How to manipulate time…
In order to take a decent long exposure time-lapse photograph, advance planning is required. This is part of the fun and satisfaction of taking a long-exposure photograph.
First, scout a location. Something that will really emphasize the captured motion. Road curves and headlights are always terrific time-lapse subjects. This was discussed in detail in an earlier post ("Why curves are sexy").
In this case a twilight shot was selected and the vantage point was atop Maiden Rock in Wisconsin. Twilight presents an added challenge because the window between just dark enough (headlights on) and too dark (details lost in the shadows) is probably only 20 to 30 minutes, depending on the time of year. Penumbra light is worthy of its own topic and will be discussed in a future entry.
First, begin by timing how long it takes traffic to enter and exit your shot. Simply compose the image in your view finder and mentally count the seconds ("one one thousand, two one thousand, three one thousand, etc…"). This will give you an approximation of how long your shutter speed will be set at. This is just an approximation, but also allows you to compose your photograph.
This brings up two good points. A tripod is critical for these long exposure images and a spare set of batteries. Long shutter exposures will quickly drain your battery.
Your camera settings should be set to manual and the automatic focusing should be turned off. Capture both a high resolution jpeg and RAW file formats.
Pick a depth of field that will capture the entire entry and exit of your subject. An aperture of 4.5 to 5.0 is plenty for a shot this far away. Adjust the ISO low enough to avoid digital noise but high enough to give you proper exposure.
But we are not interested in a properly exposed photo. We want drama.
Adjust your aperture so that you are anywhere from 1 to 2 stops under-exposed. Manually focus at a center point of the exit and entry points of your subject. Wait for twilight to begin and wait for your subjects to cooperate (hopefully).
After a few attempts, this is what was captured with an exposure of 20 seconds at f6.3 and an ISO of 100. You can see that 20 seconds was not long enough to get the light streaks from beginning to end.
Here is an adjusted attempt at 30 seconds and f7.1. The entry and exit points were captured, but the preference would have been to capture the headlights instead of the taillights. Or, ideally both, in the case of two vehicles driving towards each other.
This was taken in October and the available twilight light was quickly lost to total blackness. And without the trees and river details, it would have just been streaks of light.
Long exposure time-lapse is like fishing. Sometimes you land a luncker and sometimes you go home hungry. But you still had a good time and maybe even a beer buzz.