HOW I GOT THE SHOT: When I have to confront the chaos of the dance floor during a wedding, bar or bat mitzvah, I sometimes apply a little technical trickery to capture an interesting shot. Creating the effect seen here requires a camera which allows manual setting of two important options. The first is shutter speed, which must be slowed down to at least 1/30 second or slower to create the kind of blurring of movement and trails seen in this photo. Here, the shutter speed was 1/5 sec. The second and more important feature is an option which allows the flash to fire at either the beginning or the end of the exposure. Most of the time the flash fires as soon as the shutter is fully open, but because the speed at which the flash fires should always be faster than the shutter, you can also set the flash to pop at the last possible moment when the shutter is fully open. This is called rear curtain sync. In this mode, the shutter will remain open for an instant, recording the subject and movement with the available room light. When the flash eventually fires, it freezes the action in a burst of light. The end result is really two pictures, the pre-flash photo which records everything the camera sees up to the moment the flash goes off, and a second, sharper, well-lit image created by the flash.