INFRA-RED PHOTOGRAPHY

Otago Daily Times, Issue 21979, 14 June 1933, Page 4

INFRA-RED PHOTOGRAPHY

A CHEMICAL TRIUMPH Photography in all its branches must be numbered among the progressive arts. The experiments in producing pictures taken in whht is, for the natural eye, invisible light, forms a fascinating story. Dr Walter Clark, of the Eastman Kodak Research Laboratories, recently prepared an article covering the subject, and we are indebted to Kodak New Zealand, : Ltd., for the opportunity of producing some extracts from it. For some years, Dr Clark says, experimenters in - photography have been attempting to take, photographs by light which is either invisible or only slightly visible* to the eye, the invisible waves of light being longer than those to which the eye is sensitive. One of the great reasons for using infra-red light in photography is that it can penetrate far setter through hazy atmospheres than visible light, and iso it is very valuable for photography at great distances. Dr Clai'k’s article contains a summary of experiments which have led up to the present results. Captain Abney, one of the foremost photographic investigators of the last century, described ways of making a plate sensitive to the infra-red as far back as 1880. Professor R. W. Wood, of Johns Hopkins University, published in 1910 . a series of remarkable photographs he had taken using infra-red rays alone. Nearly 10 years ago Professor Wright photographed the Yosemite Valley from Mount Hamilton, in California, 120 miles away, using infra-red rays. In 1931 Captain Stevens, of the United States Army Air Service, made photographs* from airplanes by infra-red light, the greatest distance being 310 miles. In the following year he took photographs at a distance of 331 miles. Dr Mees, the English who is now director of the Kodak Research Laboratories at Rochester (U.S.A.), in 1931 succeeded in taking a photograph in complete darkness. The occasion was the visit of a group of distinguished executives and scientists, sponsored by the National Research Council. A booth was erected in the laboratory in which were placed 15 1000-watt electric lamps pointing towards the ceiling of the room, and over the top of the booth were placed very deep filters which transmitted only infra-red light (Wratten SSA filters'). Using one of the special new infra-red sensitive plates (Eastman Mesocyanine) hypersensitised wi th ammonia, and a lens working at f/3.0, a good negative of the group in the auditorium was obtained with an exposure of one second. Although Dr Mees had previously stated his intention of taking this photograph, he sprung somewhat of a surprise on the audience, as he was addressing them. All the lights were suddenly switched off for two or three seconds, the audience heard a dick, and later were informed that the photograph had been taken. The plate was immediately developed and shown later during the lecture. The lecturer pointed out that development of this idea might make things very unhealthy for burglars carrying out their nefarious profession in the dark. A room could contain infra-red light, which is quite invisible to the eye, and an automatic camera focussed upon a certain point would make an exposure when a lock or such like was tampered with. v--;-’ , It is a simple matter to photograph a hot body, such aS an electric flatnron, in* a totally dark room, using the invisible heat rays emitted by - the object itself. This has been done,' for instance, with a flatiron and an electrie_ soldering iron.. The results are interesting in that the variations in temperature over the surface of the object show up as variations in density on the photograph. A portrait of a plaster bust has been made in the Kodak laboratories in total darkness, using two electric flatirons as scources of invisible radiation. Good negatives were obtained using only the heat rays from these flatirons, with an exposure of one'hour at f/4.5, on sensitised Mesocyanine plates. : Scientists are of the opinion now that with the aid of infra-red rays, visibility through mist, femoke, gases, and fog bv the Human eye will be possible with special lenses Imagine the value and safety of navigators, motorists, and aviators, if such is achieved. In warfare, smoke screens from battleships and aeroplanes will no longer be a means of hidden manoeuvre. „ For infra-red photographs of landscapes where it is desired to penetrate atmospheric haze and show up objects distinctly, at very great distances, a procedure similar to that employed by Captain Stevens will lead to satisfactory results; for example, for some of his pictures ho used a material similar to the Eastman extreme red sensitive plates, hypersensitised, and a Wratten 89A filter, the exposure being one-filth of a second at F 5. In general it can be taken that for distance work in sunlight an exposure of one second at F 8 on extreme red sensitive plates, using the above filter, will give good results. Landscape photographs taken by infrared light appear quite fantastic, and are very characteristic. Green foliage is a very strong reflector of the infra-red, and therefore leaves of trees appear as if they were white. Shadows are very deep and show total lack of detail, while the blue sky appears black, since there is practically no red light in it. The photographs accompanying tins article were taken by Mr K. S. Birrell, of the Otago University. They are the first to be produced in Dunedin, and clearly demonstrate , the penetration powers, of infra-red. These familiar scenes were enshrouded with thick mist and haze, and haze when the exposures were made.