Автор: pinko
Дата: 06-05-05 23:08
http://photonotes.org/articles/eos-flash/
http://www.bobatkins.com/photography/eosfaq/flashfaq.htm
Най-общо казано - едното е А-ТТЛ, другото е Е-ТТЛ, несъвместими са, сори![[smilie11]](https://photo-forum.net/forum/smileys/smilie11.gif)
Evaluative Through-the-Lens Mode (E-TTL)
E-TTL (prestored evaluative through-the-lens flash exposure control) is a new flash mode that reads through the lens, but not off the film. Introduced for the first time in 1995, E-TTL is currently available with the EOS Elan II/IIE, Rebel G and EOS IX SLR cameras exclusively when used with Speedlites 380EX or 220EX. Utilizing a preflash fired after the shutter button has been fully depressed but before the camera's reflex mirror goes up, E-TTL uses the camera's evaluative metering sensor to analyze and compare ambient light exposure values with illumination reflected from the subject by the preflash. This data is used to calculate and store the flash output required for optimum exposure of the main subject (identified by the autofocus system), while maintaining a subtle balance between foreground and background. Though transparent to the user, E-TTL represents Canon's most advanced flash exposure control system to date.
Advanced Through-the-Lens Mode (A-TTL)
The predecessor to E-TTL, A-TTL (Advanced Through-the-Lens) is used with Speedlite 540 EZ when set for direct flash in the camera's Program mode. (TTL flash exposure control is available at other times.) Like E-TTL, A-TTL reads through the lens and concentrates its sensitivity on the area of the picture covered by the active focusing point. Unlike E-TTL, A-TTL controls flash exposure with a dedicated sensor that reads flash illumination reflected from the surface of the film during exposure. A-TTL also uses a preflash, but unlike E-TTL, the preflash is used to calculate an aperture value based on the distance that light must travel from the flash to the subject. In Program mode, the camera compares the distance-based aperture data to the ambient-based aperture data calculated by the camera's normal metering system, and selects the smaller aperture value of the two. This method ensures accurate exposure of the subject in any lighting condition. Speedlites equipped with A-TTL are fully compatible with all EOS cameras.
|
|
![[cool]](https://photo-forum.net/forum/smileys/cool.gif)
undefined)![[smilie24]](https://photo-forum.net/forum/smileys/smiley24.gif)
![[ezik]](https://photo-forum.net/forum/smileys/tongue.gif)
![[beer]](https://photo-forum.net/forum/smileys/smiley20.gif)
![[shtrak]](https://photo-forum.net/forum/smileys/shtrak.gif)
Стани фен на Фото Форум във Facebook
Фото Форум в Instagram