Complex sentence: E-TTL (Evaluative-Through The Lens) is a Canon EOS flash exposure system that uses a brief pre-flash before the main flash in order to obtain a more correct exposure.
Split into simpler sentences: E-TTL (Evaluative-Through The Lens) flash metering. It is a Canon EOS flash exposure system that uses a brief pre-flash before the main flash in order to obtain a more correct exposure.