188. Tests of a Hand Camera. In addition to the tests already described (§ 161) for profes sional cameras, especially as regards the coinci dences of the planes of the focussing screen and of the sensitive surface, the examination of the lens (§ n6) and of the shutter (§ 146), which are usually integral parts of the camera, there is need, in the case of a hand camera, to make the following tests.
In cameras with tapering bellows, see that the picture is not cut off by the bellows, espec ially when the rising front is used to any extent.
In all cameras fitted with a focussing scale, verify, either by examination of the image on the screen, or, better, by a practical photo graphic test, that test-objects such as a sheet of printed matter facing the camera, placed at the various distances marked on the scale, are really rendered sharply.
In all cameras fitted with finders it is necessary to see that there is at least a reasonable degree of agreement between the picture in the finder and that in the camera. If necessary, a finder which shows too much subject must be masked with bands of gummed black paper or with black varnish. Of the two evils, it is better that the finder should show less subject than the camera records, since the negative can be enlarged if the image is smaller than is desirable.
It is also well to see if it is possible to it a colour filter to the lens if required, and if the thread of the tripod screw fits that of the bushes on the camera so as to allow of the latter being properly fixed on the tripod.
189. Care of the Camera. A camera treated properly can give long service while retaining all its original qualities, but any wrong handling, and any attempt to force it to open or close without loosening the catches or replacing in position the various parts, may result in serious damage.
Parts where there is friction (baseboard runners, grooves of dark slides and shutters therefor, etc.) must be lubricated from time to time, preferably with graphite, e.g. with a carpenter's pencil at an angle, and with which it is easy to apply a very thin film of graphite, which considerably reduces the risk of premature wear.
A photographic camera must never be left in a damp place, for the woodwork may swell, the leather covering may come unstuck, and the metal parts may rust or become covered with verdigris. If a camera has been exposed to
rain and particularly to sea-water, it should be wiped with as little delay as possible. It should then be placed in a dry place, until the bellows are quite dry. A piece of waterproof cloth, used also as a focussing cloth, enables the camera to be properly protected when necessary. No less important than the avoidance of a fall or sudden knock is that of constant vibration which in time causes the loss of screws fixing the parts together. A camera case should not be attached rigidly to the handlebar of a cycle, nor put on the floor of a car. From time to time a polish composed of wax and turpentine should. be rubbed on the woodwork and leather cover and metal parts should be rubbed with a rag slightly greased with vaseline.
All the interior parts should be cleaned fairly frequently with a brush and dry Special precautions must be taken with dark slides and steel sheaths. They must never be left in a dark room, where it is always somewhat damp. When in process of loading and unload ing they should be placed on a perfectly dry table, secured from risk of splashings of liquid. Blackened steel rusts very easily, and the rust comes off in flakes and is likely to adhere to the sensitive surfaces and cause spots, for which there is no remedy. When slides and sheaths are likely to remain unused for a long period it is well to grease them very slightly with vaseline, but they must be freed from the grease with a dry rag before using them again. These accessories are easy to damage if clumsily handled, and a dark slide or shutter that has been bent is usually not light-tight, while a bent sheath is likely to scratch the emulsion surface of the plate behind it or to cause the changing box to jam.
A camera should never be left in a cupboard except in its case. The lens should be cleaned (§ 117) from time to time, but not to an undue extent, the surfaces being liable to injury as the result of improper cleaning. Finally, it should be remembered that the shutter must never be oiled, and that it must not be taken to pieces except by an expert.