Sky & Telescope - February 2022 - 62

Imaging Strategy
100 hours of exposure to reveal faint and
exotic structures seldom (if ever) seen
before. Little did I know that this project
would become so rewarding that it inspired
my passion to acquire incredible amounts
of data of several objects over the following
years, and lead to collaborations with professional
astronomers and NASA. Here's
how I did it - and how you can, too.
Work with What you Have
Recording ultra-deep astrophotos doesn't
require the latest, largest, or most expensive
equipment, nor even the most pristine,
dark skies. My observing location is on the
western outskirts of Auckland, New Zealand, which has a
population of 1.7 million. Although my home-built, 10-inch
f/5 truss-tube Newtonian (later upgraded to a 12½-inch f/4)
is tailored to image deep-sky objects, it's by no means the
most capable or sophisticated instrument available within the
realm of amateur astrophotography. Likewise, my QSI 683wsg
camera incorporates a KAF-8300 8.3-megapixel monochrome
CCD sensor that's neither the largest nor the most sensitive
model available. Along with this equipment, I used readily
available Astrodon second-generation RGB filters and a
3-nanometer hydrogen-alpha (Hα) filter. Until recently, the
scope resided in a commercial shed converted into a roll-offroof
observatory.
Regardless of equipment type, having a permanently ready
imaging system is the single most important factor for systematically
collecting large amounts of data. This let me take
advantage of every clear night with minimum setup time.
READY FOR ACTION The author's truss-tube
12½-inch f/4 Newtonian currently resides in a
ScopeDome 3M observatory ready to image at a
moment's notice. Note the QSI 683wsg camera
with Starlight Xpress Lodestar autoguider in its offaxis
guider port at top right.
A Good Plan
An ultra-deep imaging project requires
considerable planning because it's likely
to span many months. Suitable targets
include galaxies or galaxy clusters, which
sometimes contain very faint tidal streams
of stars left over from ancient mergers.
Planetary nebulae may display extremely
faint outer shells that become visible with
long enough exposure times. Many well-known nebulae often
reveal extended tendrils of nebulosity not visible in typical
photographs. Almost any object can reveal something new
in an exceedingly deep image. Still, composition and field of
view are important considerations. For example, targeting
the Orion Nebula (M42) with my system's narrow field of
view (42′ by 32′) is unlikely to reveal new structures because
the nebula is already very bright and extends far outside my
camera's field of view.
Targets that pass high overhead are the most suitable for
ultra-deep imaging. For optimal efficiency it's best to devote
nights with good seeing to taking luminance data and leave
color for nights with less steady conditions. This is because
the sharpness of the final image is defined by the luminance
alone, and the RGB data only provide the color information.
Minimizing downtime is important for long-term imaging
projects, so I automated as much of the process as possible by
MULTI-WAVELEGTH COMPARISON For a press release from the Chandra X-Ray Observatory in 2014, the author's deep image of Centaurus A
was combined with data from several telescopes to showcase the unique appearance of the galaxy across the electromagnetic spectrum.
Mulit-wavelength image
Visible light
X-ray light
Infrared light
Radio light
62 FEBRUARY 2022 * SKY & TELESCOPE
X-RAY: NASA / CXC / SAO; OPTICAL: ROLF OLSEN; INFRARED: NASA / JPL-CALTECH;
RADIO: NRAO / AUI / NSF / UNIV. HERTFORDSHIRE / M.HARDCASTLE

Sky & Telescope - February 2022

Table of Contents for the Digital Edition of Sky & Telescope - February 2022