TTL flashes
TTL
— TTL is an abbreviation for "through the lens". This is the name given to the method of measuring exposure based on the amount of light that passes directly through the optical system of the camera lens.TTL works on the pre-flash principle: before the main exposure, the flash produces one or more test pulses. The amount of light coming from the subject is measured by special sensors, based on this data, the control electronics sets the necessary shooting parameters, after which the actual exposure occurs. This allows you to very accurately adjust the camera and get an image of optimal quality. The interval between the test and working pulse is so small that it can be completely invisible to the naked eye (especially when synchronizing the flash by the front curtain or a short shutter speed).
Many modern camera manufacturers have their own developments and varieties of TTL technology, which differ accordingly in name: for example, Canon has E-TTL and E-TTL II, Nikon has D-TTL (in early models) and i-TTL (in later models), Sony has ADI-TTL and P-TTL, etc. Support for one or another variety directly affects the compatibility of the flash with cameras (see above), and different formats are usually not compatible with each other.
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