The new Speedlite 420EX is sure to appeal to EOS users everywhere with its combination of power, features and affordability. It's fully E-TTL compatible, and reverts to standard TTL operation when used on older EOS bodies or the T90. The fully swiveling bounce head zooms automatically over a range of 24mm-105mm. Most impressively, its Wireless E-TTL compatibility permits it to function as a "slave" unit, triggered by a 550EX; ST-E2, or MR-14EX. Any number of 420EX and 550EX Speedlites can be combined as "slave" units.