American cinematographer (Jan-Dec 1941)

Getting Normal Exposures Under Abnormal Conditions By P. C. SMETHURST THE grounds on which the system described in last month's article was chiefly attacked when the writer first brought it forward some time ago were that (a) flat scenes were overexposed on the screen, and that (b) in a very contrasty subject the shadows were much too dark. Both of these criticisms are due to a confusion of exposure and contrast. The professional cinematographer arranges contrast by reflectors, subsidiary shadow-lighting, and special filters, and if amateurs wish to obtain the same results they must naturally adopt similar measures. A flat subject appears light on the screen because the face tones remain the same brightness as when the sun is shining, but the shadows are not so dark. A similar effect is bound to appear when the sky is overcast: the lack of shadows makes the image seem over-light, although a careful examination will show that the lightest tones are still at their correct brightness level. It has often been suggested that this trouble can be cured by underexposure on a flat subject, but this merely darkens the sky until it looks leaden, and makes the face of any unfortunate person in the camera field looks as though it had not been washed for some weeks. Underexposure is never a cure for flat contrast: a special filter often is. The other complaint — of excessively dark shadows in a contrasty subject — is based on a similar misconception. If the shadows are to show detail (and every film has a limit to the range of tones it will accept) then more exposure must be given, and the face tones will be burnt out at once, but since in films face-tones are more interesting than shadow-detail (unless the latter is shown as a special close-up for a particular purpose) the result is that the shot seems overexposed. No two films have quite the same contrast, and it is always possible to choose one with an emulsion characteristic that suits one's personal feelings on these points. Whatever the choice, it is one between two evils: a hard film peps up flat scenes, but makes contrasty ones over-dark in the shadows, while a soft film shows the contrasty scenes well but)j makes the flat ones seem very dull indeed. The lack of contrast when using tele; photo lenses has usually nothing to do t with subject contrast or film contrast. but is due to light scattered all over th<image by the long lens barrel. This light may not be very high in intensity, , and thus hardly affects the lightest tones of the scene, but the shadows are fogged by the general scattered light all over them, and come out on the screen much lighter than they have any business to do. The only cure for these troubles is a long lens-hood coupled with an effects-box which cuts out all the light going through the lens which does not actually fall in the area of the camera gate, a deep yellow or red filter to keep atmospheric haze down, and some attention to the inside of the lens barrel in the form of masks. The least trace of shine on the inside of the barrel will cause quite a lot of scattered light ami reduce contrast materially. One of the important things about the intrinsic contrast of a film is that it af fects the extent to which errors in exposure are permissible in practice. It is a matter of experience, as well as perfectly good theory, that a contrasty film is more affected by a slight change of exposure than a soft one, so that in prac tice any film giving a high contrast musl be exposed as carefully as possible. The most difficult films of all to expose an color-films, and this is partially due to the fact that they effect color-separatioi by monochrome image-contrast. The flat (Continued on Page 402) ::sl' August, 1941 American Cinematographer