Second-curtain flash

This is a flash mode which can give more realistic light trail effects during slow-sync exposures. Normally, the camera will use 'first-curtain' sync. This means that the flash fires as soon as the shutter opens. The shutter may then stay open to record the ambient lighting. However, this means that an image trail leads forward from the 'frozen' flash-lit image, which can look unrealistic. The movement blur should be behind a moving subject, not in front of it. With second-curtain sync, the flash fires at the end of the exposure, not the start. This means that the 'frozen' image is at the end of the blur trail, not the start, and this looks much more realistic.