To stop action in a bright room, or when shooting outside in daylight you need a fast shutter speed, 1/1000 of a second or higher depending on the subject. But to stop action in High Speed photography you need a Fast Flash Duration. Shutter Speed is the actual speed, the duration of time the camera shutter is open letting light hit the sensor. Flash Duration is the actual duration of time that the flash is lit. These are two very different things. Camera shutter speeds can be as high as 1/4000, or 1/8000 of a second, but flash duration speeds can be much faster, upwards of 1/10,000 of a second. These very fast flash duration speeds are what photographers use to freeze water droplets, or freeze the wings of a Hummingbird in flight. There are a number of factors that determine flash duration. 1. The equipment produced by the manufacturer: There are a few units available specifically designed for fast action photography to achieve a short (fast) flash duration. 2. The lower the power output of the flash unit the faster the flash duration will be. Capacitors store the energy in the flash and release it when the flash is triggered. It takes a certain amount of time for the energy to release, thus less energy stored means less time to expend, resulting in a shorter flash duration. The shorter the flash duration means the more stopping power a flash will have. 3. When using on-camera dedicated Speedlights, which have flash sensors built into the unit, the flash duration is shorter the closer the subject (object being photographed) is to the camera. The Flash unit measures the light bouncing back off the subject and cuts off the flash output when it measures a correct exposure. Obviously a closer object requires less light that one further away, thus a closer object will result in a faster flash duration. To stop action you use the lowest power setting you can to still achieve a correct exposure. Very often these exposures are made in a blacked-out room to avoid any ambient light from influencing the exposure, also allowing for a slow shutter speed which means the camera shutter can remain open indefinitely without exposing the sensor until the flash fires.

Trip Shutters

When doing high speed photography very often the action you are trying to record happens faster than the human eye or your brain can see, or comprehend. Hence the need for an activated shutter, one that is triggered by an event rather than the human hand. Photographers utilize a number of different devices for this purpose, commonly sound, vibration, contact or beam interruption (motion) activated shutters. As each name suggests these devices are triggered by an action (eg: sound) causing a reaction (flash and camera operation) resulting in an exposure.