The Cine Technician (1943 - 1945)

130 THE C I N E T E C H N I C I A N November— December, 19 1-'< Edited by A. E. Jeakins TECHNICAL ABSTRACTS Kodachrome in the Air (Elmer Dyer, A.S.C., American Cinematographer, February, 1943). Called in to do the aerial photography for a Kodoachrome instructional on the handling of the Lockheed P. 38 " Lightening," Elmer Dyer found himself faced with some new problems. Exposure was one. Shooting for duping, as in this case, best results are got if the Kodachrome " original " is on the soft side both as to colour and contrast — that is, slightly overexposed. Dyer worked to a film speed of Weston 5 instead of the Weston 8 recommended for getting correctly exposed "originals" for projection. Camera used was a Cine-Kodak Special. While its compactness and quick magazine change were advantages, the viewfinder was found to be rather inadequate for the tricky business of following the evolutions of a fast fighter plane. Accordingly Dyer had an Akeley matched lens finder fitted to the Special. This was carried on a C-shaped bracket which fitted round the rear of the camera and was mounted so that it was aligned directly over the camera lens. As all shooting was done at infinity focus, once the finder ami camera lens had been correctly matched there was no further need to worry about parallax. The tripod was a regular Akeley gym head mounted on a high mat. This was a not entirely satisfactory arrangement as the weight of the Special was insufficient to balance the springs in the Akeley head. Dyer admits lie would have been happier with a light friction head or a Vinten lighl gyro Illumination Contrast Control (Capt. Don Norwood, American Cinematographer, April, 1943), A method of using the Norwood exposure meter to measure and control illumination contrast is 'described. An attachment consisting of a hood which fits over the hemispherial light collector of the meter is used. The hood has a lozenge sha opening so that selective measurements can be made of any sector of the surface of the light collector. Suppose a meter reading taken on the sunlit, side of a subject indicates f.5.6 and the reading on the shadow side says f.2.8 then the rain between the two readings is the illumination contrast : in this example 4 to 1. Where the cinematographer has decided that a particular scene or sequence is to be lit for a determined degree of contras 4 to 1, the method of working would be to take a reading of the key light ; assume this gives f .4 then it is obvious that the shadow lighting must be built u] give a reading of f.2. This technique would be particularly valuable in colour photography where contrast ratios have to be kept to much narrower limits than in black and white. The meter with its contrast hood can also be used to make a record of lighting set-ups for duplication at a later date. For this purpose the subject is regarded as the centre of a circle which is divided into six sectors. The meter is held at subject position, readings are taken in each of the six sectors and a record made of them. New System of Lens Calibration (Daniel Clarke. A.S.C., American Cinematographer, April, 1943). The usual system of calibrating lens apertures is based on the ratio of the diameter of the lens opening to the focal length and disregards such factors as the type of glass used in the lens, the number of elements, their respective transmission factors or the number of glass-air surface-, all of these affect the light transmitting power of a lens to such an extent that it is possibl quite considerable variations in density liferent makes of lenses. To overcome tie tern of diaphragm calibration based on the actual light transmitting charai be sties of each I been developed at the 20th Century Fox S The lens to be calibrated is screwed into one • of a light tight tube at the opposite end of which is mounted a photo-electric cell wired to ammeter. In front of the lens is a diffus source with a poltag* i ontrol and meter in circuit. To calibrate a lens the light-source is brought to a known intensity In means sistanee and checked through a master lens. The lens calibrated is substituted for thi master lens and the diaphragm si", to produce on the photo-cell meter a reading corresponding to thai produ by a setting oi E.3.2. on the master-lei T point is calibrated as F.3.2. Thereafter the si above and below this point are worked out in a similar manner. By this method it can be m ain that every lens transmits exactly the same amount of light at any givi □ op, regardless ; design or construct