How stationary and moving light sources reveal themselves in an image is strongly influenced by our aperture settings.

The length of a light trail, created by a moving light source, is dependent on the time of the exposure.

The width or thickness of the light trail is determined by the size of the aperture. The wider the aperture opening, the wider the streak of light recorded by the camera.

We will address the effects of aperture size on stationary light sources in the next post.

HOW TO : Aperture Optimization

In my earlier post exposure guidelines, I recommended shooting with an aperture setting of f5.6 at ISO 400. This was based on a relationship between your aperture and ISO sensitivity settings for recording desirable light trails.

For optimal moving light source treatment in an image, set your aperture according to the following equation and examples:

f-stop = SquareRoot ( 0.08 * ISO )

f4.0 ⇐ ISO 200
f5.6 ⇐ ISO 400
f8.0 ⇐ ISO 800

This is a rule, and you should not break it … just kidding.

It is safe to vary this by + or – one f-stop, but any aperture setting outside of this range may be less pleasing, and may render light trails that are overly thick or underly thin.

I encourage you to treat this equation as a starting point for your own experimentation, in search of your own visual aesthetics.

IMAGE : Rail Bridge, Engine Lights & River, Carlsbad, NM

This railroad bridge crosses the Pecos River. Every morning a cancellation of train engines travels north across the bridge to the railyard, where freight cars are on hold.

Yes, “a cancellation of trains” is the correct collective noun.

Five mornings I was up before dawn to capture the engine lights streaming through the frame of the bridge toward me.

I opened the shutter just as the front engine began illuminating the trusses of the bridge. My biggest challenge was to close the shutter at the right time so the streaking lights complemented the shape of the bridge.

This was my favorite of five exposures, all shot with the recommended f-stop for my film speed setting, ISO 800. The length and width of the light trails are aesthetically proportional to the bridge, matching what I envisioned in my mind’s eye.

This was a 45 to 50 second exposure taken at f8 with TMAX 3200 film shot at ISO 800. The engine lights were crossing the bridge in the image for only 5 to 10 seconds.

IMAGE TINT : GallerySteelGray

The cool steely gray toning was chosen to evoke the look of the bridge in the cold damp air. The same toning was selected for the image in my previous post.

This B&W image was toned in Adobe Photoshop with an ICC Profile I generated from my Mac App SuiteProfiler. The Profile was derived from the “GallerySteelGray”  Color Map created in SuiteProfiler.

Click these buttons to download the ICC Profile and SuiteProfiler Color Map:

EXERCISE : Aperture Settings

Seek out one or more moving light sources to photography. Take a series of bracketed exposures using the recommended ISO and aperture combination.

Perform more bracketing sessions with different apertures without changing your ISO.

Compare your results to see the difference in light trail widths. Decide what aperture to ISO ratio looks the best to you. Start using that to capture your expanded moments.

Some examples of moving light sources are headlights, flashlights and stars.

Be sure to review the Safety & Precautions Page.

NEXT TIME : “Aperture Starring”

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Three fundamental preludes to capturing an image are framing, leveling and focusing.

These are fairly simple tasks in daylight, not so easy in low light.

Composing an image on a digital monitor or in a viewfinder is more demanding at night.

Typically framing is the first order of business, but will take more discovery work than during the day. You will most likely point your camera in different directions to examine the scene for framing and focusing.

Mama always said, “Level is as level does.” Leveling is visually subjective, and is especially difficult to gauge in the dark. Often what “level” means is relative to the visual elements in the image, and should be evaluated when viewing the resulting image.

Here are some suggestions to aid you in your image quest:

HOW TO : Framing

• use a flashlight to light objects while viewing the scene
• highlight corners of the image with light sources, like a lantern
• take test shots, view on your digital monitor
• take test shots with your flash, then view
• use digital AF-assist illuminator
• increase ISO to view on your monitor

HOW TO : Leveling

• mechanical approach is to use a leveling bubble on your camera or tripod
• flexible approach is to zoom out a bit to allow room for final image adjustment

HOW TO : Focusing

• be sure to set digital Auto Focus (AF) to MANUAL
• focus at infinity first then shorten focal length until in focus
• focus on something well lit at the desired focal distance
• use a flashlight to highlight a point of focus
• take sample exposures, view on your digital monitor
• measure distance with a tape measure for close subjects

IMAGE : Gilman Tunnels, Jemez Mountains, NM

The Gilman Tunnels are two miles up the canyon from our home. The logging industry transported timber by train through these tunnels over 60 years ago.

One moonless night I drove up to photograph the tunnels during a snowstorm. In my mind I pictured a scene filled with snowfall. When I arrived it was pitch black, no light at all. It was snowing very hard but I could not see anything without a flashlight.

“What to do? What to do?”

I drove through the first of two tunnels, parked my car and left the headlights on. I then walked back through the tunnel to set up my tripod and camera.

I used a lantern to light various points to help me frame and focus. Finally I left the lantern near the entrance to add fill lighting for the tunnel and the rock wall on the left.

I zoomed out a bit to give myself some wiggle room for framing and leveling the image after the fact. Good thing, leveling my camera did not produce an image that appeared level.

This is a good example of a minimalist style image even though it was a 12 minute exposure shot at f8 with TMAX 3200 film. Did I mention that it was very, very dark?

IMAGE TINT : GallerySeleniumGoldToner

In the darkroom Selenium toning creates a cool purplish hue in the darker tones. Combined with moderate Gold toning, the highlights are shaded bluish gray. The toning effect was selected to convey the look of cold light on the rocks.

This B&W image was toned in Adobe Photoshop with an ICC Profile I generated from my Mac App “SuiteProfiler”. The Profile was derived from the “GallerySeleniumGoldToner” Color Map created in SuiteProfiler.

Click these buttons to download the ICC Profile and SuiteProfiler Color Map:

EXERCISE : Framing, Leveling & Focusing

Practice framing, leveling and focusing in a low lit room or backyard. Make use of the suggestions above to familiarize yourself with composing an image in the dark. Experiment with various approaches to discover what suits you best.

When you are comfortable, take your camera out at night, and seek out a very low lit scene. Challenge yourself but don’t overdo it. Compose and bracket to see what your camera sees.

Be sure to review the “Safety & Precautions” Page.

NEXT TIME : “The Expanded Moment”

Don’t miss my future posts! 

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