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What panning is, and why shutter speed makes or breaks it
Panning is the technique of moving the camera to follow a moving subject during the exposure. When the tracking is perfect, the subject stays in the same place in the frame while the background sweeps past, so the subject comes out sharp and the background streaks into lines of motion. The result is a photo that feels fast even when the subject is frozen, because the streaked background tells the story of speed. Racing cars, cyclists, runners, and birds in flight all suit panning, and it is one of the few techniques where a slow shutter speed is the whole point.
Two speeds fight each other in a panning shot. The subject’s angular speed, how fast it sweeps across your view, decides how far the background moves during the exposure. The shutter speed decides how long that movement lasts. A slow shutter gives the background more time to streak, but it also gives your hands more time to wobble, and any wobble blurs the subject too. A fast shutter is safer for the subject but leaves the background too still, so the photo can look like a parked car with a sharp background. The art of panning is finding the slowest shutter you can track steadily, and this calculator helps you find that number before you waste a whole session guessing.
How to use this panning shutter speed calculator
Enter the subject’s speed in kilometres per hour and its distance from you in metres. The tool works out the subject’s angular speed, which is the speed divided by the distance, and then shows how far the background streaks at your chosen shutter speed, in both degrees and pixels. Enter your target streak as well, and the tool suggests the shutter speed that produces exactly that streak. A good starting target is about 2 degrees of background movement, which gives a clear streak without demanding superhuman steadiness. Beginners often do better starting near 1/125 or 1/60 of a second for cars, and 1/30 for slower subjects, then slowing down as their tracking improves.
As a worked example, a cyclist at 36 kilometres per hour, 10 metres away, has an angular speed of about 1 radian per second, or 57 degrees per second. At 1/30 of a second, the background streaks about 1.9 degrees, which is roughly 278 pixels on a 6000 pixel wide full frame file with a 50 millimetre lens. That is a strong, visible streak. At 1/125, the same setup streaks only about 0.46 degrees, which looks mild. If you want a full 2 degree streak for that cyclist, the calculator suggests about 1/29 of a second. Use that as a starting point, not a law, because your own steadiness matters as much as the arithmetic.
Technique matters as much as the number
Stand with your feet planted and twist from the hips, not from the arms, so the camera moves in a smooth arc. Start tracking before you press the shutter, and keep moving after the exposure ends, just as a golfer follows through a swing. Keep the subject in the same spot in the viewfinder through the whole movement, and use continuous autofocus so the camera adjusts as the distance changes. Image stabilisation can help, but set it to the mode that corrects only vertical shake if your camera offers one, because full stabilisation sometimes fights the horizontal movement you want.
Expect a low hit rate, and plan for it. Even experienced photographers may keep only one frame in ten when panning at very slow speeds, so shoot in bursts and review at full size, checking the subject’s eyes or leading edge rather than the whole image at a glance. If every shot is sharp but the background is still, slow down. If every shot is blurred all over, speed up or move further from the subject, because distance lowers angular speed and makes tracking easier. Light also matters: in bright sun you may need a neutral density filter to reach slow shutters without overexposing. Treat the calculator’s suggestion as your first test speed, then adjust in third stop steps until the streak looks the way you imagined it.
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