Detective or Hand Cameras
shore in brilliant sunshine, it would be injudicious to use too small an aperture, as loss of detail in the heavy shadows would result. For ordinary workwill be found quite small enough,
while for sea and river viewswill be found large enough.
The form of diaphragm, whether Iris or Waterhouse, is not a vital question, as, unless the former is controlled from the out-side of the case, there is no advantage in its use.
The Shutter. This should be capable of accurate adjustment for various speeds, from very rapid to slow. From to
sec. will be found quite range enough. The speed at which the shutter will be required to work is governed, of course, by the rapidity of movement and nearness of moving object to the camera. Reference must be made to the tables and rules given under Instantaneous Photography for information upon this point; but as it would be impossible to make any calculation at the time of exposure, the operator must depend upon experi-ence alone to teach him all that is required on this point, although the application of these rules in the formation of a set table of distances, rapidity of movement, and speed of shutter, would be useful. For example, supposing a 4-in. focus lens is used, by a little calculation we shall find that a shutter must work at theof a second to take a man, walking at the rate of four
miles an hour, twenty yards off; and a horse at thirty yards' distance, going about twelve miles an hour, will require about of a second speed.
Plate Arrangement. For those who use spooled films, roller slides, of course, will be required ; but for the general run the question as to which is the better, dark slides or automatic changing methods, will be an all-important one.
Focussing. In many hand cameras this is altogether dis-pensed with, the use of a so-called fixed-focus lens obviating the necessity of the same ; but this we again object to on the same principle as the automatic changing arrangement is objected to - namely, the limitation of the use of the camera. The table of distances beyond which everything is in focus (see Fixed Focus) will be useful on this point, and the question of so-called fixed-focus Lenses (q.v.) will be treated of separately.
Finders. Many very successful workers in this branch of our art utterly pooh-pooh the necessity of finders ; but, speaking from personal experience, these are an absolute necessity;