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A creased and puckered
auroral curtain sheathes the zenith in clear and very
cold air (-25° F) on March 24,2001 over Fairbanks,
Alaska. A 3-second exposure with a Nikon FM-2 35 mm
camera and Nikkor 35mm f/1.4 lens on Kodak Supra 800
print film preserved its stark loveliness. Jan Curtis
As a stream of charged particles
from the Sun strikes the molecules of the upper
atmosphere, it imparts some of its energy to atoms and
molecules of nitrogen and oxygen, temporarily elevating
them to higher energy levels. As the molecules return to
their former states, they release the newly acquired
energy as photons of light. The combined release of all
these photons causes the glow we call aurora.
Photographic film is more sensitive to colors than our
eyes, which accounts for more vivid documentations in
photographs than our memories.
Equipment.
A 35 mm SLR camera with a bulb (B) setting for long
exposures is best for capturing the auroral essence. Set
it on a firm surface or a tripod. Using a shutter
release cable will avoid camera movement during long
exposures. Fast color slide films (ISO 400 and greater)
and Kodak or Fuji emulsions work well.
 Composure.
A wide-angle lens (35mm focal length or less) opened up
to full aperture should fill the frame well. Including
some of the foreground adds proportion and perspective.
Technique.
Because it is difficult to assess the brightness of the
display for the length of exposures, it is always best
to take a several bracketing shots so that at least one
may turn out decently. The longer the exposure, the
stronger the features and colors will register on the
film; however, if the aurora’s form is shifting and
changing, a long exposure will only blur things. Strong
moonlight and city lights can also wash out your
results. If you’re good at estimating comparative
brightnesses, the following guide may help:
|
equivalent brightness |
suggested exposure |
|
Milky Way |
20-30 secs. |
|
thin moonlit cirrus |
10 secs. |
|
moonlit cumulus |
1-2 secs. |
|
full moonlight |
.25 sec. |
It
is always useful to note the following data for future
reference: date, time,
observing
location, direction to aurora, length of exposure,
f-stop, focal length, and
speed and type of film.
©
Tim Herd
A great luminous
curtain swirls green and gorgeous over Wood Buffalo
National Park, Northwest Territories, Canada (60.5° N)
very early on September 5, 2003. The night was so dark
when the display began that the photographer needed a
large flashlight to set up his equipment, but the
auroral eddy grew in intensity until it illuminated the
entire forest around him. He preserved its portrait with
a 30-second exposure on Kodak Ektachrome 100 VS slide
film using a 20 mm lens on a tripod-mounted Nikon F11
camera. Mike Grandmaison. |
