Through the len (TTL)

Through-the-len works by firing the flash at the subject. The reflected light will then enter the camera through the len (hence the name) and hit the film. Some of the light that bounces off the film will be captured by an off-the-film (OTF) sensor which reads the exposure. When sensor decided that there is enough exposure, the flash bulb switches off. This happens in a split second. This technology is made to fit in film in the olden day but with digital camera photography gaining popularity, different camera manufacturers begins to modify TTL to suit the digital sensor.

You might also be interested in reading how the through-the-len was developed, Canon flash system and Nikon flash system.

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