The Canon Speedlite 580EX II Flash is Canon's top of the line hot shoe flash gun for it's line of digital SLR cameras.
The Canon Speedlite 580EX II Flash is the most powerful hot shoe flash gun made by Canon. As such, among professionals it rivals Nikon's SB-800 and SB-900 speedlites. The 580EX II works perfectly with Canon's EOS system and can be used in combination with several other flashes. On the EOS 7D, the 580EX II can be part of up to three groups of off-camera flash guns controlled through the camera's menu system and triggered wirelessly for many creative opportunities.
According to Canon:
Further development of Canon's flagship Speedlite has led to the production of the 580 EX II. This is the premier Speedlite for all photographers, including professionals. Newly designed to match with the EOS-1D Mark III in terms of improved dust- and water-resistance, body strength, and the ability to control flash functions and settings from the camera menu (EOS-1D Mark III only). Other features include improved communication reliability through its direct contacts, and recycling time is both 20% shorter than the 580EX and is completely inaudible.
