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August 29, 2010 4:09 PM   Subscribe

Going nuts...why does my camera flash no longer work with my standalone strobes?

For 3 years I have had two standing strobes and my Canon Digital Rebel XTi and the Canon Speedlite 430ex Flash. I would turn on the strobes, set the flash and point it at the ceiling, and the camera would work with the light from the strobes, triggered when my flash went off (the flash was the master, the strobes the slaves, in a wireless configuration)

Some setting must have changed on my last vacation... Now the pictures are coming out too dark. The camera is no longer in sync with the strobes. It works fine with the flash pointed at the object, but if I point the flash at the ceiling, as I've always done, the strobes fire, but the image is too dar. I believe the camera needs to pause for a fraction of a second for the strobes to fire and sync to that.

I have tried on manual and automatic settings on the XTi and ETTL and Manual modes (in the past I always did this on Manual with a 1/8 flash output and had perfect results).

This is driving me nuts...any help?
posted by arniec to Sports, Hobbies, & Recreation (7 answers total)
A few possibilities come to mind, assuming the off-camera flashes are just simple optical slaves that are triggered by a bright flash of light, and not the fancy Canon wireless E-TTL ones:
  • On-camera flash in an automatic mode. The pre-flash it emits to figure out proper flash exposure will trigger slaves before the shutter opens. It needs to be in a manual mode to make sure it only flashes once.
  • On-camera flash set for 2nd curtain sync (custom function 9?), so the on-camera flash fires just before the shutter closes, and the slave flashes fire just slightly too late, after the shutter has closed.
  • Shutter speed too fast -- set camera in manual mode and slower than 1/60th of a second.
  • Aperture too small and/or ISO setting too low for the amount of light the flashes provide (seems unlikely from what you're describing where it works fine with the on-camera flash).

posted by FishBike at 4:34 PM on August 29, 2010

Oh, and if your on-camera flash is in high-speed mode (there will be an "H" on the LCD I think), that could also potentially make a mess of things by making the slaves fire while the shutter is still in the process of opening.
posted by FishBike at 4:39 PM on August 29, 2010

If I'm understanding correctly, you've got two studio strobes that you're triggering as slaves with the 430. Do you happen to have a sync cord? If so, you could plug into the studio strobes and eliminate the 430 - if all works correctly, then its a problem with the flash. If you've got (or can borrow another camera) you can further narrow this down by trying that - at least you'll be able to isolate to source/location of the the problem, rather than trying to troubleshoot four variables all at once.

What type of strobes are you using?
posted by blaneyphoto at 5:18 PM on August 29, 2010

I hope I'm understanding your question correctly.

I do this frequently. FishBike and blaneyphoto have it pretty well nailed.

Assuming your 430ex is in manual mode, remove it from the camera, walk to with a few feet of the optical slave's on your stand mounted strobes, and manually fire the 430ex directly at the optical slave eye on one or both of them.

If the strobes fire, then you know they're OK.

Some strobe heads have a physical switch which must be set to "Slave" position for the slaves to work. Also, some strobes automatically disable the slaves when a sync cord is plugged in.

Additonally, some light modifiers like deep umbrellas and such will prevent the triggering light from your on camera from reaching the slaves eyes in some circumstances.
posted by imjustsaying at 4:35 AM on August 30, 2010

Response by poster: Sorry for lack of reply, trying to figure out brand of strobes. The strobes aren't a brand I know, but the strobes are firing every time. But I think they're just firing a fraction of a second too late as the pictures are dark but the strobes DO go off. So I'm guessing it's either a camera or flash setting to let it know it's needing to sync with the strobes? Maybe?
posted by arniec at 7:21 AM on September 4, 2010

Best answer: So I'm guessing it's either a camera or flash setting to let it know it's needing to sync with the strobes? Maybe?

Nope, there's not really a setting like that. Your external strobes should fire as quickly as they can once their sensor detects the bright flash of light from your 430ex. So since they are firing, the problem can only be that they're firing at the wrong time, or they're not providing enough light.

Expanding on my earlier comment, since I'm not sure if that was clear enough:

Basically, you need to get the external strobes to fire when the camera's shutter is fully open. The first common thing that messes that up is if your 430ex is in any kind of automatic mode. When it's in automatic mode, it emits a pre-flash to measure how much light comes back, and this is used to decide how much flash power to use for the exposure. The pre-flash happens while the shutter is closed, but it will trigger your external flashes, which can't recharge fast enough to fire again when the 430ex fires a fraction of a second later to expose the scene.

So, make sure your 430ex is in manual mode first.

The second thing that often happens is that the camera's shutter speed is set too fast. Although optical slave strobes are usually pretty fast, there may be a slight delay between when your 430ex fires and the external strobes fire. If the shutter has already closed by the time the external strobes fire, you'll get a dark picture.

So make sure you set your camera's shutter speed to something slow, like 1/60th of a second or slower. For troubleshooting purposes you can even set it to something crazy like 1 second just to see what happens.

Third, there is a custom function on most Canon dSLRs that sets whether the flash is synchronized with the "first curtain" (opening of the shutter) or "second curtain" (closing of the shutter). I think this is custom function 9 on your camera. If it has somehow gotten set on 2nd curtain sync, your 430ex will fire just before the shutter closes, and maybe your external strobes then fire just slightly too late, after the shutter has finished closing.

Setting the shutter speed to 1 second might be a good way to diagnose this if you're not sure how to check the custom function settings. If this is the problem, you'll notice a long delay (1 second) between when you press the shutter release button and when the flashes fire.

Finally, on this front anyway, the Canon flashes have a "high speed" mode. It takes a little time for the camera's shutter to open and close, so there's a fastest shutter speed where the shutter is ever fully open (usually around 1/250th of a second for the dDLRs). At any speed faster than that, the shutter is never fully open -- it's more of a narrow slit between the first curtain and second curtain that travels down the frame. If the flash was to fire once, it would just illuminate a horizontal band wherever that slit happens to be at the time. So the high-speed mode makes the flash fire many times in quick succession to fully illuminate the whole picture as the slit travels down the frame.

What does this have to do with slave flashes? Well, in high-speed mode, the flash doesn't wait until the shutter is all the way open before it starts firing. So it might be triggering the slave flashes while the shutter is still mostly closed. I would think you'd get a bright band at the top or bottom of your picture in that case. But in any case, make sure your 430ex is not in high-speed mode (it would show an H in the LCD display somewhere if it was).

Other than firing at the wrong time, the only other problems you could be having are to do with the amount of light vs. camera settings. So make sure that if your external strobes have any sort of power setting, that they're set on the maximum power. Then make sure the camera's aperture is set as wide as it will go (lowest available f-number, numerically). Set the ISO as high as it will go, too, e.g. ISO1600 or whatever your camera goes up to.

To summarize, for troubleshooting purposes, set things as follows:
  • Camera in manual mode, 1 second shutter speed and lowest f-number available
  • Camera ISO set as high as it will go
  • 430ex flash in manual mode, no "high-speed" mode selected
  • Camera flash sync set to first curtain (custom function 9)
  • External strobe power set to maximum, if it's adjustable
This should result in a horribly bright over-exposed picture, and you can back off to more reasonable settings if it does (lower the ISO, set shutter speed back at 1/60, close up the aperture to get proper exposure).
posted by FishBike at 7:59 AM on September 4, 2010

Response by poster: That did it! Thank you FishBike!
posted by arniec at 7:39 AM on September 6, 2010

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