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Ext. flash: is there a way to wirelessly trigger it without firing the int. flash?
Posted By: dosdan, 03-26-2010, 01:16 PM

Q: Is there a way to wirelessly fire an external flash unit it without triggering the camera's built-in flash?

A: You can have the built-in flash only contribute a "test" flash, but you can't have the built-in flash not fire at all - the "wireless" signalling to the remote slave flash (Sigma EF-530 DG Super) is done optically (by light reflected off the subject from the camera's test flash), not by radio.

Look at the two shots below:




The Sigma flash unit is set up on the floor pointing up at about 30 degrees and to the left of the speaker.
I'm standing up & to the right of the speaker.
In both shots the built-in flash was up.
Camera set to Wireless flash mode.

Left shot - both fired. The camera flash was weaker and provides a "fill" flash.

Right shot - the camera only contributed a "test" flash. In the K20D, this is done by Custom setting 29. Flash in Wireless Mode - Off (option 2).

So the camera test flash was too early to illuminate the final shot, but it is still flashed.

Dan.

Last edited by dosdan; 04-23-2010 at 04:29 AM.
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05-24-2010, 03:55 PM   #2
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You could buy an external wireless triggering set
03-19-2011, 03:17 PM   #3
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QuoteOriginally posted by 0rangepeel Quote
You could buy an external wireless triggering set
But then you wouldn't get P-TTL, right?
03-19-2011, 05:42 PM   #4
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QuoteOriginally posted by dosdan Quote
Q: Is there a way to wirelessly fire an external flash unit it without triggering the camera's built-in flash?

A: You can have the built-in flash only contribute a "test" flash, but you can't have the built-in flash not fire at all - the "wireless" signalling to the remote slave flash (Sigma EF-530 DG Super) is done optically (by light reflected off the subject from the camera's test flash), not by radio.
Unfortunately, without resorting to radio triggers, the answer is no. But then, as you mentioned, you lose pTTL.
The on-camera pre-flash is the signal (I believe it is the infra-red component of the signal) used to communicate with the external flash. The external flash needs to see the pre-flash. And it IS still wireless triggering though (hey, there's no wires). Even Nikon's famed CLS works in a similar manner and their external flashes needs to see the commander flash.

The best thing you can do is to make sure you've set the flash in wireless mode to off, which you've done. Or, you can always jury rig something so that the on-camera flash is directed towards your external flash, but not the subject.

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