Most of the foreseeable issues that may arise can be avoided by using a tripod and locking in manual focus. While you are moving across the plane, it can be hard to keep the focus consistent if you choose not to use manual focus. This technique requires an in-depth understanding of balancing your ambient light to flash power, a concept we cover in depth in Lighting 101. Always, always, always take a safety shot, you never know what will happen when attempting advanced lighting and photo techniques such as this.