Canon EOS Rebel T3i Flash
The Rebel T3i'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 either kit lens at wide-angle (at f/3.5) and about 7.5 feet at telephoto (at f/5.6) . The Canon T3i 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 T3i also uses E-TTL II control for both the built-in and compatible external flashes, a standard that promises and seems to deliver better, more balanced exposures. (TTL refers to "Through The Lens" metering.) Both evaluatative and average E-TTL II metering modes are available, and the flash can be timed to fire immediately after the first curtain opens, or right before the second curtain closes, allowing for motion trails that lead or follow the subject position at the moment the flash fires.
Another nice touch is the Canon T3i's Flash Exposure Lock function, 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 T3i's pentamirror housing, for use with external flash units. Like most consumer SLRs, the Canon T3i offers no PC-Sync connector for triggering studio strobes, etc. Maximum flash x-sync speed is 1/200-second.
The EOS 7D and 60D were the first Canon SLRs to support wireless flash control using the built-in flash, and the Canon T3i follows suit. That is, the T3i's built-in flash can act as a controller or commander to one or more remote wireless flashes. You can have the built-in flash contribute to the exposure, or just command the remote flashes. Like that of the 60D, the Canon T3i's wireless flash capability supports four channels and defines two groups (the 7D defines three groups). Exposure compensation and flash ratio of 1:8 to 8:1 can be set on a per-group bases, allowing a lot of control over how multiples flashes contribute to the final exposure. Additionally, there's an Easy Wireless Flash mode, which simply fixes the flash strobes to all operate as one group with a 1:1 flash ratio.
Canon's Speedlite 270EX, 270EX II, 320EX, 430EX II, and 580EX II (as well as certain of its historic flash models) 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 T3i is capable of. This can be invaluable when you want to exclude ambient light from the exposure.
Flash Test Results
Coverage and Range
A fairly powerful built-in flash, with somewhat limited coverage and inconsistent exposure. Average positive exposure compensation required.
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| 18mm @ f/3.5 |
135mm @ f/5.6 |
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| Normal Flash +0.7 EV |
Slow-Sync Flash +0.3 EV |
Coverage. Canon rates the EOS Rebel T3i's internal flash coverage at approximately 17mm, though as you can see in the top left shot, we've found manufacturers' coverage ratings are usually quite optimistic. Some of the light fall-off is due to the lens itself, though. We measured about 2/3 EV at wide-angle when wide-open when we tested the 18-135mm lens on SLRgear.com. Still. that's no where near the amount of darkening in extreme corners we see here. Coverage is more even at full telephoto but very dark, though again some of the fall-off is due to the lens itself (about 1/2 EV at 135mm and f/5.6).
Exposure. Indoors, under incandescent background lighting, the Canon Rebel T3i's flash performed well, requiring an average amount of positive exposure compensation of +0.7 EV for a bright image. The camera's slow-sync flash mode only required +0.3 EV exposure compensation for bright results, 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 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
| 12 ft | 13 ft | 14 ft | 15 ft | 16 ft | |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
 1/60 sec f3.5 ISO 100 |
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| Flash Range: Telephoto | |||||
|---|---|---|---|---|---|
| 6 ft | 7 ft | 8 ft | 9 ft | 10 ft | 11 ft |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
| 12 ft | 13 ft | 14 ft | 15 ft | 16 ft | |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
 1/60 sec f5.6 ISO 100 |
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ISO 100 Range. The Canon Rebel T3i's flash was fairly powerful, though its output was sometimes inconsistent. With the 18-135mm lens' maximum wide-angle setting, the flash range test shots showed bright results out to about 10 feet, though brightness varied somewhat from there, with 12 feet brighter than 11 feet. Flash exposures were still usable to about 15 feet, though. At full telephoto (135mm), flash intensity started out a little dim at six feet, then got quite bright at seven and eight feet before falling off rapidly after 10 feet.
| Manufacturer-Specified Flash Range | |
|---|---|
| Wide Angle | Telephoto |
 12.3 feet ISO 100 |
 7.7 feet ISO 100 |
Manufacturer Specified Flash Test. The Canon Rebel T3i's built in flash has a rated Guide Number of 13 meters or 43 feet at ISO 100. That works out to 12.3 feet at f/3.5 and 7.7 feet at f/5.6, the maximum apertures of the 18-135mm lens. In the shots above, we can see that the Canon Rebel T3i's flash doesn't quite perform to specification at wide-angle, producing a slightly dim image underexposed by about 0.3 EV. At full telephoto however, results were very bright, actually overexposed slightly by about 0.1 EV compared to the ideal exposure.
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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