High Speed How To:
Some General High Speed Stuff
The Process. High speed photography was pioneered by Harold (Doc) Edgerton at MIT back in the 1930's. Check out the Edgerton Digital Collection for additional information on Doc Edgerton and his images and techniques. High speed photography refers to using the short duration of a flash or strobe to expose an image rather than the traditional method of using shutter speed. Even with todays technology, high speed photography is the only method available to capture many fast events. While the fastest shutter speed on a camera is usually around 1/8000, the fastest strobes can fire at speed several orders of magnitude shorter. For example an air-gap flash has a duration of around 500nS (5/10,000,000 of a second). Using a strobe is the only way to freeze really fast motion.
Shutter Lag. Many of the pictures and techniques you see on this site were taken with traditional high speed photography methods. That is the shutter is left open in a dark room and the flash is used to expose the picture. Once the picture has been exposed the shutter is then closed. Some exceptions to this are the Wildlife and insect photos, in this type of photography the shutter is generally controlled by StopShot. The downside of firing the camera's shutter is the shutter lag introduced by the camera. Shutter lag is the delay between when the camera shutter button is pressed and when the image is actually captured. This lag can be up to 150mS making some shots very difficult to capture by triggering the camera. StopShot can trigger either the camera of flash depending on what you are trying to capture. We have a couple of products that can help minimize shutter lag. The first is the high speed shutter, great for high speed macro - like insects in flight. The other is the shutter interface switch, this switch will keep the shutter button on your camera pressed halfway to minimize camera response time.
The Flash. Why do we use a flash? Why can't you use the shutter to capture "high speed" events? Let's consider an example: Say you are trying to capture a pellet moving at 500 ft/s. If you used a shutter speed of 1/1000 (fairly fast as far as shutters go) the shutter would be open for 1 ms. In this amount of time the pellet would travel about 6 inches. This would make for a very streaky and blurry pellet. Now, if we use a flash that has adjustable power we can set the flash to give us a burst of light that only lasts about 50 us. Now the pellet traveling at 500 ft/s would travel only about 0.3 inches. With this flash duration we are able to capture very fast events and keep them in focus. See some of our example pictures to get a feel for what is possible.
Choosing a flash. Some care is required when selecting a flash for high speed photography. Almost any flash will work for capturing slower events like a single water drop. But a flash with a much shorter duration will be required to capture faster events like ballistics or drop collisions. Ideally the flash will have an adjustable power level. This will allow you more flexibility in the duration of flash and in adjusting your aperture for different depth of field effects. Some flashes are equipped with photo sensors that measure the light and turn off the flash when the exposure is correct. One very inexpensive option for an adjustable power flash that has manual mode is the Yongnuo YN-560 This flash is also equipped with a pc sync connection making it easy to connect to StopShot. If you are looking for something with a bit more power and flexibility check out the Paul C Buff Einstein.
A Word of Caution. Something to watch out for when using an older flash is high voltage on the hot shoe. High voltage flashes are not compatible with StopShot. The high voltage will not damage StopShot but the flashes will not trigger correctly. To find out more about high voltage flashes visit this page. The author of this page has done an excellent job of compiling a list of flashes and measured voltages on the hot shoe. He also has a section on how to measure your flash if you are so inclined (Be careful!! some flashes have very high voltages on them). If the voltage on your hot shoe is less than 40V it will work fine with StopShot.