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 get 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.

So, to separate the blades and draw the viewer into the frame, I stuck a Nikon SB-28dx 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.)

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. Love that little digital polaroid on the back of my digital camera now. (I no longer carry a flash meter.)

The lens 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 importantly, it is providing another light color and level on which to base my exposure, which allowed me to underexpose the sodium vapors to use the ambient light's color to my advantage.

Camera: Nikon D1h
Lens: Nikkor 17-35 zoom @17mm; 1/30 at f/2.8
Flash; Nikon SB-28; 1/4 power; 24mm throw
Sync: Pocket Wizard remotes

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