TTL

Glossary Terms

The acronym TTL most commonly refers to:

A diagram from Ricoh indicates two approaches to TTL exposure metering (Image rights)

Through The Lens

Usually referring to in-camera exposure metering or flash exposure control, but also used to differentiate viewfinder designs, autofocus mechanism designs, and other systems on lens-based cameras. Measuring light or focusing through the taking lens can be more accurate than separate metering, viewfinder or focus systems, as this measures the light that will reach the film, from the exact point-of-view of the lens - and so eliminates parallax and stray light from outside the frame.

But,

Transistor-Transistor Logic

TTL is a type of digital electronic circuitry which uses transistors and resistor elements (usually made of transistors) to make logic gates. It is rarely, if ever used in camera circuitry as it has fairly high power consumption.