Canon 50D Flash
Canon EOS 50D Flash
The Canon 50D'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. (Reasonably powerful, but not dramatically so.) The Canon 50D gives you a great deal 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 Canon 50D also uses E-TTL II control for both the built-in and compatible external flashes. E-TTL II is only available with the built-in flash or when the camera is paired with more recent Canon EX-series strobes.
Another nice touch is the Flash Exposure Lock button, which fires the flash 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. A Flash Exposure Compensation feature controls the flash exposure +/- 2 stops in 1/2 or 1/3-stop increments.
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 1/8,000-second maximum that the Canon 50D 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.)
Here's the rundown on Canon Speedlights and their compatibility with the Canon 50D:
|Speedlight Model||On-Camera Capability||E-TTL Wireless
|580EX II||All, E-TTL II, Thyristor||Master or Slave|
|580EX||All, E-TTL II||Master or Slave|
|550EX||All, E-TTL II||Master or Slave|
|540EZ||Manual operation only||None|
|480EG||External auto plus manual operation||None|
|430EX II||All, E-TTL II||Slave only|
|430EX||All, E-TTL II||Slave only|
|430EZ||Manual operation only||None|
|420EZ||Manual operation only||None|
|MR-14EX Macro Ring||All||Master Only|
|ST-E2 transmitter||E-TTL, attach to camera||Master Only|
|Non-dedicated shoe-mount units||Manual operation only||n/a|
|Studio strobe packs||Manual operation only, connect via threaded PC sync socket on camera body||n/a|
You'll note the references to "E-TTL remote" capabilities in the table above. Canon's Speedlight system permits TTL flash metering with multiple remote units, and even allows you to set differential power ratios between the slaved units, over a six-stop flash exposure range.
The "Flash Modeling" feature of the 550EX, 580EX, and 580EX II speedlights is quite useful. With a 550EX or 580EX connected to the Canon 50D, pressing the camera's Depth of Field Preview button causes the speedlight to fire at 70 flashes per second for about one second. This creates the illusion of a constant light source for your eyes, letting you preview the lighting on your subject when the flash fires. VERY handy, and likely to save lots of shoot/check/reshoot time!
The "X-sync" speed of the Canon 50D is 1/250-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 50D. 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 50D. (As mentioned above though, note that the ST-E2 wireless sync transmitter can also be used for AF assist during non-flash photography, a handy trick.)
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 50D 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 50D 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 Canon 50D's hot shoe also includes a waterproof seal around the base, designed to mate with the Canon 580EX II's seal, which is integrated into the flash's locking mechanism. This keeps water from seeping into this important electrical connection during wet conditions.
Flash Test Results
Coverage and Range
Good flash performance, with good intensity but slightly uneven coverage at wide angle. About average positive exposure compensation required.
|Normal Flash, +0.7 EV||Slow-Sync Mode, Default|
Coverage and Exposure. Flash coverage was slightly uneven at wide angle, but keep in mind that a 28mm lens has the field of view of about 45mm on the 50D, so the fall-off in the corners of the frame would likely be much worse with a wider-angle lens. Coverage at telephoto is much more even. Indoors, under incandescent background lighting, the Canon 50D's flash performed quite well, requiring about average positive exposure compensation of +0.7 EV for a bright image. The camera's slow-sync flash mode required no compensation, though the longer shutter time results in a warmer cast from the ambient background lighting.
ISO 100 Range. The Canon 50D's flash was bright and powerful, and with the kit lens actually did a bit better in our tests than its guide number (13 meters at ISO 100) would indicate. Set to its maximum 28mm wide angle setting, the test shots showed no falloff in brightness all the way to the 15-foot limit of our test, even though its guide number would say it should only hold strong to 12.3 feet. At its maximum tele setting of 135mm, intensity held steady all the way to 9 feet, even though the guide number says it should only work to about 7.7 feet at f/5.6. Overall, great performance from the 50D's flash...
|Manufacturer-Specified Flash Range|
Manufacturer-Specified Flash Test. The Canon 50D's built-in flash has a GN (Guide Number) of 13 meters at ISO 100, which translates to about 15.4 feet at f/2.8. (Note: we used a Sigma 70mm f/2.8 lens for this test.) In the shot above, the Canon 50D seems to perform as well as Canon says it will, producing a good exposure at the rated distance with its ISO set to 100.
Note: Our standard test method for flash range uses a fixed setting of ISO 100, to provide a fair basis of comparison between cameras. With the above test, we're also looking at whether their stated specification rings true.