Canon T90 - Flash

Flash

The T90 was the first Canon camera to support through-the-lens (TTL) flash metering. This measures the actual light levels reaching the film by measuring reflected light off the film (OTF), shutting down the flash unit once the film is sufficiently exposed. The measurement is calculated using the average reflectivity of color negative film. This system is also used on Canon's new EOS system, making the T90 the only non-EOS Canon body compatible with TTL Canon flashes. The T90's X-sync speed of 1/250 second was the fastest Canon had achieved and is better than most other cameras available at the time it was in production.

A new, dedicated flash unit, the Speedlite 300TL, was launched alongside the T90 to support its new flash modes. It has a zoomable head, capable of adjustment (by moving the head in and out) to cover the fields of view of 24, 35, 50 and 85 mm lenses. For bounce flash, the head can be rotated up to 90° vertically, 180° to the left, and 90° to the right. As well as the plain TTL mode, the 300TL supports A-TTL (Advanced TTL); here, the flash-to-subject distance is calculated using an infrared pulse with a detector mounted on the flash body. In bounce mode, however, it uses a 1/20th power pre-flash instead.

A pre-flash is also used in FE Lock mode (flash exposure lock). In this mode, the pre-flash is used in conjunction with spot metering to determine the correct exposure in advance of taking the picture. Thus, the camera can be moved to reframe the main subject off-center and still expose correctly.

For exposures slower than the X-sync speed, previous SLR flash systems triggered the flash at the start of the exposure, as soon as the first shutter curtain had finished its travel. However, for motion blurs and light trails in a longer exposure, this method gives the impression of backwards movement, since the motion trails out in front of the moving object after the flash. The T90, became the first mass-market camera to support second-curtain flash, where the flash fires at the end of the exposure, just before the second shutter curtain starts to close.

Although not identical, the current (2009) Canon Speedlite 580 EX II supports the T90 as well.

Canon also produced a dedicated macro ring flash for the camera, the ML-2. This supports TTL and manual models only, and contains two flash tubes, one on either side, which can be fired separately or together. The system consists of the flash ring itself, which fits onto the end of the lens, and a control unit which screws into the hot shoe atop the camera. The later ML-3 ring flash, introduced for the EOS system cameras, also supports the T90.