5DmkIII, 580exII and ETTL - What am I doing wrong?

Hi all,
I was taking some shots at a charity event we went to and was struggling with the flash. I tried bouncing the flash but the ceiling was extremely high so ended up just pointing the flash direct(yep I know, but that's not what this topic is about this time ).

Setting used for these shots were 1/160, f/5.6, iso 400, partial metering. ETTL.

Both images were taken moments apart in ETTL, the only difference was the second shot I pressed the M-fn prior to taking the shot.
On my old 40D ETTL mode would result in an image like the second without having to check the exposure first.
I re-read the manual this morning and cannot put my finger on what I'm missing here.

Tried to replicate your shots with my gear but both are equally exposed. Did you program something special under the M-Fn button?
BTW... how do you set 1/160 sec? I can only do 1/125 and 1/180? - Edit: OK I checked the menu and had my settings at 1/2 stop intervals - with 1/3 stop interval you can pick 1/160 .....

No, M-fn button is as factory settings. I focus with the AF-ON button and meter with the shutter button.

I don't think you can meter flash any way other than evaluative or average. In the first shot the meter must have decided the guy in the white shirt was the subject. The preflash lit the shirt and the meter set the flash power to try and make that shirt medium grey.

Second shot and the meter must have decided to make the background the subject so the flash tried to light that to medium, which cooked the subjects a bit.

I understand what you're saying Jeff, but if you look at the framing the guy hasn't moved. Why then would it meter the background. Trying to understand this.

swoffa wrote in post #15669290
... the only difference was the second shot I pressed the M-fn prior to taking the shot.

That, by default, is the FEL button. With FEL, only the very center of the viewfinder is used for flash metering. As with normal spot metering, care must be taken where you aim the camera before locking your settings.

Ok, so am I best to use centre point focus whilst using the flash in ETTL mode?

Back to the photos above then. The guy is slightly off centre and possibly not in the centre area, so shouldn't the metering been taken off the background? If so, then I'm back to my initial quandary as to why both images have such a difference in flash output.

swoffa wrote in post #15669773
Ok, so am I best to use centre point focus whilst using the flash in ETTL mode?

Back to the photos above then. The guy is slightly off centre and possibly not in the centre area, so shouldn't the metering been taken off the background? If so, then I'm back to my initial quandary as to why both images have such a difference in flash output.

Try changing to average flash metering over evaluative. Eval can make decisions based on tones that are at the focus point while average is going to just look at the whole scene and apply an average tone.

IMO average is more consistent.

Indoors - avergae
outdoors - eval

BTW - I would have started with ISO1600 or even higher to get more ambient in. Then flash for some nice fill.

Righto, I'll try those settings and see how it goes.
Not sure increasing iso would have made much difference Bobby, I took a couple at 12800 with no flash just to see the result and they were extremely dark(almost black) images.

I meant higher ISO with flash so you pick more ambient that way.

swoffa wrote in post #15673310
Righto, I'll try those settings and see how it goes.
Not sure increasing iso would have made much difference Bobby, I took a couple at 12800 with no flash just to see the result and they were extremely dark(almost black) images.

The point is you raise your ISO to let in ambient while also using flash to add fill, so that you don't get this wash-out direct flash look (or at least avoid some of it). Also helps with flash not needing to blast away so much, which saves battery and recycle times.

In these types of situations it also might be conducive to just go over to full Manual (flash and camera), pop off a couple of test shots, then just leave it there, maybe riding the FEC when you need to. (assuming FEC is available in M on a flash? I don't have one with me so cannot remember)

I didn't explain myself it seems or my logic is off(again). My thinking was if I'm raising the iso to let more light, then shooting at 12800 should allow me to see how much ambient I would be getting before turning he flash on. Getting near black images I assumed it was just too dark for even that to help. This led me to believe that my only source of light was my flash and I might as well save some noise and use 400.
Was I off track?

I'm convinced there is something wrong with 580EX2 and 5Dmk3 combination. In many circustances the shots turn out wayyyy underexposed and studying the figures reveals no reason for it when it occurs. I'm really happy with the 5D3 overall but this flash situation is serious and causes me great concern. Thankfully the body is so amazing, I just avoid flash altogether and that often saves my day. As a result of the low light capabilties, I've avoided trying to learn more about what's going wrong. I do know this, it's not me. My 5D2 or other EOS cameras, no problems with same flash.

swoffa wrote in post #15674225
I didn't explain myself it seems or my logic is off(again). My thinking was if I'm raising the iso to let more light, then shooting at 12800 should allow me to see how much ambient I would be getting before turning he flash on. Getting near black images I assumed it was just too dark for even that to help. This led me to believe that my only source of light was my flash and I might as well save some noise and use 400.
Was I off track?

Dont think it works like that because you do of course have flash spilling over the background aswell to sort of "add to it" so they won't be getting near black images.