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Old Mar 14, 2003, 11:13 PM   #1
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Default QUESTION ABOUT FLASH????

when using 2 flashes(one in-camera and the other on a stand with umbrella), is the light output additive, or does the more powerful flash overpower the weaker????

scenario:
i have my nikon 5700 popup (GN59) on a tripod, using it to trip my vivitar 285hv(120GN) on an umbrella stand. the vivitar is right next to the camera on tripod(equal distance to subject). does the more powerful 285 give the meter reading, or do the two flashes combine for a greater output??? im waiting for a studio flash meter to arrive, so im not sure how this works yet!

any thoughts out there

tia
mikey
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Old Mar 17, 2003, 4:26 PM   #2
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If they are in manual mode the power is additive. The formula for guide numbers is a might funky though. IIRC it's the square root of the sum of the squares of the guide numbers. Someone please correct me if I'm wrong.

In your situation the on camera flash is not quite a quarter as powerful as the external one so it will be overpowered pretty much. Your total guide number if I didn't screw up the formula is 133.7 Y ou only gain 1/8 of a stop compared to only using the GN 120 external flash.

Since there is such a disparity I'd turn down the internal flash to it's lowest manual setting and use it only to trigger the external flash. The whole point of studio flash is to avoid the on-axis look (usually) anyway.
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Old Mar 17, 2003, 7:54 PM   #3
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Quote:
Originally Posted by padeye
Since there is such a disparity I'd turn down the internal flash to it's lowest manual setting and use it only to trigger the external flash. The whole point of studio flash is to avoid the on-axis look (usually) anyway.
thanks, padeye. this is exactly how i want to use the 5700 flash, simply to trigger the slaves on the 285's.i may simply cover the flash on the 5700 with a strip of infrared gel. it will block the visible flash and yet trigger the slaves.

mikey
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