On Assignment: Wind Tunnel
While shooting a story on the wind tunnel at the University of Maryland's Clark School of Engineering, I wanted to grab a photo of the giant fan that creates the 100mph+ winds for studying airflow around objects.
The available light was depressingly crappy - about 1/10th of a sec at f/2.8 (ASA 400) with typical institutional sodium vapor as the color temperature. At normal exposure, it looked a lot like something you'd find in a diaper. But dropped down a stop and a half, it actually took on an intense orange color. Which ... looks kinda cool, thankyouverymuch.
So, now we have some cool tech-y ambient light. Next, let's create some tension and direction to it, using a single speedlight.
To separate the blades and draw the viewer into the frame, I stuck a Nikon SB-800 on a small light stand and set it to 1/4 power. Remembering that the shadows always point to the light source, the flash is obviously behind the bottom blade. The flash is pointed directly at the camera, but hidden by the blade.
(I do that a lot, actually. In a dark situation, mount the flash backwards on the stand then turn the head back around towards the camera. The ready light will act as a guide to help you keep something between you and a backlighting flash in a darkened room.)
So while the sodium vapors looked pretty bad at the correct exposure, they gave a neat, warm color cast when underexposed by about a stop and a half. Always consider altering the ambient portion of the exposure when faced with a light color you cannot easily balance for in camera. What looks terrible at the proper exposure might look cool and dramatic when over or under exposed.
So, now shooting at 1/30th at 2.8 (wide open and getting a saturated ambient color) I adjusted the output of the strobe by trial and error and arrived at 1/4 power as the best look on the backlight.
Note that the strobe light is not technically what you would call "properly exposed," but rather 1.5 to 2 stops overexposed. But it looks good, which is what really matters.
The beam angle adjustment of the strobe was set to 24mm to get a nice wide throw of light in the cramped area.
I like this solution because the one small back light is accomplishing a lot of things. It is providing a hotspot to lead the eye into the photo. It is separating the person walking toward the fan. It is providing a nice spray of leading-line shadows coming from the fan blades, the braces and the guy. It is lighting the floor, which shows up reflected in the bottom of the motor housing.
And most important, it is providing another light color and level on which to base my exposure. Which in turn allowed me to underexpose the sodium vapors to use the ambient light's color to my advantage.
Here's a thought: This is not a "properly exposed" photo ... at all. The ambient is underexposed by ~1.5 stops. The flash is overexposed by at least as much.
We're breaking some rules here. But together, they create the dynamic tension that makes the photo.
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