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Old Nov 22, 2011, 9:02 AM   #11
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The D3100 uses a focal plane shutter (as do all dSLRs), which consists of two curtains. When you fully depress the shutter button, the first curtain moves down, exposing the image sensor. When the top of the sensor has been exposed for the appropriate shutter speed, the second curtain starts down, covering the image sensor. At very quick shutter speeds, the second curtain will start moving down, covering the top of the sensor, before the first curtain has finished exposing the bottom of the sensor. A shutter speed of 1/200 ensures that the entire sensor will be exposed when the flash flashes. The duration of the flash during that 1/200 of a second is what controls the exposure, not the shutter speed, as when you're not using flash.

On some dSLRs, you can get faster shutter speeds, and instead of one very bright flash, the flash will flash several times at reduced power, so that every portion of the sensor will get it's own flash while the two curtains move down. The D3100, unfortunately, does not have this feature.
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Last edited by TCav; Nov 22, 2011 at 9:07 AM.
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