This is an acer seed that rotates while falling. The photo is a single long exposure (something like 2 or 3 seconds) with the light coming from a flash set to repeat mode.
The process is very simple. Put the camera on tripod, on a dark environment, set a flash left and a reflector right of the camera. Next drop the seed from a certain height and simultaneously start the exposure. The seed will start to rotate, pass in front of the camera and the various bursts of flash will register the movement.
All seems plain simple and easy, but there were some difficulties. First the starting height of the seed. In the first instants of the fall the seed does not rotate, so it plummets to the ground until, at a certain speed, it starts the rotation and slows down vertically. It turns out the best height, to get a stable flight, was about 1.5 meters above the camera. This led to a second difficulty: the seed does not always fall in the same trajectory (far from it!) and is quite challenging to get it to pass in the exact plane of focus (pre-focused, of course), or even inside the camera frame, entirely. How to overcome this problem? Easy, just do it many times. 🙂
Another interesting thing that I completely overlooked is the speed at which the seed moves. I started with 10 flashes per second, and thought this would be plenty enough. How very wrong I was! Only got 2 or 3 images of the seed in a frame. Had to go up to 60 to 80 flashes per second to get the effect I was looking for, with many close together images on one exposure.
Hope you enjoy.