Why does my flash fire sometimes and not at other times?

November 2, 2012 at 10:35 am  •  Posted in Q&A by

After many years of using a point-and-shoot camera, I bought an EOS T3i, and I’m confused about flash photography. Sometimes, the flash pops up automatically and fires, whether I want to use flash or not. At other times, when I might like to try flash, it won’t pop up. What do you recommend?
-Eddie H.

This is a common problem among users of all brands of cameras with automatic pop-up flash, Eddie. It happens when you use the AUTO mode or one of the scene modes. The camera decides when flash is necessary, like in a dark location; it then pops the flash up and fires it. But later, when you go outdoors, it may never fire the flash because the metering system will decide that extra light is not necessary. In addition, in some scene modes, like Landscape and Sports, the camera is programmed to not fire flash under any circumstances. That’s because the subject is usually too large, or too far away, to be illuminated by a small flash tube.

Switch to P mode for control over flash

While it's simple to use AUTO mode or a scene mode with any DSLR camera, neither offers you any control over flash. Switching to P mode maintains full automation but allows you to specify when flash should, or should not, fire. © 2010 Peter K. Burian

Fortunately, the solution is simple. Switch to the P (Program) mode. It’s fully automatic too but allows you to use some overrides if you wish, such as Exposure Compensation (for a brighter photo) and White Balance control, as well as control over the flash. You also get those options with the semi-automatic Aperture Priority and Shutter Priority modes, of course.

In any of these so-called creative (vs. basic) modes, the flash will always fire if you pop it into the up position. To do so, press the button on the side of the camera; it’s marked with a lightning bolt symbol and designated with a red X in the photo above. Flash can be very useful outdoors when you want to lighten shadows cast on a person’s face by a hat, for example. It’s especially valuable when a subject is against a bright background, such as the sky at sunset. As long as the subject is not much more than three or four metres from the camera, the light from the flash should reach it and provide a brighter photo.

Photo test : flash

The most important aspect of flash control is "forced flash": causing the flash to fire in outdoor conditions for extra light to lighten shadow areas or to avoid underexposure in backlighting. © 2010 Peter K. Burian

When you do not want the flash to fire—while taking photos of the interior of a huge cathedral or a very distant subject, for example—simply press it down into place to disable it. As long as you’re using one of the creative modes, it will never pop-up and fire, no matter how dark the scene is. Of course, you will need to use a tripod or a high ISO, such as 1600, for a fast shutter speed. Either will help to minimize the risk of blurry photos caused by camera shake.

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