Home Movies and Home Talkies (Jun 1933-May 1934)

94 HOME MOVIES & HOME TALKIES HOW YOUR CAMERA WORKS A Quick Guide to Successful Exposure By PERCY W. HARRIS, F.A.C.I. THIS is a month of all the year when cine cameras are most in evidence. For many of us week-ends and the hohdays are the only times when we can go out and shoot, and as in our delightful climate fine weather is generally reserved for office hours and rain for week-ends, it is not surprising that our annual fortnight or three weeks becomes a true cinematographic holiday ! A number of articles on exposure have already appeared in these pages, but as we have so many new readers we think it well to repeat some of the infoi-mation previously given and to amplify it more, perhaps, than has been done previously. The technical standard of many amateur cine films is much lower than it .should be, and far too often the apparatus and not the operator is blamed for a poor result. As we have tested and used practically every cine camera on the market we have no hesitation in saying that not one bad film in a hundred can be blamed on the camera and a similar remark can be applied to the film itself. Cine film varies in quality just as does the film used for still cameras, but we can assure you that no really bad film is sold. What, then, is the cause of most bad films ? Faiiity exposure. The cine camera is, of course, nothing more than a special camera designed to take a long series of snapshots, one after another, at a steady rate. For convenience the sensitised film is rolled up on a bobbin and fed through the camera, not continuously, but in a series of jerks. When one section of film is in position the shutter of the lens opens for a fraction of a second and immediately closes tigain. As soon as it is closed the film is moved on by clockwork for just a sufficient distance to expose a new piece of film, the lens opens again, shuts once more and once again a new piece of film is substituted. This goes on so long as you hold the release down until the roll of film is exhausted. Still and Cine Cameras In principle there is little difference between your ordinary still snapshot camera and a cine camera. In each case we have the image focused on the film, the exposure being carried out by opening and shutting the lens. When you look at a subject with your eye it seems to you brilliant or dull according to the amount of light reflected from it, but your eye does not make any permanent record and is, generally speaking, kept open all the time. Your eye is also a very sensitive organ and nature has arranged a device known as the iris (a ring-sl>aped muscle) which diminishes the aperture of the eye if the light is very bright so as to prevent the intense brightness injuring the delicate surfaces. You have noticed that in a dark room the pupil of the eye is large and in bright simlight it contracts. Actually what is hajipening is that the nerves of the eye act upon the iris muscle and cause Shooting a scene in " All on a Summer's Day," a Meteor Film Producing Society's production [Fox Photos If the camera is set up and focused a child can easily operate the release the aperture to be closed as the light increases beyond a certain amount. Now in a camera the image of the scene is focused on the film and the longer the image is focused on this film the greater is the chemical effect ])roduced. What we are aiming at is to get after our final development and printiiig an image showing the scene we have photographed in tones of black and white. If we are photographing a black-and-white chess-board there will be focused on the film a series of squares, the black squares meaning there is no light and the white squares a lot of light. Where there is no light there is no action on the film and where there is bright light action takes place. For a given scene a certain amoimt of light reaching the film will produce an excellent result. If we do not have enough light the scene will not register its detdils in shadows and if we have too much there will be far too great a light action and the whole thing will be " clogged up." Controlling Light The regulation of the amount of light reaching the film (whether it be in a cine or still camera) is therefore of great importance. There are only two ways of controlling the amount of light, one is by the time the shutter is kept open and the other is by the amount of light the lens will allow to enter. Photographic lenses are of different sizes and are rated according to the amount of light they will let in. The method universally adopted is to give the proportion of the diameter of the lens opening to the distance from the optical centre of the lens to the .sensitive material. For example, /, 8 means that a pro[)ortion of lens diameter to the distance from the lens to the film is