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Foil cues are short strips of adhesive foil attached to the edge of a 35mm projection print. They are used to facilitate auditorium and projection booth automation, often in a multiplex setting. When using foil cues, a proximity cue detector is embedded somewhere in the projector's normal thread path; when the foil cue passes through the proximity cue detector, the circuitry closes the appropriate relay and triggers the desired automated function.
Foil cues were widely used during the multiplex era, but are rarely used today. They are not considered compatible with archival best practices.
Foil cues can be used to trigger many common projectionist tasks, including, but not limited to:
- Raising or lowering auditorium lights
- Opening or closing the projector dowser
- Activating the projector change-over function
Cue proximity detectors were programmed to detect inboard foil cues, outboard foil cues, and crossframe foil cues. Several manufacturers produced foil cue readers, and many multiplex managers customized the technology to fit their specific needs. As foil cue position and function were never standardized for all theaters, they could not be applied in advance by the laboratory, distributor, or exchange manager. Foil cues were always applied by the projectionist with an eye towards the venue's specific needs, often during the print inspection and make-up process.
Consequently, an inboard foil cue could trigger a change-over on one system while triggering an auditorium lighting change on another. Best practices dictated that a projectionist remove cues from a print at the conclusion of its run; otherwise, the existing cues could inadvertently trigger undesired automation at the next venue.
Foil cues were used to facilitated a level of projection booth automation that is incompatible with archival best practices. As archival booths are expected to use a two-projector change-over system and be staffed at all times, automation is neither necessary nor desired.
Stray foil cues will not trigger inadvertent automation functionality unless a cue proximity detector has been installed. Nevertheless, archive vault staff will often remove leftover foil cues because they are viewed as a print contaminant. Older foil cues can sometimes leak adhesive, which tends to attract dirt and dust.