How ETTL II technology works to your advantage

The ability of your camera to intelligently evaluate the photo you are taking and apply flash lighting to it is the result of many years of technology advances and developments. Studio photography with multiple external strobes and lights set and controlled by the photographer, and essentially invisible/unrecognized by the camera, must be metered manually. An on-camera flash, however, has a number of evaluative measurements that the camera and flash manage and that adjust the flash’s intensity and area of coverage (the flash adjusts its area of coverage to match the focal length of the camera’s lens). Canon’s current and most advanced technology today is called ETTL II; the acronym stands for evaluative through-the-lens, meaning the camera is reading the subject through the lens for the most accurate evaluation. Canon’s higher-end flashes, the 580EX II and the 430EX, both use ETTL II technology, and are backwards-compatible if you’ve mounted them on an older camera that doesn’t support ETTL II.

As part of the flash process, ETTL II uses a virtually invisible preflash and emits a very short flash before the actual image-taking flash takes place. This preflash evaluates and gives information to the camera and flash for a proper exposure based on the reading. And, as implied by the ETTL definition, the reading taken during the preflash is done through the lens and read by a sensor within the camera. ETTL is smart enough that if the ambient light is bright enough, it adjusts the flash for fill-flash settings, powered-down from what it would shoot in a darker situation. ETTL II, the second-generation of Canon’s ETTL technology, adds superior metering capabilities and integrated distance data (its ability to meter distance from the camera to the subject) that is communicated between compatible/supporting EF lenses.

There are situations where ETTL II adjusts to accommodate the fact that the flash is in a different position, where if kept the same, ETTL II would produce an inaccurate reading for the image being taken (see 8-3). For example, macro photography often requires that you get very close to the subject where traditional flash metering is difficult to accomplish; however, ETTL II technology can adjust the reading accordingly. Another situation is when you’re performing a bounce flash (aiming your flash against a ceiling or wall instead of your subject), since the flash is (presumably) pointed away from your subject. Finally, and similar to the bounce-flash, ETTL II doesn’t work fully automatically when you’re using a remote/wireless flash because the flash is not attached to the camera and isn’t going to have a relative focal distance to that of the camera’s lens.

When you configure your flash to bounce light off the ceiling, ETTL II adjusts accordingly because its evaluative metering would not accurately measure what the flash is illuminating. Note the extended white catchlight panel.

ETTL will operate with the following Canon digital cameras — it is supported in compact digital cameras and dSLRs:

  • PowerShot G2, G3, G5, and G6;
  • PowerShot Pro 1;
  • All Canon dSLRs.


What’s the difference between ETTL and ETTL II? While both modes provide a sophisticated evaluative measurement of your subject so that your image exposes optimally, ETTL II features an improved ability for candid, on-the-fly shooting where you’re less likely to have to test your shot or use the Flash Exposure Lock (FEL) setting (see later in this chapter for more on FEL). Generally speaking, it’s better at evaluating the scene and setting a more reliable flash.

Category: Flashes

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