This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
General Lighting. The form of lighting to employ is that which will give the greatest amount of relief and roundness to the object being photographed. Harsh and strong lighting should be avoided, as this will only tend to give hard, chalky high-lights and dense shadows. The light should be soft and diffused and when it is necessary to work close to the source of light, cheese-cloth or thin paper should be hung over the windows in order to diffuse the light sufficiently. Wherever possible, the light should fall quite broadly onto the object and at a slight angle.
Illuminating Shadows. If the lighting is too con-trasty, and if there is not a sufficient amount of illumination in the shadows, a reflector of some kind, such as white muslin or white paper, should be brought into use and light reflected into the deep shadows. Where there is much detail work in a large piece of machinery, sometimes it becomes an advantage, where electric light can be had, to run a wire, with a 32 candle-power bulb attached, from the regular socket across to the machine, locating the bulb back of some parts in the foreground, excluding it from view, but at the same time arranging it so as to illuminate some parts in shadow which require more detail.
227. Where electric light cannot be had, the use of magnesium-ribbon or magnesium-powder in the regular magnesium-machine will be found the most useful addition to your outfit, for by means of the blow-tube attached to the magnesium lamp, you can blow as light or as heavy a blast of light as you desire, and you can also move about the object while blowing in the tube, thus giving uniform illumination and overcoming any harsh shadows such as would exist if flashlight were employed, which naturally could be used from one point only.
Preventatives Of Halation. Halation will often be found difficult to prevent, especially when working toward strong light, and when it is impossible to adjust the objects so as to secure the proper angle of light. Where the object is situated under bad light conditions, such as just described, any halation about it may be overcome by arranging cur-
Photographing Castings and Machinery. 139 tains behind it and before the windows, at no time lowering these curtains below the object itself, and keeping them slightly, but constantly, in motion. As the remaining parts of the view will be blocked out anyway, halation above the object will do no harm. Where curtains are not at hand (however, shops manufacturing work of this kind are usually supplied with them), one can overcome halation to a certain extent by covering, with brown paper, the lower portion of the window which comes within range of the object being photographed. In other words, have the brown paper, or background, come one foot above the top of the object, as viewed from the camera.
229. It is far better to avoid halation at the time of making the exposure than to doctor the negative after development. The selection of the proper hour for exposure, when the direct light is not so strong toward the camera, will many times assist in doing away, to a great extent at least, with the bad effect of halation. Non-halation plates should by all means be used, unless you apply the principles given in Special Development, Volume II. Even when applying this method, non-halation plates will assist materially in producing better results. (See Pages 142 and 146.)