A pneumatic release, connected to the tube controlling the shutter, can be made to bring the mechanism of the flashlight lamps into action, the ignition being caused either by a ferro-cerium spark or by a small charge of fulminate. As a general rule, all lamps which are set ready for use should be handled very carefully, and in no case should the final adjust ments be made before the charge has been added, since a premature release of the shutter may cause a serious accident, especially if the powder is being poured direct from the stock bottle. In many different types of lamp, the same operation alternately sets and releases the ignition mechanism.
The best lamps are undoubtedly those with electrical ignition, obtained by the explosion of fine metal wire (iron or copper), inserted in the powder, under the influence of a discharge. The ignition current is preferably started by the shutter itself at the moment it starts to open.' The current may be obtained from the lighting circuit or from a battery of dry cells.
Whatever the method used for the ignition of the powder, in case of a misfire, one should wait for some time before coming near the lamp, for a damp powder will often " recover " in a few seconds and flare up—possibly just when it is being examined. 2 305. In a room where it is required to make a series of flash powder exposures, precautions must be taken to prevent the smoke from In a permanent establishment, it is usual to employ a large lantern, or, better still, a glazed cabinet with reflectors at the bottom and diffusing screens on the outside of the glass, the whole being connected directly or by means of a chimney to the outside of the room. For use
away from the specially-fitted studio, a smoke trap consisting of a bag made of semi-trans parent, non-inflammable material, which acts at the same time as a diffuser, will be found very useful. The top of the bag can be hung from a metal crossbar attached to a vertical metal pole screwed at its base into a tripod, the lamp being fixed half-way up the vertical stand. The material is drawn in round the pole at the bottom end, allowing just enough room for the passage of the pneumatic tube or the wires leading to the ignition control. After each flash, the bag is opened out of doors.
306. For a portrait on a very fast plate, in the absence of any other effective illumination, using an aperture of F/8, a charge of about 30 gr. is necessary, divided into two parts, one about 22 gr. and the other about 8 gr. These are placed at least 6 ft. away from the head of the sitter, in a direction which makes an angle of about 45° to the side and also above.
The flash should take place outside the field covered by the lens, and at a sufficient distance to prevent any incandescent particles from reaching it.
If the powder is not ignited in a cabinet or a non-inflammable smoke-trap, it should be held at least a yard away from all curtains, hangings, partitions or ceilings, in order to avoid all risk of stains and of fire.
It is always advisable to include a is tle of liniment and some bandages in the flashlight outfit, so that they will be handy in case of burns.
The supply of flash Powder should always be kept in several containers, so to limit, in case of accidents, the extent of the damage to persons and property.