The new Canon Speedlite 580EX is that latest in Canon's evolution of high end, shoe mount, speedites. From the 430EZ to the 540EZ, 550EX and now the 580EX, power output and features have increased.

The new 580EX is, of course, E-TTL (and E-TTL II) compatible, and it has a guide number of 58/191 (meters/feet) at ISO 100 and 105mm focal length. It's both smaller and lighter than the 550EX which it replaces.

One major new feature for digital shooters is that the flash now knows the sensor size, and zooms the flash head to give full coverage over only the area seen by the sensor. The 550EX did not do this, and so, for example, "wasted" energy illuminating the 24x36mm frame outside that covered by the 22x15mm sensor in the 10D.

The 580EX also communicates with the 20D and 1D Mark II to ensure better white balance. If the battery charge starts to run low, white balance is adjusted to compensate for changes in flash characteristics.

The wide angle diffuser on the 580EX now gives full flash coverage for 14mm lenses (full frame), which means that it will provide full coverage for the EF-S 10-22 lens on a 20D or 300D (equivalent to a 16mm lens on full frame).