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Lighting is Easy Blog

Free resource for learning how to use off-camera flash and studio lighting.

Stopping motion and showing motion at the same time

Chuck Vosburgh - Tuesday, March 13, 2012
Photographer: Chuck Vosburgh. Subject: Abby from Hula Monsters.

Here's an example of using a slow shutter speed to show motion and control the level of ambient light along with using a flash to stop motion. First, here's the setup: This image was photographed at an event with very little ambient light. The hula-hoop has lights in it. I held the flash in my left hand and the camera in my right hand to get the flash off the camera for a better angle of light.

The specs:

1/10 second
f-9
1600 ISO

The process:

First I chose an aperture of f-5.6. I started with f-5.6 because it's a fairly large aperture setting, but still gives me a couple f-stops larger if I need it. Next, I experimented with shutter speeds until I got the background the way I wanted it to look. Not looking at the subject yet, just the background. I also knew from experience that such a slow shutter speed would cause a nice motion blur on the hula-hoop with lights in it. The next steps are to light the subject: I set the flash to one-quarter power and took a shot just to see what it would look like. In this case it was too light. To put less light to the subject I had two choices; decrease the power of the flash or use a smaller f-stop. Since changing the f-stop was easier, I settled on f-9 for the perfect exposure. Remember, the shutter speed controls the ambient light and the f-stop or power setting on the flash control the exposure of the subject.

Why this worked

Here's a breakdown of what caused this image to look like this:
The high ISO setting was necessary because it was really dark in the place
The slow shutter speed allowed the background to show just a little bit
The slow shutter speed also allowed a blur on the hula-hoop
The flash was entirely responsible for lighting the subject
Since the flash duration is so short, and it's the only thing exposing the subject, it stops the motion of the subject. The ambient light wasn't enough to show the subject at all.
So, why the blur on the hula hoop? The hula-hoop was lit a lot more than the background, but a lot less than the subject so it registered as a blur to the sensor in the camera. This was mostly good luck.
Good luck + skill = good results
The key to it all
Practice and experimentation is the only easy way to really understand how your equipment works. Go and have fun. Experiment! No one needs to see your experimental shots, but doing them is the only way to get good results when you want to.
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