Photography

Photography (from Greek, light-writing) represents a mechanical method for obtaining images by means of a special apparatus on light-sensitive surfaces. The photographic apparatus in its design represents a camera obscura—a box blackened on the inside, on one side of which is a combination of optical glasses called the objective (see), and on the other, opposite side—ground glass; the objective projects onto the ground glass an image of the objects in front of it. The ground glass serves for the best possible focusing of this image. Connected with the objective is the shutter—a mechanism that allows opening and closing the objective for a specific time, preferably 1/100, 1/50, etc. seconds or for any extended duration. The process of obtaining the image breaks down into several stages. 1) Exposure: during exposure, a light-tight box-cassette is placed in position where the ground glass was, into which is placed a light-sensitive surface capable of receiving the future photographic image. During exposure, the cassette is opened, then the objective is opened for a specific time (the plate is exposed), giving sufficient time for light to act on the light-sensitive substance; such is silver bromide mixed in gelatin (bromide-gelatin emulsion), a thin layer of which is applied to a transparent substrate—glass or celluloid film—where it dries. By closing the cassette cover and the shutter, the exposure is completed. The plate on which the image has been taken, the exposed plate, cannot be exposed to light as this may spoil the image. It can be examined and subjected to further processing only in a dark laboratory—a light-tight room illuminated by dark red light, to which the light-sensitive substance is very little sensitive. The exposed plate looks no different from an unexposed one: the image on it is invisible, in a latent state (latent image), the nature of which has not been definitely established to this day. The next stage of obtaining the image is 2) development—the process of transforming the invisible image into a visible one. Development consists of immersing the exposed plate in a solution of special substances, predominantly organic (hydroquinone, para-aminophenol, metol—methyl-para-aminophenol sulfate), in which silver bromide in those places where it has been acted upon by light is reduced to silver, the black precipitate of which constitutes the essence of the image. This precipitate has a density, within certain limits, proportional to the amount of light that fell on the plate in that particular place. As a result of development, we obtain a mirror-reversed image called a negative, the light distribution of which is the reverse compared to the original. The darkest parts of the negative will correspond to the lightest parts of the original, and the most transparent parts to the darkest. By washing the negative (3-5 minutes in running water), development is completed. In the developed negative, especially in its shadows, there remains still a considerable amount of silver bromide, unchanged by either light or developer. This remaining amount can still be changed by the action of light and developer and thereby spoil the image; therefore this residue must be removed from the negative, which is done by immersing the latter in a 20-25% solution of hypo (sodium thiosulfate), Na₂S₂O₃, which dissolves silver bromide and does not act on the silver precipitate. This operation is called fixing the negative; it continues for 15-20 min. and is followed by an hour's washing of the now light-fast negative. Development and fixing constitute the negative process, which results in an image with reversed light distribution. To obtain an image with proper light distribution, it is necessary to carry out the positive process, consisting in printing the image onto another light-sensitive surface with a paper substrate (positive) or glass (diapositive). In the modern positive process, there are the same three stages as in the negative process (exposure, development, fixing). Exposure, negative and positive processes, the scheme of which is outlined above, constitute the basic or elementary photographic process, which results in a monochromatic, flat, stationary image. Even this process has extensive application in medicine as an extremely valuable aid in the visual method of teaching. It makes it possible to photograph patients, to photograph the normal arrangement of the external parts of the human body (anatomical specimens) or their pathological changes. It makes it possible to illustrate medical books not with hand-drawn inaccurate images, but with absolutely accurate, nature-made photographs, the production of which can be easily mastered by any scientific worker in a short time. Photographing the same object at certain intervals, more or less prolonged, according to a planned program, makes it possible to clarify the process of natural development; the development of the pathological process or the result of applied treatment and constitutes one of the medical methods. Its success is promoted by the fact that between the original and its photographic image there exists a certain geometric correspondence, making it possible to draw conclusions about the dimensions of the original from the dimensions of the photograph. The study of methods for measuring photographic images constitutes important specialized branches of applied photography: photogrammetry and stereophotogrammetry (see also Microphotography). Besides the basic photographic process, special methods of photography are also used in medicine: 1) color photography, 2) radiography, 3) microphotography, 4) stereo- and 5) cinematography. - Color photography, which makes it possible to obtain images in natural colors, currently has two generally accessible methods: 1) the three-color method, which makes it possible to obtain a colored image by combining three single-colored images, colored red, green and blue, and 2) the autochrome process of the Lumière brothers, where the colored image is obtained on specially prepared autochrome plates provided with a color screen. Special branches of photography also have extensive applications in medicine: thus, stereoscopic photography, which makes it possible to perceive the depth and relief of the subject when viewing the photograph, is especially important for photographing anatomical specimens. The structure of the inner side of the skull, completely incomprehensible on a single photograph, becomes completely clear on a stereoscopic photograph. - Cinematography—see Cinematography. - Radiography—see Radiodiagnosis. There have been successful attempts to combine the stereo-, cinema- and X-ray methods, in which the work of the lungs and heart was studied (Dessauer and Eikman). However great the successes of photography, however valuable and diverse its applications, it should nevertheless be recognized that photography is not yet a completely mechanized method, and the success of the work still essentially depends on the skill, theoretical preparation, and dexterity of the operator. In the absence of these qualities, photography not only cannot be fully utilized, but can also give poor results, capable of leading to false conclusions. To avoid this, it is especially necessary to master the main principles of exposure, development, and printing. Exposure is carried out in natural and artificial light (arc lamps, Nernst lamps, half-watt lamps, etc.), as well as in the light of electric sparks in some scientific experiments. At present, the most convenient is exposure under half-watt lamps, which can be connected to the ordinary lighting network and exposure with which continues for several (a few) seconds: with two 500-candle lamps placed near the subject (1 m), the light can be well regulated and exposure continues for 3-4 seconds. In daylight exposure is extremely varied and can last from 0.001 sec. to several minutes (in a room, in a dark forest). It depends on a great many factors: 1) time of year and hour of day, 2) cloudiness, 3) latitude of the place, 4) speed of the objective, and 5) sensitivity of the plate. For systematic accounting of these factors, tables and special instruments (exposure meters) have been constructed. Insufficient exposure (underexposure) gives harsh negatives, lacking detail in less illuminated areas (shadows). Excessive exposure (overexposure) gives monotonous, contrastless negatives, giving dark, unexpressive prints. The arrangement of the subject relative to the light source should be carefully chosen by the operator, but in any case, bright one-sided light should be avoided, as it produces coarse, contrasty prints. The next operation, which is important to master practically, is development, because with skillful conduct of this process it is possible, within certain limits, to change the contrast of the negative: using diluted developer solutions (2-3 times against normal concentration), one can soften the contrasts, using more concentrated solutions—increase them.

The ability to control contrasts during development is the primary skill of a photographer, applied in both artistic and scientific photography. Development should not be interrupted too early, but only when the contrasts are sufficiently strong when viewed against the light; determining the moment when development can be considered complete is given by more or less prolonged experience. Detailed instructions can be obtained in the literature. The same can be said about exposure. Photography is a purely practical method, however it has solid scientific foundations, and it is impossible to master it without knowing these foundations and without conducting numerous conscious experiments.

A. Dondé. Photography in forensic medicine. Forensic photography, applied in the investigation of crimes, has also entered forensic medical practice as one of the research methods. The tasks of forensic photography are, firstly, the precise fixation and reproduction of various objects related to the crime, and secondly, the detection and study of details not perceptible to the eye and insignificant color shades. Therefore, recording and investigative forensic photography are distinguished. In accordance with these tasks, methods of photographic shooting have been scientifically developed in forensic photography, and special equipment is used. It follows that not every photograph can serve the purposes of investigation. In forensic medical practice, photography is used: 1) to fix the scene of the crime, 2) instruments of the crime and other objects related to it (material evidence), 3) the corpse and living persons (for determining identity, nature of injuries, for registration purposes), 4) various traces (fingerprints, footprints, dental impressions, bloodstains, etc.). In forensic medicine, therefore, recording photography is mainly used, while investigative photography is actually a division of technical expertise (forensic photographic examination). During the judicial investigation, it is often very important to reconstruct the scene of the crime. One description of the scene of the incident (inspection protocol) naturally cannot give as clear a picture as photography will. For this purpose, Bertillon proposed metric photography (photogrammetry), which allows calculating the dimensions of the depicted objects and the distances between them from the photograph, making it possible to draw up a plan of the scene of the crime. Metric shooting is carried out under strictly constant and defined conditions, which would make it possible to calculate the actual dimensions of objects and distances on the photograph. The absence of metric equipment does not eliminate the need to photograph the scene of the crime. When registering criminals, in addition to other registration methods (see Dactyloscopy, Verbal portrait), photography is also used; photographic prints are pasted on a registration card. This so-called signalistic, or identification photography is also subject to certain conditions. During identification photography, two half-length shots are taken: in profile from the right and front view at ¹/ natural size with an uncovered head; the right ear must be free, not covered by hair. For signalistic shooting, proposed by Bertillon, cameras proposed by him and a special stand with a fixed chair and head holder are used. Identification photography is also used for photographing unknown corpses - see Identification in forensic medicine, Photography of traces (fingerprints, footprints, bloodstains, etc.) is carried out at the scene of the crime, or objects with traces on them are photographed in the laboratory, if their transportation can be done without damaging the integrity of the trace. Some traces before shooting sometimes require special treatment (fingerprints). Forensic photographic shooting requires from the photographer high qualification and special training in the field of forensic photographic examination.

M. Avdeev