Sky & Telescope - January 2021 - 63

S BEST OF BOTH Edge-on spiral galaxy NGC 5866 is surrounded by faint star streams that suggest a complex history of galactic cannibalism. Although known as the Spindle Galaxy due to its appearance (left), a simple non-linear stretch (middle) brings out these star streams, but at the expense
of its inner spindle-like dust lane. Careful use of PixInsight's HDRMT tool with special attention to the transition between the outer areas and the inner
details helps to tell the entire story of this fascinating galaxy (right).

One question I often receive when delivering an imageprocessing workshop after discussing image calibration is,
"How do you know what to do next?" The answer is somewhat akin to Ansel Adams's technique of previsualization.
While Adams stressed the importance of imagining what he
wanted the final print to reveal about a subject before entering the darkroom, I approach galaxy processing based on my
initial inventory of interesting features. Each subsequent
processing decision both enhances some aspect of an image's
attributes while protecting others so that they do not suffer
in their appearance or visibility.
Galaxies are particularly well suited to this way of thinking. For example, I note a wealth of information while examining my unprocessed images of the lenticular galaxy NGC
128 and its neighbors in Pisces. A short list of interesting
features to highlight includes:
1: Faint outer tidal tails (and stellar streams around
nearby NGC 125).
2: The X-shaped nucleus of NGC 128.
3: Dust clouds extending from NGC 127 crossing in front
of the northern extent of NGC 128.
4: The same dust from NGC 127 makes NGC 128 redder
on this portion of the galaxy.
5: Small-scale details in both the nucleus regions of
NGC 127 and NGC 125.
Carefully monitoring these details during each processing step informs the final picture. As experienced processors
know, it's all too easy to introduce artifacts along the way. In
a sense, the galaxies themselves tell me what to do next.
Galaxies are by far the most numerous deep-sky objects to
observe in astrophotography. Each has its own features and
characteristics. Even if you don't adopt all of the ideas pre-

sented here, the attention you give to them will certainly help
raise awareness of what is in your hard-won data and bring
your own imaging to a higher level.

„ ADAM BLOCK is a world-renowned astrophotographer
based in Tucson, Arizona, and founder of the University of
Arizona's Mount Lemmon SkyCenter.

Reddened arm
"X" feature

H II regions,
dust lanes

Tidal tails
and loops

Inner structure

X PLAN OF ATTACK A great method when approaching any image is
to make note of important details before beginning the work. This galaxy
group in Pisces, including NGC 128 (top left), NGC 127 to its right, and
NGC 125 (bottom), boasts a number of interesting features I set out to
highlight before beginning any digital-darkroom enhancements.
sk yandtelescope.org * JANUARY 2 021

63


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Sky & Telescope - January 2021

Table of Contents for the Digital Edition of Sky & Telescope - January 2021

Contents
Sky & Telescope - January 2021 - Cover1
Sky & Telescope - January 2021 - Cover2
Sky & Telescope - January 2021 - 1
Sky & Telescope - January 2021 - Contents
Sky & Telescope - January 2021 - 3
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