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Flash duration of a stroboscope
What does flash duration mean?
The stroboscope's flash duration (duration of light emission per single flash) is analogous to a camera's shutter speed (exposure time). If you take pictures of a fast-moving subject, using slow shutter speeds will prevent captures of clear images. In much the same way, the flash duration of a stroboscope can affect the resolution of a strobe image. To observe ultrafast phenomena or an expanded image of an extremely small object, you need to use very short flash durations.
How do I determine what flash duration to use?
For observations of ultrafast phenomena or extremely small objects, you can calculate the distance the target object moves during the flash duration as follows:*
δs = v x t ÷ 1000 (mm)
δs: Amount of movement of target object per flash duration
v: Speed of target object (m/sec)
t: Flash duration (µsec)
* For example, if the target is moving at 100 m/sec and the flash duration of the stroboscope is set to 2 µsec, the amount of movement of the target object per flash duration is:
δs = 100 (m/sec) x 2 (µsec) ÷ 1000 = 0.2 (mm)
As the result indicates, the target object moves for a distance of 0.2 mm during each 2-µsec flash duration. If we assume the target object to be a square shape measuring 2 cm on each side, the amount of movement is only 1/100, so you will see a virtually stationary strobe image. On the other hand, if the target object is a square shape measuring 0.2 cm on each side, the object will appear twice as long in the direction of movement, and the resulting image will not be sharp. In the latter case, you need to use a stroboscope with a shorter flash duration, like a nano-pulse flashlight, keeping in mind the size of your target object.
Can I adjust the flash duration?
Sugawara's ESD-VF2M stroboscope has a flash duration adjustment function (range: 50 µsec to 2 msec). Some of our general-purpose models also have a range selection function to allow changes in flash duration.
In the case of the MS-230DA model, the flash duration can be varied within 6 µsec by switching the frequency range. Note that changing the flash duration also changes light intensity.
