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Old Jan 11, 2008, 7:33 PM   #1
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I tried using my Vivitar 285 flash with a flash slave as a second flash to get a portrait look with the Canon XTi built-in flash but it would not sync with any shutter speed.

Anyone know why (couldn't get an answer from a Canon rep.)
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Old Jan 12, 2008, 6:17 AM   #2
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I've moved your thread to our Studio Lighting, Flash & Other forum.

Your camera's flash is emitting a metering preflash, just before the main flash burst.

That's causing the slave to fire on the preflash versus the main flash (so, it's not contributing anything to the exposure).

One way around it is by using a Digital Aware Slave Trigger that's designed to ignore a preflash.

Wein Digital Peanut Slave Triggers at B&H

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Old Jan 12, 2008, 12:09 PM   #3
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Thank you a thousand times!
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Old Jan 12, 2008, 12:53 PM   #4
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It's my understanding that you may be able to use FEL (Flash Exposure Lock) on Canon DSLR models to get around it, too.

FEL will fire a preflash, and you could wait until your external flash recharges to press the shutter button to take the exposure (and another preflash shouldn't be needed since flash exposure is already locked from using FEL).

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Old Jan 13, 2008, 6:07 AM   #5
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JimC is correct; However you don't have to wait if you block the built-in flash by covering it with your palm when you press the FEL (*/AE lock) button. Your external slave flash won't fire then if it did not "see" the initial pre-flash!
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Old Jan 25, 2009, 8:47 AM   #6
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NHL wrote:
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JimC is correct; However you don't have to wait if you block the built-in flash by covering it with your palm when you press the FEL (*/AE lock) button. Your external slave flash won't fire then if it did not "see" the initial pre-flash!
It would keep the slave from firing, but I don't see how it solves the problem. Covering the built in flash would defeat the purpose of pre-flash in getting the exposure right. Not only do you need the pre-flash, but it seems desirable to have the slave included in the reading. In that regard, FEL seems like a better solution than the peanut. What I haven't checked is whether the subject's pupils will reopen in the time that the slave recycles. Anyone played with that?
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Old Jan 26, 2009, 9:58 AM   #7
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srobidoux wrote:
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It would keep the slave from firing, but I don't see how it solves the problem. Covering the built in flash would defeat the purpose of pre-flash in getting the exposure right.
That's true - covering the pre-flash will prevent the exposure from getting right; However you're on manual anyway with a Vivitar 285 since there's no way for the camera to modulate the Vivitar 285 remotely... (like on the Canon's EX series)

-> This method only work on manual in a studio environment with fractional flash setting on the remote strobe(s) where the camera's own exposure is a don't care...
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