If you’re under the impression that flash is a tool that’s only used to add more light, then oh boy, you’re sadly mistaken! Besides being used as a tool to craft the shape of the subject with light and shadows, a flash can also be used to freeze motion. When executed correctly, a studio strobe can do a better job at freezing motion than a fast shutter speed. But in reality, not all flash are built equal. A proper understanding of the the concept of flash duration is thus essential to determine what power settings work best for you to freeze your subjects in a crisp manner. Photographer Mark Wallace from Adorama dives into the details of flash duration in this video:
“A flash duration really impacts how motion is frozen in a studio environment.”
Unlike how we see it, a flash does not simply fire at its full power and die off instantaneously. What happens in reality is that the flash goes from zero to its full power rapidly, and then it gradually decreases to zero again. However, we don’t notice this because it all happens so quickly. Considering the gradual nature of a flash firing, there are two values that you should be familiar with:
- T5 : The time that the flash is at 50% power and greater. Manufacturers refer to this value when talking about their products.
- T1: The time that the flash is at 10% power and greater. This is a better measurement as very little of the light is left beyond T1 to affect motion.
Older flashes tend to have a longer flash duration. Modern flashes on the other hand are a lot quicker and idle for freezing motion. Also, it’s worth noting that using the flash at a lower power setting shortens the flash duration significantly. And that’s great if you want to freeze subjects.
The key takeaway is simple. If you really want to freeze fast moving subjects, get yourself some modern flash systems with a low T1 value, and use it at a lower power setting.
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