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Flash Causing Underexposed Foreground

By  Sep 29, 2009

Topics: Digital Photography

Question: I am watching your Kelby training videos and your other YouTube videos. You seem to rely a lot on the Nikon CLS system. When you take a shot, it almost always comes out looking good on the first or second try. Specifically, when you have a dark foreground and bright background, your CLS seems to expose perfectly.
When I try to do it, 99% of the time my foreground is underexposed with flash because it is reading the bright background under matrix metering. And I can sync at 1/500!
How do you do it? Are you on Matrix metering and Aperture priority? How do you account for that bright background? I tried the underexposure by 2 method, and it still doesn't work under CLS.

Answer: Okay, good question. Here we go. I do manage to often (not always!) get close in the early going because I “think like the meter,” which is advice I always dispense. Bright backgrounds mean the camera will read that value and underexpose foreground. To pull the background exposure down, if it is too bright, it additionally means dialing in minus EV into the camera’s aperture priority setting and values, which is going to—you guessed it—even more severely underexpose the foreground. Hence the flash has to power up commensurately. I have been around the block for a while with this type of situation, so I sort that out in my head fairly quickly. It is a relatively easy read to make, just something you have to practice and get used to doing.

And 1/500 will not sync with your flash unless you are in hi-speed sync mode, which has big implications for your flash power. 1/200th or 1/250th is the upper limit of traditional flash sync. Up-to-date DSLR cameras will often present an option for a “high speed sync” or “Auto FP mode.” This simply means the camera and flash will synchronize at higher shutter speeds, but only through a specialized series of pulses the flash will make through the blades of the focal plane shutter. This is effective and a very viable option in certain situations, but the pulsing of the flash (so fast you can’t see the pulses) robs the unit of flash power. Thus, adjustments have to be made to keep the flash at the upper reaches of its power ratings, and the f-stop has to be opened up wider into the f2.8 or so realm, or you have to simply layer on more and more flashes to generate A LOT of flash power, which then can get you back into more mid-range f-stops.....

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