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Monday, 16 August 2010 20:42

Light streaks traced by lights on planes in nighttime airshowDuring a nighttime airshow, pilots affix extra lights to their planes and fly aerobatics, just like a daytime show.  The planes disappear into the darkness, glare, and smoke.

A conventional photo of this scene would just show hazy spots of light in the black sky.  I wanted to artistically record the patterns traced by the planes' lights as they fly their maneuvers.

To record some significant activity, it's necessary to use a very wide angle lens, and hold the camera still on a tripod, making an image spanning several minutes.

There are several problems with this approach.

It's difficult to guess exactly where the planes will be flying.  They fly wide patterns, and it'll push the coverage limits of the widest angle lenses.  I had to guess where they may be.  If I exposed for several minutes, it'll be a long time before I can verify my guess at the composition.

It's also necessary to determine the correct exposure.  The exposure of the lights on the ground will be determined by the sensitivity (ISO), the amount of time the shutter is open, and aperture.  The exposure of the light trails is insensitive to the time the shutter is open, since the traces to not overlap for any significant amount of time.  Only sensitivity and aperture matter for the light trails.  These two types of light must be balanced in the final image.  Metering will not work.  Again, it's necessary to guess the exposure. This is a huge problem if each exposure takes minutes, and I must wait to see the results.

With a digital camera, the longer the exposure at a given sensitivity, the more noise there will be in the photo.  This noise looks like a combination of a sandy texture and/or a weak TV station's snowy picture.  With the long exposures necessary to capture some significant airplane light trails, this noise will surely be a problem.

And with a long exposure, I must hope nothing moves between my camera and my subject.

Time was limited.  The show would not go on forever.  There wasn't time for many long exposures.  I had to make them count!

Instead of making one long exposure, I decided to make relatively shorter exposures and combine the results.

I made a couple of exposures to get the camera and lens aimed at the imaginary "aerobatics box" that defines the limits of where the pilots are allowed to safely perform.

I then made a few exposures to determine the correct exposure, capture some significant motion, yet control the noise.  With a bit of watching and lots of airshow experience, I could see that a pilot, depending on the maneuver, needed 30 to 60 seconds to enter my frame, turn, and exit back out.  After a few experiments, I found that at ISO 100, f/5.6 at 30 to 60 seconds appeared to properly expose both the light traces and the ground lights.  I favored the light traces, since the planes would go away, but the ground would be around a bit!  I could later make an exposure to properly record the ground lights, but coincidentally, that was unnecessary. I also knew from experience that my camera was not too bad on noise at ISO 100 up to a minute or so.

With this, I ensured that my autofocus was disabled, and my lens focused at about infinity, as determined by focusing during the test shots.  I set out to make as many exposures as I could of the performers, at about 60 seconds each, ISO 100, and f/5.6.  If the pilot flew out of the frame and wasn't going to return immediately, I ended the exposure early, at about 30 seconds.  I got five such shots, then the show moved to a different phase.

The five exposures I got were rather empty, with just a streak or two in each.  But I could overlap them!  I opened all five in Photoshop, put each on a layer in a new image, and blended them in "lighten" mode.  This took the lightest parts of each photo, effectively using the brightest single exposure of the ground lights, then combining all the light streaks.  Since the camera was locked down on a good tripod for each exposure, they overlapped perfectly.

I did not use in-camera noise reduction.  That technique automatically makes a second exposure, the same length as the previous, energizing the sensor, but not opening the shutter.  That records only the sensor noise.  It then subtracts the second image from the first, removing much of the recurring noise from the first image.  But, the technique doubles the amount of time until the camera is available to make the next shot.  With the show on and the clock running, it was a luxury I could not afford!

With "lighten" blend mode, the lighter parts of the noise in each photo will accumulate in the blended photo.  To minimize this problem, before blending, I applied some noise reduction to each individual image.  Then, just a touch of noise reduction was needed on the final image.

The original images had a biplane parked down the taxiway in the lower right hand corner.  I would have loved for it to be larger and filling that empty spot in the lower left.  Can do in Photoshop!  I extracted the parked plane to its own layer, scaled it up to make it a significant part of the composition, and lowered it in the frame.  It created the illusion that it was parked on a taxiway that is closer than actual.  Then with some patching, I covered and put runway lights where the plane used to be.

I had a good idea what I wanted the image to look like before I started working on shooting it.  I pre-visualized it, and through carefully planned shooting and some digital darkroom work, made it happen with this successful photoillustration.  I pleasingly captured the motion inherent in the show, achieving my goal!

Huge thanks to photographer Kevin Adams.  Several weeks before I made this image, Kevin shared his masterful thinking about nighttime digital photography.  He helped me to see how to conquer the problems and assemble my image.  He saved me many trial and error sessions!  Also thanks to photographer Dan Waters for helping me imagine the results while chatting over eggs and coffee.

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Last Updated on Friday, 05 November 2010 13:45
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