Flash duration

Flash Duration = High Speed Photography

Most modern digital cameras can shoot at a maximum shutter speed of 1/8000sec but that is not fast enough to capture a speeding bullet, so how has all these images been captured?

Often these images are captured with shutter speeds of 1-2sec or longer? The reason for this is that they are captured in near total darkness with a very short burst of light (flash duration). Fast flash durations can be created with standard flash guns for example :

Canon 580ex

1:1 Power = 1/1000second

1:2 Power = 1/2000second

1:4 Power = 1/4000second

1:8 Power = 1/9000second

1:16 Power = 1/15000second

1:32 Power = 1/21000second

1:64 Power = 1/30000second

As you can see these can give you much faster times than 1/8000sec shutter speed. Special units are available that will produce a flash duration even faster such as the Microflash Ultra which can produce a flash duration of 1/100,000sec and the Hensel Speed Max which can produce a  flash duration of 1/66,000sec.    

The table above shows that to achieve the faster duration times you need to reduce the power output, the offset being reduced light, to overcome this you need to get the lights as close as possible to the subject or to use multiple flash units.

One of the benefits of shooting in a dark studio with an open shutter is that it removes the problem of “shutter lag”. Shutter lag is the time taken from when you press the shutter button till the camera fires the shutter (not including the time it takes to meter and focus). The time taken is only a fraction of a second but when your shooting at such fast speeds any shutter lag would need to be added in timing.

When checking your flash duration data sheet you may see t.5 or t.1, these are terms used on how the rating was timed. T.5 (most popular) is the time a flash outputs more than 50% light and t.1 is the time flash outputs more than 10% light. A t.5 flash duration of 1/30,000sec, your t.1 time will be roughly 1/3rd of this = 1/10,000sec. These figures are important as it is this 1/20,000sec time difference that could cause some motion blur.