E-TTL Question

[Skid]

Ok, so I just got a 580 (wow! - it REALLY does dwaf my 400D heh), and have been playing with it none stop much to the dismay of my wife -- anyway, I took a photo of my xbox controller on my sofa, direct flash wise - shooting on M camera wise, and E-TTL (I presume) on the flash. Cool, it works, etc however the photo looks too harsh.. so next I try to bounce the flash off my celing, and what can I say the photo looks a million times better. I've read about bounce and so on, but you really do have to see the results to appreciate it first hand. My question is, did the flash unit calculate the additional power needed to bounce the light off the celing, to expose the controller properly? - and is that because the flash knew it was being bounced as the head was pointing up, rather than straight? Or was it a fluke that the setting was powerful enough to bounce the light?

I've just started on the 2nd part of the flash guide from photonotes.org, but wanted to confirm what I'm thinking is right above.

thanks!

[Rellik]

Yes Yes and no fluke.

[riyazi]

When you change the position of the flash head to any other position other than straight on, the ETTL function is switched off. This is because the flash has no way of finding out distance unless it is position head on.

[Skid]

Ok. thanks but riyazi you've just confused me - if ETTL is off, how can the flash no how much to pump out - surely it must have emitted a pre-flash burst to see how much flash to pump out to expose properly?

[fashioneyes]

I believe when the flash is not straight on ETTL 2 is switched off and the flash goes back to ETTL mode.

ETTL 2 mode also uses the focus distance from the lense to adjust power output.

[riyazi]

Ok. thanks but riyazi you've just confused me - if ETTL is off, how can the flash no how much to pump out - surely it must have emitted a pre-flash burst to see how much flash to pump out to expose properly?

I believe when the flash is not straight on ETTL 2 is switched off and the flash goes back to ETTL mode.

ETTL 2 mode also uses the focus distance from the lense to adjust power output.

ooops sorry in my hurry I misunderstood your question. I think 400D newbie explained it perfectly :)

[Skid]

:P np hehe

[PacAce]

When you change the position of the flash head to any other position other than straight on, the ETTL function is switched off. This is because the flash has no way of finding out distance unless it is position head on.

I believe when the flash is not straight on ETTL 2 is switched off and the flash goes back to ETTL mode.

ETTL 2 mode also uses the focus distance from the lense to adjust power output.
Just to clarify, E-TTL is NOT turned off when the flash head is in the bounce position. E-TTL is still employed no matter what position the head is in as long as the flash mode is set to E-TTL.

The version of E-TTL used, i.e. the original E-TTL or the newer E-TTL II, is determined by the camera body, not the flash which is compatible with both ETTL versions. The older EOS bodies (prior to 1Dmk2) all employed the original E-TTL. With the 1Dmk2 and later models, E-TTL II is used. And bodies cannot switch between the two E-TTL versions.

What you may be confused about is the fact that E-TTL II can make use of the distance information available from some Canon lenses. This distance information is used in the algorithm to determine exposure when the flash head is pointed straight ahead. If the head is in the bounce position, the distance information is not used to determine exposure. However, the algorithm used is still E-TTL II, not E-TTL.

Hope that clears things up a little for you.

[PacAce]

BTW, to answer the original question posted by Skip, in ETTL mode, a preflash is fired whether the head is pointed straight ahead or in the bounce position. The light from the preflash is reflected back to the camera and metered. Based on how much light is reflected back and a few other factors like distance info, if flash is pointed ahead, ambient lighting, etc., the camera determines how much light will be required to properly expose the shot. As long as the amount of light required falls within the capability of the flash, you should get a decently exposed picture assuming the subject or scene is of average tone (not too bright nor too dark).

[Skid]

Ok thank you. I'm sure I've read my 400D employs E-TTL II, but it could be wrong... It'll do me for now anyway! :)

I just wanted clarification that I was understanding what was going on really,so yeah that's great :)

[PacAce]

Ok thank you. I'm sure I've read my 400D employs E-TTL II, but it could be wrong... It'll do me for now anyway! :)

I just wanted clarification that I was understanding what was going on really,so yeah that's great :)
Yes, your 400D does employ E-TTL II. :)

[fashioneyes]

OK to correct my original post ... and to quote from "Flash Photography with Canon EOS Cameras"

Cases in which distance data is not used.

Distance data is not always used by E-TTL II. There are three very significant cases in which distance data is not used, aside from the obvious case when it isn’t available because the lens doesn’t provide it. These three conditions are bounce flash, macro flash and wireless E-TTL flash.

http://photonotes.org/articles/eos-flash/#ettlii