Slave Flash

[mhkitchens]

I am new to the use of slave flash. I am using a Canon Xti, a dedicated Promaster TTL flash, a homemade better bounce card, with the camera set in the P mode. I have setup a slave for a fill flash bounced from a white umbrella. All my photographs turn out under exposed using the slave. If I turn the slave off the exposure is normal. It is evident that I do not know how to use a slave properly. Does anyone have comments that may help?

Thanks

 

[reg]

Tried to take it out of P mode?

 

[Big Mike]

Welcome to the forum.

Firstly, how are you triggering the slave? If it's an optical trigger, it may be getting triggered by a pre-flash. Canon flash units use a preflash for flash metering, so I assume that an off-brand TTL flash would as well. If that's the case, you could find another way to trigger the slave or just put the master flash into manual mode (no preflash).

Then, as noted, you will need to take the camera out of P mode and use manual mode.

 

[mhkitchens]

It is an optical trigger and I see no pre-flash and uses infrared to focus. The slave is firing at the same time as the main flash. I have experimented in AV mode and Manual mode and am making some progress but still not up to par.

Thanks!

 

[davebmck]

You probably can't see the preflash. It is very fast. I don't know if that flash supports ETTL on your camera like the canon flashes do, but it sounds like the TTL metering is working with your on camera flash only. When you use an optical flash, the master can only trigger it. It cannot communicate with it, so it can't have it pre-flash and meter the light is putting out.

I think what may be happening is that the pre-flash is triggering the optical flash, so it is firing slightly ahead of the main flash. This is also probably confusing the TTL metering. There should be a way to turn off the preflash, but you will have to use the flashes manually.

Here is some good reading on Canon flash photography: http://photonotes.org/articles/eos-flash/