Please read this account of a minor odd moment in strobe lighting and tell me if you know what went wrong.
I was photographing interiors and my kit includes both Einsteins and speedlights, Canon and Vivitars. In a small bathroom I planned to shoot from the door and snuck an Einstein head up next to me such that the head pointed straight up at the ceiling over my head. Satin 7.5 inch reflector. Dialed down to something like 100, 200WS, because it was a small bathroom and light in overall color (white ceiling). Attached directly to the 1DsMk3 by its own Buff-supplied PC cord. 17TSE on the body.
This body had been used on other rooms with just Einsteins (multiple heads) all good so far.
I had placed a Canon 580EX in the bathtub to brighten up the shower curtain and the matte-finished tile. It was mounted on a small stand up on top of a Phottix Odin receiver into which I had plugged a FlashZebra orange optical slave made for Canon triggering (FlashZebra has different models.) Odin "on" and set for Group A, Channel One. The speedlite was behind the white translucent cloth curtain pointed away from the lens. The Odin was underneath it and the slave stuck out the "back" of the Odin toward the camera position and therefore toward the strong pulse from the Einstein.
What went "wrong"? This: On first curtain setting only the Canon's light showed up in the exposure. Everything fired, though, and apparently at the same time. Tried it about five times. Get this - I was dragging the shutter to let a ceiling light show in the image, so I wasn't anywhere near 250th. No banding showing on the screen. Change to second curtain and it works fine.
The same combination did it in another room a bit later. Again, second-curtain "fixed" the problem.
Nothing strange about those second-curtain images in post.
Tonight I pulled what may or may not be the same Einstein head and tested the setup. I should have marked the head! Works fine on both first- and second-curtain. WTF? Presumably the Canon is going off milliseconds after the Einstein, as it's the Canon speedlite on a slave.
OK, anyone, any ideas?
(As an aside: One of the things that bothers me about my 580 and 550 is their lack of a PC connector, because when not at an event I think of them as small manual strobes to be hidden here or there or lighting a corner that just fades due to required placement of the bigger units. Before the purchase of the Einsteins this motley crew of Canon and Vivitar units was my only kit for interiors. In most cases optical slaves are fine for that kind of work. The Vivitars have a connector, albeit a proprietary one.)