Information Exchange
A major distinction of APS film was the ability to record information other than the image. This information exchange was most commonly used for print aspect ratio, but could also be used to record the date and time that the photograph was taken, store a caption, and record exposure data such as shutter speed and aperture setting. This information could be read by the photo printing equipment to determine the print aspect ratio, print information on the back (or, rarely, the front) of the photograph, or to improve print quality.
Two methods for storing information on the film were employed: "magnetic IX" and "optical IX". Optical IX was employed on less expensive cameras and disposable cameras, and employed a light source to expose a small section of the film, outside of the image negative area. This method was limited to determining the print aspect ratio of the finished print.
Magnetic IX was used in the more expensive cameras and allowed for a great deal more information exchange. Most cameras with magnetic IX automatically recorded the exposure date and time on the magnetic layer, with more advanced models allowing the user to specify a predetermined caption to be printed on the photo or record the exposure settings, as well as determine print aspect ratio. Magnetic IX caused some problems for photo processors, who found their magnetic reading heads had to be cleaned frequently, or that their equipment's ability to print this information was limited.
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