shows microstructures that are differentiated mainly by their coloring. The reasons why a stereo microscope having a cantilever stand is better than a regular bench stereo microscope for analyzing graphisms: Stereo microscope with cantilever stand classic stereo bench microscope The ordinary stereo microscope has the advantage of being significantly cheaper than the microscope with a cantilever stand. Normally this economic microscope already has a set of two illuminators (transmitted and reflected light). However, precisely because they are built into the mechanics of the instrument, these illuminators do not allow flexible maneuvering. Moreover the small size of the operating area under the optical unit makes this instrument unsuitable for analyzing a document. Depending on the graphisms to be observed, especially if they are located on the far edges of the exhibit, the sheet must be folded or rotated by 90 or 180. T his problem also occurs when the graphisms are located in the central area of the sheet. On the contrary, these problems do not occur when using a stereo microscope with a cantilever stand. For example it is perfectly possible to inspect an A3 sheet of paper or a thick dossier from which the document to be inspected cannot be removed. Regarding the illumination systems, the stereo microscope with a cantilever stand was conceived deliberately without any accessory of this type to leave the user free to choose the sources of light most appropriate to the needs of the moment. On the following pages we will see a more detailed description of the various illumination systems available. 5

6 The Forinst XTS O1 stereo microscope is made up of the following components: 1. Stand 2. Lenses 3. Micrometric focus knob 4. Macrometric focus knob 5. Ring nut 6. Locking knob 7. Eyepieces 8. Trinocular head Macrometric and micrometric focusing This instrument uses a coaxial mechanism for macrometric and micrometric focusing. Knob 4 adjusts the macrometric focus while knob 3 adjusts the micrometric focus. After inserting the document to be examined on the base of the stand, adjust the macrometric focus knob and then optimize the micrometric focus of the image by using the micrometric adjustment knob. The locking ring nut is for adjusting the friction to prevent the trinocular microscope unit from sinking under its own weight. This prevents an undesired contact between the lenses and the document being examined microscopically. 6

7 Illumination units supplied with the instrument There are various systems for illuminating graphisms, depending on the characteristics of transparency, opacity, reflectance of the inks. In the photograph above, you can see the stereo microscope complete with the illumination set supplied with it: 1) Illuminator having a dichroic spotlight emitting cold light (white) by means of two metal sheaths having semi-rigid adjustable optic fibers; 2) Ring illuminator emitting diffused light (white) in high-frequency fluorescence; 3) Illuminator emitting diffused light (white) by means of a dichroic spotlight with adjustable intensity and orientation; 4) Small raised glass shelf for easy viewing of documents under light transmitted by optic fiber sheaths as shown in the figure. The most frequently used systems are reflection and diffusion. The former uses light from a source of incandescent (or fluorescent) light. On the contrary, when using transmission lighting, the source of light, completely traverses the graphisms and highlights the areas of dark/light transition, as well as areas having a partial or total absence of inking (e.g. in the grooves generated by a rolling ballpoint pen). 7

8 Using the technique of transmitted light, it is easy to recognize text generated by a laser printer as opposed to an inkjet printer. The semi-rigid sheaths also make it possible to illuminate the surface of the paper texture, even in sharp angles (nearly grazing) to highlight the depth of the grooves (or the relief of the toner) or determine the presence of the blind grooves, etc. Obviously, the operator must become familiar with the above-mentioned illuminators in order to autonomously decide which one is most suitable depending on what must be highlighted. In this regard, we suggest you read the specific documentation. Note: if the document being examined does not require a source of transmission light, you need not use the glass platform. OPTIONAL ACCESSORIES Object glasses and lenses crease the magnification factor High sensitivity cameras for IR and UV recording Ring illuminator with a flexible sheath having a polarizing filter and mechanical ring nut to allow the filter to be rotated 360 Solid-state ring illuminator (white LED) Battery-operated solid state IR illuminator Additional lenses to create a considerable distance between the microscope and the document to be analyzed UV fluorescent illuminator Solid-state IR ring illuminator Object micrometer on transparent slide (1 cm divided into 100 parts) 8

9 TECHNICAL PERFORMANCES SPECIFICATIONS OF STEREO MICROSCOPE Mod. FORINST XTS O1 DEPENDING ON AVAILABLE OPTICAL SYSTEMS 4 4 Note: only some optical systems indicated on the table are supplied with the stereo microscope. For additional optical systems, contact Forinst of Turin, to tell us your specific application needs. 9

10 Some examples of graphisms viewed by the stereo microscope and later acquired and digitalized by a digital camera 10

11 FORINST FORENSIC INSTRUMENTS TORINO (ITALY) 11