23. Advantage Of Large Cameras

Advantage Of Large Cameras. Larger cameras, however, have their advantages, the first of which is the greater facility offered for composing the picture on a large-size ground-glass; and second, when a lens of great focal length is used, it is easier to emphasize the sharpness of the different details of the image, if necessary to do so.

24. Advantage Of Small Cameras

Advantage Of Small Cameras. One great advantage in using the smaller plates for practice work is, that one can make a great many more exposures, at less cost, than with the larger plates, and when a good small negative is secured it can be enlarged to any size desired. When the serious side of commercial work is considered, however, the use of large plates will be found a decided advantage in practically every respect, and no outfit would be complete without large and small cameras.

25. Lenses

Lenses. That the lens be of good quality is even more important than that the camera should be a high-grade one. Owing to its depth of focus the ordinary rapid rectilinear lens is, perhaps, fully as desirable for all around commercial work as any of the more expensive types. This lens must, however, cover the plate sharply to the edges and give good definition in all parts of the subject. The anastigmat lens has its advantages when shortness of exposure and the most minute definition are essential features. Rectilinear lenses are far cheaper than anastigmat, and unless thoroughly familiar with the latter instruments and capable of handling them, it is much better to hold to the rectilinear lens. For certain classes of work, and especially for copying, the anastigmat lens, with its great covering power and flatness of field at large apertures, is superior to the rectilinear lens, but the one point against it, however, is its lack of depth of focus when used at full aperture.

26. Doublet Lenses are divided into two classes or groups, according to the various focal lengths which may be secured by using different combinations. Where the front and back combinations of a doublet lens have the same focal length when used separately, the lens is termed a symmetrical one. On the other hand, if the front combination has a different focal length from the rear combination, it is termed an unsymmetrical or convertible lens. In a symmetrical lens the focal length of either the front or rear combination is almost double that of the combined lens. In the unsymmetrical lens one of the separate combinations is almost double the focal length of the combination, while the other cell has a focal length of about one and a half that of the combination.

27. The majority of hand cameras and view outfits are fitted with either the one or the other type of lenses, the unsymmetrical ones being a trifle more expensive than the symmetrical. All rectilinear lenses can be used either as single lenses or in combination, but anastigmat lenses are not all so constructed that their sections can be used individually. For complete information regarding lenses see Volume VI.

28. The most useful all around lens for interior photography is one of medium focal length, or about equal to the base of the plate on which it is intended to be used. For exterior photography and detail work the focal length of the lens cannot be too long, providing you have room in which to work. When it is necessary to photograph a building in a narrow or crowded street, a lens of the wide-angle type (which is one of short focal length) will be required in order to secure the subject in the position desired and obtain the effect wanted. A 5 x 7 convertible lens, having 7 1/2-inch focal length, will be made up of two lenses having a focal length of about 11% inches and 14 inches, respectively. A 10-inch lens will be made up of 16 1/2 and 19-inch lenses.

29. It is a good plan to bear in mind that one should use the longest focus lens that will include the amount of view required. The judicious use of the convertible (sometimes called trifocal) lens will assist one very materially to improve the balance of a picture much more effectively and easily than by altering the position of the camera.

30. Although wide-angle lenses are absolutely necessary in many cases, they should not be employed where one of greater focal length can be used. Although a wide-angle view is optically correct, it is always visually faulty, and for this reason a picture does not appear correct that embraces a wide angle. On account of the extreme perspective produced with a wide-angle lens the resulting picture gives the appearance of great distance or depth, and in this respect gives untruthful rendering. For instance, the interior of a narrow room, which can only be photographed with a wide-angle lens, will appear in the photograph to be fully twice as deep as would be the case if it were possible to make a photograph with a normal-angle lens. It is often absolutely impossible to employ the normal lens,

however, and in order to secure a photograph at all, the wide-angle type of instrument is used. It is sufficiently important to warrant the wide-angle lens being included in the commercial photographer's necessary equipment,

Illustration No. 1. Adjustable Tripod Head. See Paragraph 32

Illustration No. 1. Adjustable Tripod Head. See Paragraph 32.