Chronicle

Conference on Scientific and Technical Applications of Photography and Cinematography

The Commission on Scientific Photography and Cinematography of the Academy of Sciences of the USSR organized a conference on scientific and technical applications of photography and cinematography, which took place in Moscow on December 14–16, 1949.

Separate sessions were devoted to astrophotography and spectrography, high-speed photography and cinematography, electron photography, and microphotography.

The meeting was opened by the chairman of the Commission, Corresponding Member of the Academy of Sciences of the USSR K. V. Chibisov, who outlined the significance of photography in science and technology and its importance for the economic life of the country. K. V. Chibisov pointed out the principal features of the photographic method of research that determine its wide application: its documentary character; the possibility of measuring images or transforming them; the possibility of recording very short-lived or, conversely, very long-lasting phenomena; further, the ability to sum the action of light, simultaneously to record a number of details and to obtain images in natural colors or in rays of a definite region of the spectrum; then, the spectral range of sensitivity of the photographic layer, considerably greater than that of the eye or other receivers; and finally, the presence in the layer of sensitivity to elementary particles.

The photographic methods used may be divided into the following: a) projection (when an image of the object is cast by means of a lens onto the layer), b) shadow (for example, X-ray photography for medical and defectoscopic purposes), c) recording (for example, spectrophotography or the photographing of oscillograms), and d) the transformational method now being developed, in which an image is obtained as a result of transforming one form of energy into another.

Researchers working in the field of the theory of photographic processes met at this conference with workers who make practical use of photography in various branches of the national economy, and with workers who produce light-sensitive layers. The close connection between theory and practice is a reflection of that Bolshevik principled approach in science which Comrade Stalin teaches us. K. V. Chibisov greeted Comrade Stalin and concluded his address.

The report by the director of the Pulkovo Observatory, Corresponding Member of the Academy of Sciences of the USSR A. A. Mikhailov, was devoted to the application of photography in astronomy. At present most astronomical observations are made with the aid of photography. In all their diversity they may be divided into two large groups—astrometric and astrophotometric. The requirements imposed on light-sensitive materials for astrophotographic work are very

varied. Industry still quite inadequately satisfies the needs of astronomers for special plates.

A large collective effort to compile a stellar atlas was begun many years ago and continues to the present day. Since it was begun on nonsensitized plates, now, when it is necessary to compare photographs taken at intervals of 30–40 years, these works require completely nonsensitized plates.

The photosensitive layers used for astrometric work must be, if possible, fine-grained, have a large latitude and, accordingly, a small contrast coefficient, while their Schwarzschild exponent should, as far as possible, approach unity. The glass onto which the emulsion is poured in the manufacture of these plates must be perfectly flat and sufficiently thick. In astrophotometric work, photographic plates are required that are sensitive to different regions of the spectrum, possess great latitude, and are characterized by standardization with respect to photosensitivity and complete uniformity of the layer. For a number of astronomical tasks, plates sensitized in a special way are needed; for example, when photographing prominences and the solar corona during eclipses, a very high sensitivity to the green part of the spectrum is needed, where the coronal line is located. Photographing celestial objects in infrared rays with wavelengths of 1000 mμ and even longer is of great importance.

The report by Academician G. S. Landsberg was devoted to the role of photography in spectroscopic investigations. The speaker emphasized that spectroscopy reached its greatest flowering when photography was applied to the study of spectra. It made it possible to carry out precise measurements of spectra and helped establish spectral regularities. All the greatest discoveries in the field of the structure of the atom are due to spectrophotography.

To characterize the scope and precision of spectroscopic investigations, one may point out that modern tables contain about 100,000 spectral lines, whose wavelengths are determined in angstroms with an accuracy to the third decimal place. It should be noted that at present the resolving power of photographic layers already lags behind the resolving power of spectral instruments. Often, in order to obtain a measurement accuracy of 0.01 Å, it is necessary that the resolving power of the layer amount to several hundred lines per millimeter.

In some investigations, given the present sensitivity of photographic layers, exposures of up to one hundred hours have to be used. Therefore, a further increase in the photosensitivity of these layers is extremely important.

When photographing objects of low intensity, for example phenomena of molecular light scattering or light scattering on sound waves, photographic plates must have a sufficiently high Schwarzschild exponent, possibly close to unity, and at the same time both high photosensitivity and high resolving power are needed.

Particularly high and difficult-to-fulfill requirements are imposed on plates used for photographic photometry. These plates must possess high photosensitivity along with great contrast and broad and slight fog.

In conclusion, the speaker noted that modern methods for recording weak intensities (counters, photomultipliers) are beginning to compete with photographic methods. In photosensitivity—

they are little inferior to photographic layers, but have the advantage that they often make it possible to obtain quantitative results directly in the course of observation. The speaker believes that the new methods may prove to be a serious competitor to the photographic method. In order that the latter should not lose its position in spectroscopy, further intensified work is needed on improving the quality of photographic plates.

The report of Prof. Yu. N. Gorokhovsky was devoted to methods of photographic photometry. Considering the various techniques used in this field of measurements, the speaker tried to determine the limits of their applicability. In photographic photometry the blackening produced by the object under study is compared with the blackening obtained under the same conditions on the same layer from a standard source. One can dispense with a standard in the case where the photosensitive layer is entirely homogeneous in its properties and its sensitometric properties have been well studied. A. V. Markov proposed a distinctive method of photographic photometry in which a continuous sensitogram, obtained on the same layer as the image being investigated, is used as a measuring wedge for densities and for the direct determination of the effective amounts of illumination.

Obtaining correct results in photographic photometry is impeded by: 1) the different spectral composition of the radiation of the object studied and of the standard sources; 2) the existence of deviations from the reciprocity law; 3) the dependence of the form of the characteristic curve on the spectral composition of the light; and 4) the dependence of the form of the characteristic curve on the development conditions. The speaker noted that in the ultraviolet region the dependence of the contrast coefficient \((\gamma)\) on wavelength is very different for highly sensitive and low-sensitivity layers. Whereas for the former the contrast coefficient is almost unchanged, for the latter it decreases considerably as one moves farther into the ultraviolet. One of the most important sources of errors in photographic photometry is the nonuniformity of development, caused by the diffusional character of the development process. In addition, in photographic photometry it is necessary to take into account the nonuniform transmission of the objective of the photographic system over the field and the light scattering within it, which leads to a distortion of the shape of the characteristic curve. When measuring blackening densities, the dependence of density on the aperture of the photometer objective must be taken into account.

The speaker discussed in detail the great importance, in photographic photometry, of the geometrical dimensions of the image of the object. For small image dimensions, the blackening density obtained, besides the factors mentioned above, depends to a considerable degree also on light scattering in the layer and on boundary effects during development. If the photosensitive layer is illuminated by a parallel beam, then, as I. I. Breido showed, when the image dimensions are reduced the blackening density obtained first increases and then falls. When the layer is illuminated by a diffuse beam, only a decrease in density is observed. Correspondingly, in the case of an image of a slit 15 microns wide, the photosensitivity under illumination by a parallel beam was only 50% of the sensitivity under the same exposure conditions but with an image width of 500 microns; with a diffuse beam the sensitivity in the case of an image of 15 microns amounted to only 20% of the sensitivity in the case of an image of large dimensions.

The use of multilayer color films for photographic photometry, in the speaker’s opinion, is sharply limited by the fact that they

in principle do not allow monochromatic colors to be reproduced, and in them there occurs a mutual influence of the elementary layers during their joint development, which makes the sensitometric properties variable as a function of the color of the object.

In a short communication, Corresponding Member of the Academy of Sciences of the USSR D. D. Maksutov characterized the new photographic meniscus objectives developed by him, which, while having very small dimensions, have a focal length of up to 1 meter and an aperture ratio of up to 1:2.8. The resolving power of these objectives is about 100 lines per millimeter.

In the report by Doctor of Technical Sciences P. G. Tager, the problem of the photographic recording of electrical processes by means of light modulators was considered in detail. This type of recording plays a decisive role in a number of scientific studies and areas of technology; its significance is determined by the broad range of rates of processes subject to recording. Thus, one can obtain oscillograms of processes lasting from hundred-millionths of a second to several days. The development of methods for the photographic recording of electrical oscillations made possible the existence of such important fields of technology as phototelegraphy and sound cinematography. Soviet scientists and inventors have done a great deal for the development of these fields of technology.

Of great importance in the photographic recording of electrical oscillations are light modulators, in which the magnitude or direction of the luminous flux changes under the action of some factor. The speaker gave a detailed survey of existing light modulators. They may be divided into two groups. The first group includes light modulators that merely change a luminous flux coming from a constant source of light; the second group includes those that themselves are modulated light sources. The speaker dealt in especially great detail with the significance of cathode-ray tubes, widely used in various fields of science and technology. Thus, for example, television is based on the use of cathode-ray tubes, first employed for this purpose by the Petersburg professor B. L. Rozing as early as 1907. The combination of cathode-ray tubes with photographic materials possessing high resolving power and photosensitivity makes it possible to carry out phototelegraphic transmission of text at a speed of many thousands of words per minute.

Candidate of Physical and Mathematical Sciences V. N. Verntsner delivered a report on the features and possibilities of electron microphotography. The electron microscope is a powerful means of observation, having a resolving power two orders of magnitude greater than that of optical microscopes. Soviet electron microscopes, produced serially by our industry, possess a resolving power of up to 20 Å and a useful magnification of up to 100,000 times. In view of the fact that the specimen examined in an electron microscope is placed in a high vacuum and is penetrated by a stream of electrons, the preparation of specimens must be carried out with particular care. Usually the objects studied are deposited on an exceedingly thin organic film, a film \(10^{-5}\) millimeter thick. Most often films of collodion are used, but in individual cases it is replaced by inorganic films of quartz, aluminum, or aluminum and beryllium oxides. The structure of massive materials is studied on replicas.

Visual study of an object with the aid of an electron microscope is usually concluded with photographic recording. Since the photographic material must be in a high vacuum, the first requirement imposed on it is the smallest possible evolution of gases. Therefore, for electron microphotography, more suitable—

are more suitable for plates than films. The emulsion should be, as far as possible, contrasty, poor in gelatin, and fine-grained, so as to allow a subsequent enlargement of 10–15 times. It has been established that plates of low sensitivity to ordinary light possess high electron sensitivity. When interpreting electron microphotographs, it is always necessary to take into account that a high vacuum and a powerful electron beam can substantially alter the object during observation.

In the report of Corresponding Member of the USSR Academy of Sciences S. Z. Roginskii, there were presented the extensive investigations, carried out by the speaker and his collaborators, of topochemical processes performed with the aid of the electron microscope. The electron microscope made it possible to study very conveniently one of the groups of chemical reactions in the solid phase, namely the decomposition of crystalline hydrates. In these reactions, gas molecules are initially evolved with the formation of pseudomorphs after the original crystals. At first even the electron microscope does not make it possible to observe the system of molecular pores arising during weathering and penetrating the solid product of the reaction. The following stage in the decomposition of crystalline hydrates, carbonates, and permanganates is the enlargement of the molecular pores to sizes visible in the electron microscope. With further decomposition of the solid reaction products, especially upon heating, recrystallization and contraction of the pores occur.

The work of A. B. Shekhter showed that in these processes a major role is played by the migration of atoms and molecules along the surface. The speaker emphasized that all the principal photographic processes—the formation of the latent image, development, and so on—are typical topochemical processes having much in common with those described above.

The report of Doctor of Technical Sciences E. M. Brumberg was devoted to the method of color microphotography in invisible rays developed by the speaker. In this method, color transformation is used, consisting in the fact that three color-separation photographs are made in rays of different wavelengths in the invisible regions of the spectrum, and positives printed from these color-separation negatives are synthesized into a color image by means of the three primary zones of the visible spectrum. In this way, the slightest differences in the selective absorption of invisible rays are made extremely evident. Since most substances, colorless in the visible region, differ greatly in their absorption in the ultraviolet and infrared regions, we are able to recognize easily combinations of colorless substances. The method of color transformation has been successfully applied to the study of the chemical composition of various biological objects. It is also of great benefit in microchemical and chromatographic analysis.

Soviet optical industry is producing special microphotographic installations for color transformation. The achromatic mirror micro-objectives contained in them make it possible to obtain sharp microphotographs in ultraviolet light even in cases where focusing is performed in visible rays.

Candidate of Technical Sciences I. A. Chernyi gave a report on methods of high-speed cinematography. The speaker indicated that although it is possible to take individual groups of photographic images with extremely high frequency, obtaining a true cinematographic image suitable for projection on a screen is possible only with a frequency of up to 10,000 frames per second. At a frequency of up to 250 frames per second, the film in the motion-picture camera can move intermittently; at higher shooting frequencies it is necessary to use continuous film motion, applying the appropriate optical compensation,

The speaker examined in detail various methods of optical alignment and pointed out all the difficulties that arise when increasing the filming frequency. One of the most important obstacles is the inertia of the film and of the moving parts of the camera. Therefore very high filming frequencies, on the order of hundreds of thousands of frames per second, can be obtained only with cameras in which the film and most of the other parts remain motionless, and only one light mirror rotates. Naturally, at extremely high filming frequencies it is necessary to dispense with any shutters and to resort to intermittent illumination by means of special light sources.

At the concluding session of the Conference two reports were delivered. Candidate of Technical Sciences V. Ya. Mikhailov presented a communication on photographic materials for scientific and technical purposes. The speaker characterized both the necessary assortment of special photographic materials and the capabilities of industry in this respect. Approximately one year before the present conference, the Commission on Scientific Photography and Cinematography had asked all interested organizations for information on the nomenclature and quantity of special photographic materials required by them. Unfortunately, only very few organizations responded to these inquiries. Therefore, at present, only the requirements for materials used in spectroscopy and astronomy, as well as for reproduction and printing purposes, can be precisely formulated.

At the same session Prof. Yu. N. Gorokhovsky delivered a report on the life and work of two outstanding figures of Russian photographic technology—V. I. Sreznevsky (1849–1937) and E. F. Burinsky (1849–1912). The name of the first of them is associated with the creation of the first aerial-photographic apparatus and special photographic materials for it (1886), a special camera for the expedition of N. N. Przhevalsky in Tibet (1882), and other original photographic cameras for scientific and technical purposes. V. I. Sreznevsky was an indefatigable popularizer and propagandist of the newest ideas and methods of photography; he was the founder and editor of the excellent journal Photographer, which was ahead of similar foreign publications, and the author of the Photographer’s Reference Book, which appeared in three editions and is superior to the highly regarded photographic reference book. He was the principal organizer of the Russian photographic technical community in the 1880s and 1890s, and after the Great October Revolution was one of the founders of the Higher Institute of Photography and Phototechnics (now the Leningrad Institute of Motion-Picture Engineers). E. F. Burinsky is rightly considered the creator of forensic photography. He developed an exceptionally subtle method for increasing the contrast of a photographic image, which, under the extremely limited capabilities of the photographic layers of that time, made it possible to photographically reveal the invisible.

After the close of the conference, a demonstration was arranged of various popular-science films shot by the studio of popular-science films and by various scientific institutions. Among them were black-and-white and color documentary films, color footage of surgical operations, and high-speed and slow-motion filming of various phenomena.

K. S. Lyashkov