Off camera flash underexposure

I figured this has been discussed before but could not find it. Anyway, I have a Rebel XT and a 580EX II plus a Promaster 7500DX.When using these flashes off camera on a bracket with the canon off camera cord I may get sometimes 10 or more flashes and then the flash indicator light is no longer in the viewfinder,the flash still fires but the image is totally dark. I have to take the flash off the bracket, put it back on and then it will start working again maybe for 30 or more flashes..sometimes only 5 before messing up again. Very unnerving to do a wedding and you have no idea when your flash will fail. Both the 580ex II and promaster flashes are doing this. Camera and flash contacts are clean and pins are fine. Flashes started doing this right out of the box. On another forum 2 more photographers posted a message on this same problem with their 30D\'s. Then another one said he has had the same problem with his 1D and speedlite flash, not the 580ex for 2 years now. Canon is no help on this matter of course. Does anyone have any idea the solution to this besides selling the ettl equipment and using auto flashes? My vivitar 283 and Promaster 5950 in auto mode do not do this, they fire everytime and every image is great..is this a problem with ettl II? Last night I shot 10 images of the same subject, letting the flashes fully charge between shootings and on #8 the flash indicator was no longer in the view finder and image was totally dark and yet the flash fired.Solution please?

It's happend the same to my 30D .If I set it to ETTL mode ....the flash will last about 30-50 image (bateries fully charge) But if I use Manual flash ...it's last for about 100-150 image ( I am not sure exactly number of shot) .

I did wedding also ,so I pick up the Battery pack CP-E4 ( http://www.bhphotovide​o.com …t_Battery_Pack_​CP_E4.html ) and that is last for long time with manual flash 1/4 power setting.

QX56 wrote in post #4803295
It\\\'s happend the same to my 30D .If I set it to ETTL mode ....the flash will last about 30-50 image (bateries fully charge) But if I use Manual flash ...it\\\'s last for about 100-150 image ( I am not sure exactly number of shot) .

I did wedding also ,so I pick up the Battery pack CP-E4 ( http://www.bhphotovide​o.com …t_Battery_Pack_​CP_E4.html ) and that is last for long time with manual flash 1/4 power setting.

I cannot set flash functions in my Rebel XT, but I shoot my rebel in manual. If I read your post correctly, you are referring to batteries being exhausted after so many images..correct? I am referring to the ettl II system messing up..the flash still fires but the flash indicator in the viewfinder disappears and then the flash still fires but the image is dark. I have to take the flash off the bracket, then put it back on and it is good for sometimes up to 30 to 40 shots before misfiring again. If I shoot in P mode the problem is so much worse, about 1 out of every 5 shots is screwed up.I just email from Canon and they want me to send the flash back to the factory..I told them the flash itself is not the problem because photographers all over are all having the same problem..the problem is the ettl system itself. I have a batter pack also but that doesn\'t help. If the system was made properly it seems like it would not be going on in the first place.

The flash function (manual)is on the flash ...not the camera . If you go to the flash ...push the button Mode Or hold it for a few second until it flashing to Manual ..and use the dial button or set button to select the number (flashing)indicate the flash power ,then use the dial button to adjust the flash power .That should help your flash use less batteries power .

What kind of batteries are you using ?

I've tried rechargeables, alkalines and even my lumedyne power pack..it isn't the batteries..the flash isn't running out of battery power, it has plenty..something is causing the flash to lose communication with the camera. I got a message from a photographer on OURPPA forum and he has had this problem with his 1D for 2 years now, then 3 more photographers all with different cameras reporting the same problem. One of them with a brand new 5D out of the box and the 580EX II out of the box, same problem..so it isn't the power...it isn't losing power..it is losing signal or something. I shot 20 shots of the same subject last night and #19 was all dark and the flash indicator light failed to show in the view finder when this happens but the flash is fully charged and it isn't in low light focusing either..

i get something similar too - i can use the test button to fire and the flash is fine - but (and I haven't strobed either) after about 10-20 shots, i get totally under-exposed shots.
i'm using a 350D and a 580 flash.

Yep, I can use the test button too and it will fire...also, my pre-flash will not register any readings either when the flash indicator is not in the viewfinder even though the flash still fires. Canon has a major problem on their hands..One photographer said when he manually focused his stopped doing that..well, that didn't help me so it isn't tied to focusing as far as my system is concerned. If this is the way it will be and there are no solutions I'm going to sell my 580ex II and promaster 7500DX and go to automatic flashes..I tried the manual mode and auto mode in the flash but that is totally underexposed on every shot so that isn't a good answer either. External metering for the flash is the pits. The entire ETTL II system is flawed it seems. Canon wanted me to send the flash, lens and camera to them to be looked at. I told them since I only have 1 and I have jobs to do that would not be feasible and since so many others are having the same problem, they need to examine their entire system.

This sound like what happened to me last night... I took 2 nice bright pictures of my teddy bear and it came out very nice. (equipment Rebel Xt, 430Ex, and the AB800 w/sync on = strobe). This happened in P, M , (Av was ok but blurry) mode

It could be me because I am a newbie. I didn't change the settings but 20 minutes later, all the imagers are dark and unable to see... I will post later.

Shooting, are you using both flashes at the same time? One on the Canon off Shoe Cord II and one as slave?

No, I tried one..took it off and then tried the other since they are both dedicated digital flashes.

jackies35 wrote in post #4808018
This sound like what happened to me last night... I took 2 nice bright pictures of my teddy bear and it came out very nice. (equipment Rebel Xt, 430Ex, and the AB800 w/sync on = strobe). This happened in P, M , (Av was ok but blurry) mode

It could be me because I am a newbie. I didn't change the settings but 20 minutes later, all the imagers are dark and unable to see... I will post later.

I first used Program Mode and now using Manual but no difference.

Can you try shoot manual flash ?

QX56 wrote in post #4809368
Can you try shoot manual flash ?

Ok I\'ll give that a shot and let you know..I\'d hate to do that because about every flash has manual, I paid good money for this technology only to find it is so unpredictable in it\'s problems it is virtually useless.

Ok it works fine in Manual..my goodness everything is totally washed out but it works..took 50 shots and none failed. Of course I\'ll only be using my flash on a bracket when situations don\'t let me bounce like dark wood ceilings and walls and colored walls

Here are the pictures I mentioned about.

Focal Length: 50mm
Exposure time: 0.125
I really don't like putting the camera in M mode because all my images comes out blurry... I need a tripod... I am a very nervous girl... These images must have been in P mode. I don't think i put the camera in Manual mode. Anyway, this is what everything look like before I decided to take a couple of shots with my neice.

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