› ›photoshop user› february 2016112
One general guideline to avoid star blur is known as “the
500 rule.” Simply divide 500 by the focal length of your lens,
and that equals the longest exposure, in seconds, you can use
before the stars start to trail in your shot. For example, using
a 20mm lens on a full-frame camera, divide 500 by 20, giving
you 25 seconds, the longest time you can expose before the
stars appear to move.
If you plan to capture star trails through a long exposure,
a lower ISO gives you much less noise, and the light absorbed
by the lengthy time exposure can capture the detail needed.
Wide-angle lenses work best to cover larger portions of the
sky, but any lens can be used; just recognize that the longer
the lens, the more opportunity for camera shake, as well as
a smaller aperture that’s tougher to see through, requiring
careful focus and a higher ISO setting. Faster lenses, ones
with larger maximum apertures, are also a benefit since the
wider openings make it easier to see through the viewfinder,
allow more light to hit your sensor, and give you the option
to use lower ISOs for less noise.
To balance artificial light with ambient starlight, the arti-
ficial light you provide, or that’s provided through another
source, must match closely to the extremely dim ambient
light level of the stars. Go outside that limited range and your
exposure is lost due to the difference between an extremely
bright artificial light and low-level starlight combined, hence
an unrealistic final scene or a ton of post work to recover
the image. Waiting for the campfire to lower to a flicker was
the key to this image, while artificial light from a headlamp
was used to add a touch of detail to the glacial erratic sitting
below a star-filled sky. The RAW file was exposed at f/4 for
15 seconds using ISO 1600 with an 18mm lens.Step Four: Once you have a solid RAW
file to work with, various postprocess-
ing techniques in Lightroom CC can
help you stretch the capabilities of
your image sensor, pulling out extra
detail while correcting other imperfec-
tions. Using presets to fix night scenes
may not be the best option, as every
situation and exposure requires spe-
cific recovery and adjustments. Take
this Yosemite image of a tent below
the Milky Way. The balance of the tent
glow and the nighttime sky are a bit
high in contrast, but not enough to
lose detail in either area. Initial adjust-
ments are done in the Lens Correc-Step ThreeStep FourADOBE PHOTOSHOP Lightroom Magazine › ›