At 09:42 PM 01/23/2001, you wrote: >Could someone give me a one paragraph tutorial on the difference between >e-ttl and a-ttl? I hope that <one paragraph> was just a suggestion. :-) This was given to me by Canon's Chuck Westfall. It was written a year or so ago and does not mention some newer products. -------Product Overview------- Whether it's a bright summer day or a moonlit room, EOS Speedlites emit just the right amount of light to illuminate subject and background perfectly. The system couldn't be easier to operate: when the camera is set to Full Auto Mode (Green Zone) or "P", the EOS and Speedlite begin working together. The shooting conditions are evaluated as soon as the shutter button is pressed halfway and the appropriate aperture and shutter speed are set automatically. With EOS cameras featuring the AIM system*, flash exposure control is linked to the active focusing point for optimum exposure of the subject. In addition, EOS Speedlites incorporate a variety of advanced modes which help realize the full potential of the photographer's expertise and creativity. *An abbreviation for "Advanced Integrated Multi-point Control System," AIM is Canon's original multi-point autofocusing and metering system which links evaluative metering, partial metering and flash metering to the active focusing point. It enables the user to concentrate on composition and take better pictures more easily without having to first place the subject at the center for AF lock. ---------Key Features--------- 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. 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. Through-the-Lens Mode (TTL) =========================== TTL (Through-The-Lens) is the automatic flash exposure control mode used by the small pop-up flash units built into some EOS cameras. It is also available with Speedlites 380EX and 220EX when used with EOS cameras other than the Elan II/IIE, Rebel G and EOS IX. Additionally, TTL is the standard flash mode for Macro Ring Lite ML-3, Speedlite 200E, Speedlite 480EG and Speedlite 540EZ (except when set for direct flash in the camera's Program mode as outlined above). TTL is identical to A-TTL in almost every way, except there is no preflash. It can be used in every camera exposure mode. In Program mode, TTL always selects an aperture value based on the level of available light. Flash Exposure Lock (FEL) ========================= FE Lock (Flash Exposure Lock) provides an AE lock function for flash photography. Available exclusively with the Elan II/Elan IIe, Rebel G or EOS IX equipped with Speedlites 380EX or 220EX, FE Lock takes advantage of the camera's AIM system and partial metering capability to isolate flash readings to a small part of the picture area. With FE Lock, the Speedlite 380EX or 220EX preflash fires when the camera's AE lock button is depressed, storing AF and metering data for up to 16 seconds. This provides enough time for adjustments: Not only can the shot be recomposed, but the background exposure can also be altered for maximum creative control. FE lock is extremely useful when you wish to place the main subject in a part of the picture area that is not covered by one of the three focusing points. It can also eliminate potential exposure errors caused by unwanted reflections from highly reflective surfaces like windows or mirrors. High-Speed Synchronization (FP Flash) ===================================== The FP flash mode of Speedlites 380EX and 220EX allows the EOS Elan II/IIe, Rebel G and EOS IX SLRs to synchronize E-TTL flash exposure at any shutter speed. Therefore, even in bright daylight conditions, a fast lens can be used at a wide aperture to blur the background and emphasize the subject in portraiture, for example. FP flash is automatic and simple to use. It is available in Intelligent Program, Shutter-priority AE, Aperture-priority AE, and Manual modes. Flash Exposure Compensation =========================== Flash exposure compensation adjusts the level of illumination provided by the flash, and is therefore an important method of creative control for all kinds of flash photography. It's particularly effective for fine-tuning the balance between foreground and background exposure during fill-in flash, but it can also be effective to compensate for extremely bright or dark tones in the subject. Built into Speedlite 540EZ (up to +/- 3 steps in 1/3 step increments), flash exposure compensation is also built into the EOS-1N & RS, A2/A2E, and Elan II/IIe. Second-Curtain Synchronization ============================== Instead of firing the instant the shutter opens, Second-curtain Sync fires the flash at the end of the exposure, allowing streaks of light to flow naturally behind the movement of the subject. Originally invented in 1986 by Canon with the T90 and Speedlite 300TL, Second-curtain Sync is currently available with Speedlite 380EX when used with the Elan II/IIe or EOS IX, as well as with Speedlite 540EZ when used with any EOS camera. -- regards, Henry Posner Director of Sales and Training B&H Photo-Video, and Pro-Audio Inc. http://www.bhphotovideo.com * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
