Ever wonder when to use the ADI or the TTL flash which is found in the Sony DSLR's? Read more after the jump.
The ADI flash system can actually be found only in the Sony Alpha system. Basically in the ADI flash system, the camera will measure the true distance of the object and power the flash according to the distance between the object.
As for the TTL flash which you can find it many other DSLR brands, the camera will measure the light around the subject and power the flash accordingly. The camera will ask the flash to fire two burst of light with in a very very short period of time until you wouldn't notice it. The 1st burst of light will tell the camera the ambient lighting and then the camera will calculate set the power settings appropriately. The 2nd burst of light is only the real flash that will illuminate the subject.
The external flash uses the TTL system by bursting out a preflash to get the exposure of the ambient and then fire a second flash to fill/ correct the exposure based on the information obtained from the 1st flash.
The ADI and TTL flash has its own strong points and you should know when to use them properly. Some said that the TTL is sometimes not accurate. when there is a black or white background because the exposure is calculated based on how much light is being reflected during the preflash. Therefore in this kind of situation its best you use the ADI flash as the exposure can be calculated much more accurately based on the subject's true distance. ADI flash should be used when the subject is behind a glass or window too.
You should not use ADI flash when you are attaching diffuser or other light shaping tools to your camera as your camera won't know that these stuff is being attached and might underexpose the flash power.
As for white or black background, depending on how you are metering, TTL flash should work well. ADI flash can only work accurately if the subject is directly in front of the flash being fired. If you bounce the flash, the camera will automatically switch it to TTL mode. This is because the camera won't be able to know the flash to subject distance in bounce mode.
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