reach the sensor, and that includes the ambient
light that is present in all cities at night. This
light pollution can really be a problem when it
comes to photographing star trails because the
light from the cities is so much brighter and it
can cause areas of the image to be overexposed.Putting it all together
Here are some of the things that will make your
star trails work out better, and give you the long,
curved trails that many agree look best:
■ Point north. If you point your camera north,
or when in the Northern Hemisphere at the
North Star or Polaris, you will create the cir-
cles that many feel are the best-looking star
trails, as can be seen in Figure 7-20.
■ The length of the exposure. It doesn’t matter
if it is a single exposure or a stacked exposure,
the total exposure time needs to be long
enough to show the movement. That means
30 minutes or longer to get some good trails
going.
■ Focal length. The wider the angle of view,
the more the lines will curve, and if you have
a fisheye lens, that works even better. Keep in
mind that the fisheye also distorts anything in
the foreground that is close to the edge of the
frame.
■ Location. The clearer the sky, the easier it is
to see the trails, and the farther away from the
city, the less ambient light bleed there will be.
If you live away from a city, then you can go
out and just try the long exposures needed, but
if you live in a city, you might not have a clear
sky, so I suggest that you practice with getting
the right settings and taking some long expo-
sures close to home before heading out and
away from the city to capture a star trail.to create a single file, and the best solution to this
is to use Adobe Photoshop Extended and the
built-in Image Statistics script. This script makes
the stacking process very easy, but at this point is
only available in the Adobe Photoshop Extended
version. Just do the following:
- Open Photoshop Extended.
- Click File ➪ Scripts ➪ Statistics. This opens
a dialog box that allows you to select the files
to combine, as shown in Figure 7-19. - Change the stack mode to Maximum.
- Select the images you want to stack.
- Click OK. The file is then opened in
Photoshop, but it needs to be converted from
a smart object to a regular layer.
7-19
ABOUT THIS FIGURE The statistics script displays a dialog box
in Photoshop Extended.
Ambient light
One of the most important factors in getting a
good light trail image is the location of the shoot.
The best areas to take these types of images are
where there is as little ambient light as possible
because of the really long exposures. The longer
the shutter is open, the more light is allowed to