PTTL

PTTL, short for preflash TTL, is a flash metering method used in some camera and flash systems to automate exposure. In PTTL, a brief preflash is emitted before the main flash. The light from this preflash is measured through the lens by the camera’s metering sensor, and that data is used to determine the power of the main flash for the actual exposure. The result is intended to produce a properly exposed image without manual flash adjustments.

PTTL is an early TTL system that was commonly associated with Nikon equipment in the 1990s and 2000s, and it appears on various Nikon speedlights and compatible third-party flashes. It is often mentioned in contrast to later TTL implementations such as i-TTL, which introduced more refined metering and processing. While PTTL generally provides convenient automatic exposure, it can be less accurate in certain situations, such as scenes with extreme brightness or darkness, highly reflective subjects, or multi-flash setups, where the preflash may not perfectly represent the lighting during the main flash. Photographers may compensate using exposure compensation, flash exposure compensation, or by switching to manual flash settings when precise control is required.

PTTL remains a reference in discussions of legacy TTL systems and is encountered primarily on older Nikon bodies and flashes, as modern gear increasingly favors newer TTL implementations. See also TTL, i-TTL, and E-TTL for related flash metering concepts.