Does FEC only work with Canon ETTL flash and accessories?

I see many accessories, including those from Canon that indicate they are TTL but not ETTL. Does the device have to support ETTL to allow FEC from the camera or will it respond to FEC with devices that are TTL compatible?

Canon used to have TTL flashes (EZ line), which on some cameras also did A(dvanced)TTL. I liked TTL better then A-TTL.
The newer EX series of flashes uses ETTL(2). All digital cameras need an ETTL flash. When using a 540EZ for example, you can only use the flash in M mode. No (E)TTL functionality whatsoever.
Main difference between TTL and ETTL(2), is that ETTL uses a preflash to determine flash exposure, with TTL the flash output is measured off the film during the exposure.
Some Canon accesoires are not compatible with ETTL (allthoug I can't imagine why) like the older TTL extention cords IIRC.

TMR Design wrote in post #2342603
I see many accessories, including those from Canon that indicate they are TTL but not ETTL. Does the device have to support ETTL to allow FEC from the camera or will it respond to FEC with devices that are TTL compatible?

See bottom of p. 107 of your 30D users manual.

TMR Design wrote in post #2342603
I see many accessories, including those from Canon that indicate they are TTL but not ETTL. Does the device have to support ETTL to allow FEC from the camera or will it respond to FEC with devices that are TTL compatible?

FEC only works with ETTL-compatible (not TTL) flashes. The camera can control the output of a flash only if it is ETTL compatible and part of that control is FEC. So even though you may be able to use non-ETTL compatible flashes on your camera, you can only use them in manual or built-in auto mode (on the flash, not the camera) so that also precluded being able to use FEC.

Thanks guys. Sometimes if I don't fully understand something it's a little harder to extract that information without actually asking a pointed question.

Never be afraid to ask questions here since a lot of us have all been in the same situation at one point in or another.

And there are a lot of folks here who are more than willing to give you an answer.

Also, FEC doesn't work in ETTL-II 'Average' mode.

roli_bark wrote in post #2806585
Also, FEC doesn't work in ETTL-II 'Average' mode.

Incorrect.

FEC works with custom function 14 set to 1 (average) whether I adjust it on my 20D or my Sigma flash.

Curtis N wrote in post #2806841
Incorrect.

FEC works with custom function 14 set to 1 (average) whether I adjust it on my 20D or my Sigma flash.

How come ? My 5D user's manual says differently:

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Oh ... BTW, 2 posts above I meant [of course] - Automatic FEC ...

Automatic FEC is a different animal, apparently.
Further discussion in my post in this thread.