Last week I had an assignment to photograph some west coast swing dancing. The venue was virtually dark which made a straight available light photo out of the question. The solution? A long exposure (one second in this case) with a pop of flash at the end of the exposure (also called rear curtain sync). Because the shutter is open for a long time, it pulls in some of the scarce available light but anything that is moving is going to be a bit blurred. Which in this scenario, I think works pretty well in capturing the motion of the dance. But I still wanted you to be able to see some detail in the dancers and that is where rear curtain sync flash comes in. By having the flash go off at the very end of the long exposure and burns in some of the detail of the dancers. The exposure ends before there is an opportunity for more blurring to occur.