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a simple way to avoid camera shake which
ruins many a time exposure.
So how long should you leave the lens uncov-
ered? Under dark skies with ISO 400 film and
a 50mm f/2.8 lens you can expose for up to
about 20 seconds before the motion of the
stars becomes evident as small trails on the
film. However, if the sky is exceptionally dark
and the camera is pointed toward the north,
especially in the vicinity of the Pole Star,
Polaris, then you may take exposures up to
two minutes or more since the diurnal motion
of the stars are much less pronounced there.
To finish the exposure, place your palm in
front of the lens (again without jogging the
camera) and unlock the cable release.
If you are feeling artistic then it always pays to
have some foreground subject to 'frame' the
stars. A gnarled old Oak tree devoid of leaves
with its 'fingers' stretching to the sky would
make a good silhouette for an atmospheric
picture! A word about processing: with the
advent of the high street 1 hour processing
booth you can get very quick results with
print films that use the C41 process. But do
make sure that the technician knows that your
subject matter is astronomical since it is very
frustrating to return to pick up your hard-
earned snaps only to be told that the roll was
unexposed - they're just not used to seeing
tiny white dots! Just tell them to print all
frames regardless. If you can intersperse the
pictures with everyday terrestrial scenes then
so much the better, since this makes it easier
for them to note the edge of a frame - nothing
is more infuriating than an otherwise perfect
night sky scene negative that has been care-
lessly cut in half.
With practice you will be able to photograph
scenes of great beauty, especially if you have
used colour film to capture the myriad
colours of the stars. You may notice, too, that
you have photographed things that you didn't
notice at the time, like the streak of a meteor
as it burned up in our atmosphere in a flash
of incandescence or the longer trail of an
a rtificial satellite as passed through the
camera's field of view. Rarer sights such as
moonbows and aurorae may also be captured
by the attentive astrophotographer arm e d
with no more than their tripod mounted camera.
CLEANING
As with any quality optical instrument, lens or mirror surfaces should be
cleaned as infrequently as possible. Front surface aluminised mirrors, in
particular, should only be cleaned when absolutely necessary. In all cases avoid
touching any mirro r surface. A little dust on the surface of a mirror or lens
causes negligible loss of performance and should not be considered reason
to clean the surface. When lens or mirror cleaning does become necessary,
use a soft camel-hair brush or compressed air to gently remove the dust.
If a telescope's dust cover is replaced after each observing session, cleaning
of the optics will seldom be re q u i re d .
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