Off-the-film metering (OTF) is a metering system that determines correct exposure by measuring the light reflected directly from the surface of the film during the exposure itself. This real-time feedback allows the camera to make highly accurate exposure adjustments, particularly when using flash.
Pioneered by Olympus in cameras such as the OM-2n, OTF metering became an important advancement in exposure control. It is especially useful in flash photography, where it helps regulate the amount of light emitted to achieve consistent and balanced results under varying shooting conditions.