Right click on the node (little box) that, by default, is on the left extreme of the green line and enter any number you like.
As for how to shoot it…
I assume you are not FILMING this, but video taping.
If it were film, we would be talking about how fast the film moves through the camera.
With video, you will have to experiment with shutter speed. A very high shutter speed (e.g. 10,000th), will give you much clearer individual frames, but there will be more time elapsed between them.
A slower shutter speed will have less change in position between each frame but will have more motion blur.
Gary Kleiner
