Canon offers a broad range of accessory electronic flash units for the EOS 40D. They can be mounted to the flash accessory shoe, or used off-camera with a dedicated cord that plugs into the flash shoe to maintain full communications with the camera for all special features. They range from the Speedlite 580EX (see Figure 7.6), which can correctly expose subjects up to 24 feet away at f/11 and ISO 200, to the 220EX, which is good out to 9 feet at f/11 and ISO 200. (You’ll get greater ranges at even higher ISO settings, of course.) There are also two electronic flash units specifically for specialized close-up flash photography.