David Vogt, a professional photographer, took the above gorgeous photo of the Milford Oval, my favorite town center in New Hampshire*, with a drone. It’s a fabulous shot; I love it … but I’m puzzled.
Look at the four cars in the left hand side of the picture. They are driving towards the drone (the Oval is one-way, counter-clockwise seen from above), yet look at their headlights. The streak of light caused by the camera shutter being open extends *in front of* the body of the car, not behind it as you would expect if the car is moving toward you! As a reader said when he sent me the picture, they look like Star Wars light sabers.
Neither of us can figure out how this happened. I assume it’s some function of digital photography, but I’m just guessing. Perhaps the amount of light gathered while the shutter is open falls off with a hockey-stick graph, so that there’s only enough light to record the car body for an instant, yet enough light to record the headlight for another half-second.
Anybody out there have a better explanation?
*One reason it’s my favorite: It is in the shape of a triangle, its official name is Union Square, and it’s known as The Oval. A geometer’s delight.
Behind the fourth car is another set of sabers, however you can’t actually see the car. It appears that the four cars are moving slow enough to have a slight drag, and the lights look like lasers because of how far headlights throw out light, and the slow movement of the cars would move that light forward enough to make it look like sabers…. Maybe?
Digital cameras use an electronic “shutter” that allows the image to be captured onto the photo sensitive array for a specific period of time. In this case, the shutter is not “closing tightly”, meaning that capturing of very bright signals still occurs after the shutter is intended to be closed. After the shutter is closed, the processor inside the camera begins reading the array of pixels, compressing it, then storing it to memory and all that takes time so some areas of the pictures are going to show the effect more than others depending on the pattern the processor uses to read the array. In this case, the processor is probably doing the compression “on the fly” while it is reading the pixels making it even slower. Better cameras would transfer the image to a temporary buffer first to better preserve the image. At least that is my educated guess.