Magazine article American Cinematographer

Ask ASC

Magazine article American Cinematographer

Ask ASC

Article excerpt

It's "winter" here in Los Angeles, where the blustery winds whistle down the canyons and sub-balmy temperatures plummet to below 50 degrees Fahrenheit (taking into account the "breeze-chill factor"). By January, Santa's gone from Hollywood Boulevard, the celebrations are over, and the city's inhabitants retreat to their poorly insulated bungalows to wait, shivering, only venturing out to see this year's "serious" films. Hopefully the following question, which concerns filming in hot, dry desert climes, will help us stay warm until spring (it usually shows up around the first week in February).

Q: Having shot a documentary in the Antarctic, I am aware of many of the difficulties associated with cold weather photography: short battery life, the cold limiting the flex of the film through the camera, frostbite, etc. I am also aware that when the moisture content of film drops, an atmosphere can be created in which the static charge builds and can become permanent, unwanted additions to the negative. Should a director of photography be as concerned with static marks appearing on film in extremely hot conditions, where the moisture content of the film drops as well? Could you relate the specifics as to why this does or does not happen? - Steven D. Smith, Whittier, CA

A: Extremes of relative humidity are a threat to all photographic materials, even at moderate temperatures. An object becomes charged with static electricity when it gains or loses electrons. Charged materials seek to return to a neutral state by movement of electrons. When electrons jump back and forth between materials, it's known as a release of static electricity, or "electrostatic discharge." The most common example is the "sparks" you see in the bed sheets on a dry summer night. Static markings on film are caused by the same type of discharge, and they appear on the developed film emulsion as marks resembling lightning, tree branches, or fuzzy spots. Since the early 20s, most film stocks have been coated with an anti-static backing, but extreme temperature and humidity conditions can overcome this generally effective measure.

Buildup and release of static energy is exacerbated by either extreme of humidity, but when static difficulties occur, they can usually be traced to the use of film which has a very low moisture content. Dry desert conditions are no exception; the problem is in fact compounded. A charged piece of film attracts dirt and dust - the nemesis of all desert film productions.

Extremely low relative humidity is not as serious as high, but if it falls below 15% for a considerable time as is common in desert regions, an electric humidifier should be installed and set to maintain a relative humidity of 40 to 50% in the storage area.

Film is adequately protected against moisture loss as long as the original packaging is intact. Static markings are not likely to occur if the film is loaded and exposed within a short time after the original packaging is opened. This is the best defense against static markings. There are several other techniques which seem to work, however.

Paul Bourque, National Technical Manager for Motion Picture Agfa Photo Division, who was consulted for this answer, gave the following recommendations:

"For a warm, dry desert environment, there is a quick, inexpensive fix to the problem. …

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