View Full Version : What's the difference between TTL, e-TTL, e-TTL II?

22nd of November 2007 (Thu), 20:54
I can't really see a major difference between these different flash metering modes. Is there much of a difference? Or is it just marketing nomenclature?

Curtis N
22nd of November 2007 (Thu), 21:14
"TTL" began as a generic abbreviation for "through the lens". Today it's generally used to refer to the flash metering systems that measured light reflecting off the film surface and squelched the flash in real time.

This system didn't work with digital cameras, and manufacturers developed alternatives. Canon called theirs E-TTL, which was updated a few years ago with a new version they call E-TTL II.

The various versions of E-TTL and similar systems of other manufacturers utilize a pre-flash to calculate the required flash power before taking the shot. The film-based TTL systems did not use a pre-flash.

I encourage you to read the EOS Flash Bible (link in my sig) for a more thorough explanation.

22nd of November 2007 (Thu), 21:59
This "tip" will explain the gross difference between TTL and ETTL (along with the two other common flash metering methodologies), and there is no gross difference between ETTL and ETTL-2, it is a very subtitle one. But, there are differences between ETTL and ETTL-2.


Enjoy! Lon

22nd of November 2007 (Thu), 22:03
The only area in which I can see a difference between E-TTL I and II is that the latter doesn't use the auto focus point to measure the output but looks at the ambient light and uses the pre-flash to compare areas in the scene before determining output.

23rd of November 2007 (Fri), 10:17
Thanks so much for the replies. That all helps a lot.