TTL
Through-The-Lens. Most SLR cameras have built-in meters that measure light after it has passed through the lens, a fea- ture that enables exposure readings to be taken from the actual image about to be recorded on film, whatever the lens'angle of view and regardless of whether a filter is used.
TTL auto flash
The camera'slight sensor measures flash light, as reflected by the subject on the film and shuts off the flash when measure- ment indicates correct exposure. Because the sensor that controls the flash receives light through the lens, TIL auto flash can be used for bounce photography, fill-in flash, multiple flash photography, etc. An additional advantage of TIL auto flash is that you can use a wide range of aperture settings, while ensuring correct exposure.
