Canon's infrared trigger. This little device could be amazing if they incorporated a radio system inside but I guess that is asking for too much... although not a perfect system due to its "inline of sight" feature, it does have a neat feature. For prime lens shooters, this is a great way to help you focus in low light, locking focus. When you are dealing with shallow depth of field, 1.2, 1.4, 1.8, this is gonna be your best friend. In addition, this device's main feature is the ability to trigger any of Canon's speedlights off camera.