Canon Speedlite 550EX. Canon Speedlite 550EX, the latest companion flash for use with the new Canon EOS-3 AF 35mm SLR Camera and other Canon EOS series of cameras supporting E-TTL automatic flash output. In this issue of Films & Accessories, the focus is on the new Canon Speedlite 550EX that is designed as the companion flashgun for the latest Canon EOS-3 AF 35mm SLR camera. Not only does this new Speedlite provide both E-TTL and TTL automatic flash output with EOS cameras, it also provides Canon's first ever Wireless Autoflash System when used with its companion, the EOS-3. E-TTL (Evaluative Through-The-Lens) autoflash is Canon's most advanced flash metering system. It is featured in the latest EOS cameras and Speedlites (EX series). With the EOS-3, the E-TTL autoflash system uses a 21-zone evaluative metering sensor to obtain natural looking, balanced flash pictures. Three variables are taken into account to determine the optimum flash exposure: 1. Ambient light reading 2. Preflash reading 3. Focusing point-weighted reading After recognising the scene's brightness distribution and subject position, the camera calculates the proper flash exposure for the main flash. With non E-TTL EOS dedicated Speedlites, the EOS-3 uses off-the-film A-TTL or TTL 3-zone flash metering. High Precision with 21 Zones Since the EOS-3 has many more focusing points, the number of metering zones was increased to 21. Flash metering is initially weighted on the active focusing pointís metering zone. If an object with abnormally, strong reflection is detected in any of the other metering zones, its reading is factored out to prevent incorrect exposure. FE Lock Similar to AE Lock, FE (Flash Exposure) Lock enables you to lock the flash exposure reading for any part of the picture. The EOS-3ís FEL button fires a preflash and the flash reading is stored in memory. You can then recompose the shot and retain the desired flash exposure. << Back to Main . 1 . 2 . 3 . 4 .