Multi Off Camera Flash

zbo2408 · Jun 26, 2012

Equipment
1. Canon Rebel XSi
1. Canon Speedlite Transmitter ST-E2
2. Canon speedlite 430 EXII

My first plan of attack is shooting an ancient tree during the blue hour... I plan to have the 2 speedlites close to the tree one left of the camera one right of the camera with the camera a little further back from the tree.

I have never used off camera flash or multiple flashes before. Could anyone link me to some resources that will help me understand how to use this equipment? (I've had the camera and 1 flash for several years just ordered the transmitter & second speedlite, they should be here friday)

Dao · Jun 26, 2012

Most of the peole I know use Radio tragger. So I am not sure about the ST-E2.

As for off camera flash, you should able to find more info by searching the word "Strobist".

pgriz · Jun 26, 2012

Technically, it should be possible to use the ST-E2 to trigger the speedlights and do it in e-TTL mode, so that the camera controls the speedlight output. But that can be very hit-and-miss. I have found it simpler to set the power manually, and use a radio trigger (or you can use the ST-E2) to trigger them. Part of the question is how much contribution you want from the ambient. Let's say, hypothetically, that you do want to have ambient, but you want it to be 1 stop underexposed. Let's also say that you're happy with an aperture of f/4. If you meter the scene, you may get something like 1/500 at f/4. To get a one-stop reduction in ambient, you'll need 1/1000 at f/4. But your synch speed is 1/200. So you'd need to set your shutter at 1/200 and your f/stop at f/9. Now, your 430 has a guide number of 141 (at 105mm setting of the flash zoom), which means you need to be at about 12 ft. from the subject to get full exposure from the flash. If you have another 430 set at the same distance, you'll overexpose your subject, so you may want to either move the flash further away, or you may want to reduce the power of the flash to (say) half power. Now take a shot and see how the exposure appears. If the ambient is where you want it, but the flash overexposed the subject, then reduce the power on the flashes some more, or move them further away. Do NOT adjust the aperture, as that will also affect your ambient exposure.

I use a flash meter to determine my power settings on my flashes. But the first step is to decide how much the ambient needs to contribute. That determines the basic exposure setting. Then I set the power levels on the flashes to get the right amount of contribution from each flash. Then I fire the whole thing and check the histograms to see if my calculations were accurate. Usually, I'm able to dial in my exposure & power levels to the right levels within two shots.