Mixing flash light and continuous light while having a longer exposure time is an interesting technique to show objects in motion. With the fast flash duration you see the subject sharp and frozen and at the same time a blur effect occurs due to the continuous light. Working with broncolor equipment such as the Move or the Scoro power pack allows you to freeze even very fast movement. With the Scoro power pack you can reach a flash duration (t0.1) up to 1/10000 s, with the Move up to 1/8500 s.
Here an example to explain the process: The grapes are hanging from a black thread, and are swung from right to left.
Continuous light: The shutter speed is set to 1/4 s, because this is the time the grapes need to swing from one side to the centre of the image. I used the modelling light of a MobiLED (30W LED), with a blue gel from the right side. The blue gel is used only to give some blue colour in the blur, not to correct the colour of the modelling light. To reach a visible blur with 1/4 s exposure time, aperture 11 was ideal.
Here’s the image with only the modeling light of the MobiLED:
Flash light: Second step was adding the flash light to freeze the movement of the grapes. I used a picolite with a Fresnel from the left side, without modeling light as the blur should only come from the right side. As I wanted the flash at the end of my exposure, I set my power pack on a delay of 0, 24 s.I then set the necessary power on the Scoro and checked what the fastest flash duration with that power was: I reached a flash duration of (t0.1) 1/7000 s, fast enough to freeze my flying grapes. If the flash would have been too bright, I would have decreased the power, reaching even faster flash duration. If the flash wouldn’t have been bright enough, I would have increased the power.
If by increasing the power the flash duration would have been too long, I then would have had to open my aperture more, and in consequence do something to have a darker continuous light, like moving my MobiLED further away from the grapes.
Here’s the image with only the flash light of the picolite, as you can see the movement of the grapes is frozen:
Once both the flash light and the continuous light are correctly set, I shoot with both on, and here is the end result:
Modelling light 30 W LED
Important: If the blur is too dark, you can’t change the brightness of it by choosing a longer exposure time. If you do so, as the swing of the grapes has always the same speed, the brightness is the same.
Example by Nadia Winzenried, broncolor photographer, workshop and seminar instructor.