Complex sentence: The Canon FT is one of a series of three basically identical cameras released around this time, the first was the Canon FX which had a built-in meter, but was not TTL, it used a window on the camera body front.
Split into simpler sentences: The Canon FT is one of a series of three basically identical cameras released around this time. The first was the Canon FX which had a built-in meter, but not through-the-lens (TTL) metering, instead using a window on the camera body front.