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Canon's E-TTL autoflash system was built upon the TTL and A-TTL flash systems.
E-TTL (Evaluative TTL) autoflash is the most advanced flash system. It blends conventional Speedlite technologies with new Speedlite technologies to suit the next generation.
E-TTL autoflash aims to produce lighting which looks natural. It had its beginnings with the two conventional flash systems described next :
EF 17-35mm f/2,8L USM,
1/125s
f/4 |
TTL Auto Flash |
| TTL autoflash is based on TTL (Through-The-Lens) metering. Flash illumination reflected by the subject is metered during exposure with a dedicated sensor aimed at the camera's focal plane. Since the 1980s, almost all SLR cameras have used various forms of TTL autoflash metering. TTL autoflash is executed as shown in the figure below. The flash is fired and reflected by the subject. The reflected light enters the lens and it is metered by a flash metering sensor in the camera. As soon as the reflected light reaches the optimum exposure level, the flash is cut off automatically. |
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A-TTL (Advanced Through-The-Lens) autoflash is a Canon developed flash technology which is more advanced than TTL autoflash.
When A-TTL is used in the camera's program mode, the flash aperture is determined by two items of data. First, the existing light level is metered by the EOS camera and the correct aperture value is obtained for it. Then the Speedlite fires an infrared preflash to determine the subject's distance and the aperture value is calculated for it. These two aperture values are then compared and a suitable flash aperture is set. Also, in bright lighting conditions, flash reduction control is used to obtain a more natural-looking picture. |
Part of Canon "Flash Work" / E-Version © by Daniel ROCHA
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