Canon XS Flash

Canon XS Flash

The Rebel XS's built-in flash has a guide number rating of 43 feet (13 meters) at ISO 100, translating to a range of about 15 feet at ISO 100 with an f/2.8 lens. (About average power for a DSLR.) The Canon Rebel XS gives you a lot of control over flash exposure, allowing you to adjust flash and ambient exposure independently of each other, in one-half or one-third EV increments. This makes it very easy to balance flash and ambient lighting for more natural-looking pictures. The Rebel XS also uses E-TTL II control for both the built-in and compatible external flashes (according to Canon this includes the older 550EX flash, as well as the newer 580EX and 580EX II), a standard that promises more balanced exposures.

Another nice touch is the AE/FE Lock button (marked with an asterisk*), which fires the flash (when deployed) under manual control before the actual exposure, to determine the proper exposure setting. This struck me as very handy, akin to the more conventional autoexposure lock function for handling difficult ambient lighting conditions.

Several of the more impressive features of the Canon flash system depend on the dedicated EX-series speedlights. Among these are true FP (focal plane) flash sync, flash exposure bracketing with external flash units, flash modeling, and E-TTL II exposure control. FP sync requires a flash unit to provide uniform light output for a relatively long period of time, which the flash achieves by pulsing its high speed strobe multiple times as the two shutter curtains travel across the sensor plane, revealing only a small section of the sensor at a time. Uniform, long-duration flash pulses like this permit use of shutter speeds as high as the 1/4,000-second maximum that the Canon XS is capable of. This can be invaluable when you want to exclude ambient light from the exposure. (FP sync mode is referred to as "high speed" mode on the Canon 550EX, 580EX, and 580EX II flash units.)

The "X-sync" speed of the Canon XS is 1/200-second. When used with higher-powered studio strobe systems, Canon recommends a maximum shutter speed of 1/60-second or slower, to accommodate the time/intensity profile of such units.

A final benefit of the dedicated Canon speedlights is that they carry powerful autofocus assist illuminators that can extend the range of the built-in AF assist light of the Canon XS. For example, the AF assist beam on the 550EX is rated as good to about 50 feet, versus the roughly 13 feet of the pulse flash on the Canon XS.

Canon's E-TTL II flash exposure system also works with certain lenses to include object distance data into its calculations so it can adjust the flash power accordingly. A preflash is fired and the resulting readings compared to the ambient light reading for each of the camera's 35 metering zones from just prior to the flash, to identify and compensate for specular objects (that is, very reflective surfaces). In instances where most cameras would underexpose an image because of a reflective object in the frame, the Canon XS will ignore the brighter areas and expose the subject correctly in most instances. This is designed to help shooters like event photographers -- especially wedding photographers, whose cameras are constantly forced to balance a bright white dress against all manner of reflective materials on the clothing of others, in addition to the usually black tuxedos of the groomsmen.

The Canon XS can also control some aspects of an external flash from the Flash Control menu. You can set the flash to not fire when mounted and powered on, which is useful for using the flash as an AF-assist beam. You can also set Flash Exposure Compensation, and set E-TTL II to Evaluative or Average.

The internal flash always operates in E-TTL II mode. No manual mode, where you can set power as a percentage of full power, is provided. Red-eye reduction, first and second-curtain sync, as well as slow-sync modes are offered. The built-in flash cannot act as a wireless master or controller, however an external flash such as the 580EX II mounted on the XS can act as a master to multiple, remote slaves.