It's the longer shutter speed that creates the effect as the shutter is open long enough to catch the lights
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(or whatever)
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'moving' through the shot
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(same thing you get with camera shake but controlled for effect, like panning shots where you get a blurred background but focused subject).
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The smaller aperture is just a function of the camera to keep the exposure correct.
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ISO setting makes no difference to the effect.
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.
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.
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it's just there to cope with differing amounts of light.
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The tripod though is essential.
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.
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.
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otherwise the long exposure would mean camera shake effecting all of the image
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R.
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