In order to avoid unnecessarily setting up the camera to see if a given stand point is suitable, a view meter should be used. Several forms are available, per haps the simplest being a rectangular wire frame, the size of the plate employed, to one side of which is fastened a cord of a length equal to the focus of the lens. In use, the wire frame is held in front of the eye at the distance indicated by the cord, when the amount of view included within the rectangle at once shows what would he visible on the ground glass of the camera, if set up at the same spot. If lenses of different focus are used, it is possible to mark their various lengths on the same cord, by knots or other means, so that the view meter becomes available with any lens. The rectangle of the meter may be smaller than the plate, if desired, provided the length of the cord is reduced in the same proportion.
Some workers recommend the use of a small pocket tape measure as a view meter. In order to mark this for the purpose, first erect the camera in front of some view with a number of prominent objects whose position is readily noticed, and carefully ascertain which of these are visible at the extreme edges of the ground glass. Then, standing in a line with the
camera, hold the tape measure straight out in front, in a horizontal position, with one end between the finger and thumb of the left hand. Now, with the arms fully extended, place the left end of the measure so that it comes against the object seen in the extreme right on the screen, and slide the left-hand finger and thumb towards the other end of the measure, keeping it taut meanwhile, until they come over the object marking the opposite extremity of the view. When this is marked on the measure it is ob vious that, in future, if the latter is held straight out before the eyes as before, the amount of view coming between one end and the mark previously made will be the same as that which would be shown on the camera screen. Different lenses may be tested in this way, and, suitable marks being made on the measure, it becomes possible to tell at once which lens will be the best to use on a given view from any settled standpoint.