The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Depth of Focus                          Detective or Hand Cameras
in a great measure. If, when the negative has been fixed, the amateur finds that his judgment has not been correct, he has, fortunately, methods of increasing or decreasing the density, as described in the operations of Intensification and Reduction (q.v.).
Depth of Focus. See Focal Length.
Detail. The definition of each minute part or parts of the material of a picture, whether in the negative or print therefrom.
Detective or Hand Cameras. These are cameras of par-ticular designs, so constructed as to be portable and unlikely to attract attention. Their name is legion ; their makes diversity itself; and to attempt to include even a brief description of them would be beyond the limits of space at our command. Practi-cally, however, hand cameras may be divided into two main classes: {a) those with automatic plate or film-changing appa-ratus ; (b) those with dark slides. Each must decide for him-self which pattern meets most nearly his requirements ; but we can consider the individual parts of the camera.
The Lens. As one of the chief features of detective work is the portrayal of objects situated at varying distances from the camera, it is obvious that lenses with great depth of Focus (q.v.) are required; and as this property decreases with increase of focal length and aperture, we are limited in our choice to certain forms and apertures of lenses, although the great advance made lately in practical photographic optics has given us instruments which afford valuable assistance. It will be found that, generally, lenses of short focus - i.e., which have a focus about equal to the longer base of the plate which they are intended to cover, thus for a quarter-plate aor 5-in. focus lens
- should be used. The doublet form of lens will, generally, be found the best, though single or landscape lenses, working at a large aperture,will often serve.
The Diaphragms or Stops. The question of aperture is governed by two considerations - the first, that of depth of focus ; and the second, the actinic power of the light. As the first increases with diminution of aperture, the smaller the diaphragm the greater the depth of focus ; but as this is also governed by the second consideration, it is obvious that, except for brightly lit scenes, such as seascapes and river views, and work on the sea-