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Manufacturing technic of a lenticular product
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---- Making a lenticular product requires not only a sound knowledge of optics, of binocular vision, of computing and of the graphic chain, but also stringency in work and substantial precision throughout the manufacturing process. The expertise includes: The design images The effects *Animation Animation is a sequence of images making up the full range of an expressed movement or the gradual transformation of objects (known as morphing) or enlarging and reducing in size by zooming. *3d To really understand the functioning of images in three dimensions, we need first to know how the brain uses images perceived by our two eyes to recalculate depth. If an object is photographed from different angles, the images obtained cannot be superimposed. In the same way, images received by our two eyes are different. The brain interprets these differences to estimate depth. These may be images that represent a panoramic observation suitably organized around a point, thus giving the impression of movement. The result will be that depth is perceived. The sources *Photography *Image synthesis *Illustration The tools Lenticular mastering The word "lenticule" is a synonym of "lens", but may also have the meaning of a leaf of long thin lenses. Pre-printing The printing lenticular The offset press UV: The equipment must be adapted to print on sensitive thermoplastic materials. With, for example, a table margin has a central cord aspirant. Venturi Technology ensures optimal guidance sheets between groups of printing. The press must allow adjustments in steps of 10 µ (Circonférentiel, sideways, through). The steps between the groups printing must allow the location of UV driers interchangeable with drawers. The inking rollers, dampening and blankets must be resistant to UV radiation and detergents. A regular cleaning and washing is necessary. The temperature ink is recommended. The viscosity higher abrasion and UV inks increase the temperature of the ink into the ink. The balance ink / water is less stable than for conventional inks. A cooling tables ensures stability ink for a printing quality consistent throughout the draw, reduced spraying inks and the fouling of the machine. The installation of agitators ink is highly recommended. They prevent solidification of high viscosity inks. The UV inks are very abrasive, so dosing cylinders must be designed to prevent friction and prevent the deterioration of the plastic sheets that protect the inkwell. At the reception, an outing lengthened with plates guide sheet "Venturi" cooled water, stainless gripper bars without shadows and away format and a tinted glass facade of protection filtering UV-light reflective. The heat, ozone and the smell of varnish and ink were evacuated without negative influence on transfer sheets. UV dryers: The Ultraviolets, in the electromagnetic spectrum, are between 100 and 380 nm, whereas the area of visible ranges between 380 and 700 nm. It is therefore necessary to use a lamp specific if we want the ink to dry properly. The UV spectrum is divided into three parts: * UV-C radiation (100-280 Nm): They make it possible to primarily reticulate ink or varnish on the surface and ensure a fast and complete final reaction. * UV-B radiation (280-315 Nm): They are essential to reticulate in-depth film of ink. * UV-A radiation (315-380 Nm): They are the rays closest to the visible light, they ensure the hardening of the layers of in-depth ink. Today, there are different types of UV driers, but generally, dryers lamps containing mercury vapor is the most employees. Indeed, these lamps emit UV radiation in a broad spectrum and provide an optimum drying. The power lamps commonly used is 160-200 Watts / cm. Ink: *The pigments: The choice of pigments in the formulation of UV inks has been difficult in the early years because of the partial absorption of UV radiation in some of them (eg. Titanium dioxide, black and dark pigments). The result is a slow drying of the film and possibly curing a difference between the surface and the interior of the film. In addition, some pigments (particularly blacks and dark) can react with photoamorceurs, which inhibits the process of drying. Since then, photoamorceurs privileged pigmented for products, such as inks, are selected to have a higher efficiency of absorption systems non-pigmentés in the region 330 to 400 nm. In addition, the selection of pigments must take into account their compatibility with the monomers and prepolymers. It should be remembered that the wet resins correctly (what hard resins acrylates) on the one hand, but also that the system is stable. It may indeed be a spontaneous without UV curing during storage, in which case it is necessary to add a stabilizer. Finally pigments gold and silver are very difficult to implement for the sake of causing a spontaneous reaction gelling and / or sensitivity to amines. It is noted in recent years a trend in the performance of materials that allow drying with reflectors "cold" for example (aluminum structure) of dry increasingly dark colors. *The prepolymers: The prepolymers are the equivalent of resins used in inks non-UV. These are molecules that contain insaturations and who are not completely polymerized. With radical mechanisms, prepolymers are used type acrylate / methacrylate or unsaturated polyester resins, while with cationic mechanisms, they are epoxy resins or phénoxides and vinyl ethers. Free radicals from photoamorceurs initiate the reaction of polymerization of monomers and prepolymers. The second phase is the spread of the polymerisation reaction which can gradually increase the size of macromolecules and therefore viscosity, which gradually solidifies the ink film. Reactions termination lead to the absorption of free radical polymer during polymerization. This may involve combining two reactions macromolecules, a macromolecule and photoamorceur, a macromolecule and oxygen in the air to form peroxides, etc.. Peroxides are undesirable because they inhibit the reaction to continue, and they can modify the physicochemical characteristics of the ink film in question. *The monomers: The monomers are sometimes called reactive diluents. They play an equivalent solvent inks quickset: pigment wetting and adjust the rheological properties. In addition, they participate in the polymerization reaction. *The photo-amorceurs: The photo-amorceurs are products which, under the effect of UV radiation, provide reactive species (free radicals or cations) likely to initiate the chain reaction involving prepolymers. Today, 90% of the formulations are based on mechanisms radical and 10% on cationic mechanisms. In EB inks, photo-amorceurs are not necessary. The electrons provide enough energy to initiate polymerization reactions between different prepolymers and monomers or oligomers. Thus, the formula of an EB ink is generally the same as that of a UV ink without photo-amorceurs. *The additives and inhibitors: The additives are added in small quantities to adjust their rheology, increase the stability of the ink or give a particular feature (slippery, and so on.). The inhibitors are needed to avoid a premature gelling system. The products most commonly used are hydroquinones and derivatives. Most waxes used in conventional inks can be used in UV ink: polyethylene, PTFE (polytetrafluoroethylene). There are sometimes silicone to improve the slip leaves on one another. *Diluents: Diluents play several roles: adjustment of rheological properties, solubilization of solid prepolymers, pigment wetting, improve the properties of the final dry film. In EB and UV inks, reactive diluents are, which means they are involved in the polymerization reaction with prepolymers. This allows a formulation with 100% dry matter. This role is filled mainly by monomers containing acrylates functions. They can be classified according to the number of functional groups. Diluents monofonctionnels regardless viscous confer flexibility in the ink film while polyfunctional thinners, very viscous, making especially the reactivity drying. The number of these compounds actually used in the formulation of ink is relatively small because many of them are discarded because of their toxicity, their volatility or their smell. It should be noted that a working group consisting of HSE (Health and Safety Executive-England), BG (Berufsgenossenschaften-Germany) and the CNAMTS (Caisse Nationale d'Assurance Maladie des Travailleurs Salariés) study all aspects related to a correct use of UV printing. They work particularly on the classification of components not yet included in the European directives. Anchorage Water: *The TH (Title Hydrotimétrique), water hardness: The natural water contains, in general, the state dissolved metallic salts such as iron salts and alkaline salts such as calcium salts. These salts can rush, they cause then scaling or settle on drying leaving traces whitish. Calcium is primarily responsible for these problems. It is dissolved in water in the form of bicarbonate, and when the water evaporates in the heat, it is deposited and precipitates in the form of calcium carbonate, more commonly known as "limestone" . Water hardness is directly related to the amount of calcium carbonate contained in a liter of water. It is expressed in milligrams per liter or degrees Hydrotimétriques. One degree equals 10 milligrams of calcium per liter of water. Up to 10 °, the water is very sweet From 10 ° to 20 °, the water is sweet From 20 ° to 30 °, the water is a bit harsh From 30 ° to 35 °, the water is hard Beyond 35 °, the water is very hard *Incidence of water hardness on the mooring: Generally speaking, it will avoid working with water with a degree hydrotimétrique higher than 25. A degree hydrotimétrique higher than 25 can induce changes in pH. Also, when water is hard, there is a phenomenon of "frosting" of inking rollers and blankets. This phenomenon is explained in the following manner: microscopic examination of the surface of a roller or a blanket, shows it is composed of a multitude of pores which makes "love" ink and resistant to water. When the water is hard, alkaline salts, such as limestone, are deposited and clogging the pores. The surface of the roller or blanket becomes gradually "love" of the water and resistant to ink (Effect of Icing). Glaze keeps an inking perfect. *The pH (potential hydrogen): Pure water, the chemical formula is H20, is slightly ionized. H2O < > H + + OH- The compound hydrogen called H + cation and is acidic. The compound OH (a hydrogen atom H and one oxygen atom O) and anion is called basic. In pure water, there are as many as cation anion. They say while the pH of the water is neutral. When the water is pure, the value is equal to 7. The pH are expressed on a scale from 0 for very acidic solutions at 14 for very basic solutions. If one adds to this an acid water, it increases the amount of H + cations, pH then descends to values between 7 and 0. The higher the pH is low, the solution is more acidic. On the contrary, if this pure water we add a base or a product alkaline, it increases the amount of anions OH-, pH increases to values between 7 and 14. The higher the pH, the higher the solution is basic or alkaline. *Effects of pH in offset printing: Taking into account all the previous settings, we must maintain the pH of the water wetting between 4.9 and 5.4 in order to succeed a good impression. Outside these limits, some problems may occur. If the pH is too low, so if the solution is too acid, there is a risk: Ill-inking rollers. Wear areas printers. Corrosion of ferries and water pipes. If the pH is too high, so if the solution is neutral or alkaline, there is a risk Sailing due to the emulsion ink / water, the resulting definition of a bad point and a loss of density. *The interfacial tension and the surface tension: Water and oil do not mix, there are, at their interface separation, a force which prevents the mixture of both liquid and the need to overcome such a force if one wants to cause the mixture of these two liquids. This force is the interfacial tension. If now, we are paying a liquid to a solid, liquid will set more or less the surface of the solid. A force exists between the liquid and solid objects more or less at anchor. In some cases, the anchorage is totally impossible, for example, mercury on the glass. This force is called surface tension. The interfacial tension and the surface tension can be measured in dynes / cm. These tensions are very delicate to measure, they require laboratory apparatus very sophisticated. These devices are called tensiometers. *Importance of surface tension and interfacial tension in offset printing: It is these elements that relies offset printing. On the one hand, the basic principle lies in the opposition between the ink (fat) and water. Over the interfacial tension between the two bodies, the less they are mixed, so there will be less chance of forming an emulsion (mixture of ink and water). On the other hand, the fundamental principle is the anchor of the plate in water and ink. Over the surface tension of the fount solution is lower making the anchorage of the plate is good. Water runs well on the plate, it forms a thin film and continuous. *The conductivity: It is the property of a body to transmit electric current. This property is measured with a conductivity. It is actually a probe fitted with two electrodes that are plunging into the water harbor and for measuring the amount of current passing. It is expressed in milli or micro siemens per centimeter. The addition of a wetting product water wetting has little influence on the pH. The conductivity measurement is very important because it helps to determine the exact quantity of product wetting to add to the water. *Importance of conductivity in offset printing: The conductivity measurement is a measure, fine and reliable, content to be added as an addendum wetting in water anchorage. It helps determine the ideal amount of the additive to be used. Post-printing Expertise of a lenticular Defects on conception: *Double images on the relief and in depth: The main reason is an exaggeration of the 3-D effect from angles of view or an insufficient number of frames. Observation of the visual must not show doubling, small jumps or a fuzzy image, especially on objects in relief or in depth. For some visuals, where the foreground and background are fuzzy or shaded, this exaggeration can prove to be an advantage, but in most cases, the detail and precision required do not allow this. *Image remanence (ghosting): This is due to poor treatment of the source images and also transitions where demand for an effect goes beyond the limits and technical possibilities of the system. This problem is manifested by image remanence. This gives the impression that the images do not really disappear. Logically the transitions should be clear and precise. One must be aware, however that even if the lens focuses our vision, the entire print (the master) appears more or less by transparency and in accordance with the lighting of the visual. Prepress defects: *Synchronisation of the print (master) with the pitch: The chief reason is poor calibration of the material. This is a lack of anticipation. The passage of one visual to the other must be simultaneous over the entire format. But when this problem appears there is a time lag in the effects. At one end of the visual we have one effect and at the other end another effect on the same incline (impression of a veil or curtain crossing the visual). This phenomenon is felt less for the 3-D effects, but is manifested by a jump of the transverse image. *Discordant harmonics: This phenomenon is unfortunately very common, and is explained either by incorrect calibration of the support or by incorrect parametrisation of the prepress operations. It is manifested in particular by streaks that appear parallel to the lenticules during the phases of transition from one visual to the other. Printing defects: *Colour synchronisation: One of the main difficulties in lenticular printing is colour synchronisation. The causes are varied, they may come from a malleable material, incorrect printing conditions and adjustments, or again a dimensional differential of the engraving of the offset plates in each colour. This poor marking is shown by doubling of the visual; a lack of clarity; a streak of colour or wavy colours (especially for four-colour shades) during a change of phase by inclination of the visual. *Synchronisation of parallelism of the printing to the lenticules: The origin of this problem is a fault in the printing and forcibly generates a phase defect. The passage from one visual to another must be simultaneous over the entire format. But when this problem occurs, there is a lag in the effects on the diagonals. At the end of one diagonal of the visual, we have one effect, and at the other end we have another. *Phasing: In most cases, the problem comes from the standard of the cutting of the material. Nevertheless, poor printing and rectification conditions may also be behind it. In theory, for a given angle of observation, one and the same visual must appear, for the entire batch. As a general rule, the angle of vision is around 45°, and this angle must be in agreement with the sequence provided by the master. If the images have a tendency to double perpendicularly (for 3-D) or if the images provided for observation to the left appear to the right (top/bottom), there is a phasing problem. Defects of cutting: Scanning microscopy: These images show the irregularities of cut in edges of sheets.
This defect generates one thus shifts impression compared to the duckweed a dephasing. The knowledges of this technology includes: The manufacturing of lenticular The chemistry of thermoplastics (PET) Polyethylene: This material has a very simple structure, the simplest of all polymers trade. A polyethylene molecule is nothing more than a long chain of carbon atoms with two hydrogen atoms attached to each carbon atom (CH2-CH2) n. Polyethylene is produced by polymerization of ethylene (CH2 = CH2, gas). Polyethylene provides fiber with excellent mechanical properties (dropping since 120 oC), due to the alignment of their molecular structure (in the axis of the fiber). The fibers are flexible, translucent and resistant to chemical agents. The polyethylene component of polyethylene terephthalate (PET), rigid and transparent copolymer lenticular. Polyethylene is biodegradable (using microorganisms in nature), then giving water (H2O) and carbon dioxide (CO2), and also photodégradable (light), but residues remain in the ground.
*Some tests and to recognize the particularity polyethylene.
The optical lenticular Angle of view of a lenticular: A priori, the angle of vision should match the angle that must be an observer to scan the entire printing reserved for a lenticule. Data entries: * Network of lenticular * Ray of the lenticule 190.5 µ (scanning microscope gives 196 µ) * Thickness of 457 µ *Index-resin Lenstar 1557 Data calculated:
Focal distance of a lenticular network: A priori, one could think that the focal distance is with the tangent of the back of a lenticular sheet, there or is the impression. Is this well the case? Data input: * Lenticular Network of 75,45 LPI is pitch of 336,65µ * Ray of the duckweed 190,5µ (the microscope with sweeping gives 196µ) * Thickness of 457µ * Index of the resin Lenstar 1,557 Data calculated:
Influence of the angle of vision about the desired effects: *Preamble The offset printing of Lenticular to its limits. The linéatures frame used vary with the printer (300, 400, 600 lpi), and its ability to reproduce without a frame with a body fat enough. The size of the dot is dependent on the frequency and value of the item (we do not include the shape of the item). For example, with a frequency of 400 lpi and raster value of 50%, the dot's size 31.75 µ (25.4 mm / 400 * 50%). However, the axis between him remains invariable 63.5 µ (25.4 mm / 400). In other words, for a lenticular of 75 LPI with a pitch of 336 µ, a printing frame frequency 400 does feel that by 5 points to a color in a lenticule (336 / 63.5 = 5.29). A master consisting of a complicated web of images, it is unrealistic to believe that a dot can participate in the printing of more than one interlaced image. Can we conclude that the maximum number of images can be printed full screen 400 is 5 pictures? Let us not forget that as a general rule impressions are four-color (4 colors), the abundance of other colors, and vote accordingly, the other items frame, increases the definition. Experience shows that for a network of 75 LPI and printing frequency 400 four-color, an interweaving two dozen images is reproducible. The bases are thrown and you can calculate yourself the maximum number of images that are reasonably low copied for another network and another screen frequency. *Animations Ideally, for entertainment, is to have a vision as broad as possible. Indeed, the objective is to move as slowly as possible sequence of animation to allow for a broader vision focused on the same picture of the sequence. The images will be more "clean", in any case, less disturbed by the images next to each other. *The images highlight For 3D is the opposite, in fact we have to find a good compromise. A viewing angle closed allow both eyes to observe a maximum of images (a gap of more meaningful image for the same angle), which will increase the depth of relief. However, the phasing in printing will be more difficult to maintain. The functioning of the binocular vision The visual function: The sense of sight understands the meaning of light, color vision, visual acuity and visual field is apprehended that the detail of things, the distance at which they are seen and the terrain. It is the eye that the sense of sight. It is similar to a camera, which the plate is the sensitive retina, the development is provided by the lens; guidance to the point to set out the muscles oculomoteurs; the concept of relief and appreciation of distances are due primarily to binocular vision. The lenticular (English: lenticular) returns to each eye a different image for him specifically. The retina, which plays a crucial role in vision, is composed of two kinds of cells: the cone photoreceptor cells and photoreceptor cells with sticks. It is a question of morphology, and it is common to speak simply of cones and rods. That portion of the retina is made up of cones of the retina daytime. It has enabled us to see things in a precise way: it gives visual acuity, it also provides color vision. There are 7 million cones, located mainly in the central part of the retina. The sticks are more numerous: 130 million. They bring light sensitivity and the perception of motion. *The sense light The sticks are a thousand times more sensitive than cones to light stimulation. As the central region of the retina (macular region) contains only cones, it does not react to light, at night, resulting in a central scotoma (spot). To see a star, it is necessary to look a little next door, at 4 ° from the point of fixation. The retina adjusts to the vision in the dark. Quick in the first ten minutes, the adjustment is completed in thirty minutes. The night vision is optimal in the blue. *The visual field The field of vision extends all around the point of fixing up 95 ° temporal side, 60 ° side nasal and 56 or 57 ° up and down. In the daytime visual field, the best visual acuity is right in front of itself is the point of attachment. As one moves away from the fixation point, the vision is less and less good. However, in the peripheral visual field, the concept of motion is good. *The color vision These are the cones that give the sensation of color. As is the posterior pole of the eyeball that their density is the highest, in the central part of the vision that colored the feeling is the best. The theory of trichromatic color vision is the most commonly accepted. According to her, there are three kinds of cones, allowing the vision of three primary colors: blue, green and red. The mixture of these three colors can achieve all others. The sensitivity of the eye to light radiation is between ultraviolet and infrared (880 to 750 nanometers). *The visual acuity The acuity is the ability to distinguish details of the objects. At five meters, a distance considered infinity optics, the shortest distance between two points is seen separately underpinned by an angle of one minute, it is acknowledged that this power angular resolution of one minute is a vision of ten tenths measured using different optotypes: small objects of everyday life for children (birds, houses, cycles, etc.). rings broken for the illiterate, numbers and letters in other cases. Near vision seeks accommodation. The visual assessment of an object is done by some sort of palpation: fixation of the eye moves by jerks around the set point. The depth perception: The monocular vision do we perceive that the direction where the point that we see. This point can move on the line of sight where it is located, without it occurs, in the impression received by the eye, no changes other than in relation to the size of the circle formed broadcast on the retina, and as the movement does not exceed the length of the line of accommodation, this change in the distribution circle has no value. Thus, the monocular vision tells us not immediately apparent that the position of the line of sight which we must seek the point that we see. To get a full understanding of the disposition of real objects in space, we still need to know, on the line of sight, the distance from the eye of each of the points that we see. A knowledge of the surface dimensions of the field must be added that of the deep. Experience teaches us daily that we consider also the third dimension, with varying degrees of accuracy. How can we know the distance between our eye and objects? The means of achieving recognition and the shapes of objects in space can be placed in two categories quite distinct. The first contains the results of our experiment on the nature of objects we see and can not, of course, mean that representations of distance. In the second category are the feelings that give us a real perception of distance and are *1 ° awareness of the effort required accommodation *2 ° observation with the help of accommodation movements of the head and body *3 ° the simultaneous use of both eyes. I. The results of our experiment on the nature of objects we see We are here to explore what we can discern, compared to the third dimension of the visual field, when we look at only one eye, and without moving the head, objects that are pretty remote or low enough so that their net observation requires no effort sensitive accommodation. The elements that we use in these conditions are primarily the prior knowledge of the size of the objects, then that of their form, knowledge plus the distribution of the shadows and the degree of transparency of the air intermediary. On the same subject, seen different distances, gives retinal images of different sizes and comes in different visual angles. Plus it is far more visual terms under which it occurs is small. We can appreciate the distance at which an object is known of magnitude, according to the size of the angle or visual, which is the same, according to one of the retinal image. To the knowledge of the greatness addition, in many cases, the form of objects, especially in cases where they are partially mask. When we see, for example, two objects including one cache in the other party, we conclude that the first is in front of the second. Even when their form is absolutely unknown, it is sufficient, in most cases, noting that the profile of the object earlier continues without interruption after encountering the object later, to distinguish them from each other . In many cases it is sufficient to know or presume that the subject has received some form of regularity, to arrive at a correct interpretation of body image perspective that we offer, or the subject, or a design that represents it. When we see objects known, we can admit that their rights are angles, and that their surfaces are planar, cylindrical or spherical. This suffices for a perspective drawing us allows us to form a correct notion of these objects. We understand without difficulty, and we interpret correctly the design perspective, even though it is very complicated details. If shadows are exactly reproduced, the preview becomes easier. When you look at these objects known, trained mainly parallelepipeds rectangular, cylindrical and spherical surfaces, bringing them sufficiently for the preceding sections are on the retina on a scale significantly greater than the after parties, the representation correct perspective we received no indication, in general, only one interpretation, and it is easy to recognize the position more or less remote of the different parties. But if the point of view is very distant objects, or if they present a very small relief, interpretation can become indecisive. We can see similar effects on a large number of drawings linear perspective, those, for example, who are regular body, geometric projection (that is seen from a far distance). The same board or angle may seem sometimes back, sometimes sheet. Often representation change spontaneously representation that we can always change voluntarily when strongly represents another interpretation. From these observations are approaching those we made on the apparent reversal of relief molds or fingerprints, but added that the influence from the shadows. If we place the mold hollow so that it is informed with an oblique incidence by daylight, which produces shadows well marked, by looking with one eye, it is believed easily see a model highlight of the mold or the fingerprint. When looking at the mold binoculairement, illusion ceases most often. The same is true when the head moves or object illusion occurs more easily than the eye and the object are more immobile. In addition, a lighted terrain normally incident should also oblique projection, plan on the merits, a significant shadow that naturally default on the mold seen in relief. It follows from there, a kind of magical lighting terrain; that seems to come from inside. If it is, in general, much more difficult to see reliefs replaced by hollow, it would like because that relieves the IDB few shadows that prevent their taking convexities to concave shapes. The shadows are important even greater than the variation that sustains the lighting side of a body with their inclination in relation to the incident rays. When we see a surface illuminated, illuminating the body must be in before this surface, and if it receives a shadow, it is necessary that the body which plans this shadow is also placed forward of this surface. It therefore follows is a report of geometric determined between the body planning the shade and the surface who received it. We are beginning to see, in relation phenomena pseudoscopiques, the crucial role of the shadows in the interpretation of visual phenomena. The lighting provides us with yet another data to assess distances, and especially those distant objects, the so-called aerial perspective. It is under that name obfuscation and changing color images of distant objects suffer as a result of incomplete transparency layer of air between the objects of the observer. Plus the air is thick between the eye of the observer and the object away, the more the color of the object changes, either in blue, when darker or red when lighter than air layer intermediary. The means we have seen so far and serve at the discretion of the third dimension, are also of interest and importance to the psychological point of view, because their review gave us an opportunity to see what is the impact of the experience on our sensual perceptions, we might have thought acquired in a manner immediately and without the assistance of any action psychic. We can only have learned through experience that the laws so varied lighting, in the shadow of the aerial perspective, training and timing of the prospects of different geometric body, those whose training request a long habit and not acquired until long after birth. And yet these data are sufficient, in many circumstances, to arouse in us notions perfectly alive, and as sensual, shapes and conditions of space, but we have no awareness of the role that has just play the comparison between the printing and the current and prior similar impressions. These associations are also representations unconscious qu'involontaires; though their production is subject to the laws of our minds, as they are needed by a natural force blind, they seem to do the same basis as currently impressions from the outside, and , Therefore, anything that these associations of ideas, based on prior experience, add to our feelings of the moment, is presented to us, as well as those feelings themselves, as given immediately, without active intervention on our part The results obtained thus do not distinguish from direct perception, but in reality they are only representations, in the pure sense that we have attributed to that word. II. The feelings that give us a real perception of distance *1 °) Accommodation of the eye. There is no doubt that a person who has studied the changes in his accommodation and who knows the feeling of the muscular effort required by these changes, is able to say whether it allows for a distance large or small, to when she sets an object or an optical image. But the evaluation of the distance, using this method, is exceedingly imperfect. *2 °) The comparison of images that presents a perspective when looking at objects in different viewpoints. This method of comparison can be done in two ways either monoculairement, moving his head and body, either binoculairement, using two different pictures that provides the same object simultaneously to both eyes. As both eyes occupy a somewhat different position in space, they also see under viewpoints slightly different objects placed in front of us and the images they receive from these objects exhibit, as a result, the same difference the successive images that would receive the same eye by moving from a corresponding quantity in space. When we move, the objects that are still left behind, and they seem to drag us in the visual field, in a direction opposite to that of our movement. The same thing happens, but more slowly, for distant objects, while very distant objects, retain an invariable position in the field of view, as long as we do not change the direction of our bodies and our head. It is easy to see that when we move, the apparent angular velocity of objects in the visual field is inversely proportional to their distance true; so that the apparent speed of movement can draw some conclusions on the actual distance . The objects at different distances are also apparent relative motion. Those who are farthest seem to move, in relation to others, in the same direction as the observer; closest to appear to move in opposite directions. It follows is a very clear notion of the difference in distance. It is mainly through changes in the image printed by retinal body movements, that people can acquire eyed notions accurate forms solid objects that surround them. If we look monoculairement objects irregular and unknown, the representation we get their form is wrong, or at least uncertain. But as soon as we move, we get a notion accurate. We should not forget this point, which we have not yet brought all the necessary attention in all experiments physiological optics because it is assessing the distance an image or object seen in any way, it should be very careful not to move his head in relation to the object it would result in a determination as relatively good enough and accurate enough for the real distance, using the apparent displacement and products. *3 °) Simultaneous use of both eyes. The changes in the retinal image as a result of the movement do we show the differences in distance with the help of the comparison that we establish between the current image and those who immediately preceded in the eye, and whose we have preserved the memory. A comparison is even more uncertain when it is done with the help of memory when she serves for two simultaneous sensations. For this reason, the evaluation of distances using the images simultaneously in both eyes is far more comprehensive, safer and more accurate than what can be accomplished by the movement of the head as their amplitude n 'barely exceeds the distance between the two eyes. Each eye presents an image perspective objects before us. But as the two eyes do not occupy the same position in space and that as a result, they watch the object beneath views a little different, it follows that the two images prospects they plan differs also slightly between them. These differences are similar and the same value as those occurring when looking at the field of view with one eye, the eye by moving a distance equal to the interval in both eyes. So while the monocular vision, with stillness of the head, merely determines the direction where the perceived point, binocular vision gives facts sufficient observation to determine more distance from this point, at least as the data show sufficient accuracy, and it is suitable uses. In general, the accuracy of determining the distance is even less than that distance itself is greater, because the very distant objects no longer significantly different images in both eyes. It acquires, by this means, notions of distance overly sensual accurate and clear. That's what it can be demonstrated with the help of images that represent the two sides that produced an object in both eyes of an observer. If we look at an object represented by a painting or a drawing plane, the two eyes are absolutely the same retinal image, whereas if we look at the object itself in volume in reality, it necessarily produce images retinal different in both eyes. We have seen a single image plane, with a view both eyes must constantly produce an impression other than the sight of the object it represents. But if we look at each show a different image to each one that would be in the shape of the object itself, we are able to produce, on the two retinas, the same feeling that actually produce the Three-dimensional object, so the two images give us, in these circumstances, the same body notion that the object itself. Thus, the two images that must produce a dimensional effect, must meet two different perspectives of the same subject, taken at different points of view. They can not therefore be such, it is necessary, however, compared with those of the infinitely distant points, the images of the points are closer even more left in the drawing for the right eye, and even in addition to the right one for the left eye, that the objects themselves are closer to the observer. If one is therefore drawings superimposed so that the images infinitely distant points coincide them, the images of objects will be all the more that these discarded objects are more neighbors. We can give this distance the name of stereoscopic parallax. This parallax is positive if the issues are diverted to the left to the right eye and right to his left eye. The parallax stereoscopic offer the same value for all objects which are at the same distance from the plane of the drawing. If the design is not infinitely distant points, can not be determined that the differences in the parallax stereoscopic compared to any point on the object. The parallax from this starting point is positive for the other points closer together, and negative for the points farthest See Also
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