One of the most useful flash photography tricks everyone should learn is how to capture motion using flash. It often comes in handy especially when you need to freeze movement in an indoor setting (like weddings, events, or parties). Adorama TV and Mark Wallace have put together a simple experiment that you can set up at home to help you learn about how moving objects appear differently in ambient light and when flash is used.
Exposure basics tell us that to freeze action, you need a fast shutter speed. The faster the movement, the faster your shutter speed needs to be. To make a good exposure, however, your fast shutter speed needs more light. But you can’t really use a larger aperture, as the larger it is, the less sharp and focused your subject tends to be as the depth of field gets shallower. So, what do you do? You use flash to illuminate your subject well enough so you can use both a small aperture to keep your subject sharp and focused, and a fast shutter speed to freeze the movement.
In the simple exercise above, Mark first demonstrates what happens when you try to photograph a moving object in ambient light only, and using aperture-priority mode in f8. What’s actually happening is, because the meter senses that there’s not enough ambient light to make a good exposure, the camera chooses a slower shutter speed to compensate for the small aperture. That shutter speed — 1 and 1/2 second exposure in the case of the demo — is not enough to freeze the ball at how fast it’s swinging.
Now, what happens when you use a flash? You illuminate your moving subject well enough to make a balanced exposure even if you’re shooting at f8, 100 ISO, and a fast shutter speed of 1/250 seconds. Depending on the flash power and duration — how long it delivers a certain amount light to the subject — you can go for really fast shutter speeds and freeze virtually any kind of movement! Once you’ve mastered freezing movement using flash, you might want to move on to more advanced techniques, like rear curtain sync mode, to get even more creative results.
Want more photography tips and tricks from Adorama? Head to their YouTube channel to see more of their video tutorials.