A-TTL X E-TTL

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I would like to know about the difference using the A-TTL or E-TTL for Flash Photography? I thank you in advance for answers....

Andre

-- Andre Menezes (pizzarelli@mailcity.com), September 30, 1999

Answers

Hi, I don't know the technical details of those two technologies. I can just try to share some experience of using those two systems. The accuracy of E-TTL seems higher than A-TTL, quite significantly. Especially under extreme conditions. Such as, a person stand in an open area. No reflection except from the subject itself. Then, E- TTL is found to be more accuracy than A-TTL. Moreover, E-TTL support FEL. It's flash AEL, which is quite useful. Hope this help a bit.

-- Colin (colinleeq13572@yahoo.com), October 04, 1999.

I think E-TTL uses a visible light pre-flash and the full evaluative metering system to determin exposure. A-TTL is just a method of approximating flash to subject distance via an IR pre-flash. As suggested above, E-TTL is a better system and generally produces better results. It's only problem is that the visible preflash will trigger optical slaves in a multi-flash system.

-- Bob Atkins (bobatkins@hotmail.com), October 04, 1999.

A-TTL:

"Advanced" TTL flash uses a 1/20th strength preflash (IR in direct mode, visible light in bounce mode) to determine how much light is added to a scene by the flash and how far down the aperture can be stopped while still providing adequate exposure with the flash. This aperture is compared with the aperture that would be selected by normal Program mode (within the constraints of the body's flash sync speed and lens' widest available aperture). The smaller of the two apertures is selected. When the shutter button is fully depressed, the flash fires and is quenched using the TTL flash circuitry.

TTL:

Through-the-lens. Often used to refer to the metering system in an SLR camera where exposure is determined through the lens and not by some external light meter. Also used as in "TTL flash metering".

-- Peter Szutkowski (szutek@geocities.com), November 19, 2000.


And...

E-TTL (Evaluative Through-The-Lens) In E-TTL autoflash mode, the preflash occurs the moment the shutter is released (direct mode or in bounce mode), with ambient light monitored and calculated. Correct flash output is instantaneously determined to obtain a balance between ambient light and flash. Even in complicated lighting situations, such as when an unusually strong reflection is detected outside the active focusing point's metering zone, flash exposure is correctly controlled.

-- Peter Szutkowski (szutek@geocities.com), November 19, 2000.


In reference to Bob's comment about the pre-flash triggering optical slaves, I thought I'd add my experience. I'm using two 550EX's for main and fill and two slaves for hair light and b/g lights. One slave wasn't affected by the preflash while the other was. On that one, I tried a Wratten ND filter over the slave sensor but the filter I had on hand was too strong and then the slave didn't get triggered at all. But I discovered that one small piece of Scotch tape did the trick.

Paul

-- Paul Ferrara (paul@columbusoft.com), November 22, 2000.



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