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Re: (meteorobs) Photographing Aurora
Becky
The exposure tables below should work reasonably well with a 35mm SLR
format. Your chances of obtaining 'perfect' exposures will be
increased if you bracket each shot (ie deliberately under and over
expose a few frames). 400 ISO rated film is the standard for auroral
photography, though very bright displays will benefit from a finer
grained film of 200 ISO. Here, in Scotland, most auroral
photographers prefer to use colour slide film as opposed to negative
film. The aurora occupies large areas of sky, so, a 50mm or 28mm lens
would be best, with the aperture fully opened. I've never attempted
any astronomical photography in arctic conditions, but, I'm sure a
mechanical shutter mechanism would be advantageous, given that battery
power is going to quickly drain in sub-zero temperatures.
In order to correctly assess the best exposure you'll firstly have to
estimate the aurora's brightness. This is a fairly simple procedure
and is normally based on the following 4-point scale:
1) Very faint aurora, similar in brightness to the Milky Way.
2) Moderate, comparable in brightness to moonlit cirrus cloud.
3) Bright aurora, comparable in brightness to moonlit cumulus cloud.
4) Much brighter than 3; perhaps able to cast shadows.
Then, the exposure times below, based on a lens setting of f2 on 400
ISO film, should do the trick.
Aurora
Brightness Exposure (Secs)
1 60
2 20-40
3 10-20
4 5-10
Other points to bear in mind when photographing aurorae are:
1) Star trailing may become objectionable on exposures over 30-40
seconds.
2) Active displays (fast moving forms) will require shorter exposures,
otherwise the auroral structures will be blurred.
3) Compositionally, it always helps to include foreground detail in
your photograph. This also gives a better sense of scale.
4) The aurora is easier to see and photograph in the absence of
moonlight and local light pollution.
Tom
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Tom McEwan
E-Mail: tmcewan@kersland.u-net.com
NLC Info: http://www.personal.u-net.com/~kersland/nlc/nlchome.htm
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