Rear (2nd) Curtain Flash

From buffer

There is one style of flash photography I really like. It involves capturing movement with your flash. A rear curtain flash is a flash that is fired as your shutter is closing. As oppose to a front curtain flash that fires right as your shutter is open. You might ask your self what is the difference?

The best way to think about rear curtain flash is to image 2 photos being over imposed on one another. The first picture is whatever you set your camera up for. But the second picture is a movement frozen in time, captured and placed on top of the first image.

So lets look at this picture I took (free hand without a tripod). I set my camera to 0.6 seconds and f5 to capture the ambient lighting and stationary scenery at ev=0 exposure. The first part of the picture captured the scene. The second part of the picture is produced right before my shutter closed and the flash is fired. This flash acts like an instant image capturer and imposes the final captured moment on to the original image. As you can see there is a stream of light following the biker. This stream of light is from the motorcycle's headlight. the reason why the light streaks across the picture is because the frame was open for 0.6 seconds. During that 0.6 second my camera was unable to grab a frozen image of the actual biker. However, once the flash fired it burned the frozen moment in time on top of the existing image. That is why you see streak of light as well as a perfect image of the biker.