INVISIBLE PHOTOGRAPHING.

Auckland Star, Volume LXIII, Issue 139, 14 June 1932, Page 6

INVISIBLE PHOTOGRAPHING.

Our double-page picture to-day —a photograph taken from Old Park, Dover —demands some explaining (says "The Times" of May 9). Two things about it will probably be noticed at once —the extraordinarily clear and wide range of the French coast which it presents, and the strange whiteness, almost suggestive of snow in a winter's landscape, of the grass and foliage in the foreground. The photograph, however, was taken only the other day, when there was no snow on the ground, and in an atmosphere, moreover, which made the French coast all but invisible to the eye and to the ordinary camera. The picture is, in fact, the outcome of a method of photography which lias been possible for some time, though it is only lately that the process has reached the present practical stage. It is now no longer necessary for a photographer to wait upon the weather when he wishes to photograph distant objects or scenery which the thickness of the atmosphere prevents him Prom seeing. His camera has acquired the power of penetrating mist and haze, or rather disregarding them as though they were not, and of recording objects within its range as clearly as if the image were presented through the. most translucent atmosphere. The secret of this new photography can be succinctly explained. One of the reasons why it is impossible to see far in misty or hazy weather is because the moisture in the air scatters the .light; but the light is scattered also on a fine day, though less when the light is yellowish or reddish, as towards sunrise or sunset. Bed light, indeed, is scattered less than blue. The problem, therefore, has been how to use 'the infra-red light in the atmosphere, and to exclude all the light in the atmosphere which is not infra-red. This is achieved by a so-called filter, or suitably-dyed piece of gelatine, placed in front of the lons. It allows infra-red rays alone to penetrate and to carry the image; and, though infra-red light is invisible to the eye, the. sensitive material employed in the camera is responsive to it. Thus by an' infra-red sensitive plate photographs can be taken at distances not possible in the ordinary way with a telephoto camera, and objects revealed which the eye c-annot see. The effect, it is true, is that the appearance of a landscape is altered to the eye —hence 'the whiteness of the Dover verdure in to-day's picture; but the outlines are true and are of a distinctness not obtainable before. The French coast, it must be added, has been brought all the nearer by a magnifying lens; but on"" the day of the photograph the unaided eye could barely see it, and the direction for the camera was worked out by compass. The photographer was some 300 feet above sea level. The fascination of further experiments from hitrher altitudes and across greater distances can be imagined.