whats the difference between auto/TTL flash?

how do you even turn this auto mode on?

i currently use 580EX but get baffled hearing this all the time... i tend to have high speed sync on, i get that H/lighting icon (i think) and tend to dial in FEC -1/ 2/3 etc, so i take it thats manual mode?

but what is this auto mode i hear? and how do you actually leave TTL on? I tend to fire flash off walls/ceilings if that helps someone to explain it more?

Traditionally, "auto" flash utilizes a light sensor built into the flash unit. The flash unit measures its own light reflecting off the subject, in real time, and turns off the bulb when sufficient light has been produced. Old-fashioned flash units work this way and usually work very well. The camera's aperture and ISO need to be set to match the settings on the flash unit.

The original 580EX does not have the built-in light sensor or circuitry to operate this way. It's a dedicated flash that requires the camera's TTL (film) or E-TTL (digital) system to tell it how much light to produce. The recently released 580EX II is the first Canon Speedlite with the option to use either TTL, E-TTL or traditional auto modes, and has the sensor and circuitry to enable this.

TTL and E-TTL systems can be described as forms of "automatic flash metering", but they are different from "auto" flash in the traditional sense.

If you are using E-TTL with +/- FEC, it's still E-TTL. FEC simply adjusts the output up or down from what it considers "normal".

Manual flash is entirely different. In manual mode, you tell the flash how much light to produce. Period. Full power, half power... all the way down to 1/128 power. There is no metering of any kind involved.

High speed sync is a different functionality. HSS can be used in E-TTL or manual mode.

Much more information on all of this in The EOS Flash Bible (link in my signature).

Yup thanks, but that bible is literally that, massive lol

Yeah my flash states TTL on the top left, guess just keep using it as I do should be sufficient

Curtis,
thanks for taking the time to explain this. I appreciate the information!
Tom

excellent summary.........read as much as you want, but short summaries like that from someone in the know seems to help alot more. cheers

Thanks Curtis, that explanation has helped me a lot too.
Ray

Yella Fella wrote in post #2874484
Yup thanks, but that bible is literally that, massive lol

Yeah my flash states TTL on the top left, guess just keep using it as I do should be sufficient

Does it say TTL or E-TTL? There is a difference. While I don't have a 580EX and I don't know what that unit says, my 550EX says E-TTL. The E stands for evaluative - the pre-flash that is used to determine how much light you really need.

Perhaps there is no difference on the 580EX?