Sky & Telescope - June 2023 - 56

JUNE 2023 OBSERVING
First Exposure
taking a sequence of shots, one right
after the other. You'll want to minimize
the delay between each individual exposure,
so set your camera to high-speed
continuous mode and turn off features
such as image review or long-exposure
noise reduction - these significantly
increase the shot-to-shot time.
An image sequence opens up several
SKY LIGHT Even at a dark-sky location, moonlight can affect an image. A waxing lunar crescent
is about to set, but its light is bright enough to partially wash out this 30-second exposure
made with a tracking mount and a Canon EOS RP camera working at ISO 1600.
Camera trackers permit longer exposure
times without the risk of star trails and
let you take advantage of slower lenses
and those with longer focal lengths. You
can also utilize lower ISO settings to
improve image quality. The main limitation
is that foreground objects, such as
trees or mountains, will start to blur
as your camera tracks the stars. This is
why many trackers offer a special, halfspeed
(0.5×) setting that lets you split
the difference between pinpoint stars
and a sharp landscape.
When evaluating your shots, don't
rely solely on your camera's rear screen.
Although " chimping " (as the activity
is humorously known) gives you an
overall sense of the image quality and
composition, the camera's bright display
can trick your dark-adapted eyes into
believing an underexposed image looks
fine. Instead, trust the histogram. This
graphic shows the brightness range
of the recorded pixels. (Check your
camera's instruction manual to find out
how to enable this valuable feature).
The histogram of a well-exposed
image will have a hump fully separated
from the left side of the screen
while not extending much past the
halfway point of the graph. You should
56 JUNE 2023 * SKY & TELESCOPE
also avoid over-exposing your images
because this will wash out the vivid colors
in the stars you're trying to capture.
Finally, shoot in RAW (not JPEG)
mode. This will let you adjust the
image's white balance after the fact
and recover more highlight and shadow
detail during post-processing.
Compelling Compositions
While it's tempting to point your
camera straight up to capture as much
of the Milky Way's expanse as possible,
you'll get more appealing images if you
include the horizon. The silhouette of a
distant mountain range, or some nearby
trees framing your subject, will make
your photos more compelling. On calm
evenings, nearby lakes and rivers can act
like mirrors to reflect the sky, thereby
adding impact to your composition.
Try shooting images in both horizontal
and vertical orientations. A
horizontal image emphasizes features in
the landscape and works well when the
Milky Way is rising or setting. A vertical
orientation is a better choice when you
have a tall tree in the shot, or when the
Milky Way is arching high overhead.
Once you've got the framing and
exposure settings sorted out, consider
important post-processing options.
After you've downloaded the individual
frames onto your computer, you can
stack them together with software
such as Adobe Photoshop, Affinity Photo,
DeepSkyStacker, or Sequator. By averaging
the pixel values across a large number
of sequential shots, random digital
background noise is smoothed out, producing
a cleaner photo that allows for
more extensive post-processing. Stacking
is particularly helpful for removing
airplane and satellite trails. (Turn to
page 54 of the April 2022 issue for more
about image stacking.)
Alternatively, you can combine a
sequence into a stunning time-lapse
movie. The Photos app in Windows
allows you to add a set of images to a
timeline and then export them as a
video. On a Mac, you can do the same
thing using iMovie or QuickTime. Timelapse
sequences shot from a fixed tripod
will show the apparent motion of the
stars drifting across the sky from east
to west. Conversely, those captured on
a sky-tracking platform or equatorial
mount will reveal the somewhat surreal
sight of the Earth's western horizon tilting
up to cover the stars, which remain
fixed in the frame.
Finally, I always recommend bringing
along binoculars or a small, wide-field
telescope so you can enjoy views of the
sky while your camera busily clicks away
in the background. After all, if you've
made the effort to travel to a dark-sky
location, you have the perfect opportunity
to soak in the amazing sight of our
home galaxy in real time.
¢ TONY PUERZER is a retired professional
photographer and avid amateur
astrophotographer with a constant longing
for clear, dark skies. He calls Vancouver
Island, British Columbia, home.

Sky & Telescope - June 2023

Table of Contents for the Digital Edition of Sky & Telescope - June 2023