Camera type: Single Lens Reflex (SLR)
Lens Mount: FL/FD bayonet/breech
Approx. dates of manufacture: FT: 1966-1970, FTb: 1971-1977
Approx. original price: FT: $239 (1968); $169.95 (1974)
Approx. street value: FT: Low-moderate, FTb: moderate
Two important types of technology drove the development of the 35mm SLR camera in the 60s and 70s, until autofocus took over. One was the metering system and the other was the lens mount. Prior to the mid-60s, most 35mm cameras used screw-mount lenses. But the big companies, such as Canon and Nikon, created bayonet-mounts that solved a lot of the problems with screw-mount lenses. Canon named its bayonet mount the FL mount, and the first Canon SLR to use this mount was their FX.
With the bayonet mount, Canon could now advance their work on the metering system. Early cameras had no meters on them whatsoever. But as meters became smaller and better, they began showing up on the camera bodies. The FX, for instance, has an external sensor and a little needle and scale on the top of the camera body.
The FT was the next big step: it offered through-the-lens (TTL) metering, which meant that the meter saw what the film saw, which reduced discrepancies between the light hitting the film and the light hitting the meter's sensor.
The problem now was that the scene had to be metered in stopped-down condition, meaning the lens had to be set to its shooting aperture to get a proper meter reading.
In 1971, Canon rolled out a new mount which it called the FD. The new lens mount was almost identical to the FL but it allowed the FD-compatible cameras the ability to meter with the aperture wide-open, which simplified and sped-up the whole process. FL lenses could be used on the new cameras, but the FDs could not be used on the old cameras.
Rather than kill off some of its old cameras, Canon updated them and added a b designation, so the FT became the FTb, and the TL became the TLb. An FTb is an FT that can accept FD mount lenses. Same with the TL and TLb.
Canon later revised some of its cameras again, though with smaller changes, and added an n designation. In this case the FTb became the FTbn. The cameras aren't marked with the n designation, though. You have to know what to look for to tell them apart.
FTs were mid-tier cameras, but many people looked at them as a somewhat scaled-down F-1 at an affordable price. They're excellent student cameras, were valued by pros as back-up cameras, and by many amateurs who found them to be very rugged and capable. Their prices have held up very well—a good FTbn may still fetch more than a younger, more capable AE-1.
For more information: Canon Camera Museum
Modern Photography magazine camera test (FT): August 1966
Modern Photography magazine camera test (FTb): August 1971
Camera manual: Orphan Cameras.com