Photography Tidbits

Otherwise known as the Evaluative Through the Lens System, the E-TTL system was introduced in 1995 with the debut of the Canon Elan II/50 Camera. Even if the metering process is still done through the lens of the Camera, the E-TTL system is a more advanced system and operates on dissimilar system to that of the TTL system. In addition, the E-TTL system is not backward compatible. The E-TTL system functions by firing a pre-flash, whose brightness is known, from the flash unit to ascertain the exact level of flash exposure. This is achieved by measuring the pre-flash light which is reflected off from the scene. The camera then calculate the correct flash pulse to get a mid tone level on the subject.

The E-TTL is more advanced than the TTL or A-TTL system because the algorithm of the E-TTL system is able to fill flash daylight photos better. It is also connected to the auto focus point and as such the exposure result is better and finer grained than the multiple zoned TTL flash system. Currently the system is supported by all late model Canon EOS film cameras and the digital range after the introduction of the Canon D30. The progression of the operation of the E-TTL system is as follows:

Once the shutter button is depressed halfway the ambient light metering process runs it normal course of operation. Aperture size and Shutter speed are programmed by the user or camera depending on which mode the camera is operating under. After the shutter button is press down all the way, the camera fires a pre-flash from the flash unit. The light which is reflected of the scene is then measured by the metering system to ascertain the right power output for the actual flash pulse to get the correct exposure level.

If you are taking pictures under bright lighting conditions, the camera auto filled reduction feature will operate to reduce the flash intensity from ranges between 0.5 to 2 stops. The internal mirror then flips up to expose the film or sensor during the shutter run. After the shutter closes, the mirror will flip back down. If the camera has such a feature as a warning light for confirming the flash exposure operation, then it will start to glow.

The main drawback of the E-TTL system is that the pre-flash will cause those who blink quickly to be photographed while in mid blink. The predicament gets worse when you use the second curtain sync with a slow shutter speed. To get around this problem, you can after firing the pre-flash wait a short while before commencing the main flash burst. It would be wise to forewarn the subjects that you are just firing a pre-flash so that they will not assume the actual picture has been taken.