A-TTL X E-TTL

[andre_menezes]

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....

 

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Andre

[colin8]

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.

[bobatkins]

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.

[peter_szutkowski]

A-TTL:

 

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"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.

 

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TTL:

 

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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]

And...

 

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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.

[paul_ferrara]

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.

 

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Paul