E-TTL flash metering system, or otherwise know as Evaluative Through The Lens system, was introduce in 1995 by Canon with the debut of the Elan II/50 camera. Even though the metering is still done through the lens, the system works on an entirely different principle from that of the TTL system. Furthermore this system is also not backward compatible. The E-TTL system operates by firing a per-flash of known brightness from the flash unit to determine the correct level of flash exposure. It does this by measuring the Pre-flash light which is reflected off the scene. It then calibrates the correct flash pulse to achieve 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:

First, the ambient light metering process takes places once the shutter button is depress halfway. The user or camera determine the aperture size and shutter speed depending on what mode the camera is running under. After that, when you depress the shutter button all the way down, the camera fires a pre-flash from the flash unit. The reflected light from the scene is then calculated by the metering system to establish the correct power output for the main flash burst in order to get the right exposure level.

If the photo taking session is taking place under bright lighting conditions, then the auto filled reduction process will work to reduce the flash output from a range of 0.5 to 2 stops. The camera’s mirror then turn over to expose the digital sensor or film. At the same time, the shutter remains open to expose the sensor or film during the duration of the shutter run. After the shutter closes, the mirror will revert back to its original position. If the camera has a warning light to confirm the flash exposure, it will then glow.

However the main disadvantage of the E- TTL system is the fact that the pre-flash can cause those who blink quickly to be photograph while in mid blink. The problem is compounded when one uses the second curtain sync with a slow shutter speed. One way to overcome this problem is to fire the pre-flash first, then wait momentarily before actually firing the main flash pulse. Of course you must not forget to forewarn the subjects incase they think that the actual photograph has been taken when you fire the pre-flash.

Similar Posts:

• Canon Camera Basic Guide Flash metering
• The Canon Guide to the E-TTL flash metering System
• TTL Flash Metering System of the Canon Camera
• The Canon TTL Flash Metering System
• Canon EOS Flash Photography Explained

Tags: Photography

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