Amateur Photographer & Cinematographer (1935)

January 30th, 1935 Tut AMATEUR PHOTOGRAPHER 6 CINEMATOGRAPHER a screen it seems to expand as you watch it ? It is an optical illusion of some sort, and it may apply to other subjects besides flowers, but it is an argument for not running through the slides too quickly, Secrets of the Circus. A unique meeting was held the other evening in close proximity to Olympia, when a crowded assembly of doctors had before them, one by one, for demonstration and dis¬ cussion, the various freaks and oddities appearing at Mr. Bertram Mills’s circus. These included a charming lady midget, standing twenty-six inches high and confessing to twenty-four years, some giraffe¬ necked ladies, a tattooed man, and the like. Every one of them in turn was photographed with a flash camera, and enjoyed that with the perfect abandon of the showman, but, what was more, some of them underwent the ordeal of X-ray photography too. One gentleman was known as the “ human ostrich,” and swallowed various objects, whereupon he was taken down to the X-ray room, and presently a picture of his stomach was exhibited to the audience, showing indubitably that one of the objects at any rate had reached that organ, having really been swallowed and not conjured with. Bad Weather Photography. Photography is a sunlit art, but we have never noticed any dis¬ inclination of its devotees for bad weather. Indeed, it has sometimes been levelled as a reproach against pictorialists that they are too fond of threatening skies and rain-washed pavements. But Miss Mary Field, whose name is so well known as a producer of nature films, told an audience recently that she was very anxious to experiment much more with bad weather photography. In her belief we are not standing up enough to the problems which bad weather imposes. She was showing a film of farm operations, which, of • course, go on in good weather and bad, and one very successful sequence showed ploughing in a snowstorm. The entire film in question, although it occupied less than half an hour to show, took Miss Field and the photographer and others concerned a year to make. What it illustrated was the various operations on the wheatlands of East Anglia from one October to the next. One difficulty was for the camera-man to remember his lighting from one month to the next, so as, while suggesting the variety of the seasons, to get a unity of effect. Readers’ Problems Selected queries on topics of general interest to readers will be fully dealt with on this page week by week. Other replies appear as usual on the last page. Colour Values. I know that ortho, and pan. plates register colours better than ordinary plates, but have only a vague idea of the exact differences. Can you inform me just ivhat colours each kind of plate can record ? J . M. (Hampstead.) We will try to give you an idea, but this cannot be done simply by giving lists of names of colours. The diagram will serve to give an approximate idea of the problem, and show why there is no single exact ans\ver. The diagram is of a spectrum such as can be obtained by refraction. The verticals are the Fraunhoffer lines, and if you can refer to a colour illustration of a spectrum this will make things clearer by showing in what position and colour these lines fall. At the bottom are degrees and figures showing the wave¬ lengths in Angstrom units, such a unit being 1/1,000, oooth of a millimetre. Roughly speaking, the colours, starting from ONMIKHh C F bE D C the left, are : To 400, ultra-violet ; to 420, violet ; to 450, indigo ; to 490, blue ; to 520, blue-green ; to 570, green ; to 590, yellow ; to 640, orange ; to 700, red ; then infra-red. If a plate is exposed to such spectrum colours, the densities resulting from each can be measured, and an irregular curve obtained. In the diagram the curve which reaches least of all towards the red end is that of an ordinary plate. The next curve, reaching rather farther in this direction, is typical of/a plate orthochromatised with erythrosine. The third curve, reaching into the red, exemplifies a plate panchromatised with isocyanines. It will be seen that all the plates are sensitive to blues, violets, and ultra-violets. This particular diagram is a modification of one given by M. Clerc in “ Photography, Theory and Practice.” Similar diagrams would vary considerably in the resulting curves according to the character of the original emulsion and the dye used in colour-sensitising it. A curve showing the apparent luminosity of the spectrum colours as seen by the eye would be very different from the density curve B CL A given by any photographic plates. By giving longer exposure it would be possible to extend the reach of the curve given, say, by an ordinary plate ; but only to a limited extent, as the more actinic rays would cause over-exposure, and even reversal. The vigorous action of the blue and violet rays can be effectually checked by the use of yellow filters, which prevent over-exposure of these rays while sufficient exposure is given to extend the curves towards the red end. The curves then approximate more closely to that indicating the visual effect. In practice the matter is still further complicated by the fact that objects reflect rays other than those which, by their predominance, give their charac¬ teristic colour. 6 96