What does "hidden photographic image" mean. The theory of the hidden image The process of forming a hidden image in the photoemulsia

From this point of view, the hidden image consists of small groups of metallic silver atoms on the surface or inside microcrystals of halide, resulting from a redox reaction caused by a photo effect. In the process of manifestations, these groups serve as a catalyst leading to the restoration to the metal form of the entire crystal. With large exposures, the metallic silver is restored on the scale visible to the eye, forming a visible image without manifestation. Such a phenomenon is characteristic of photographic materials with the so-called "daytime" or "visible manifestation", mainly photographic.

However, the widest possible extent received a technology requiring the chemical manifestation of an invisible latent image. In this case, the manifestation acts as an image amplifier, therefore, the second-type photocurrents have photosensitivity, several orders of magnitude exceeding the same parameter in photo paper with visible manifestation.

Education mechanism

For the first time, the concept of the hidden image appeared after the opening of Talbot, which in September 1840 completed the development of the canopy. As a result of the treatment of exposed photosensitive paper with a solution of gallogenthitrate (mixtures of nitric acid silver with a gallium and acetic acids), it appeared visible image. This made it possible to sharply increase the photosensitivity of silver chloride and reduce the necessary shutter speed from half an hour that were required without chemical manifestation, up to two or three seconds. The first hypothesis about the nature of the hidden image was expressed by Francois Arago, who believed that the cause of the phenomenon was becoming the ability to restore before the metal form of those microcrystals of halide, in which microscopic groups of silver atoms become a manifestation of manifestations were formed.

The current idea of \u200b\u200bthe mechanism for the formation of a hidden image is based on a quantum-mechanical theory proposed in 1938 by British physicists-theorist Ronald Gurney (English. Ronald Wilfred Gurney.) And Nevil Mott (English Nevill Francis Mott.). It is based on the assumption that the real silver halide microcrystal has impurities in the form of microscopic inclusions, and crystal lattice defects. Under the influence of thermal oscillations of the ions, of which the lattice consists, regularly leave it, and some silver ions are not able to return back, moving in interstitial space. The photon fell on the emulsion is absorbed by the halogen ion, and the vacant electron emitted in this is "potential pit." This is the name of the zone of reduced energy, in which there is an impurity, and where the relationship between ions is broken. Photoelectron, captured by the pit, charges it negatively, and attracts the nearest intersselsal silver ion. As a result, the ion recombines with an electron and turns into a neutral atom.

In turn, a halogen atom (for example, bromine), formed from Ion in the process of absorption of a photon, forms a so-called positive "hole", which gradually moves to the surface of the microcrystal by the relay transmission of an excess electron to neighboring halogen ions. Once on the surface of the microcrystal, the hole is associated with gelatin, which prevents the oxidation of the centers of the hidden image. The process, accompanied by the reduction of the silver atom, can repeat repeatedly, forming microscopic colloidal particles of silver, which received the name of the substraters of the hidden image. Such subcentrators are not able to cause a microcrystal manifestation, but they play an important role in various methods of increasing photosensitivity. A critical mass that allows you to catalyze the restoration of the entire microcrystal during manifestation, is at least four silver atoms and is called the manifestation center.

Further studies have shown that the theory of the Gurney Mott explains the processes only partially. It was improved by J. Mitchell (eng. J. W. Mitchell.) Having proved in 1957 that the connection to the center of the photosensitivity of the intersensive silver ion is preceded by its photoelectron neutralization. At the same time, the hidden image can be formed without the participation of the light sensitivity centers, but two to three silver atoms obtained by their independently form an unstable center, which received the title "Precedre" in the literature (Eng. Pre-image Speck). Studies of the late 20th century suggest that in the early stages of exposure, the centers of the hidden image are formed by the Mitchell mechanism, and with fairly large exposures there is a Görni Mot theory.

Photosensitivity

The most effective way to increase the light sensitivity of the emulsion lies in education as much as possible potential pits, that is, the defects of the crystal lattice of silver halide. Microcrystals with an ideal lattice have low photosensitivity, since most photoelectrons, without meeting defects, recombine with ions, and do not participate in the formation of a hidden image. Defects may be shifts of crystalline layers, microcracks, or foreign inclusions. Defects of the lattice are intentionally created in the process of preparing a photographic emulsion, at the stage of chemical maturation. To do this, salts containing palladium, platinum and iridium are added, as well as gold compounds.

Schwarzshild effect

The low efficiency of the participation of photoelectrons in the formation of a hidden image leads to a violation of the law of interoperability (Schwarzschild effect). These violations can occur in two cases:

Too short exposure

With very short excerpts, despite the high level of illumination, the law of interoperability is broken, at the same time reducing photosensitivity and contrast. The phenomenon is especially characteristic of photoemuls, manufactured according to outdated technologies. With very short exposures in microcrystals, too few manifestation centers are formed, instead of which unstable subcentrators are synthesized, which are not capable of recovering the exhibited halide. This is due to the simultaneous formation of too much photoelectrons.

The effect has become a problem for modern technology of digital photo printing, in which the photographic paper is exposed to a laser beam with a very short effect on each portion of the photoemulsion. Therefore, most photographic materials intended for digital mini-photo laboratories are made on the basis of chlorosrebry emulsion, in the smallen degree of rejection of intercoulations. In addition, the effect can be reduced by special additives into emulsion layers, increasing the number of lattice defects. A similar problem is characteristic of a film recorder, in which the film light is also exhibited by a laser beam. This is reflected in the structure of counterparts of special varieties designed to print a double negative.

Too low light

This effect is most important in astrophotography, where the photo material is exhibited with very small light intensities and long excerpts. This is explained too short stability of subcentrators who do not have time to grow to stable manifestation centers during the waiting for the following photons. The phenomenon leads to a decrease in photosensitivity and increasing contrast.

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Notes

Literature

• E. A. Iofis. PhotoKinotechnics. - m .: "Soviet encyclopedia", 1981. - P. 301, 377. - 449 p. - 100,000 copies.

• A. V. Rishko. 1. 3 The nature of the sensitivity of silver halide. The formation of a hidden and visible photographic image // Basics of photographic processes. - 2nd ed. - St. Petersburg. : "Lan", 1999. - P. 70-74. - 512 p. - (textbooks for universities. Special literature). - 3000 copies. - ISBN 5-8114-0146-9.

• A. V. Rishko. Basics of black and white and colored photoccessses / N. N. Zherdetskaya. - m.: "Art", 1990. - P. 15-18. - 256 p. - 50,000 copies. - ISBN 5-210-00390-6.

• Michelle Frizo. NEW HISTORY OF PHOTOS \u003d Nouvelle Histoire de la Photographie / A. G. Hirsty, A. V. Shestakov. - St. Petersburg. : Machina, 2008. - 337 p. - ISBN 978-5-90141-066-0.

• FOMIN A.V. Chapter II. Chemical action of light // / T. P. Buldakova. - 3rd. - m. ,: "Legomombytizdat", 1987. - P. 53-55. - 256 p. - 50,000 copies.

• K. V. Chibisov. Essays on the history of photography / N. N. Zherdetskaya. - m.: "Art", 1987. - P. 37-41. - 255 s. - 50,000 copies.

Excerpt characterizing a hidden image

Bald Mountains, Vince Nikolai Andreic Bolkonsky, were in sixty versts from Smolensk, behind him, and in three versts from the Moscow road.
On the same evening, as the prince gave orders to Alpathić, the desal, demanding from the princes Mary databa, told her that since the prince was not entirely healthy and does not take any measures for his security, but according to the letter of Prince Andrei, it is clear that staying in the Bald Mountains It is unsafe, then he respectfully advises her to write with Alpatha to the head of the province in Smolensk with a request to notify her about the state of affairs and as far as the danger that bald mountains are exposed. The desala wrote a letter to the governor, which she signed, and this letter was given to Alpathić with the orders to submit it to the governor and, in case of danger, return as soon as possible.
Having received all orders, Alpatych, accompanied by homemade, in a white fluff hat (princely gift), with a stick, as well as the prince, went to the leather kibechka, laid down the top three saves.
The bell was tied, and the puments are laid with pieces of paper. Prince did not allow anyone in the Bald Mountains to ride with a bell. But Alpatych loved bells and bubber bubber in the far road. Court Alpatić, Zemsky, Butter, the cook - black, white, two old women, boy Cossack, Couter and various yard accompanied him.
The daughter lay behind the back and under it the stente down pillows. The old woman was tapering the knot. One of the coofers attacked him at hand.
- Well, well, women fees! Baba, women! "Puffy, said the patter of Alpatych exactly as the prince said, and sat down into kibitka. Giving the last orders about the work of the Zemsky and in this, without imitating the prince, Alpatych took off his hat with a bald head and crossed him three times.
- You, if that ... you go back, Jacob Alpatych; For the sake of Christ, we will have a chance, "the wife shook him, hinting for rumors about the war and the enemy.
- Baba, women, women fees, "Alpatych said to himself and drove, looking around himself around himself, where with yellowed rye, where with dense, still green oats, where there are still blacks that were just beginning. Alpatych was driving, admiring on a rare harvest of the Svorovoy this year, looking at the strips of rye peel, on which someone where they began to heal, and did their economic considerations about sowing and cleaning and whether the princely orders were not forgotten.
Two times feeding the road, in the evening of August 4, Alpatych came to the city.
On the way, Alpatych met and overtook the sumports and troops. Handing to Smolensk, he heard distant shots, but these sounds did not hit him. It was stronger than the fact that, approaching Smolensk, he saw a beautiful field of oats, which some soldiers mowed, obviously, for food and in which they stood a camp; This circumstance struck Alpathić, but he soon forgot him, thinking about his business.
All the interests of Alpatić's life have already been limited by one will of the prince, and he never came out of this circle. All that did not touch the prince's orders, not only did not interest him, but did not exist for Alpathy.
Alpatych, having arrived in the evening of August 4th to Smolensk, stopped behind Dnipro, in the Gauchenian suburb, at the inn of the courtyard, at the Ferrapontov janitor, who has already had a habit of stopping. Feratovs Twelve years ago, with the light hand of Alpathić, having bought a grove by Prince, began to trade and now had a house, a stall courtyard and a flour shop in the province. Ferapontov was a fat, black, red forty-year-old man, with thick lips, with a thick shadow nose, the same cones over black, frowning eyebrows and a thick belly.
Ferapontov, in the vest, in the Sitzu Rubach, stood at the shop, which went outside. Seeing Alpatić, he approached him.
- Welcome, Jacob Alpatych. People from the city, and you are in the city, "said the owner.
- What, from the city? - said Alpatych.
- And I say, the people are stupid. All the French is afraid.
- Dollays and women! - Alpatych said.
- So I judge, Jacob Alpatych. I say, the order is that they will not be allowed, "he also, right. Yes, and men of three rubles from the submission asked - there is no cross on them!
Jacob Alpatych listened inattentively. He demanded Samovar and hay horses and, drunk tea, went to bed.
All night by the innovative yard moved on the street troops. Another day, Alpatych was put on Camzole, which he put on only in the city, and went on business. The morning was solar, and with eight hours it was already hot. Dear day for cleaning bread, as Alpatych thought. At the city from early morning, shots were heard.
With eight hours to gun shots joined cannonal pallets. There were a lot of people on the streets, somewhere hurrying, a lot of soldiers, but also, as always, droves, the merchants stood at the shops and the service was in churches. Alpatych walked into the shop, in the present places, by mail and to the governor. In the present locations, in the shops, everyone spoke about the troops, about the enemy who had already attacked the city; Everyone asked each other, what to do, and everyone tried to calm each other.
The house of Governor Alpatych found a large number of people, Cossacks and a road crew belonging to the governor. On the porch, Jacob Alpatych met two gentlemen of nobles, of whom he knew. A friend familiar him, former correction, spoke with the heat.
"After all, this is not a joke to joke," he said. - Well, who is one. One head and poor is so alone, otherwise, after all, thirteen family is a family, but all the property ... brought to disappear to everyone, what is it for the bosses after that? .. Eh, he would notice the robbers ...
"Yes, well, will," said another.
- And what is the case, let him hear! Well, we are not a dog, "said the former correction and, looking around, and saw Alpatych.
- A, Yakov Alpatych, why are you?
"According to the orders of his arrangement, to Mr. Gubernator," Alpatych answered, proudly raising his head and laying his hand for the sinus, which he always did when he mentioned Prince ... - they were ordered to order to inform about the situation, "he said.
"So here's find out," the landowner shouted, "they brought that neither the sub-center, nothing! .. Here, do you hear? He said, pointing to the side where the shots were heard from.
- brought to die all ... Robbers! - He said again and came down from the porch.
Alpatych shook his head and went to the staircase. There were merchants, women, officials, silently surrounded among themselves. The cabinet door turned out, everyone got up from the places and move forward. An official ran out of the door, I talked about something with a merchant, I clicked a thick official with a cross on the neck and disappeared again at the door, apparently, avoiding all the views and questions addressed to him. Alpatych advanced and the next time the reservoir of the official, having laid his arm the shrouded on his hand, turned to the official, feeding him two letters.
"Mr. Baron Asha from General Annef Prince Bolkonsky," he proclaimed so solemnly and significantly that the official addressed him and took his letter. A few minutes later the governor accepted Alpathić and hastily told him:
- Follows the prince and Princess, that I did not know anything: I did on top orders - here ...
He gave the Paper Alpathi.
"And however, because the prince of unhealthy, my advice to go to Moscow." I am now going now. Follows ... - But the governor did not negotiate: the door ran into the door and the dove officer and began to speak French. On the face of the governor brought horror.
"Go," he said, nodding Alpatha's head, and began to ask something from the officer. Greedy, frightened, helpless views turned to Alpatić when he left the governor's office. Unwittingly listening now to loved ones and all the increasing shots, Alpatych hurried to the storage courtyard. The paper gave the governor Alpathić was as follows:
"I assure you that the city of Smolensk has not yet to be the slightest danger, and it is incredible that it threatens her threatening. I am with one, and the prince of Bagration, on the other hand, we go to the connection before Smolensky, which will take place on the 22nd, and both army will be to defend the compatriots of their entrusted to you, while their efforts are removed from them from the enemies of the Fatherland or until they explete them in brave them Rows to the last warrior. You see from this that you have the perfect right to calm the residents of Smolensk, for who we protect two so brave troops, he can be confident in the victory of them. " (Prescription Barclay de Tolly Smolensk Civilian Governor, Baron Asha, 1812.)
The people restned restlessly through the streets.
Superior to the riding of the age with homemade kitchenware, chairs, cabinets, and then, went out of the gates of houses and drove through the streets. In the neighboring house, Ferapontova stood wagons and, saying goodbye, tired and talked to women. Rocking dog, lying, drunk before the laid horses.
Alpathych is a hasty step than he walked usually, entered the courtyard and went straight to the shed to his horses and a wagon. Kucher slept; He woke him, ordered to lay and entered in the sen. In the master's doors, children's crying, observing sobs of women and an angry, hoarse cry of Ferapontova were heard. The cook, like a frightened chicken, was fixed in the Seine, as soon as Alpatych entered.
- To death killed - the hostess Bil! .. So Bil, so looked off! ..
- For what? - Alpatych asked.
- She was asked to go. Women's business! You take away, says me, do not destroy you with small children; People, says, all left, what, say, are we then? How I shouted to beat. So beat, so looked like!
Alpathić, as it were, nodded to these words approvingly and, not wanting to know anything, went to the opposite - the shopping door of the hill, in which his purchases remained.
- The villain you, the destroyer, - shouted at this time thin, a pale woman with a child in my hands and with a headscarf with a head, torn out of the door and running around the stairs to the courtyard. Ferapontov came out for her and, seeing Alpatić, recovered the vest, her hair, yawned and entered the hube for Alpathić.
- Al do you want to go? - he asked.
Without responding to the question and without looking at the owner, turning out their purchases, Alpatych asked how much the owner should have followed.
- Hall! Well, the governor was? - asked Ferapontov. - What decision came out?
Alpatych answered that the governor did not resolutely told him.
- In our case, will they be taken away? - said Ferapontov. - Give up to the expense of seven rubles behind the fodder. And I say: there is no cross on them! - he said.
"Selivanov, he landed on Thursday, sold flour to the army for nine rubles per Kul. What about drinking tea? - he added. While she was laid by horses, Alpatych with Ferapontov got drunk tea and talked about the price of bread, about the crop and favorable weather for cleaning.

hidden photographic image

Hidden photographic image (latent image) An invisible image that occurs in the photosensitive layer of photographic materials in the process of its exposure. In the manifestation, the hidden image turns into visible as a result of the selection of silver atoms in the centers of the hidden image, and the silver concentration increases a million times or more.

Hidden photographic image

an invisible change that occurs in a photosensitive material under the action of optical radiation and converted during photographic processing in the human eye perceived by the human eye for this transformation, called visualization, is used in classical photography. and. in photographic emulsions to catalyze (see below) the reaction of the recovery of silver halides (AG HAL, HAL º BR, CL, I, most often Br) to AG; In the electrophotography ≈ the ability of S. F. and. electrostatically attract pigment particles, etc.

In the given definition of S. F. and. Only its main property is allocated to serve as the cause and precursor of the visible image. Such a definition is common to a wide variety of processes of its formation (photochemical changes in crystals of photosensitive salts, transverse "crosslinking" molecules in photosensitive polymers, changes under the action of the light of the surface charge distribution in polarized or charged dielectrics or volume charge in semiconductors, etc.).

S. F. and. It is a "recording of images of objects or other optical information (spectrum, interference pattern, etc.). The subsequent viewing of this entry by the eye in principle is optional to read recorded information directly from S. F. and. (for example, holographically or electronic beam). However, with any method of such reading S. F. and. gives a signal much weaker than the visible image obtained from it, its level does not exceed the level of interference; As a result, its noise immunity is low. In addition, S. F. and. It is not always fairly stable in time to keep it for a long time without visualization.

In the most common photographic process on the layers of Aghal emulsions in the gelatin of S. F. and. Form small groups of AG atoms, located at certain points of the surface or the volume of Aghal microcrystals, ≈ t. n. Centers S. F. and. These groups (atoms in them are not yet associated with the crystal lattice) arise as follows. Under the action of an exhibiting light in semiconductor microcrystals Aghal occurs internal photoeffs: electrons of halide ions are released. In addition, in Aghal crystals, there is always a certain number of free moving AG + ions, "knocked out" from their places as a result of heat oscillations (heat loosening of the grid). Electrostatically attracting each other, free electrons and ions are recombined (see the recombination of ions and electrons) ≈ neutral AG atoms arise. This process is localized where various violations of the lattice structure of Aghal are located on the surface of the microcrystals, first of all. Climbing particles (in particular Ag2S), which are formed during the manufacture of a photoemulsia. Formation of centers S. F. and. On each such impairment is a multiple repetition of two elementary acts: capturing a photoelectron from the microcrystal volume (electronic stage) and electrostatic attraction to the electron of the AG + ion (ion stage). With small illumination, the 1st stage flows slowly (the electrons are rarely coming), and the resulting neutral AG atom may ionazing before the next photoelectron is free. Thereby the likelihood of the education center S. F. And., necessarily consisting of not one, and from several atoms, slows down, which causes a decrease in photosensitivity with an increase in exposure (see non-reforative phenomenon).

During the manifestation of photographic (visualization of S. F. and.) The exposed Aghal microcrystals are restored to the metallic AG. One of the developer components (manifesting substance) is adsorbed on microcrystals and transmits them with electrons, it is oxidized itself. Such electron transmission is possible only if there are C. F. and., which should be in contact with the molecules of the manifesting agent (i.e., on the surface of microcrystals). In the absence of centers S. F. and. Recovery reaction does not proceed; Consequently, they play the role of catalysts in this reaction. Every time the center of S. F. and. It is charged, acquired an electron, this charge is neutralized by one of the nearest AG + ions, and the process of turning Aghal in AG continues until the microcrystal is completely restored. T. about., Visualization in the case of halogen of silver photoemulsions to a great extent increases the amount of product of the primary photochemical reaction.

Quantum Education S. F. and. In Aghal microcrystals (the ratio of the number of silver neutral atoms for the absorbed radiation quanta) is close to 1.

Consequently, for the emergence of the center. S. F. And. containing usually from several atoms up to several tens of atoms, one Aghal microcrystal should be absorbed from 10 to 100 quanta. After restoring (manifestation), the AG microcrystal contains 108≈1010 AG atoms, which corresponds to the gain to 109 (with respect to the number of absorbed quanta). Strengthening S. F. and. It occurs in other photographic processes, but not to such an extent. Therefore, the usual process on the emulsion layers of Aghal is unsurpassed by sensitivity, although in some indicators (for example, according to the visual characteristics), it is inferior to a number of other offered (by 1976), processes.

Lit.: Maclar P. V., physical processes in the formation of a hidden photographic image, M., 1972; Miz K., James T., theory of the photographic process, trans. from English, L., 1973.

L. L. Kartuzhansky.

The photo has become one of the first methods, widely and organically perceived by criminalistic and creatively adapted to peculiar conditions for the study of material evidence.

Employees of forensic experts as specialists in the production of investigative actions and operational-search activities and how experts should perfectly understand the essence of the photographic process and know the characteristics of the photographic materials used, to, based on the specific source conditions, select the most appropriate photographic materials and optimal shooting and processing modes.

In this chapter, I tried to consider the black and white photographic process and present a detailed image forming mechanism.

Physico-chemical essence of the photographic process

The process of forming a photographic image is the most complicated multistage physicochemical process, which includes the following main steps:

chemical maturation (the creation of silver light sensitivity centers in the preparation of halogen-separated emulsion) - is carried out in the production of photographic materials;

exposure (the formation of the centers of the hidden image in the photochemical action of light on silver halides) - occurs directly when photographing on photosensitive materials;

chemical and photographic processing (obtaining a visible image) - is carried out when manifest and secured the image.

With a black and white photographic process, the manifestation allows you to obtain a visible silver image, the fastening is intended to dissolve the unsecured silver halides, followed by washing from the photocloor. In addition, there are a number of auxiliary and additional processes that contribute to improving sensitivity, image quality and improving other characteristics of the photographic process.

Chemical maturation is carried out in the production of photographic materials. This stage of the photographic process is not considered here, as it is the production technological process of the photographic industry. The photographer, as a rule, is dealing with already ready-made various photographic materials and chooses them by certain characteristics.

Formation of hidden image

In the solid state of silver halides (Aghal - AgCl, Agbr, Agi) form crystals. In chloride crystals (AGCL) and bromide (AgBR) silver, halogen ions are located in the vertices and centers of Cuba.

Silver ions are located in a similar way, and the cube formed by them is shifted relative to the cube determined by the halogen ions. Such crystals belong to the class of granetable cubic crystals. These crystals exist in the form of aggregate clusters representing the repetition of the structure in the directions of the three coordinate axes. If AGCL and AGBR are precipitated at the same time, mixed grazent cubic crystals are formed, in which the grid angles are occupied by chlorine ions and bromine ions. AGI silver iodide at room temperature and normal atmospheric pressure forms a different crystal structure, however, bromide and silver chloride in the presence of low concentrations of AGI are formed during the deposition of mixed grazent cubic crystals.

The form of crystals depends on the precipitation process. Crystals can be cubic, in the form of octahedron, lamellar or irregular. However, the internal structure is always like that. The average grain size of silver halide is approximately 1000 nm, it contains about 1010 granetable cubes.

The real crystal halide has deviations from the perfect structure. Due to the violations of the equilibrium conditions of growth, the capture of impurities during crystallization under the influence of various influences in the structure of the crystal there are disorders - the so-called defects (silver ion leaves its normal position in the crystal lattice and freely wanders in international space). These defects and numerous foreign inclusions in the crystal lattice form light sensitivity centers, which are both centers for concentrating silver atoms as a result of light action. The level of sensitivity depends on the magnitude of these centers: the larger the centers, the higher the photosensitivity. Usually the growth of centers is accompanied by an increase in the size of microcrystals, so highly sensitive photographic materials are coarse-grained, and small-sensitive - fine-grained.

The graininess of the photosensitive layer depends on the grain of the image - the heterogeneity of the blazing of a uniformly exposed and the manifested portion of the photo material. The grainy structure of the image reduces its clarity. Lines, torn to individual grains, become uneven, contours - bliss. Increased graininess worsens image quality. The process of forming a hidden image is as follows. When exposure to the photographic layer, the rays power quanta is absorbed by silver halide, while the photolysis reaction occurs

2AGHAL \u003d 2AG + Hal2

In the exhibited halides, the centers of the hidden image are formed. Silver remains in a crystal in the form of clusters from several silver atoms (minimum 4 atoms) to hundreds, and halogen in the form of duitomic molecules goes into the surrounding space.

The formation of a hidden image is associated with the size and distribution of light sensitivity centers in terms of silver halide microcrystal. Only large centers of the hidden image are manifested, they are called manifestation centers; Small centers do not cause manifestations. The more the light fell on the photo material when exposed, the larger the particles that make up these centers, and the faster the manifestation will go. In the sections of the photo material that were not subjected to the action of light quanta, the reaction of photo polyesis does not occur and the centers of the hidden image are not formed.

If the exhibited photo material does not show in a timely manner, the hidden image may disappear: the components of its silver atoms are again connected to the halogen atoms and form the source substance - silver halide. This phenomenon is called "the regression of a hidden image", which is enhanced by storing the exposed photo material in a warm, wet, contaminated atmosphere and decreases at low temperatures.

When exposure under the action of light in microcrystals Aghal.forms hidden image consisting of several metallic silver atomsAG o. The hidden image becomes visible during the manifestation. The formation of a hidden image flows into two stages.

Electronic Stageleaves for 1 -14 - 1 -15 p. In this case, the quantum of light, the energy of which is equal hV, falling on the surface of the crystal lattice of silver halide Aghal., absorbed by ion Br. - , as a result, one electron e. - breaks off from the ion orbit of the ion and becomes free:

Br. - + hV = Br. + e. - where

h.- Permanent Planck, v.- the frequency of electromagnetic oscillation. The free electron enters the center of light sensitivity and creates a negative charge on it.

Ion stagephotochemical process: Ions that appeared free silver AG + Migrate according to the crystal lattice and under the action of electrostatic forces are attracted to a negatively charged center sensitivity, after which they are neutralized and converted into silver atoms:

AG + + e. - = AG o.

As a result, the center sensitivity is gradually increasing in the amount, turning after the cessation of light in hidden image consisting of several metallic silver atomsAG o. . Metal silver AG o. Has black opaque color. Hidden it is called because these several atoms AG o. It cannot be detected without a very strong electron microscope, but their presence is necessary to obtain a visible image with further chemical processing.

The exposure process must be considered statistically. So, the more the light quanta will go on a photosensitive layer, the greater the likelihood of the formation of a hidden image. If the grains of the photoemallation of unequal in size, then larger microcrystals will contain a greater number of surface sensitivity centers and, therefore, with equal amounts of lighting, the extraction of large grains of halide silver turns out to be more likely.

3. The process of manifestation.

After shooting, the exposed photographic material is subjected to special chemical photographic processing to convert the hidden image to the visible. The main stage - manifestation, is carried out in solutions of some chemicals, most importantly of which manifesting substanceit has a restorative effect on microcrystals of exhibited halogen silver. In the manifestation of silver ion is restored to the silver atom, and the exhibiting substance is oxidized, thus, a redox chemical reaction occurs.

The recovery process begins with a hidden image, which, having electrical conductivity, transmits the electrons from the ions of the X silver ions in the microcrystal:

AG + + Red - = AG + OX.where

AG+ - Silver atoms resulting from the reaction. The substance has a kind of large, loose, linked to each other of tangle threads. In the reflected and transmitted light, such silver has a neutral gray color, it is formed by visible photographic blaracing,

Oh- Oxidized form of exhibiting substances.

As the exposed grain occurs, the size of the silver particle increases with ever-increasing speed. During the manifest, the mass of silver is 10 10 times larger than when exposed.

The process of manifestation begins on the surface and as the evaporations of the exhibiting substances are gradually distributed into the depths of the emulsion layer. Thus, the time of manifestation can be adjusted by the amount of redundant grains AgBr..

Not restored when manifesting microcrystals AgBr.deleted upon subsequent processing of the photo material in the fixing solution.

Thus, under the action of light and subsequent photochemical treatment in the photoemulsia, opaque grains of metallic silver, forming visibleeye photographic blackening.

Hidden image - The change generated in a silver bromide under the action of light, not directly detected, but conditioning the exhibitibility of the emulsion layer. This change is so little that is invisible even in an electronic microscope with an increase of 50,000-100,000 times. The mechanism for the formation of a hidden image is found in its main stages. If the act sub-light quantum gets into the emulsion microcrystal, the energy of this quantum is spent on the bursting of one electron from the ion of the crystal grille of silver bromide. The photoelectron formed is freely moving along the crystal (see photoconductivity) until it encounters a trap. Such a "trap" can serve an alien adherence to silver bromide, mostly the smallest particles of metallic silver, which are created in the process of maturation of the emulsion. These particles (light sensitivity centers) are located mainly on the surface of microcrystals, although some of their number is also in depth. The light sensitivity center, which captured electron, acquires a negative charge and attracts a silver interruption ion (see the crystal lattice), which, connecting with an electron, forms a silver atom that is delayed at the center of photosensitivity.

This process is repeated, and the light sensitivity center turns into a steady substrate of the hidden image. The subcentre consists of several silver atoms, but can not serve as the center of manifestation, i.e. it is not the active center of the hidden image. The subcentrators play an important role in practically important methods for increasing photosensitivity - hypersensylization - and enhance the hidden image. With further illumination, the subcentre is frozen to the size of the center of the hidden image, and the microcrystal becomes manifest (see the manifestation of photographic, theory).

Simultaneously with surface centers of the hidden image, smaller depth centers of the hidden image are formed. Since ordinary developers do not contain sufficient solvents of silver bromide, they cannot reach the deep centers of the hidden image and show the microcrystal. Therefore, the presence in the crystal of a large number of deep high-temperature sensitivity centers competing in relation to the capture of photoelectrons with surface centers leads to a decrease in photosensitivity. After pulling out an electron by a quantum of light from a bromine ion, the latter turns into an atom of a bromine, which moves along the microcrystal before going to the surface, where it is associated with the gelatin or other bromine acceptor. In the absence of a bromine acceptor, the latter can again turn the silver of the hidden image to bromide silver (see Solarization) and the light sensitivity of the emulsion layer decreases.