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 superior to the TTL and A TTL system because its algorithms is better at applying natural and subtle fill flash to daylight photos. The E- TTL is also linked to the auto focus point which results is better and finer grained exposure than that of the multiple zoned TTL flash sensor system. The E-TTL system is supported by all recent Canon EOS film camera as well as the Digital Camera after the introduction of the Canon D30.The sequence of 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.
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.
The E- TTL is superior to the TTL and A TTL system because its algorithms is better at applying natural and subtle fill flash to daylight photos. The E- TTL is also linked to the auto focus point which results is better and finer grained exposure than that of the multiple zoned TTL flash sensor system. The E-TTL system is supported by all recent Canon EOS film camera as well as the Digital Camera after the introduction of the Canon D30.The sequence of 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.
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.
About the Author:
Tim Harris is a canon camera enthusiast. For tips on choosing and buying cameras, do check out Canon OS Camera website. Camera 40D Digital Rebel XTI 3D Blog
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