To save time and avoid damage, cameras and other equipment should be made ready well in advance of departure. It is well worthwhile to have the equipment thoroughly overhauled and cleaned, preferably by the original manufacturer, who should be advised as to the type of climate in which it will be used. Cases, packing material, and moisture-absorbing material (desiccant) should be obtained for the equipment and supplies. Protection during transportation and storage is readily obtained by the use of hermetically sealed cans, metal-foil bags, or other water/va-por proof containers, and a suitable desiccating agent. If the containers have been properly sealed and contain an adequate quantity of desiccant, they will protect the contents practically indefinitely. There is, however, one reservation and caution: if precision instruments that require lubrication with certain types of light oils are subjected to high temperatures while in such packing, the oils may evaporate, leaving a gummy residue on the instrument bearings. This situation may prevent proper equipment functioning until the equipment can be cleaned and re-lubricated properly.
The protection of equipment that is in active use requires a somewhat different approach. The relative humidity caii be lowered in an equipment storage cabinet that is not used for film storage by burning electric light bulbs or operating an electric resistance heating unit continuously in the lower part of the cabinet. The number of lamps should be adjusted to keep the temperature about 10° above the average prevailing temperature. Air spaces and small holes should be provided at the top and bottom of the cabinet and through the shelves to allow a slow change of air to carry off moisture introduced by the cameras and equipment. The positions of the holes should be staggered on the different shelves in order to produce a more thorough change of air. Since high relative humidity favors the growth of fungus on lenses, filters, and other surfaces, storage in such a cabinet will help reduce the fungus growth and may prevent it entirely.
Electric dehumidifiers are now appearing in stores in many of the larger cities in tropical regions. With these units, whole rooms and their contents can be dehumidified, provided they can be closed to outside air penetration. In dehumidified rooms, the humidity will not increase rapidly during short power failures, as it would in heated closets or cabinets. In a small, tightly sealed room, an average unit iii operation for 12 hours out of 24 can keep the relative humidity below 60%. This should be checked about once a month with an RH meter or sling psychrometer. When it is not practical to use a hot cabinet or electric de-humidifier, equipment should be stored in an airtight case containing plenty of desiccant. Two cans of silica gel the size of shoe-polish cans will do a very good job of drying equipment in a sealed ten-gallon paint can (one with a gasket and a "pound shut" lid).
A half-pound bag of silica gel works well in a gasketed 55-gallon "open top" drum that can be sealed with a cover. However, where shipment and handling are involved or where the containers are to be opened briefly a few times, double or even triple the quantity of gel will provide a reserve of protection. Properly dehydrated containers will momentarily feel cool to an inserted hand due to rapid evaporation of the normal skin moisture. The sensation is brief, but can be easily detected if one is looking for it. Its absence means the silica gel needs replacement or regeneration.
If none of these methods are practical, and the equipment must of necessity be left in an atmosphere of high relative humidity, the equipment should be opened and exposed to the sun at frequent intervals in order to drive out moisture. The exposures, however, should be kept short in order to avoid overheating. Cameras loaded with film should not be exposed to the sun any more than necessary.
Cameras should always be protected from excessive heat because many of the lenses used on cameras are composed of several elements of glass cemented together. Because some cements melt at 140°F (60°C) and begin to soften at 120° F (49°C), it is obvious that the lens elements might become separated or air bubbles might form if the lens were heated to such temperatures. Cameras should not be handled roughly or subjected to sudden jarring when used at high temperatures because any slight shock might change the position of the lens components.
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