ELI5: How can themeparks snap a crystal clear picture of you on a rollercoaster going 70mph

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Motion blur occurs when the camera takes too long to generate the image. By the time the last bit of information is taken, the image has changed noticeably. So if all the information is taken in a very short moment, that difference is very small and the image looks sharp. However since the camera has less time to collect the light for the picture, shorter exposure times need a brighter scene. So the flash needs to be stronger or the scene just needs to be very well illuminated.


To further the other comments – if the location where they choose to take the photo is lit primarily by the flash (and I’ve not seen a roller coaster photo where that is not the case) then the duration of the flash effectively becomes the shutter speed (because the image is lit by the flash – and the camera can only capture an image while the flash is “on”). Flashes can have *extremely* short durations (1/1000 down to 1/20000 of a second) this means that they are really good at stopping motion.


Three things: 1. They use fast shutter speeds. That means that the shutter is only open for a very short period of time to gather data. And during that short period of time, you don’t move much. Imagine you took a video at 3200 frames per second, then advanced it frame by frame. The movement would be almost imperceptible. That is how much you move while the shutter is open. They probably shoot at 1/3200th or even 1/6400th. The down side to having the shutter open for such a short period is that there is not much light that gets through in such a short period of time, so… 2. They use bright, fast flashes. That flash will pulse with each shutter click and it will be timed to illuminate the riders for the same length of time. So the riders are getting hit with a very bright light for only 1/3200th of a second and anything that happens outside of that window is too dark to really process. 3. They use angles to their advantage. Look out the side window of your car on the highway and things will be zooming by and you can’t really focus on them. But look out the windshield and you can easily focus on approaching items. Cameras have a depth of focus. These particular cameras are set to focus on a point in space that is let’s say…3 feet deep. So as the riders are approaching the camera from the background toward the foreground, they will remain in focus for 3 feet as they pass through the camera’s view. In 1/3200th of a second, they will probably move less than a quarter of an inch. So there is plenty of time to capture them in focus. But if that camera were placed perpendicular to the coaster train and shooting from the side, the riders would zoom through the view much faster. It’s the difference of trying to catch a baseball thrown toward your face and trying to catch a baseball thrown *past* your face from the side. It’s much easier to see it coming straight on.


A blurry pictures is normally due to one of two things: 1. Unfocused lens 2. Moving subject In normal cases a camera needs to find the subject, focus on it and take a picture before these settings need to be changed to keep a clear picture. In a rollercoaster camera you place the camera in a set place and calculate the focus of the lens and the position of the subject before the picture is taken. When the train reaches a camera trigger the camera takes a picture of this already decided place. Anything there will be sharp. The trigger sensor helps the camera to know when the subject is at the “right” spot. This in combination with a decent flash is what results in a clear picture.


They can use a fast shutter speed because they have the flash lights. If the lights didnt flash when you went past there wouldn’t be enough light hitting the lense in the time you were there, so the image would be dark. If the shutter speed is lower you get motion blur.