I was taking some shots the other night to get an image of the person dreaming to comple my
Dream Car image for this months competition.
I had my Canon 20D tripod mounted and a single flash fireing into a brolly off to one side. The flash was being triggered at this stage by a cable linked to the PC socket on the camera. I then decided that I needed a bit of fill in flash from the pop up on the camera. I took this opertunity to get rid of the wire trailing across the room to the brolly flash and fitted a remote light sensing trigger that would sense the pop up firing and fire the brolly flash.
Took the shot, the pop up fired, the brolly flash fired and guess what - the image was DARKER
Hadnt really got time to mess around then so refitted the cable from camera PC socket to brolly and this time I got the fill in the I wanted.
This morning I've had the chance to experiment and see what happening. I set everything up and took some pictures of a white wall (which weren't that exciting
) but did enable me to see the amount of ilumination I was getting by looking at the resultant histograms - see attached). I had the camera set on manual 125 sec f8.0 ISO 100, flash sync set to 1st curtain sync (although I tried 2nd curtain and the results are the same)
First I took just the wall to guage the amount of ambient illumination. Then just the pop up flash to see how much light that was giving and then added the remote flash triggered by the slave. This is where thing get really odd and the illumination was LESS. How can that be
Then I tried the remote flash only triggered by the cable, then flipped the pop up as well. This gives the result I expected but didnt get using the slave trigger ie more light than either the remote or the pop up alone. I wondered if the remote slave was not acting fast enough to trigger the remote flash before the shutter closed. So I set up a second remote flash unit. Triggered the first one by the cable and the second one by a slave unit. White out - which proved that the slaves are acting fast enough. Flipping the pop up again resulted is a drop in ilumination - again slightly lower than the pop up + wire triggered remote on their own
Can anyone explain whats goin on and how to set things up for using multiple flashes triggered by slaves AND using the pop up of in fill?