Why are photos darker with flash enabled even when the flash is physically blocked?
Asked 7/10/2016
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I took photos through a small opening that only allowed the camera lens through. The camera’s flash/LED was blocked by the barrier, so no flash light could reach the subject. But when I shot with flash enabled, the images came out much darker and duller than when I shot with flash disabled.
Why does enabling flash change the photo if the flash itself is blocked? Which result is closer to the real scene: flash on or flash off?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
29
Your camera will have anticipated the extra light provided from the flash, and adjusted the exposure to compensate. Because this extra light has been blocked out. The exposure is now wrong.
Additionally, when the flash fires, your camera is likely to use a different white balance setting to accommodate the difference between the flash light and the other lights in the scene. This shouldn't result in a different brightness, but may lead the colours in the image to look very different.
Originally by user46386. Source · Licensed CC BY-SA 4.0
user46386
10y ago
0
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Because the camera changes its exposure behavior when flash is enabled, even if the flash light never reaches the subject.
With flash on, the camera expects extra light from the flash and adjusts exposure accordingly. It may use a faster shutter speed and/or other settings meant for flash photography, which reduces the contribution from ambient light. Since your flash was physically blocked, that expected light never arrived, so the photo ends up underexposed and looks darker.
Many cameras also change white balance when flash is enabled, so color can look different too.
So the darker “flash-on” image is not more accurate in this situation—it is simply exposed for a flash that never illuminated the subject. The “flash-off” image is usually the more accurate representation of the ambient scene, assuming it is properly exposed and not blurred by a slow shutter speed.
If the flash cannot reach the subject, turn flash off and expose for the available light.
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