Why does lightning look split or skewed in video—is it real or a rolling-shutter artifact?
Asked 10/3/2018
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I captured a thunderstorm on a digital camera and one frame shows the lightning bolt looking distorted, as if parts of it were recorded at different positions. Is this a real atmospheric effect, or is it caused by the camera? I'm specifically wondering whether the sensor readout timing in video/electronic capture can create this kind of lightning distortion.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
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Cameras design utilizes several different shutter designs. The DSLR (Digital Single Lens Reflex) typically use a focal plane shutter design. Such a shutter is favored when the camera supports interchangeable lenses. This is because the shutter resides at the rear of camera body; it hovers just above the surface of the image sensor. This design features a curtain with a slit. When the shutter button is actuated, the curtain with its slit opening travels across the image sensor. The shutter speed is the clock time it takes to travel the width of the slit. In other words, if the shutter speed is set to 1/125 of second, the curtain moves 1 slit width in 1/125 of a second. If the shutter speed is set faster, the width of the slit is set narrower, if the shutter speed is set slower, the slit width is set wider.
In my opinion, this image was taken during a lightning flash. The flash of light produced by lightening can be quite short (milliseconds). I think the shutter speed was set fast and as fortune happened, the lighting strike caught the lighting flash as the shutter was in motion. The part of sensor uncovered, recorded an image that was well exposed. Part of the slit travel exposed the sensor without the benefit of the lightning strike, this region of the chip is under-exposed. We see this happen all the time when the photographer is using an electronic flash. If the blitz of the flash and the shutter slit motion are not synchronized, we get this effect. Let me add, it’s not easy, perhaps impossible, to synchronized a shutter with a lightening flash.
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
7y ago
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This is most likely a camera artifact, not a strange form of lightning. The effect matches rolling shutter behavior.
In many digital cameras—especially in video mode—the sensor is not captured all at once. Instead, the image is read line by line, so different parts of the frame are recorded at slightly different times. Lightning changes extremely fast, so one part of the bolt may be captured a fraction of a moment before another. That can make the bolt look bent, split, shifted, or duplicated.
A mechanical focal-plane shutter can also expose different parts of the sensor at slightly different times, but the effect is especially noticeable with electronic shutters and video because sensor readout is slower. So your general idea is correct: the distortion comes from the timing of image capture, not from the lightning itself.
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