312. A very important use to which photography has been put is catalog illustrating. There is scarcely an article advertised that is not photographed and the illustration employed in advertising literature. Various machines and office appliances, and almost all manufactured articles, are photographed so as to show their exact appearance, and in the case of instruments and machinery, they are photographed in sections, illustrating the mechanism and manipulation.

313. Photographs for this purpose require clear, sharp detail, with uniform illumination over the entire object. The matter of background or foreground, as a rule, for this class of work is of no consequence, as the object is usually blocked out on the negative before the prints are made; or, in many cases, prints are supplied to the engraver direct from the negative without blocking, when the artist employed in the engraving establishment will paint over the print, blocking out all objectionable parts, building up and strengthening the outlines, weak parts, etc. So the photographer's work is merely the producing of the best direct photograph possible, so that the engraver has a good basis on which to work.

314. The Lens

The Lens. The best lens to use for this class of work is one of fairly long focus. The focal-length of the lens should be at least twice the longest side of the plate. This will permit of the camera being placed far enough away from the subject to give accurate perspective. A wide-angle lens should never be used unless it becomes necessary owing to working in confined quarters, where the object is immovable. A wide-angle lens will not give a true rendering of the object; it invariably gives a flat and distorted image, the front of the object being decidedly out of proportion to the rear. The ordinary rapid rectilinear lens, or an anastigmat lens, may be used very satisfactorily. Both, however, should be stopped to at least f. 16, in order to secure good depth of focus. If the distance from the front of the subject to the rear is considerable, and the camera is quite close to the subject, a smaller aperture will have to be employed, to be sure that all parts are absolutely sharp.

315. Background

Background. As a rule, the background for the majority of articles should be perfectly white. When articles are arranged on a table or similar support for photographing, a drapery of some neutral tint may be employed, covering the table and extending back of it to a height sufficient to give a background for the articles being photographed. It matters but little what the material is which you use for a background, as all the space surrounding the object is usually blocked out in the negative, but canvas or muslin is usually employed. Where the background is admitted as a part of the picture, then such goods should be employed as are in keeping with the articles being photographed. Generally some soft, plain drapery of a neutral tint is used.