FLASH PROBLEMS

[HOMEYJAMES]

I am trying to use 2 flashes with my 10d. When both flashes fire, the pic is very dark. One flash looks great but I need more light. Shooting on man. with a 550. What gives??????? Homey

[Pekka]

Sounds pretty odd problem. And you have the flash on camera set to "master" and the other "slave" on same channel? Do you see the flashes fire? Is the second flash towards the camera (i.e. affects metering)?

[HOMEYJAMES]

Both flashes fire, but the second flash is not a Canon and it is triggered by the first flash. It doesn't matter where it is positioned...in front, out to the side...Homey

[ohenry]

Perhaps if you provided the settings you're using, someone may offer some suggestions.

[Tom W]

The Canon E-TTL system does shoot a reduced output preflash for the purpose of metering before the main flash. It happens so quickly that most people don't notice it. But, if your secondary flash is triggered by the light produced from the primary flash, it is very possible that it is firing on the preflash instead of the main flash. That means that it is done flashing before the shutter even opens.

[PacAce]

The Canon E-TTL system does shoot a reduced output preflash for the purpose of metering before the main flash. It happens so quickly that most people don't notice it. But, if your secondary flash is triggered by the light produced from the primary flash, it is very possible that it is firing on the preflash instead of the main flash. That means that it is done flashing before the shutter even opens.

And not only that, if the preflash is triggering the other non-Canon flash, then the camera will get a false reading and think that there's too much flash and hence "tone" down the main flash. That should explain why the picture is severely underexposed when both flashes are used but not when only the main flash is used.

[Tom W]

The Canon E-TTL system does shoot a reduced output preflash for the purpose of metering before the main flash. It happens so quickly that most people don't notice it. But, if your secondary flash is triggered by the light produced from the primary flash, it is very possible that it is firing on the preflash instead of the main flash. That means that it is done flashing before the shutter even opens.

And not only that, if the preflash is triggering the other non-Canon flash, then the camera will get a false reading and think that there's too much flash and hence "tone" down the main flash. That should explain why the picture is severely underexposed when both flashes are used but not when only the main flash is used.

Yes, that is correct. The additional light from the other flash will fool the metering system. Glad that you pointed that out, Leo!

[Steveo31]

The Canon E-TTL system does shoot a reduced output preflash for the purpose of metering before the main flash. It happens so quickly that most people don't notice it. But, if your secondary flash is triggered by the light produced from the primary flash, it is very possible that it is firing on the preflash instead of the main flash. That means that it is done flashing before the shutter even opens.

And not only that, if the preflash is triggering the other non-Canon flash, then the camera will get a false reading and think that there's too much flash and hence "tone" down the main flash. That should explain why the picture is severely underexposed when both flashes are used but not when only the main flash is used.
Yea, good points you guys. I totally forgot about the preflash. It happens so fast.... If you shoot something in a dark room, you can see it in the viewfinder before the shutter goes. If you are the subject, you can't see it. At least I can't... hehe.

[tracyh]

But he does say that he's shooting on manual. Not sure if he's referring to manual on the camera or manual mode on the flash. If it's manual mode on the flash, then the output should be consistent, shouldn't it? ETTL wouldn't override....?

[slin100]

But he does say that he's shooting on manual. Not sure if he's referring to manual on the camera or manual mode on the flash. If it's manual mode on the flash, then the output should be consistent, shouldn't it? ETTL wouldn't override....?
Correct. So, he was definitely referring to M mode on the camera.

[HOMEYJAMES]

All you guys were right on the money !!!!!! It was the preflash causing the problem. I'm using a trigger NOW that is made for a preflash and it works great. Thats or all of your input......Homey