In use, the cardboard pack is placed in an adapter interchangeable with the dark slides of the camera. This having been done, the rear tab (the tab of the safety cover) is so as to uncover the first film. After the first film has been exposed it is transferred to the rear compartment by pulling the tab marked No. i until there is felt a resistance, due to the extra thickness of the film and adhesive strip. The protruding length of the band of black paper is then torn off by pulling it sideways against the metal edge of the adapter. The changed film remains attached to a sheet of black paper bearing the number r, thus allowing of the negatives being identified. The second film is then in place ready for exposure. After it has been exposed it is changed by pulling tab No. 2, and so on. When the twelfth film has been changed the pressure plate is pressed against the cut-out and closes it. The pack can then be removed from the adapter in daylight and replaced by a fresh one.' After removing the exposed films from the cardboard box the latter is thrown away.
With the object of reducing the cost of films used in this manner, metal containers of pattern identical with that of the cardboard casing described above have been manufactured. These may be reloaded in the dark with bands of paper supplied ready for placing in the case.
Various devices have been suggested for incorporation in film packs to enable a note to be made on each film at the time that the photograph is taken, but nothing practical has been evolved as yet.
x87. Tripods and Pocket-supports for Hand Cameras. An exposure of second is usually the longest that can be given with the camera held in the hand without risk of movement due to the involuntary movements of the body. While some cameras can be placed level on a table or a window-sill, it is not always possible to find a steady support or a wall conveniently placed against which to hold it. If the user is not to be greatly limited in his work with a hand camera, an indispensable accessory is a tripod, or at any rate one of the many patterns of pocket accessories by which the camera may be fixed to a very large number of natural supports. 1 A hand camera must therefore have on two of its sides a bush of the standard Continental screw-thread (§ 157), or at least the Anglo American In the case of a camera fitted with a changing box which needs to be placed flat on its back (lens pointed directly upwards) when changing the plate, it would be troublesome to screw and unscrew after each exposure. For such cameras a small board is often supplied for screwing on to the tripod, the camera being simply placed on the board either upright or It is of course not possible to consider the use of the solid wooden tripods made for portable professional apparatus, for such a tripod would be heavier and more bulky than the camera itself. Nearly always telescopic metal tripods
are used, in which the legs are divided into sections sliding one in another. The rigidity of an extended leg leaves more to be desired, as the diameter of the tubes is smaller and the number of sections is increased with the object of reducing the length for carrying. Weight for weight, it is preferable to use tripods with aluminium tubes of large diameter fitted with brass slide-sleeves rather than tripods with slender brass tubes. Tubes of triangular section can be quite sturdy without the total section of the tripod being too large, as the legs fit closely against each other. The length of the legs is regulated by drawing out a greater or less number of sections. As a rule, the sections lock automatically as each is fully extended (some tripods with cylindrical legs have a bayonet catch), and for closing all that usually needs to be done is to press one catch on each leg, the whole leg then collapsing on applying a fairly sharp push.
Some manufacturers supply tripods which can be taken to pieces and spare parts obtained to replace any that become worn, but metal stands which do not bear a manufacturer's mark are usually irreparable.
Tripods have been supplied, though not to a large extent, with a screw ring around the head by means of which the degree of opening of the legs can be regulated and the tripod can thus be prevented from slipping. It has also been suggested that the head should be fitted with a thick disc of felt or rubber, the elasticity of which permits the camera being rotated without having to turn the whole metal tripod.
There can also be obtained commercially ball and-socket heads, usually of too light a construc tion, and panoramic heads for the same purposes as with professional cameras (§ 157).
Lastly, let formal mention be made of the walking-stick tripods, usually inconvenient either as sticks or as stands.
The pocket supports have their uses. They usually comprise a base, with screw, for the camera, and a ball-and-socket uniting the base to a kind of joiner's clamp. The latter enables the fitment to be fixed to the back of a chair, handlebar of a cycle, fence, or door frame. In some cases, the support can be fixed to a tree trunk or mast by a steel ribbon or chain which can be drawn tight by an excentric fastening. It is necessary to avoid absolutely the supports in which there is a wood-screw for fixing into tree-trunks, a practice injurious to the tree and likely to bring the user into trouble.