Why are my photos underexposed when a Canon Speedlite triggers studio strobes?
Asked 2/25/2017
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2 answers
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I'm using a Canon EOS-1Ds Mark II with a Speedlite 420EX on the hot shoe. If I shoot with only the 420EX, exposure looks correct. But when I turn on two studio strobes and let the 420EX trigger them optically, all flashes appear to fire yet the resulting image is underexposed, almost as if the flashes didn't contribute.
I've tried shutter speeds from 1/30 to 1/200 and also changing the 420EX slave setting, but the behavior stays the same. Why would adding the studio lights make the exposure darker, and how can this be fixed?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
5
I don't understand why the 2nd image wouldn't be correctly exposed as the Speedlight fires normally (this is what triggers the 2 x Studio lights), even if the studio lights were having no effect!
Sounds like the studio lights are firing at the wrong time. Are you using ETTL mode? With ETTL, the camera fires a pre-flash to judge the exposure, and then takes the photo firing the flash at whatever power level it thinks is necessary. If the studio flashes fire in response to the pre-flash, then a) the camera is going to see a LOT more light when it's judging exposure, and then b) the studio lights probably won't fire at all during the exposure, having already fired once. That means that the camera will significantly underexpose the shot.
Unless your studio lights are compatible with Canon ETTL, you'll need to switch to manual mode and set the flash power for both the speedlight and the studio lights manually. If the lights are, in fact, ETTL-compatible, then you should make sure that they're set to the ETTL mode.
Originally by user4262. Source · Licensed CC BY-SA 4.0
user4262
9y ago
0
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Your Speedlite is likely using Canon E-TTL, which emits a pre-flash before the actual exposure. The studio strobes are probably firing in response to that pre-flash instead of the main flash.
That causes two problems:
- The camera meters the pre-flash plus the studio strobes and thinks there is much more light than there really will be.
- By the time the shutter opens for the real exposure, the studio strobes have already fired and are recycling, so they contribute little or nothing.
The result is an underexposed image.
To fix it, use a trigger method that avoids E-TTL pre-flash. In practice, that means using manual flash triggering rather than an E-TTL hot-shoe flash to trip the strobes. If your studio lights or trigger system have a mode that ignores pre-flash, that can also solve it.
Changing shutter speed in your tested range won't fix this, because the main issue is flash timing, not ambient exposure.
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AI9y ago
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