OTF, or Off the Film, refers to a metering method in which exposure is measured directly from the light reflected off the surface of the film during the actual exposure. This allows the camera to automatically adjust the flash output or exposure settings in real time.
OTF metering is commonly used in through-the-lens (TTL) flash systems, ensuring accurate illumination and balanced exposures. By measuring the light that reaches the film itself, photographers can achieve consistent results across varying lighting conditions without manual calculations or test shots.