Canon T2i Flash
The Rebel T2i's built-in flash has a guide number rating of 43 feet (13 meters) at ISO 100, translating to a range of about 12 feet at ISO 100 with the kit lens at wide-angle (at f/3.5) and about 7.5 feet at telephoto (at f/5.6) . The Canon T2i 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 easy to balance flash and ambient lighting for more natural-looking pictures. The Rebel T2i 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 models), a standard that promises, and seems to deliver, better, more balanced exposures. (TTL refers to "Through The Lens" metering.)
Another nice touch is the Canon T2i's Flash Exposure Lock button, which fires the flash under manual control before the actual exposure, to determine the proper exposure setting. This struck us 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.
As you'd expect, there is a dedicated flash hot-shoe on the Canon T2i's pentamirror housing, for use with external flash units. Like most consumer SLRs, the Canon T2i offers no PC-Sync connector for triggering studio strobes, etc. Maximum flash x-sync speed is 1/200-second.
In common with almost all Canon SLRs (the sole exception being the EOS 7D), wireless remote flash is only possible when using an external Speedlite 580EX II (or the now-discontinued 580EX) flash strobe, or the Speedlite Transmitter ST-E2, mounted on the camera. Canon's Speedlite 270EX, 430EX II, and 580EX II (as well as certain of its historic flash models) also enable advanced features such as true FP (focal plane, referred to as HS) 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, long enough for the focal plane shutter curtain to fully traverse the sensor plane. Uniform, long-duration flash pulses like this permit use of shutter speeds as high as the 1/4,000-second maximum that the Canon T2i is capable of. This can be invaluable when you want to exclude ambient light from the exposure.
Flash Test Results
Coverage and Range
A moderately powerful flash with uneven coverage at wide-angle with the kit lens. Average positive exposure compensation required.
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| 18mm @ f/3.5 | 55mm @ f/5.6 |
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| Normal Flash +0.7 EV |
Slow-Sync Flash +0.3 EV |
Coverage. The Canon T2i's flash coverage was quite uneven at wide-angle. (The 18mm example above was shot with the T2i's Lens Peripheral Illumination Correction enabled by default, so falloff due to the lens itself has been corrected.) The flash's coverage was much more even at telephoto.
Exposure. Indoors, under incandescent background lighting, the Canon T2i's flash performed quite well, requiring about average positive exposure compensation of +0.7 EV for a reasonably bright image. The camera's slow-sync flash mode only required a +0.3 EV boost, though the longer shutter time results in a warmer cast from the ambient background lighting.
| Flash Range: Wide Angle | |||||
|---|---|---|---|---|---|
| 6 ft | 7 ft | 8 ft | 9 ft | 10 ft | 11 ft |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
| 12 ft | 13 ft | 14 ft | 15 ft | 16 ft | |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
 1/64 sec f3.5 ISO 100 |
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| Flash Range: Telephoto | |||||
|---|---|---|---|---|---|
| 6 ft | 7 ft | 8 ft | 9 ft | 10 ft | 11 ft |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
| 12 ft | 13 ft | 14 ft | 15 ft | 16 ft | |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
 1/64 sec f5.7 ISO 100 |
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ISO 100 Range. The Canon T2i's flash was bright and fairly powerful. Set to its maximum 18mm wide-angle setting, the test shots showed no appreciable falloff in brightness out to about 12 feet. At full telephoto, flash intensity started out a little dim, but maintained good brightness until about 9 feet at 55mm.
| Manufacturer-Specified Flash Range | |
|---|---|
| Wide Angle | Telephoto |
 12.0 feet ISO 100 |
 7.5 feet ISO 100 |
Manufacturer Specified Flash Test. The Canon T2i's built in flash has a rated Guide Number of 13 meters or 43 feet at ISO 100. That works out to 12 feet at f/3.5 and 7.5 feet at f/5.6, the maximum apertures of the kit lens at wide-angle and telephoto respectively. In the two shots above, we can see that the Canon T2i's flash performs almost to specification, producing usable but slightly dim images at both zoom settings. At wide-angle, the exposure is only about 1/6 EV lower than ideal, while at telephoto it's underexposed by about 1/2 EV.
Note: Our standard test method for flash range uses a fixed setting of ISO 100, to provide a fair basis of comparison between cameras. We've now also begun shooting two shots using the manufacturer-specified camera settings, at the range the company claims for the camera, to assess the validity of the specific claims.
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