Now it's nighttime and you've got your camera on a tripod, pointed at an interesting scene--like this skyline with a passing train, for instance, or maybe a busy city street. If you have a manual mode, use it to set your camera's aperture to a middle setting (like f/8) and set a 4-second exposure. Take the shot and check the result in the LCD. This initial exposure might make your photo look overexposed. If you see that happening in your LCD after you take a photo, compensate in your next photo by using a smaller aperture setting (a larger f-number). And if you want longer light trails, lengthen the exposure to 8 or 15 seconds.