Monday, March 20, 2006

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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Camera: Nikon D1h
Lens: Nikkor 17-35 zoom @17mm; 1/30 at f/2.8
Flash; Nikon SB-800; 1/4 power; 24mm throw
Sync: Pocket Wizard remotes

Next: Abstract Concrete


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15 Comments:

Anonymous Sacramento Photographer said...

This photo moves from being average to very good with the addition of the person in the scene.

One thing I would have tried in addition is to gel the light behind the rocket in maybe blue to make it really dynamic.

June 20, 2006 1:50 AM  
Anonymous Anonymous said...

Question:

From an ethics point of view, how is changing camera settings such that the color of the sodium vapor lights are not what the photographer witnessed different than doing the same thing post-exposure?

Are you allowed to do post-exposure color correction, etc. of this nature in photojournalism?

January 02, 2007 2:29 PM  
Anonymous Anonymous said...

Random aside..

While the flow speeds in the test sections of subsonic wind tunnels like the one you've shown here can be hundreds of miles an hour, if you were to stand in front of that turbine while it was going full speed you'd only feel a little breeze.

January 03, 2007 6:07 PM  
Anonymous Anonymous said...

on ethics ..

1. every person sees the same scene differently - - what is reality?
2. every photograph is a manipulation: the time it is taken, the view you put in or leave out, color versus B/W - - The world is mostly in color, but do we think B/W is an unethical manipulation? Then throw away all pictures by Ansel Adams, and some others also!

waterwin - The Netherlands

January 26, 2007 2:39 AM  
Blogger spike said...

Great shot. The guy walking has a great leg position - was that a one-off or are there 9 other shots where his silhouette doesn't look so good? ;-)

March 18, 2007 9:29 PM  
Blogger GJS3rd said...

I shoot freelance for a newspaper. Photos are often used to substantiate a story. Creative lighting and exposure of a subject in a news story shouldn't be an issue unless the lighting of the scene, person or object conveys a difference in the information to the reader. If a story was about injuries in a dimly lit workplace, the photo should accurately depict the ambient light in such a location. Of course, if it were an unlit area, prone to total darkness, you could still photograph the hazards in the area with flash to show the hazards while clearly describing the darkness in the article.
J - Alabama

December 10, 2007 5:33 PM  
Blogger Blaise said...

Amazing shot. Well done. I would have been baffled had I been asked to photograph the scene.
A pleasure reading your site!

January 09, 2008 6:10 PM  
Anonymous San Francisco Wedding Photographer said...

This is great shot. Did you try to use "light painting" technique here.
Hide under the each blade and lit it up separately. Perhaps this way you get get more dramatic shadows on the walls. But nevertheless it is a great photograph!

Joseph

February 07, 2008 1:41 AM  
Blogger BMW1602 said...

this shot would look great in 3D to bad you didn't shoot a stereo pair!

January 07, 2009 4:08 AM  
Blogger Lola said...

Can someone please clarify what reference point he is using here for over exposing the flash? The following sentence in the wind tunnel confuses me: "This photo is underexposed by 1 2/3 stops for the ambient (understand this alright) but it's the next explanation..." and the flash is one stop overexposed". From what? Im assuming the flash is on manual and there are not other flashes (because you don't mention any) so you aren't over exposing this flash by one stop in comparison to the setting on your other or key flash.
Another quick thing about balancing ambient and flash and daylight. Ok so say you are in a place and it is quite dark, the auto reading you will get will give you an incredibly slow shutter, say 1/2 sec, so then you are looking to under expose a stop or two when you bring in your light?
Please help, Im getting really stuck on this, and I've watched the dvd's and taken notes!

January 12, 2009 11:06 AM  
OpenID josephineki said...

hi Lola,

Maybe just play around with the settings and try it out? =) I personally think sometime people get too stuck on the numbers / settings game. I heart Strobist for the inspiration and techniques but once understood the placement and effects of lights, we should be encourage to use our imagination ;')

July 09, 2009 4:00 PM  
Blogger Dan Rohr said...

Great picture, and great web site. Thanks very much for sharing your experience.

Dan

July 19, 2009 2:35 AM  
Blogger Carla said...

Fantastic site, learnt so much about off-camera flash;
thanks for your google-juice!
CARLA

July 13, 2010 7:30 AM  
Blogger Adrian Spencer said...

"The ready light will act as a guide to help you keep something between you and a backlighting flash in a darkened room"

That is a work of God like genius! Superb!

August 16, 2013 3:24 AM  
Blogger frosti8 said...

This is an excellent shot by all standards,
P.S this site is great, thanx!!

September 07, 2013 3:42 AM  

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