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.
As mentioned earlier, the E=TTL system is more advance than that of the TTL or A-TTL system because of its algorithms. With better algorithm programming, the system is fill flash daylight pictures more efficiently. Apart from this, the E-TTL system is coupled to the auto focus point and this result in better and finer grained pictures than even those multi points TTL flash systems. Currently all late modeled Canon EOS film cameras support the E-TTL system. The digital range of camera adopted the E-TTL system after the Canon D30 was introduced. How the order of operation of the E-TTL system is as listed below:
When the shutter button is depressed halfway, current ambient light level are metered in the normal way. Aperture and shutter speed are set by the camera or by the user depending on the mode of operation selected. Once the shutter button is depressed down all the way, the flash unit fires a pre-flash from the main flash unit. The reflected light is then calculated by the metering system to determine the correct power output for the actual flash burst to achieve the correct 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. - 16035
As mentioned earlier, the E=TTL system is more advance than that of the TTL or A-TTL system because of its algorithms. With better algorithm programming, the system is fill flash daylight pictures more efficiently. Apart from this, the E-TTL system is coupled to the auto focus point and this result in better and finer grained pictures than even those multi points TTL flash systems. Currently all late modeled Canon EOS film cameras support the E-TTL system. The digital range of camera adopted the E-TTL system after the Canon D30 was introduced. How the order of operation of the E-TTL system is as listed below:
When the shutter button is depressed halfway, current ambient light level are metered in the normal way. Aperture and shutter speed are set by the camera or by the user depending on the mode of operation selected. Once the shutter button is depressed down all the way, the flash unit fires a pre-flash from the main flash unit. The reflected light is then calculated by the metering system to determine the correct power output for the actual flash burst to achieve the correct 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. - 16035
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
