ENGINEERING PHOTOGRAPHY Most of the technical considerations that apply to architectural photography apply equally well to engineering subjects. The truth of vertical lines must always be preserved by keeping the features that cannot be seen from any other position. One of the most important considera tions in engineering photography must always be to show the essential features of the work in an effective manner. Technical knowledge, or even a slight acquaintance with engin eering practice, will be exceedingly valuable to the photographer who undertakes work of this character. The object of the photograph is to illustrate the working of the machine ; to show most plainly its principal working parts and the manner in which its object is attained. Subject to these considerations, an oblique view should always be taken, if possible, in preference to a full front or side view. By choosing a position that gives a good perspective, the relief and projection of the various parts are shown, as well as their solidity and their relation to each other. In a view taken from the front, the sense of relief is largely lost ; the machine appears flat, its functions are not well shown, and its working is much more difficult to follow. The diagrams at A show plainly the reasons for this ; they represent a plan of a machine with the camera F placed in different positions. Sharp definition throughout is essential. Whenever possible, machines should be painted a good medium grey or lead colour, this assisting in rendering detail effectively throughout, and par ticularly in the shadows and light parts. The colour should be quite dull, a glossy surface being very undesirable. Bright parts may generally be left untouched, as they then look more natural than if painted white, as sometimes advocated. Paint gives an effect suggesting wood.
In many subjects difficulties in working may present themselves, and require ingenuity com bined with photographic skill to overcome. In sensitive plate vertical, whether the view of the machinery necessitates looking upwards or down wards. In many cases abnormal points of view
have to be taken, and the camera may have to be raised several feet in order to show essential photographing a subject with a long range of dis tances, the following method has been very efficient. The subject was some electrically con trolled railway points, and it was very necessary to show the mechanism between the rails as large as possible. The camera was placed about eight or ten feet from the principal part of the subject, but signals and other objects five or six hundred feet away were included, and all had to be sharply defined. The distance was entirely at the top of the picture, and the foreground at the bottom, the camera being placed as in diagram B. By tilting the camera downwards and using the swing-back, as shown at C, sharp ness was obtained throughout by using a medium aperture, as the foreground A in the diagram was focused at a in the camera, and the distance at b. Previously it was found that with the back and front of the camera parallel, f/64 failed to render the different planes reasonably sharp.
In all engineering subjects wide-angle lenses should be avoided as much as possible. In photo graphing complete workshops or very large pieces of machinery, they may be absolutely necessary, but for single machines of small or moderate size, a medium-angle or a long-focus lens should always be used.
In many cases machines can be photographed out of doors, and this is frequently preferable to the lighting in many workshops.
In most cases, engineers wish to have a dear white background for all isolated pieces of machinery ; this necessitates painting out the background on the plate (see " Blocking Out, or Stopping Out "), unless the work may be left to the process-worker's retoucher.
Photographing workshops is treated in the article " Factories, Photographing in," and notes on the exposures for these subjects are given under the heading " Exposure Tables."